gardner’s syndrome (familial adenomatous polyposis)

7/21/2019 Gardners Syndrome (Familial Adenomatous Polyposis)

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IntroductionIn 1951, Eldon Gardner reported a disease in a familyfrom Utah (USA), characterised by diffuse intestinalpolyposis, osteomas, fibromas, and epidermal orsebaceous cysts, which seemed to have an autosomaldominant pattern of inheritance.1 The study of thatfamily was initiated in 1948 when a premedical student

in a genetics class called attention to a neighbourfamily in his home town that seemed to have anunusually high incidence of cancer, including severaldeaths as a result of cancer of the lower digestive tract.The family members were visited and found to beinterested in having a study made, and they werecooperative in clinical investigations.1

Cloning of the adenomatous polyposis coli (APC) genein 19912 was followed by identification of mutations inthis gene in families described as having either familialadenomatous polyposis (FAP) or Gardners syndrome.3,4Therefore, Gardners syndrome has been deemed avariant of FAP (OMIM:#175100), rather than a distinctsubtype of the disease, and is the term used to describe

the clinical manifestations of patients with FAP in whomthe extraintestinal features, such as osteomas, skintumours, and soft-tissue tumours, are especiallyprominent. However, close investigation has shown thatmost patients with FAP have at least subtle Gardnersmanifestations.4 A review of FAP is beyond the scope ofthis paper, but several excellent comprehensive reviewsare available in the published work.3,4

In this Personal View, we discuss aspects of FAP, suchas extracolonic manifestations, relevant to our postulationthat the tissues involved in Gardners syndrome have adisorder affecting the primary cilia present in theirnormal cellular counterparts (figure 1).5

At least 1015% of patients with FAP develop desmoidtumours. Most of them are located in the abdominal walland intra-abdominally, and constitute the second mostimportant cause of mortality in patients with FAP(figure 2).6,7 Current treatment options for desmoidtumours include: non-steroidal anti-inflammatory drugsor antioestrogens, chemotherapy, surgery, or radiotherapy.

However, evidence for their effi cacy is poor, partly becauseit comes from small, non-controlled studies.4,10

Osteomas are usually asymptomatic and are typicallylocalised in the mandible, but can also appear in the skulland long bones. Dental abnormalities, such assupernumerary and impacted teeth, are also a commonfeature (figure 2).8 Skin tumours include: epidermalcysts, lipomas, leiomyomas, and fibromas.

Gardners syndrome (familial adenomatous polyposis):

a cilia-related disorderEncarna B Gmez Garca, Nine V A M Knoers

Familial adenomatous polyposis (FAP) is an autosomal dominant form of intestinal polyposis and colorectal cancercaused by germ-line mutations in the adenomatous polyposis coli (APC) gene. The term Gardners syndrome is usedto describe extracolonic manifestations, such as osteomas, skin cysts, congenital hypertrophy of the retinal pigmentedepithelium (CHRPE), and desmoid tumours (aggressive fibromatosis), that are especially prominent in families withFAP. We postulate that a ciliary dysfunction is the underlying pathogenetic mechanism of extraintestinal manifestationsin patients with FAP. This postulation is based on the presence of common clinical manifestations (ie, cysts, retinalabnormalities, and fibrosis) in Gardners syndrome and cilia-related disorders. Additionally, both APC and the ciliahave degradation of -catenin as the common downstream target in the Wnt-signalling pathway. Mutations in APCcausing Gardners syndrome are clustered in a region encoding a series of amino-acid repeats responsible for thebinding to -catenin. Proofs of principle that -catenin could be the key mediator of the ciliary disorder also rely in the

findings that overexpression of -catenin induces polycystic kidney disease, and CHRPE phenotypes in animalmodels. Other candidates for the common link between Gardners syndrome and cilia-related disorders are theAPC-binding proteins: end-binding protein 1 (EB1) and kinesin-family-member 3a (KIF3a), both of which are ciliaryproteins involved in intraflagellar transport. Finally, pathogenetic similarities between some ciliopathies andextraintestinal tumours in FAP suggest a cilia defect. Understanding extracolonic manifestations in the context ofFAP as a ciliary disorder might add new therapeutic options for patients with Gardners syndrome.

Lancet Oncol2009; 10: 72735

Department of Genetics and

Cell Biology, University Medical

Centre, and Research Institute

for Growth and Development

(GROW), Maastricht,

Netherlands

(E B Gmez Garca MD);

Department of Human

Genetics, Radboud University

Nijmegen Medical Centre,

Nijmegen, Netherlands

(Prof N V A M Knoers MD)

Correspondence to:

Dr Encarna B Gmez Garca,

Department of Clinical Genetics,

University Hospital Maastricht,

P O Box 5800,

6202 AZ Maastricht, Netherlands

Encarna.Gomezgarcia@gen.

unimaas.nl

Figure : Immunofluorescence microscopy of primary cilia in NIH3T3

fibroblast cells

Primary cilia were stained by use of an antibody against the cilia-specific -tubulin

isoform (red rods). Nuclei were stained by use of 4,6-diamidino-2-phenylindole

(DAPI; blue). The EB1 protein was stained by immunofluorescence using an

antibody against EB1 (green). Reproduced with permission from reference 5.

ElsevierLtd


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Although not initially described by Gardner, congenitalhypertrophy of the retinal pigmented epithelium(CHRPE) is a common manifestation of FAP,3,4 and itsdiagnosis by bilateral lens fundoscopic examination10wasimportant in the era before DNA diagnosis (figure 2).However, when the identification of APC mutationsbecame possible, CHRPE was also detected in a small

percentage of the general population. Therefore,nowadays, the value of CHRPE is restricted to theidentification of affected relatives from families with FAPand CHRPE manifestations.11

Cilia-related disordersCilia are hair-like cellular organelles that have motilityand sensory functions. Motile cilia are important formoving fluids and particles over epithelial cells and formotility of sperm. Primary cilia are single non-motileorganelles found in nearly all cell types in mammals.12,13Cilia are unique antenna-like structures, which probethe extracellular environment for molecules recognisedby their receptors. This sensory function allowscilia to mediate many cell-signalling pathways thatregulate growth, survival, and differentiation of cells

during embryonic development and cell homeostasis.Known signalling pathways mediated by ciliary activityare the Wnt-signalling pathway, sonic-hedgehog(Shh)-signalling pathways, and platelet-derived growth-factor receptor (PDGFR) signalling pathway. Becauseprotein synthesis cannot occur in cilia, all structuraland signalling components have to be activelytransported into the cilium by intraflagellar transportproteins. Intraflagellar transport is bidirectional, allowstransport of axonemal components, and is part of thesensory activity of the cilia.1214

In view of the many roles of cilia in development andphysiology, it is not surprising that defects in cilia havebeen noted to be associated with a wide range of human

diseases, such as cystic kidney disease, retinal degeneration,liver fibrosis, and brain malformations. Evidence suggeststhat ciliary defects can lead to a broader set of developmentaland adult phenotypes, collectively called ciliopathies.A detailed overview of known ciliopathies is provided inthe table, showing the wide range and partial overlap ofdisease manifestations caused by defects in ciliary structureor function. In general, pathogenic overlap of diseasemanifestations results from homologous genes that havesimilar functions or proteins that are part of the samepathway. Indeed, several ciliary proteins shown to beinvolved in nephronophthisis, Joubert syndrome,Senior-Lken syndrome, and Meckel syndrome all interactat the molecular level.1216

To explain how certain mutations in APCcan cause aciliary disorder, we did a search of the published work forcommon links between APC and the ciliary pathwaysand for relevant genotypephenotype associations inFAP. We summarise the findings of both searches, thedifferent lines of evidence that support our postulation,and the molecular candidates that link both pathways.

Signalling pathways shared by APC and ciliaWnt pathwaysCilia act as a switch between the canonical Wnt pathwayand non-canonical (also known as planar-cell polarity[PCP]) Wnt pathway (figure 3). In early development,

A

C

B

Figure :Manifestations of Gardners syndrome

(A) Dental panoramic tomogram showing several well-defined opacities around

the periphery of the mandible corresponding to osteomas. Reproduced with

permission from reference 8. (B) Fundus showing many typical pigmentedpatches of congenital hypertrophy of the retinal pigmented epithelium in a

patient with familial adenomatous polyposis. Reproduced with permission from

reference 9. (C) CT-scan showing a large (2315 cm) intra-abdominal desmoid

tumour that extends into the liver and abdominal wall. Reproduced with

permission from reference 7.

(A)MacmillanPublishersLtd;(B)LippincottWilliams&Wilkin

s;(C)AmericanMedicalAssociation


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Primary clinical features Gene(s) and protein(s) Putative cellular function Cellular localisation

Primary ciliary

dyskinesia (PCD)

Sinusitis, bronchiectasis, infertilty,

hydrocephalus, situs inversus

DNAH, axonemal dynein

DNAI, axonemal dynein

Ciliary motility

Ciliary motility

Motile cilia

Motile cilia

Autosomal

dominant polycystic

kidney disease(ADPKD)

Kidney, liver, and pancreatic cysts,

intracranial aneurysmsPKD, polycystin-1

PKD, polycystin-2

Cell-cell or cell-matrix interactions; mechanosensation;

interacts with polycystin 2 to produce non-selective cationchannel permeable to Ca2+

Probable channel protein; interacts with polycystin 1

Primary cilia, basal bodies, focal

adhesions, desmosomes

Primary cilia, basal bodies, focal

adhesions, endoplasmic reticulum

Autosomal recessive

polcystic kidneydisease (ARPKD)

Kidney cysts, liver fibrosis PKHD, fibrocystin/

polyductin

Putative receptor protein acting in collecting duct and

biliary differentiation; interacts with polycystin 2

Primary cilia, basal bodies

Nephronophthisis (NPHP)/Senior Lken syndrome (SLS)

Juvenile, type 1 Kidney cysts, retinal degeneration

(10%), liver fibrosis, oculomotor

apraxia, cerebral vermis aplasia

NPHP, nephrocystin Adaptor protein; associates with signalling molecules in cell

adhesion and actin cytoskeletal organisation and with

-tubulin (main component of primary cilia)

Primary cilia, basal bodies,

centrosomes, focal adhesions,

adherens junctions

Infantile, type 2 Kidney cysts, retinal degeneration(10%), situs Iiversus, liver fibrosis

NHP, inversin Primary cil ia function and involved in cell-cycle; controllingbalance between different canonical and non-canonical

Wnt-signaling cascades; left-right axis determination

Primary cilia, basal bodies,centrosomes, cell-cell junctions,

nucleus

Adolescent, type 3 Kidney cysts, retinal degeneration(10%), liver fibrosis

NPHP, nephrocystin-3 Might mediate, with nephrocystin and nephroretinin, acommon developmental pathway in primary cilia ofepithelial kidney cells; involved in Wnt-signalling cascades

Cilia, basal bodies, centrosomes, retinalconnecting cilium

Juvenile, type 4 Kidney cysts, retinal degeneration

(10%), oculomotor apraxia, liver fibrosisNPHP, nephroretinin Cell-cell and cell-matrix adhesion signalling; cell division Primary cilia, basal bodies,

centrosomes, adherens junctions

Senior Lken

syndrome

Kidney cysts, retinal degeneration with

early onset (100%)NPHP/ICQB,nephrocystin-5

NPHP/CEP,

nephrocystin-6

Unknown, interacts with retinitis pigmentosa GTPase

regulatorRegulates intra cellular protein traffi cking; role in cell

division?


centrosomes, retinal-connecting ciliumPrimary cilia, centrosomes, nucleus,

retinal connecting cilium

Nephronophthisis Kidney cysts NPHP/GLIS,GLIS2

NPHP,NEK

Transcription factor, important in sonic-hedgehog (Shh)signalling and maintenance of renal tissue architecture

Cell-cycle regulation?

Primary cilia


Joubert syndrome

and Joubert-related

disorders(cerebello-ocular

renal syndromes

[CORS])

Kidney cysts (nephronophthisis),

retinal degeneration (100%),

cerebellar vermis dysplasia

NPHP/CEP,nephrocystin-6

NPHP, nephrocystin

AHI, Jouberin

NPHP/RPGRIPL,

RPGRIP1L

MKS/TMEM, Meckelin

Regulates intra cellular protein traffi cking; role in cell

division?

Adaptor protein; associates with signalling molecules

involved in cell adhesion and actin cytoskeletal organisation,and with -tubulin (a major component of primary cilia)

Signalling molecule?

Component of cilium-related Shh-signalling; necessary for

establishment of left-right asymmetry and patterning of

neural tubes and limbsCiliogenesis

Primary cilia, centrosomes, nucleus,retinal-connecting cilium


centrosomes, cell-cell junctions

Primary cilia, basal bodies, cell-cell

junctionsCilia, basal bodies. Retinal-connecting

cilium

Ciliary membrane

MeckelGrubersyndrome (MKS)

and Meckel-like

cerebro-reno-digitalsyndromes

Kidney and liver cysts, polydactylyCNS malformations, hydrocephalus

MKS,MKS1

MKS/TMEM, MeckelinNPHP/CEP,

nephrocystin 6

NPHP/RPGRIPL,RPGRIP1L

CiliogenesisCiliogenesis

Regulates intr acellula r protein traffi cking; role in cell

division?Component of cilium-related Shh-signalling; necessary for

establishment of left-right asymmetry and patterning ofneural tubes and limbs

Basal bodies, centrosomesCiliary membrane

Primary cilia, centrosomes, nucleus,retinal connecting cilium

Cilia, basal bodies, retinal-connecting

cilium

Bardet-Biedl

syndrome (BBS)

Central obesity, polydactyly,

progressive retinal degeneration,

hypogenitalism, obesity, renalanomalies, learning disabilities/mental

retardation

BBS-BBS, BBS1-BBS12

NPHP/CEP,

nephrocystin-6

Involved in intraflagellar transport; involved in

non-canonical Wnt-signalling pathway; possible role in

Shh-signalling pathway; chaperonin (BBS6, 10, 12)Regulates intr acellula r protein traffi cking; role in cell

division?

Primary cilia (intraflagellar transport

complexes), basal bodies,

retinal-connecting ciliumPrimary cilia, centrosomes, nucleus

McKusick-Kaufmann

syndrome

Hydrometrocolpos, polydactyly,

congenital heart malformations,

kidney cysts

BBS, BBS6 Involved in non-canonical Wnt- signalling pathway;

chaperonin


Alstrm syndrome(ALMS)

Kidney cysts, retinal degeneration,sensorineural deafness, diabetes

mellitus, mental retardation,

hypogenitalism, infertility, obesity

ALMS, ALMS1 Ciliogenesis; mechanosensation Centrosome, basal bodies

Jeune syndrome Chondrodysplasia, constricted thoraciccage, respiratory insuffi ciency, retinal

degeneration, Kidney cysts,

polydactyly

IFT, IFT80 I ntraflage llar tra ns port; es se ntia l for de velop men t an dmaintenance of cilia

Basal bodies, centrosomes

(Continues on next page)


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only the canonical pathway is needed, but later on during

embryogenesis, PCP is also needed to align the mitoticorientation of proliferating cells.12

In the absence of extracellular fluid flow, canonical Wntsignalling predominates, which inhibits glycogensynthase kinase-3- (GSK3) from activating the-catenin degradation complex.1214 In the presence offlow, intracellular release of calcium induces increasedexpression of inversin, which in turn switches thecanonical Wnt-signalling to non-canonical Wnt-signalling, favouring -catenin degradation by axin, APCand GSK3 (the -catenin degradation complex).Therefore, in normal conditions, both APC and ciliarestrain the canonical Wnt signalling pathway. However,in cells with a mutated APC, the APC protein is not able

to down-regulate -catenin levels,17

and in cells withdysrupted ciliogenesis, the absence of cilia results inpredominant canonical Wnt-signalling.18Both situationsresult in an accumulation of -catenin in the nucleusand, therefore, overactivation of the Wnt transcriptionalactivities. In polycystic kidney disease, the most commoncilia-related disease, defects in the PCP pathway are theunderlying cause of dysregulation of the growth ofepithelial kidney cells, leading to renal cysts.18However,abnormalities in the Wnt-signalling pathways can alsoaffect ciliary function, and transgenic mice overexpressing-catenin can develop polycystic kidney disease.19,20

PDGFR pathway

PDGFR- is a tyrosine-kinase receptor located within theciliary membrane. In normal fibroblasts and in theHT1080 fibrosarcoma cell line, the binding of its ligand,PDGF, which is present in the extracellular flow, inducesdownstream cellular responses via signalling pathways,such as the MEK/ERK cascade (figure 4). These pathwayslead to cell growth, cytoskeletal changes, and cellmigration and differentiation.13,21,22 In the PDGFRsignalling pathway, -catenin forms a complex withPDGFR leading to cell migration.21A connection betweenthe cilia and FAP is shown in a study by Signoroni andcolleagues,23 in which PDGFR activation in desmoidtumours was noted.

Sonic-hedgehog (Shh) pathway

The Shh signalling pathway (figure 4) has an importantrole in the embryonic development of the neural tube andlimbs.12Primary cilia play a crucial part in mediating Shhsignalling. The transcription of Shh target genes is regulatedby the ratio of Gli (glioma) activators and repressors. Inmutant cells with aberrant or absent cilia, the the ratio ofGli activators to repressors is changed, which can lead toboth gain-of-function and loss-of-function phenotypes.12

Mutations in SUFU, a ciliary protein that localises tothe distal tip of the primary cilia, have been shown to pre-dispose to sporadic medulloblastoma.22The link betweenAPC and cilia in the Shh pathway relies on kinesin-family-member 3a (KIF3a), which belongs to the kinesinsuper-family of microtubule transporting proteins.1214

This protein is one of four proteins that are essential forcilia formation in Shh-dependent cells. APC and -cateninare transported by KIF3a along the microtubules, andaccumulate in the tips of the cilia, suggesting that thismight be important for the function of APC in regulatingcell migration.24,25

APC, genotype, and phenotype correlationsThe human APCgene is a tumour-suppressor gene thatconsists of 8532 base pairs spanning over 15 exons; thereare also other minor isoforms that contain 21 exons.2TheAPC gene encodes a multifunctional protein, with themost common isoform consisting of 2843-amino acids.3APC down-regulates -catenin and is also involved in

several other fundamental cellular processes including:adhesion, migration, organisation of the actin and micro-tubule networks, spindle formation, chromosomesegregation, and apoptosis.17Two functionally distinct intra-cellular localisations of APC have been reported.26 Onepool is localised at the basal membrane in association withmicrotubules and participates in microtubule-associatedfunctions. The second pool is recruited by axin and formsthe -catenin destruction complex. This APC is sequesteredin cytoplasmic punctuate structures known as axin puncta,which prevent its microtubule-associated functions.

As shown in figure 5, APC has many domains by whichit interacts with different proteins, including the Wnt

Primary clinical features Gene(s) and protein(s) Putative cellular function Cellular localisation

(Continued from previous page)

Leber congenital

amaurosis (LCA)

Retinal degeneration NPHP/CEP,

nephrocystin-6LCA5, Lebercilin

Regulates intra cellular protein traffi cking; role in cell

division?

Unknown

Primary cilia, centrosomes, nucleus

Microtubules, centrioles, primary cilia,retinal-connecting cilium

Oro-facio-digital

syndrome (OFD)

Kidney cysts, mental retardation,

polydactyly, malformations in oral

cavity and face

OFD, OFD1 Implicated in intraflagellar transport Basal bodies, centrosome

Von Hippel-Lindau(vHL) disease

Hemangioblastomas, CNS and retina,kidney carcinoma, pheochromocytoma

VHL, pVHL Initiation of ciliogenesis; maintenance of cilia? Primary cilia

GLIS2=GLI similar protein 2. RPGRIP1L=retinitis pigmentosa GTPase regulator interacting protein 1-like. IFT80=Intraflagellar transport protein 80.

Table:A summary of human hereditary ciliopathies


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components (-catenin, axin, and KIF3a) and the cyto-skeletal regulator end-binding protein 1 (EB1), and withmicrotubules.17,25 APC binds -catenin by a series of15 and 20 amino-acid repeats. Three 15-amino-acidrepeats bind to -catenin, but do not down-regulate it.Each of the seven 20 amino-acid repeats bind to -catenin,but only the second one is essential for such binding. 27However, although the binding of -catenin to APCfragments needs only a single 20 amino-acid repeat, thepresence of at least three of these repeat sequences isneeded for its downregulation. The binding domainof APC for axin lies interspersed between theseamino-acid repeats.3APC binds KIF3a along the entireArmadillo repeat domain.17

APC mutations (somatic and germ-line) are mostlylocated at exon 15, which is 75% of the coding sequence,

and about 60% of the these mutations are clustered in asmall region, the mutated cluster region. 95% are pointmutations (small deletions or insertions and nonsensemutations) resulting in a truncated protein.3The findingsof several reports3,6,2835 aimed at the identification ofassociations between the location of the mutation andthe manifestations characteristic of Gardners syndromeare summarised in figure 5.

Miyaki and co-workers33have shown that the numberof 20-amino-acid repeats that are conserved after two-hitAPCmutations are constant. Classic FAP has one repeatwhereas attenuated FAP has two or three. Additionally,they showed that the number of repeats also correlatedwith the risk of developing desmoid tumoursie, most

of the mutations causing desmoid tumours conserve atleast two of the seven 20-amino-acid repeats that bind-catenin.27,33Therefore, the number of -catenin repeatsis not only crucial for determining whether -catenin canbe downregulated, but is also different in the pathogenesisof desmoid tumours compared with the pathogenesis ofcolon polyps. In line with this finding, an earlier reportedvariant of FAP, hereditary desmoid disease,36 which ischaracterised by the presence of multifocal fibromatosis,osteomas, and epidermoid cysts, but no colon polyps, iscaused by a germline truncation mutation at codon 1914,containing three of the seven 20-amino-acid repeats.Colon polyps also differ from desmoid tumours in theirsomatic mutations. Somatic mutations in patients with

FAP occur non-randomly, and the position of thegermline mutation is a major determinant of the somaticmutation.34Loss of heterozygosity in desmoid tumours iscaused by deletion of the second APC allele, thereforeleaving no intact repeats in that allele, whereas in colonpolyps it is caused by somatic recombination, whichleaves an equal number of repeats.33,34

The products of C-terminal truncated APC, resultingfrom mutations causing Gardners manifestations, havein common the loss of several amino-acid repeatsinvolved in the binding and downregulation of -catenin.By use of correspondence analysis to identify associationsbetween the different manifestations of FAP, Bertario

and colleagues30

identified a significant associationbetween mutations found beyond codon 1256 and theoccurrence of epidermoid cysts, desmoid tumours,osteomas, and dental abnormalities.

DiscussionThe molecular basis responsible for the differentextracolonic manifestations of FAP, resulting frommutations in specific regions in the APC gene, hasremained elusive until now. Some postulations suggestthat the tumour-suppressor activity of APC variesaccording to several factors, such as the target tissue,the mutation site, or the length of the APC transcripts.

Polycystin

IFT

IFT

Ciliary membrane

Axoneme

Basalbody

Ca2+

Ca2+

Ca2+

NO FLOWCanonical Wnt signalling

FLOWNon-canonical Wnt signalling

Gardners syndrome:

overexpression of -catenin

Frizzled

Frizzled

Degraded -cat

Apical plasma membrane

DSH

Gsk3

Gsk3

Centrosome

Centrosome

WNT

-cat

Gene X

Nucleus

-cat

APC

Axin-cat

DSH

MutatedAPCGsk3

Axin

-cat

Gene X

Nucleus

Basalbody

A

B

Inversin

Figure : Schematic representation of the Wnt-signalling pathway shared by APC and cilia

(A) Canonical Wnt signallingin absence of extracellular fluid flow, only the canonical Wnt pathway is active. The

result is stabilisation of cytoplasmic -catenin, which translocates to the nucleus and acts as a transcriptional

coactivator. (B) Non-canonical (PCP) Wnt-signallingpresence of fluid flow switches the canonical Wnt-signalling

to non-canonical Wnt-signalling, favouring -catenin degradation. Mutated APC causes loss of -catenin binding

and loss of -catenin downregulation, resulting in predominant canonical Wnt signalling. DSH=Disheveled.


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Other investigators have suggested that theheterogeneity of clinical manifestations might beexplained by factors other than the APC gene, such asenvironmental factors or independent geneticfactors.6,37

We postulate that Gardners syndrome, as it is calledthe variant of FAP with prominent extracolonicmanifestations, is a cilia-related disorder. This postulationis based on different lines of evidence, which will now bediscussed.

FAP and cilia disorders share phenotypic featuresAs shown in the table, the most frequent diseasemanifestations in ciliopathies are: (renal) cysts, retinalabnormalities, brain abnormalities, and (liver) fibrosis.Cysts (skin), fibrosis (desmoid tumours), and retinalabnormalities (CHRPE) are also present in Gardnerssyndrome.

Defects in proteins of the photoreceptors have beenidentified as the cause of the retinal degeneration presentin congenital Leber amaurosis syndrome, Senior Lkensyndrome, Bardet-Biedl syndrome, and Alstrm syndr-ome.13Although CHRPE has always been believed to be abenign disorder, evidence from studies using modernopthalmological techniques to visualise the retina,suggests that patients with CHRPE have retinal thinningand photoreceptor loss.38 Therefore, as in other

ciliopathies, evidence exists for retinal degeneration.The presence of cysts in the kidneys is not only afeature of polycystic kidney disease, but also a featureof most of the currently known ciliopathies. However,cysts in the kidneys have not been described in patientswith FAP, and the same is true of epidermoid cysts inthe ciliopathies. Although localisation of the cysts mightbe due to the tissue specificity of the mutant proteininvolved, there is proof that either a mutated APC orthe overexpression of -catenin can induce a polycysticrenal disease phenotype in transgenic mice.19,20 Bothstudies show that dysregulation of the canonical Wntsignalling pathway can also lead to polycystic kidneydisease and can predispose to the development of renal

neoplasia.Fibrosis of the liver is a feature of some ciliopathies,such as autosomal recessive polycystic kidney diseaseand nephronophthisis, whereas aggressive fibromatosisis a feature of both FAP-associated and sporadic (causedby somatic mutations in -catenin) desmoid tumours.In both of these tumour types, upregulation ofcyclooxygenase-2 (COX2) leads to a sustained autocrineor paracrine activation of PDGFR.23Therefore, Signoroniand colleagues23have proposed the use of tyrosine-kinaseinhibitors (eg, imatinib and sunitinib), in addition toCOX2 inhibitors, to block the PDGFR family for thetreatment of these tumours.

However, the question remains as to why activation of

PDGFR in desmoid tumours does not result in cellmigration and differentiation, as opposed to whathappens in healthy fibroblasts.13,21,22We postulate that theanswer to this question might be related to differentligands or method of activation in normal fibroblastsversus desmoid tumour cells.

Although osteomas have not been previously includedwithin the list of abnormalities noted in ciliopathies, ithas been shown that osteoblast differentiation and boneformation require that both intraflagellar transport andcanonical Wnt-signaling are intact, because loss of-catenin results in defective differentiation of the bonecollar.39

PDGFR

KIF3a

Ciliary membrane EB1SUFU

GLI AGLI R

Basalbody

No Shh signalling


GLI R

Patched

Centrosome

Gene X

Nucleus

A

SMO

Ciliary membrane

PDGF

GLI A

PDGF signalling

No PDGF signalling

Basalbody

Shh signalling

Transcription ON

Transcription OFF


MEK/ERK

Patched

Centrosome

Gene X

Nucleus

B

SMO

SMO

Shh

Figure : Schematic representation of the sonic-hedgehog (Shh) and platelet-derived growth-factor receptor

(PDGFR)-signalling pathways shared by APC and cilia

(A) No signalling. (B) Signalling. Binding of Shh turns off Gli-repressive (GLI R) processing and the active form of Gli

(GLI A) activates transcription of target genes. The PDGFR-pathway is initiated with PDGF binding and induces

downstream signalling via the MEK/ERK pathways. Abnormal ciliary function in Gardners syndrome might also

rely on disrupted binding of end-binding protein 1 (EB1) or KIF3a and defective transport of APC.SMO=Smoothened. SUFU=Suppressor of fused Drosophila homolog.


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APC and cilia have -catenin as a common targetSeveral lines of evidence point at -catenin as thecommon link between Gardners syndrome andciliopathies. Both APC and the cilia cellular pathwayshave -cateninas a common downstream link in the Wntsignalling pathway.3,4,1214-catenin, together with the cilia,is also implicated in the PDGFR signalling pathway,which modulates changes in the cytoskeleton andregulates cell migration.20The fact that -catenin is thekey mediator of Gardners manifestations is alsosupported by experiments in Drosophila with inactivatedAPC.40Inactivation of APC resulted in overexpression ofthe -catenin homologue and a phenotype comparable toCHRPE. Conversely, when the expression of -catenin

was reduced, it induced a reversal of the CHRPEphenotype.40Similarly, overexpression of -catenin, eitherdirectly19or by inactivation of the APCgene in transgenicmice,20induces polycystic kidney disease.

Additionally, certain genotype and phenotype associationsin Gardners syndrome are evident. In particular, mutationsin the regions of APC causing Gardners syndromeresult in the loss of some of the amino-acid repeats involvedin -catenin binding and downregulation (amino acids10202035).3,2832,36,37 Furthermore, the difference in thepathogenesis of desmoid tumours and colon polyps lies inthe different -catenin levels achieved with the mutatedAPC proteins.27,33

By considering the evidence mentioned so far, wepostulate that the presence of a mutated APC in FAPcauses an overexpression of -catenin, which, in turn,renders the non-canonical ciliary pathway non-functionaland probably also affects ciliogenesis, resulting inphenotypic manifestations of ciliary disease in FAP, suchas CHRPE and cysts.

Other proteins as candidate linksOther proteins that act as mediators of putative ciliaryabnormalities and the manifestations present inGardners syndrome might be those whose binding isaffected by a truncated APCie, axin, EB1, and KIF3a.Therefore, the candidate APC domains that can cause

such alterations are: the region encompassing theamino-acid repeats, the C-terminal (EB1 binding)domain, and the armadillo region, respectively.

Axin binding sites are interspersed within the series of20 amino-acid repeats that bind -catenin (figure 5).Thus, axin binding is also affected by most of the APCmutations. Additionally, axin forms part of the -catenindegradation complex.12,13 However, axin is not a knowncilia-related protein, and, therefore, its relevance to thefunction of cilia is uncertain.

The presence of EB1 has been reported in fibroblasts,where its absence reduces primary cilia assembly andinhibits ciliogenesis (figure 1),40Additionally, EB2, the rat

Oligomerisation

domain

Armadillo

region

-catenin binding sites

Axin binding sites

-catenin binding and down-regulating domains

MCR (11941392)

Human Disc Large (HDLG)binding site

APC protein

wild type

15 AA repeats

10206 57

0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800

453 767 1170 1265

1020453 767 1170 1265

1256

2035 2200 2400 2559 2771 2843

20 AA repeats

CHRPE (4531444)

Desmoid tumours (13102011)

Osteomas (4571513)

Dental abnormalities (4571560)

Basic domain EB1 binding site

Figure : Localisation of mutations associated with Gardners features in the APC protein

Wild-type APC protein with functional domains is shown at the top. The encompassing codon numbers are indicated between brackets. MCR=mutation cluster region. Truncated translated regions of

the protein corresponding to the different FAP phenotypes are shown beneath. The mutation associated regions are marked in black. The translated domains inside each region are shown in colour,

and those outside the mutation associated regions are shown in grey. CHRPE=congenital hypertrophy of the retinal pigmented epithelium. Reproduced with permission from reference 3.

OxfordUniversityPress


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homologue of EB1,41is one of the proteins present in thephotoreceptor-cell axonemes. The protein components ofthe photoreceptor cell that connect the cilia of the retinalrods and cones participate in: the intracellular transportthrough the cilia; the morphogenesis of the outer segmentdisc, which contains the photo pigment opsin; and in themaintenance of discrete membrane domains.40,41

The fact that most of the mutations found in APCcausea truncated protein without the carboxyl-terminal EB1binding region3 might explain how mutations in APCcan cause a ciliary disorder, provided that the absence ofbinding to APC results in functional abnormalities ofEB1. This notion might well be the case if the functionsso far attributed to EB1 do not rely on the protein itself,but on the proteins that it transports, such as APC. Thereview by Giardiello and colleagues37about genotype and

phenotype associations in FAP suggests that the loss ofthe EB1 functional domain plays a major part in thedevelopment of Gardners phenotype. The researchersshowed three codons to be associated with multiplicity ofextraintestinal manifestations: 1465, 1546, and 2621.37Whereas the first two codons are located in the -cateninbinding domains, the predicted mutated protein resultingfrom mutations in codon 2621 is located in the EB1binding site domain, and has all the -catenin bindingdomains intact. Therefore, the possibility exists that afunctional defect in EB1 as a result of defective binding toAPC, might, by itself, be responsible for CHRPE andother extracolonic phenotypic manifestations of FAP.

Alternatively, because APC mutations that cause

Gardners syndrome can also occur at the 5

end of the-catenin binding regions, it is possible that the cause ofGardners manifestation might lie in the more proximal,armadillo domain of APC. However, findings publishedby Ahmed and colleagues40 suggest otherwise. Whentesting three mutant APC alleles from Drosophila (twocontaining a stop codon within the armadillo region anda third containing the whole armadillo domain and twoseries of amino-acid repeats from the -catenin bindingdomain) the researchers showed that all three alleles hadthe same phenotypeie, retinal neuronal degenerationand pigment-cell hypertrophy.

However, in our opinion, this finding does not excludean important role of the armadillo domain and its binding

protein KIF3a in the pathogenesis of other FAP mani-festations, such as cerebellar medulloblastoma. Indeed,mutations in SUFU, a ciliary protein (figure 4), have beenshown to predispose to sporadic medulloblastoma.22Inactivating mutations in SUFU result in an illegitimateactivation of the Shh signalling pathway,22and, therefore,medulloblastoma belongs to the spectrum of clinicalmanifestations of cilia disorders. Like SUFU, KIF3a is anessential ciliary protein in neural cells, where it transportsAPC and -catenin along the microtubules and accumulatesthem in the tips of the cilia.25A truncated APC without thearmadillo repeat could be absent from the cilia in neuralcells, which might impair cell migration and, therefore,

could contribute to the occurrence of medulloblastoma inFAP. Mutations associated with medulloblastoma in FAPare clustered in the region encompassing the codons6791224.42 Although this region includes part of thearmadillo region, there are also mutations distal from itwithin the region of 15-amino-acid repeats that causemedulloblastoma. Therefore, a major role of KIF3a in thedevelopment of this tumour can not be established.

Other extraintestinal tumours result from cilia disordersWe found similarities that suggest that, in addition todesmoid tumours and medulloblastoma, other extra-intestinal tumours in patients with FAP can also resultfrom a ciliary disorder. Indeed, as occurs in von HippelLindau disease, where renal-cell carcinoma is preceded bythe formation of renal cysts,13desmoid tumours,43hepato-

blastoma,44

papillary thyroid carcinoma,45

and periampullarycarcinoma46 have been reported to originate from cysticlesions.

Therefore, by looking at the connections between theoncogenic manifestations in FAP and the ciliary diseasemanifestations, an exciting new perspective of thefunction of the cilia takes shape: the role of cilia inoncogenesis. In addition to VHLand SUFU, a few othercilia-related genes have been shown to be frequentlymutated in sporadic cancer in humans.21 As Mans andcolleagues22 have proposed, the participation of cilia inthe Shh-signalling, Wnt-signalling, and PDGFR-signallingpathways indicates an important role of the cilia incarcinogenesis, and the possibility exists that cilia act as

tumour suppressor organelles. We propose FAP as thedisease model to study this postulation.In this Personal View, we have provided arguments for

a new insight into the pathogenesis of FAP, explainedfrom the perspective of a ciliary defect. From thisperspective, the generation of Gardners manifestations,and the extraintestinal tumours noted in patients withthis syndrome, can be understood and explained by themany connections between APC and the cilia. Additionally,this notion opens a new range of potential therapeutic

Search strategy and selection criteria

Data for this Personal View were obtained by a search of

PubMed using the following terms: Gardners syndrome,Genotype AND phenotype AND correlations, APC,

Beta-catenin, EB1, ciliary disorders, primary cilia,

cysts, desmoid, osteomas, CHRPE, papillary thyroid,

medulloblastoma, and periampullary carcinoma. Only

papers published in English were used. No limitation in date

range was introduced. Information on APC and -catenin was

obtained from: OMIM, gene and protein sequences, conserved

domains, and the 3D databases from the US National Institute

of Health website. TheAPCmutation database was consulted

using the database at the Institute of Medical Genetics in

Cardiff, Wales, UK (HGMDR, copyright Cardiff University 2008).


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possibilities for the treatment of patients with FAP.Finally, as a result of the broad range of tumour types thatoccur in FAP, this disease seems to be an ideal model forexplaining the role of cilia in human neoplasia.

Contributors

EG had the idea for the paper, did the literature search, writing, andcontributed some of the figures. NVAMK helped with writing andcritical review of the paper and supplied the table and figures 3 and 4.

Conflicts of interest

The authors declared no conflicts of interest.

References1 Gardner EJ. Follow-up study of a family group exhibiting dominant

inheritance for a syndrome including intestinal polyps, osteomas,fibromas and epidermal cysts. Am J Hum Genet1962; 14:37690.

2 Groden J, Thliveris A, Samowitz W, et al. Identification andcharacterization of the familial adenomatous polyposis coli gene.Cell1991; 66:580600.

3 Fearnhead NS, Britton MP, Bodmer WF. The ABC of APC.Hum Mol Genet 2001; 10:72133.

4 Galiatsatos P, Foulkes WD. Familial adenomatous polyposisAm J Gastroenterol2006; 101:38598.

5 Schrder JM, Schneider L, Christensen ST, Pedersen LB. EB1 isrequired for primary cilia assembly in fibroblasts. Curr Biol2007;17:113439.

6 Sturt NJH, Gallagher MC, Bassett P, et al. Evidence for geneticpredisposition to desmoid tumors in familial adenomatous polyposisindependent of the germline APCmutation. Gut2004; 53:183236.

7 Hemmer PH, Zeebregts CJ, Van Baarlen J, Klaase JM. Image of themonth. Arch Surg2004; 139:223.

8 Payne M, Anderson JA, Cook J. Gardners syndromea case report.Brit Dent J2002; 193:38384.

9 Tiret A, Parc C. Fundus lesions of adenomatous polyposis.Curr Opin Ophthalmol1999; 10:16872.

10 Vasen HFA, Mslein G, Alonso A, et al. Guidelines for the clinicalmanagement of familial adenomatous polyposis (FAP). Gut 2008;57:70413.

11 Houlston RS, Fallon T, Harocopos C, Williams CB, Davey C, Slack J.Congenital hypertrophy of retinal pigment epithelium in patientswith colonic polyps associated with cancer family syndrome.Clin Genet1992; 42: 1618.

12 Bisgrove BW, Yost HJ. The roles of cilia in developmental disordersand disease. Development 2006; 133:413143.

13 Fliegauf M, Benzing T, Omran H. When cilia go bad: cilia defectsand ciliopathies. Nat Rev Mol Cell Biol2007; 8:88093.

14 Davenport JR, Yoder BK. An incredible decade for the primarycilium: a look at a once-forgotten organelle. Am J Renal Physiol2005; 289:F115969.

15 Cantagrel V, Silhavy JL, Bielas SL, et al. Mutations in the cilia geneARL13Blead to the classical form of Joubert syndrome.Am J Hum Genet2008; 83: 17079.

16 Oti M, Huynen MA, Brunner HG. Phenome connections.Trends Genet2008; 24:10306.

17 Aoki K, Taketo MM. Adenomatous polyposis coli (APC): amulti-functional tumor suppressor gene.J Cell Sci2007; 120:332735.

18 Benzing T, Simons M, Walz G. Wnt signalling in polycystic kidneydisease.J Am Soc Nephrol2007; 18:138998.

19 Saadi-Kheddouci S, Berrebi D, Romagnolo B, et al. Early developmentof polycystic kidney disease in transgenic mice expressing an activatedmutant of the -catenin gene. Oncogene2001; 20:597281.

20 Qian CN, Knol J, Igarashi P, et al. Cystic renal neoplasia followingconditional inactivation of Apc in mouse renal tubular epithelium.

J Biol Chem2005; 280: 393845.

21 Theisen CS, Wahl JK, Johnson KR, Wheelock MJ. NHREF links theN-cadherin/catenin complex to the platelet derived growth factorreceptor to modulate the actin cytoskeleton and regulate cellmotility. Mol Biol Cell2007; 18:122032.

22 Mans DA, Voest EE, Giles RH. All along the watchtower: is the cilium atumor suppressor organelle? Biochim Biophys Acta2008; 1786:14125.

23 Signoroni S, Frattini M, Negri T, et al. Cyclooxygenase-2 andplatelet-derived growth factor receptors as potential targets intreating aggresive fibromatosis. Clin Cancer Res2007; 13:503440.

24 Corbit KC, Shyer AE, Dowdle WE, et al. Kif3a constrains-catenin-dependent Wnt signalling through dual ciliary andnon-ciliary mechanisms. Nat Cell Biol2008; 10:7076.

25 Jimbo T, Kawasaki Y, Koyama R, et al. Identification of a linkbetween the tumour suppressor APC and the kinesin superfamily.Nat Cell Biol2002; 4:32327.

26 Faux MC, Coates JL, Catimel B, et al. Recruitment of adenomatouspolyposis coli and -catenin to axin-puncta. Oncogene2008;27:580820.

27 Rubinfeld B, Alberts I, Porfiri E, et al. Loss of -catenin regulationby the APC tumor suppressor protein correlates with loss ofstructure due to common somatic mutations of the gene.Cancer Res1997; 57:462430.

28 Wallis YL, Morton DG, McKeown CM, MacDonald F. Molecularanalysis of the APC gene in 205 families: extendedgenotype-phenotype correlations in FAP and evidence for the roleof APC amino acid changes in colorectal cancer predisposition.J Med Genet1999; 36: 1420.

29 Davies R, Armstrong JG, Thakker N, et al. Severe Gardnersyndrome in families with mutations restricted to a specific regionof the APC gene. Am J Hum Genet1995; 57:115158.

30 Bertario L, Russo A, Sala P, et al. Multiple approach to theexploration of genotype-phenotype correlations in familialadenomatous polyposis.J Clin Oncol2003; 21:1698707.

31 Bisgaard ML, Blow S. Familial adenomatous polyposis (FAP):genotype correlation to FAP phenotype with osteomas andsebaceous cysts. Am J Med Genet2006; 140A: 20004.

32 Bertario L, Russo A, Sala P, et al. Genotype and phenotype factorsas determinants of desmoid tumors in patients with familialadenomatous polyposis. Int J Cancer2001; 95:10207.

33 Miyaki M, Yamaguchi T, Iijima T, et al. Difference in characteristicsof APC mutations between colonic and extracolonic tumors of FAPpatients: variations with phenotype. Int J Cancer2008; 122: 249197.

34 Latchford A, Volikos E, Johnson V, et al. APCmutations inFAP-associated desmoid tumors are non-random but not justright. Hum Mol Genet 2007; 16:7882.

35 Nieuwenhuis MH, Vasen HFA. Correlations between mutation sitein APC and phenotype of familial adenomatous polyposis (FAP): areview of the literature. Crit Rev Oncol Hematol2007; 61:15361.

36 Eccles DM, van der Luijt R, Breukel C, et al. Hereditary desmoiddisease due to a frameshift mutation at codon 1924 of the APCgene. Am J Hum Genet 1996; 59:1193201.

37 Giardiello FM, Petersen GM, Piantadosi S, et al. APC genemutations and extraintestinal phenotype of familial adenomatouspolyposis. Gut 1997; 40: 52125.

38 Shields CL, Materin MA, Walker C, Marr BP, Shields JA.Photoreceptor loss overlying congenital hypertrophy of the retinalpigment epithelium by optical coherence tomography.Ophthalmology2006; 113:66165.

39 Haycraft CJ, Zhang Q, Song B, et al. Intraflagellar transport is essentialfor endochondral bone formation. Development2007; 134:30716.

40 Ahmed Y, Hayashi S, Levine A, Wieschaus E. Regulation ofArmadillo by a DrosophilaAPC inhibits neuronal apoptosis duringretinal development. Cell1998; 93:117182.

41 Schmitt A, Wolfrum U. Identification of novel molecularcomponent of the photoreceptor connecting cilium byimmunoscreens. Exp Eye Res2001; 73:83749.

42 Attard TM, Giglio P, Koppula S, Snyder C, Lynch HT. Brain tumorsin individuals with familial adenomatous polyposis. A cancer registryexperience and pooled case report analysis. Cancer 2007; 109:76166.

43 Amiot A, Dokmak S, Sauvanet A, et al. Sporadic desmoid tumor. Anexceptional cause of cystic pancreatic lesion.JOP2008; 9:33945.

44 Miller JH. The ultrasonographic appearance of cystichepatoblastoma.Radiology1981; 138:14143.

45 Ishay A, Elmalah I, Luboshitzky R. Papillary carcinoma in athyroglossal duct cyst. IMAJ 2008; 10:31213.

46 Ohtsuka T, Inoue K, Ohuchida J, et al. Carcinoma arising incholedochocele. Endoscopy 2001; 33:619.


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gardner’s syndrome (familial adenomatous polyposis)

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