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A medical perspective
Lecture 11:Cell biology 2014 (12/2 -14)
Definitions of disease:• When something is wrong with a bodily
function• A state that places individuals at increased risk of adverse consequences• Etcetera
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The cause of different diseases
Infectious diseases
CancerDiabetes
Heart disease AllergyMendelian/Genetic
diseases
100% genetics 100% environment
Complex multi-factorial diseases
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Three cytoskeleton systems: distinct but overlapping functions
- Cell shape and integrity
- Intracellular organization
- Motility of the whole cell or cellular appendages
Actin filaments
Intermediate filaments
Microtubules
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4Intermediate filaments and epithelia blisteringCytosolic intermediate filaments support:
1) Cell-cell contacts (desmosomes: cadherins)
2) Cell-ECM contacts (hemidesmosomes: integrins)
Mutations in keratin 5 or 14 cause Epidermolysis bullosa simplex (1/40 000), a disease manifested as blistering of the epidermis.
Alb
ert e
t al F
ig. 1
6-21
2.
1.5 + 14
1 + 10
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Consequences of dysfunctional nuclear lamina
Lamin A, B & C: intermediate filament proteins stabilize the nuclear envelope
Laminopathies are genetic diseases manifested as either:
I. Dystrophy of skeletal and/or heart muscles, caused by mutations affecting Lamin A/B or proteins attaching lamins to the nuclear envelope
II. Progeria, caused by mutations in the lamin A gene, or in a lamin A processing enzyme. This result in excessive farnesylation. A farnesyltransferase inhibitor, initially developed to target oncogenic Ras, delays progression.
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The actin cytoskeleton – an overview
• Support of the plasma membrane
• Cell migration
• Contraction
CytokinesisMuscle contraction
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Dysfunctional actin regulation in Wiskott-Aldrich syndrome
Manifested by:• Thrombocytopenia
• Eczema (skin blushing)
• Immunodeficiency syndrome
- Wiskott-Aldich syndrome (1/150.000) is caused by mutations in the Wiskott-Aldrich syndrome protein (WASP)
Deficient migratory and phagocytotic capacity of immune cells
- Can only be cured by a hematopoietic stem cell transplant
Underdeveloped cortical actin results in defective platelets
WASP Arp 2/3
WASP Arp 2/3 ZZZZ
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Pathogenic E. coli: actin dependent colonization
Enteropathogenic E. coli induce actincontaining pedestals in intestinal epithelia
Virulence factorsthat activate N-WASP
Activation of Arp 2/3
Loss of absorptive surface is onecause for the associated diarrhea
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1.
2.
3.
4.
5.
1-3) Phagocytosis and escape from phagosome
ActAActAActA
Arp 2/3
4) Bacterial multiplication
5) Penetration of a neighboring cell through actin based motility
Listeria: actin dependent motility
video 24.3-listeria_parasites
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The microtubule system - an overview
- Intracellular organization
Chromosome segregation
- Cell motility
Cell polarisationand transport
Movement of cellular appendages
Organelle positioning
Golgi
ER
Chem
otactic agent
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Lissencephaly: defective neuron migration
Normal brain Lissencephaly brain
mutated in many cases loss of dynein ( )dependent centrosome reorientation defective cell polarization
- Lissencephaly ("smooth brain," 1/30.000) is a disorder characterized by the lack of normal convolutions (folds) in the brain
- 1/30 000 births, early death in severe cases
Lis1
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Non-functional cilia in Kartagener syndrome- Kartagener syndrome (1/20.000) is caused by mutations affecting cilia specific dynein - Manifested by respiratory infections, infertility and situs inversus
Upper respiratory epithelia
NormalPatient with
Kartagener syndrome
Bacteria is not cleareddue to defective cilia
Bacteria is caught in mucus and cleared bya cilia mediated flow
Goblet cell
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Microtubule-poisoning drug: Taxol
• Alkaloid ester isolated from the bark of Taxus brevifolia (Pacific yew)
• Stabilization of microtubules
Treatment of breast, lung and ovarian cancer
Prevention of restenosis of coronary stents(Surface coating of stents local action)
Therapeutic uses:
Major side-effects: Bone marrow suppression, gastro-intestinal upset and peripheral neuropathy
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Microtubule-poisoning drug: Vinca alkaloids
• Isolated from Catharanthus roseus
• Sequesters tubulin
Treatment of leukemia, lymphoma, breast,lung, prostate, skin and testicular cancer
Therapeutic use:
Major side-effects: Bone marrow suppression, gastro-intestinal upset and peripheral neuropathy
• Named: Vinblastine, Vincristine, Vindesine and Vinorelbine
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X X
X X
X X
X X
X X
X X
Progression towards malignancy involves : i) uncontrolled proliferation, ii) resistance to apoptosis, iii) cell migration, iv) tissue invasion
Metastasis
An oncology perspective on signal transduction, cell growth, checkpoints, apoptosis and the cytoskeletons
animation 20.2 -contact_inhibitionvideo 20.1 -breast_cancer_cells
Clonal evolutionSelection of malignant clones
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16Two distinct types of ”cancer genes”
Gene YGene Y
Tumor suppressors
Two independent events
Loss-of-function
Gene XGene X
Oncogenes
A single genetic change
Gain-of-function
On
OffOn
Off
On
OffOn
On
Dominant phenotype
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Definitions: oncogenes and tumor suppressors
Ras
p53Rb
An oncogene is a gene that when mutated, or overexpressed, contributes to converting a normal cell intoa tumor cell (constitutive activity dominant phenotype)
A tumor suppressor-gene is a gene whose loss, or inactivation, contributes to converting a normal cell into a tumor cell (recessive phenotype)
Bcl-2
CKI
point mutation overexpression
Inactivating point mutations or loss of the entire gene(germ line mutation in one allele and/or acquired somatic mutations) 17
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Cell type specific proliferative signals
Cell type A Cell type B Cell type C
RTK Wnt Hedgehog
Cells from different tissues express distinct sets of growth factor receptors and signaling proteins
Alterationsin tumors: RTK signals Wnt signals Hedgehog signals
Major mitogensignaling pathway:
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G1
myc
Ras
Raf
Erk
XGF Wnt
Dishevelled
b-catenin
G1 myc
Frizzled
G1 myc
RTK
Gli
Fused
Patched
Smoothened
Gli
SuFu
Hedgehog
GSK-3b AxinAPC
Aberrant proliferative signals in tumors 19
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The
retin
obla
stom
a pa
thw
ay
Cdk G1
Cdk S
Rb
DNAreplisome ORC
Cdc6PP
p15Mitogen signaling
E2F
HPV E7
p21p16
Insensitivity of tumors to anti-growth signals
TGF-b
viral
20 = germ linemutations identified
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Survival factor signaling
Caspase 9 Caspase 3
Apoptosis
BH3only
Caspase 8
Adaptor
Deathreceptor
Ligand
BaxBcl-2
Evading cell death (apoptosis)
p53
Cyt. C
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Randomly acquired oncogenic mutations drives tumor progression
1. Self-sufficiency in proliferative signals
3. Evading cell death (apoptosis)
2. Insensitivity to anti-growth signals
4. Limitless replicative potential
5. Sustained angiogenesis
6. Metastasis capability
1
2
3
4
5
6
Mutation
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Same “diagnosis” but different set of mutations
1 2 3 4 5 6
X XX1 2 3 4 5 6
X X
X
Patient A with diagnosis X
Patient B with diagnosis X
X
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1013
Controlled and co-ordinated divisions
Cell death and replacement risk for mutations & chromosomal instability
How many somatic mutations during a life time?
Uncontrolled divisions Tumors
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– Human diploid genome: ~6 x109 bp
– Only some few errors per replication cycle
– Average t½ of cells is 7 years (range: 24h to >100 years)
Year 1-15
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Other genesCancer related genes
Time
Normal cells have a very low rate of mutations
Due to the low normal mutation frequency, progression to a fully malignant tumor is statistically improbable
How come that malignant tumors have either a lot of mutations (~10 %) or chromosomal aberrations (90 %)?
(~400 genes are frequently altered in tumors, 6 to 80 genes per “patient”)
Random mutation
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Genomic instability: Two distinct levels
1. Defective DNA repair (MIN)
2. Chromosome segregation errors (CIN)
X
Mutation in a gene encoding some enzyme required for DNA-repair
No repair many mutations accelerated tumor progression
X
Mis-segregation due to a defective a gene that encodes some protein essential for high fidelity chromosome segregation
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Other genesCancer related genes
Time
MIN reflects an escalated mutation rate
DNA repair (TS)
?? Often uncertain which ones of all the mutations that contribute to tumor progression
1 2 3 4 5 6
Genetic alteration
MIN: mini-satellite DNA instability (due to defective DNA repair)
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CIN through excessive centrosomesTwo centromes
More than two centrosomes
miss-segregation aneuploidyCIN: Chromosomal instability
Kinetochore attachments satisfy the spindle checkpoint
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Centrosome
CIN through loss of APC
Kinetochore
Centromere
The tumor suppressor gene productAPC functions as a MT plus-end stabilizing protein ( ) that facilitatesstable MT-kinetochore connections
AC
APC
CIN: Chromosomal instability
Satisfied spindle checkpoint
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1) A normal cell
2) A tumor cell with a (partially) defective spindle checkpoint
CIN through a defective spindle checkpoint
Delayed anaphase until all kinetochores are attached
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Genomic instability and tumor progression
xx
”Selection barriers”
Too much genetic
instability
”Optimal” genetic instability
A stable genome
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Principles of cancer treatment
Surgery-
Chemotherapy-
Radiation-
Impossible to remove all cancer cells
Targets both cancer- and normal cells
Side-effects
General chemotherapy: drugs that interferes with: i) DNA-replicationii) DNA structureiii) The function of the microtubule-system
Chemotherapy may also include cell type specific drugs. E.g. inhibition of hormone dependent tumor growth
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Selective killing of tumor cells by chemotherapy
x x
Mutations that inactivate various checkpoints are common in malignant tumors no cell cycle arrest in patients treated by chemotherapy!