Stimulation of CD95 (Fas) blocks T lymphocyte calcium channels through sphingomyelinase and sphingolipids

Departments of ^*Physiology I, ^‡Radiooncology, and ^§Neurology, University of Tübingen, Gmelinstr. 5, D-72076 Tübingen, Germany

Edited by Bertil Hille, University of Washington, Seattle, WA, and approved August 26, 1999 (received for review April 5, 1999)

Abstract

Calcium influx through store-operated calcium release-activated calcium channels (CRAC) is required for T cell activation, cytokine synthesis, and proliferation. The CD95 (Apo-1/Fas) receptor plays a role in self-tolerance and tumor immune escape, and it mediates apoptosis in activated T cells. In this paper we show that CD95-stimulation blocks CRAC and Ca²⁺ influx in lymphocytes through the activation of acidic sphingomyelinase (ASM) and ceramide release. The block of Ca²⁺ entry is lacking in CD95-defective lpr lymphocytes as well as in ASM-defective cells and can be restored by retransfection of ASM. C2 ceramide, C6 ceramide, and sphingosine block CRAC reversibly, whereas the inactive dihydroceramide has no effect. CD95-stimulation or the addition of ceramide prevents store-operated Ca²⁺ influx, activation of the transcriptional regulator NFAT, and IL-2 synthesis. The block of CRAC by sphingomyelinase metabolites adds a function to the repertoire of the CD95 receptor inhibiting T cell activation signals.

Footnotes

↵ † To whom reprint requests should be addressed. E-mail: alepplew{at}uni-tuebingen.de.
↵ ¶ E.G. and F.L. contributed equally to this work.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations:

CD95L,

CD95 ligand;

ASM,

acidic sphingomyelinase;

CRAC,

calcium release-activated calcium channels;

[Ca2+]i,

intracellular Ca2+ concentration;

TG,

thapsigargin;

NPDA,

Niemann–Pick Disease type A;

TCR,

T cell receptor;

PHA,

phythaemaglutinin