THE IMPORTANCE OF THE GTP-BINDING PROTEIN TISSUE TRANSGLUTAMINASE IN THE REGULATION OF CELL-CYCLE PROGRESSION

Tissue transglutaminase (tTgase) is a GTP-binding Ca2+-dependent enzyme which catalyses the post-translational modification of proteins via epsilon(gamma-glutamyl) lysine bridges, Recent evidence suggests that the GTP-binding activity of tTgase may be important in intracellular signalling thus explaining some of the diverse suggested roles for the enzyme, In the following work a malignant hamster fibrosarcoma (Met B) has been stably transfected with both the full length tTgase cDNA (wild type) and a mutant form of the cDNA,whereby the active site cysteine (Cys 277) has been replaced by serine, Expression of this mutant cDNA leads to a protein with GTP binding activity which is deficient of protein crosslinking activity, When synchronised into S-phase and allowed to progress through the cell cycle tTgase transfected clones (both mutant and wild type), when compared to transfected controls, show a delayed progression from S-phase to G(2)/M when analysed by flow cytometry which appears to be elicited by the G-protein activity of the tTgase.