DIFFERENTIAL REGULATION OF DISCRETE APOPTOTIC PATHWAYS BY RAS

The products of the ras genes are known to regulate cell proliferation and differentiation; recently, they have been found to play a role in apoptosis, The expression of oncogenic p21(ras) in a number of cell t ypes, including Jurkat (a human T lymphoblastoid cell line) and murine fibroblasts, makes the cells susceptible to apoptosis following suppr ession of protein kinase C (PKC) activity (PKC/Ras-mediated apoptosis) , Engagement of Fas antigen, a potent effector of apoptosis, activates cellular p21(ras), which may be required for completion of the cell d eath program. To further investigate the role of p21(ras) in the regul ation of apoptosis, the cellular mechanisms employed in these two apop totic processes in which Ras activity is involved (PKC/Ras-related and Fas-triggered apoptosis), was explored. Increasing p21(ras) activity by expressing v-ras or by treatment with an antisense oligonucleotide to the GTPase-activating protein was found to accelerate the Fas-media ted apoptotic process in Jurkat and mouse LF cells. PKC/Ras-related ap optosis was associated with, and required, cell cycle progression, acc ompanied by the expression of the G(1)/S cyclins, In contrast, Fas eng agement, although inducing a vigorous and PKC-independent activation o f endogenous p21(ras), did not alter cell cycle progression, nor did i t require such progression for apoptosis, Both the protein synthesis i nhibitor cycloheximide and cyclin E antisense oligonucleotides partial ly abolished PKC/Ras-mediated apoptosis but had only a moderate effect on Fas-induced apoptosis, In contrast, the CED-3/interleukin-1 beta-c onverting enzyme (ICE) protease inhibitor Z-VADfmk efficiently suppres sed Fas-induced apoptosis and only marginally inhibited PKC/Ras-mediat ed apoptosis, Induction of both pathways resulted in activation of the Jun NH2-terminal kinase/JUN signaling system. These results suggest t hat different cell death programs, such as PKC/Ras-mediated and Ras-me diated apoptosis, may be interconnected via p21(ras) and perhaps Jun N H2-terminal kinase/JUN, In response to various death stimuli, p21(ras) may act as a common intermediate regulator in the transduction of apo ptotic signals.