CD95/Fas induces cleavage of the GrpL/Gads adaptor and desensitization of antigen receptor signaling

The balance between cell survival and cell death is critical for normal lym phoid development. This balance is maintained by signals through lymphocyte antigen receptors and death receptors such as CD95/Fas, In some cells, lig ating the B cell antigen receptor can protect the cell from apoptosis induc ed by Cogs. Here we report that ligation of Cogs inhibits antigen receptor- mediated signaling. Pretreating CD40-stimulated tonsillar B cells with anti -CD95 abolished B cell antigen receptor-mediated calcium mobilization, Furt hermore, cogs ligation led to the caspase-dependent inhibition of antigen r eceptor-induced calcium mobilization and to the activation of mitogen-activ ated protein kinase pathways in B and T cell lines. A target of Cogs-mediat ed caspase 3-like activity early in the apoptotic process is the adaptor pr otein GrpL/Gads, GrpL constitutively interacts with SLP-76 via its C-termin al SH3 domain to regulate transcription factors such as NF-AT, Cleavage of GrpL removes the C-terminal SH3 domain so that it is no longer capable of r ecruiting SLP-76 to the membrane. Transfection of a truncated form of GrpL into Jurkat T cells blocked T cell antigen receptor-induced activation of N F-AT, These results suggest that cogs signaling can desensitize antigen rec eptors, in part via cleavage of the GrpL adaptor.