Cell cycle phase-specific survival of CD95 ligand-challenged Jurkat cells:Upregulation of heat-shock response

An important means of regulating T-cell function occurs via physical deleti on (cytolysis) of unnecessary/unwanted T cells. Among cytolytic pathways, C D95 (Fas)-based killing plays a prominent role. Although activation of T ce lls results in rapid upregulation of surface CD95 expression, sensitivity t o CD95-based killing lags behind. To assess determinants of resistance to C D95-based killing, we used Jurkat cells as a model. Analysis of the 10% sur vivors of a LD90 dose of CD95 ligand (CD95L) at 24 h demonstrated them to a rise preferentially from the S + G2/M phases of the cell cycle and to remai n clustered in S + G2/M without undergoing cell division. Protein immunoblo t, immunocytochemistry, and RT-PCR analyses demonstrated that hsp72 was mar kedly upregulated in CD95L survivors within hours of CD95L challenge, indic ative of a heat-shock response. Indeed, exposure of Jurkat cells to bona fi de heat shock did markedly upregulate hsp72 and, upon subsequent CD95L chal lenge, did greatly enhance cell survival with persistent clustering to S G2/M. These findings collectively suggest that in response to a CD95L insul t, development of a heat-shock response above some critical threshold level can protect against lethality. This raises the possibility that exaggerate d and/or protracted heat-shock responses under an vivo conditions may favor the survival of T cells (including autoaggressive T cells) that otherwise would be destined to die via a CD95-based pathway. (C) 2001 Academic Press.