Fas-mediated apoptosis of proliferating, transiently growth-arrested, and senescent normal human fibroblasts

Previous studies suggest that apoptotic signaling may require proteins that are critical to cellular proliferation and cell cycle regulation. To furth er examine this question, proliferating, transiently growth-arrested, and s enescent normal human fibroblasts were induced to undergo apoptosis in resp onse to two distinct mediators of apoptosis-Fas (APO-1/CD95) death receptor and staurosporine, Ligation of the Fas receptor in the presence of cyclohe ximide or actinomycin D resulted in apoptosis of proliferating cells, cells transiently growth arrested by gamma-irradiation or serum starvation (i.e. , G(0) arrest), and permanently growth-arrested senescent fibroblasts, Prol iferating and G(0)-arrested cells were also susceptible to staurosporine-me diated apoptosis. Surprisingly, gamma-irradiated cells did not undergo stau rosporine-mediated apoptosis, and remained viable for a prolonged time. Fas -mediated apoptosis of senescent fibroblasts was evidenced by chromosome co ndensation and by activation of caspase-8 and -3, proteases crucial for the execution of the Fas apoptosis pathway, In addition, ligation of the Fas r eceptor in G(0)-arrested cells did not result in the activation of p34(cdc2 ) kinase, arguing that activation of this kinase is not essential in this a poptotic process. From these studies we conclude that proliferating, transi ently growth-arrested, and senescent normal human fibroblasts are susceptib le to apoptotic signals and that apoptosis is not necessarily dependent upo n cell cycle or proliferative state of the cell. (C) 2000 Academic Press.