GTP-binding-defective forms of tissue transglutaminase trigger cell death.
Tissue transglutaminase (TGase-2), which binds GTP and catalyzes the cross-linking of proteins (transamidation), has been implicated both in the promotion of cell death and in the protection of cells against apoptotic insults. However, a novel transcript originally identified from the brains of Alzheimer's patients, encoding a truncated form of TGase-2 (called TGase-S), shows strong apoptotic activity. TGase-S exhibits no detectable GTP-binding capability, suggesting that its ability to induce cell death might be due to its inability to bind GTP. Thus, we have examined whether eliminating the GTP-binding capability of full-length human TGase-2 would prevent it from conferring protection against apoptotic challenges and instead convert it into a protein that causes cell death. A number of point mutants of human TGase-2 defective for binding GTP, as well as a mutant that shows impaired GTP-hydrolytic activity, were generated. Similar to what we had found for TGase-S, there was a time-dependent decrease in the expression of the GTP-binding-defective TGase-2 mutants in different cell lines, whereas the expression of wild-type TGase-2 and the GTP hydrolysis-defective mutant was sustained. Moreover, the GTP-binding-defective TGase-2 mutants induced cell death. The cell death responses triggered by these mutants were not due to their transdamidation activity, because double-mutants that were both GTP-binding- and transamidation-defective also stimulated cell death. Therefore, these results point to the inability to bind GTP as being sufficient for the apoptotic activity exhibited by the TGase-S protein. They also highlight a novel example of how the loss of GTP-binding activity can convert a protein that provides protection against apoptotic stimuli into a cell death-promoting factor.
Datta
Sunando
S
Department of Chemistry and Chemical Biology, Baker Laboratory, College of Veterinary Medicine, Cornell University, Ithaca, New York 14853, USA.
Antonyak
Marc A
MA
Cerione
Richard A
RA
D000818:Animals; D001665:Binding Sites; D016923:Cell Death; D002460:Cell Line; D019204:GTP-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic; D006160:Guanosine Triphosphate / Q000378:metabolism*; D006801:Humans; D006868:Hydrolysis; D051379:Mice; D008958:Models, Molecular; D009154:Mutation / Q000235:genetics; D011485:Protein Binding; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D017434:Protein Structure, Tertiary; D011503:Transglutaminases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
D006160:Guanosine Triphosphate; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D011503:Transglutaminases; D019204:GTP-Binding Proteins