Stimulation of phosphatidylinositol turnover is a key event for Fas-dependent, activation-induced apoptosis in human T lymphocytes.

We have analyzed the requirements for activation-induced apoptosis in Jurkat T cells expressing the heterologous human muscarinic type 1 receptor (HM1R; J-HM1-2.2 cells) that is coupled to phosphatidylinositol turnover through a protein tyrosine kinase-independent, G protein-regulated mechanism. Triggering of HM1R with the agonist carbachol is sufficient to induce apoptosis in J-HM1-2.2 cells. Apoptosis is also induced in J-HM1-2.2 cells by triggering of the TCR. Calcium influx, intracellular Ca2+ increase, calcineurin function, and de novo protein synthesis are necessary for receptor-controlled apoptosis. However, blocking protein kinase C with a specific inhibitor does not abrogate receptor-induced apoptosis. Furthermore, HM1R-induced apoptosis is inhibited by blocking Fas ligand/Fas interaction with an antagonist anti-Fas Ab, and Fas ligand mRNA and protein are expressed in J-HM1-2.2 cells stimulated through the HM1R. Therefore, protein tyrosine kinase activation is not an absolute requirement for receptor-controlled Fas ligand expression. Taken together, the results demonstrate that stimulation of phosphatidylinositol turnover can induce apoptosis through a Fas-dependent mechanism that requires calcineurin stimulation, but not protein kinase C activation.