The importance of the GTP-binding protein tissue transglutaminase in the regulation of cell cycle progression

Abstract

Tissue transglutaminase (tTgase) is a GTP-binding Ca 2+-dependent enzyme which catalyses the post-translational modification of proteins via ϵ(γ-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the full length tTgase cDNA (wild type) and a mutant form of the cDNA whereby the active site cysteine (Cys 277) has been replaced by serine.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.