Perturbation of membrane microdomains reduces mitogenic signaling and increases susceptibility to apoptosis after T cell receptor stimulation

Acid sphingomyelinase-deficient (asmase(-/-)) mice generated by gene targeting abundantly store sphingomyelin in the reticuloendothelial system of liver, spleen, bone marrow, and in brain. Liver cells of asmase(-/-) mice accumulate sphingomyelin and glycosphingolipids in purified lipid bilayers of microsomes, Golgi, and the plasma membrane, but cholesterol is depleted in the plasma membrane. Detergent-insoluble glycolipid-enriched membrane microdomains (GEM) can be isolated from hepatocytes, embryonic fibroblasts, and splenocytes of wild-type, but not of (-/-) mice, by sucrose gradient density centrifugation. asmase Lck and other Src-family kinases are reduced in isopycnic fractions of asmase(-/-) splenocytes compared to GEM-containing fractions of wild-type cells. The proliferation of (-/-) T lymphocytes is reduced, whereas their asmase susceptibility to Pas-induced apoptosis is increased after T cell receptor (TCR) stimulation. TNF receptor I signaling remains unimpaired. The perturbation of GEM impairs tyrosine phosphorylation and, consequently, mitogenic signaling of the TCR, Reduced MARK activity-dependent FLICE-like inhibitory protein (FLIP) expression in asmase(-/-) T lymphocytes increases their sensitivity towards Fas-mediated apoptosis.