The 55 kDa Tissue Transglutaminase Cross-Linking Active Isoform TG Induces Cell

Death

Danstan Mogire

INTRODUCTION•Tissue transglutaminase (T.G.C) is a protein enzyme with a variety of functions some of which may include apoptosis (cell death). This experiments tries to prove that tissue transglutaminase plays a significant role in cell apoptosis by playing some role in the formation of the apoptotic bodies since some traces of T.G.C could be detected after apoptosis.

•Tissue Transglutaminase is the most widely expressed member of the Transglutaminase family and almost all cell types in the body express it to varying extents.• Among its many supposed functions, it appears to play a role in wound healing, apoptosis, and extracellular matrix development. •The primary function of Tissue Transglutaminase is Transamidation

Transamidation

Deamination

Transamidation

Acyl DonorsAcyl Acceptors

Reactions catalyzed by the transamidase activity of TGC

An isopeptide bond forms when the ε-group of a peptide bound lysine is the acyl-acceptor resulting crosslinking of two proteins.

Water molecule as an acyl-acceptor to deaminate a peptide-bound glutamine residue and convert it to a

glutamate residue.

A primary amine acts as acyl-acceptor, resulting to an isopeptide bond which are resistant to disruptive physical or chemical forces

The crosslink does not have to be an isopeptide bond. A primary amine can act as

a crosslinker between two proteins.

Gundemir S, Colak G, Tucholski J, and Johnson G.V.W. (2012) Transglutaminase 2: A Molecular Swiss Army Knife Biochim Biophys Acta ; 1823(2): 406–419.

REGULATION

Activation of TGC has been shown to be accompanied by large conformational changes, switching from a compact (inactive) to an extended (active) conformation. As shown in the figure on the left.

Compact/Inactive Extended /Active

The transamidating activity of TGC is regulated in cells by reversible conformational changes of the protein. This which shifts TGC to the “open” (extended) conformation, thereby unmasking the enzyme's active center, and inhibition by GTP, GDP, and ATP, which constrains it in the“closed” (compact) conformation

 It requires calcium as a cofactor for transamidation activity. Transcription is increased by retinoic acid

Role In DiseaseTGC is best known for its link with celiac disease. Anti-transglutaminase antibodies (ATA) result in a form of gluten sensitivity.

TGC is also believed to be involved in several neurodegenerative disorders including Alzheimer, Parkinson and Huntington diseases.

This conclusion was reached because TGC is the most prevalent neuronal transglutaminase, and in the human brain increases in TGC expression have been observed in a number of chronic or acute neuropathological conditions. Due to this up regulation, it was hypothesized that TGC facilitates neuronal cell death in neurodegenerative diseases.

TGC expression is elevated in multiple cancer cell types and is implicated in drug resistance and metastasis due to its ability to promote mesenchymal transition and stem cell like properties.

The Eight Isoforms of Transglutaminase

Name Gene Activity Chromosome

Factor XIII (fibrin-stabilizing factor) F13A1, F13B coagulation 6p25-p24

Keratinocyte transglutaminase TGM1 skin 14q11.2

Tissue transglutaminase TGC/TGM2 ubiquitous 20q11.2-q12

Epidermal transglutaminase TGM3 skin 20q12

Prostate transglutaminase TGM4 prostate 3p22-p21.33

TGM X TGM5 skin 15q15.2

TGM Y TGM6 unclear 20q11-15

TGM Z TGM7 testis, lung 15q15.2

Fig. 1 Genomic organization of the human TGC gene isolated from foreskin P1 genomic library shown in scale (kb). Top: Genomic organization. Exons (13) are shown in solid boxes and labeled by Arabic numbers. Introns(12) are represented by open boxes and indicated by Roman numerals.

Fraij BM and Gonzales R (1997) Organization and structure of the human tissue transglutaminase gene. Biochimica et Biophysica Acta (BBA) - Gene Structure and Expression, 1354: 65 - 71

Genomic Organization and Structure

• Difference between TG and TGC

Fraij BM (2014) The 55 kDa Tissue Transglutaminase Cross-Linking Active Isoform TG Induces Cell DeathWILEY PERIODICALS, INC. DOI 10.1002/mc.22134

EXPERIMENTAL METHOD1. MDA cells were grown in 5% CO2 at 37 degree C, were grown in DMEM supplemented with 10% FBS and Maitotoxine.

2. Grow the MDA cells in a flask using a media and applied Retinoic Acid through out keeping them in incubator and changing the media within 2 to 3 days accordingly. Split the cells using Trypsin, centrifuge at 5 kps and collect them using a 5X Buffer in a tube..

EXPERIMENTAL METHODS: Column ChromatographyGradient dependent column chromatography was performed using Ammonium Bicarbonate or Tris as the mobile phase. Samples were collected manually.

• Protein separation was obtained by salt gradient. Lower size isoforms eluted early at 0.1-0.2 M NaCl and the Full length TGC eluted at 0.3-0.6 M NaCl.

• The NH4HCO3 showed a significant variation on the salt gradient, and was better than the TRIS to isolate the bands at ~55 KDa

EXPERIMENTAL METHODS: SDS/PAGE/ Western Blot7. After collecting the samples add 5X buffer, sonicate and run the Polyacrylamide gel electrophoresis for 1 hr. and 15 min. Prepare the second step which is running the western blot. After the bands are transferred on the membrane wash with TBS and add Primary antibody wash for about 1 hr., wash with TBST (2X) and TBS (1X), and Secondary antibody, wash for about 2 hrs. and develop using the color reagent to identify the bands.

EXPERIMENTAL METHODS

• We applied 50 ul of the sample to identify the bands.

• We identified bands approximately around 55 KDa, the red mark on the figure above shows the position of the isoforms of the transglutaminase.

Protein expression was examined by Western Blot

Results

The results on the left go on to show evidence of a higher rate of cell death with the increase in transglutaminase expression both in retinoic acid treated cells and in transient transfected cells. We demonstrate for the first time that the highest rates of apoptosis were found in cells transfected with the potent TG isoform

Apoptotic cells were quantitatively identified with a hemocytometer shown below

Conclusions and Discussion• The results support our hypothesis, that the

cross- linking active TGC isoform is a potent inducer of apoptosis.

• It helps to clarify the role of TGC isoforms in transglutaminase activity.

• These results suggest that the 55 kDa TG isoform may have significant roles in the physiologic events of both healthy and diseased tissues.

REFERENCES• Gundemir S, Colak G, Tucholski J, and Johnson G.V.W. (2012) Transglutaminase 2: A Molecular Swiss Army Knife Biochim Biophys Acta ; 1823(2): 406–419.

Fraij BM and Gonzales R (1997) Organization and structure of the human tissue transglutaminase gene. Biochimica et Biophysica Acta (BBA) - Gene Structure and Expression, 1354: 65 - 71

Fraij BM (2014) The 55 kDa Tissue Transglutaminase Cross-Linking Active Isoform TG Induces Cell DeathWILEY PERIODICALS, INC. DOI 10.1002/mc.22134

ACKNOWLEDGEMENTS• Dr. Bassam Fraij

• Dr. Rush Oliver

• Mohammed Munir