Retinoic acid-induced tissue transglutaminase and apoptosis in vascular smooth muscle cells

Retinoids exert antiproliferative and prodifferentiating effects in vascula r smooth muscle cells (SMCs) and reduce neointimal mass in balloon-injured blood vessels. The mechanisms through which retinoids carry out these effec ts are unknown but likely involve retinoid receptor-mediated changes in gen e expression. Here we report the cloning, chromosomal mapping, and biologic al activity of the retinoid-response gene rat tissue transglutaminase (tTG) , Northern blotting studies showed that tTG is rapidly and dose-dependently induced in a protein synthesis-independent manner after stimulation with t he natural retinoid all-trans retinoic acid (atRA), The induction of tTG wa s selective for atRA and its stereoisomers 9-cis and 13-cis RA, because lit tle or no elevation in mRNA expression was observed with a panel of growth factors. Western blotting and immunofluorescence confocal microscopy showed an accumulation of cytosolic tTG protein after atRA stimulation. Radiolabe led cross-linking studies revealed a corresponding elevation in in vitro tT G activity. The increase in tTG activity was reduced in the presence of 2 d istinct inhibitors of tTG (monodansylcadaverine and cystamine), atRA-induce d tTG mRNA and protein expression were followed by a significant elevation in SMC apoptosis. Such retinoid-induced programmed cell death could be part ially inhibited with each tTG inhibitor and was completely blocked when bot h inhibitors were used simultaneously. These results establish a role for a tRA in the sequential stimulation of tTG and apoptosis in cultured SMCs. at RA-mediated apoptosis in SMCs seems to require the participation of active tTG, suggesting a potential mechanistic link between this retinoid-inducibl e gene and programmed cell death.