INHIBITORS OF CGMP-DEPENDENT PROTEIN-KINASE BLOCK SENESCENCE INDUCED BY INACTIVATION OF T-ANTIGEN IN SV40-TRANSFORMED IMMORTAL HUMAN FIBROBLASTS

Immortal human fibroblasts isolated following transfection with thermo labile simian virus 40 T antigen lost division potential upon shift up in temperature due to heat inactivation of the antigen. Such cells sh owed a concomitant change in the distribution of a mortality marker, m ortalin, from a juxtanuclear cap like distribution of immortal cells t o a uniform cytosolic distribution of mortal cells. We made an attempt to modulate the above inducible system of cellular senescence using v arious protein kinase inhibitors. Among the indolocarbazole type inhib itors tested, only KT5823, defined as a specific inhibitor of cGMP-dep endent protein kinase, blocked the loss of division potential as deter mined by cell growth and colony forming ability. This inhibitor also p revented the above change in mortalin distribution due to temperature shift. In addition, the isoquinoline sulfonamide derivatives H8, H9, H 88 and H89, all shown to inhibit cGMP-dependent protein kinase, suppre ssed the senescence. Inhibitors specific to other types of protein kin ases, protein phosphatases or tyrosine kinases tested had no effect. S ince there was no difference between the effective and non-effective i nhibitors in their effects on cell cycle progression, cell cycle arres t by itself cannot account for the above phenomenon. These results sug gest that a signaling pathway possibly mediated by cGMP-dependent prot ein kinase is involved in the induction of cellular senescence.