title: Caspase-mediated degradation of T-cell receptor zeta-chain.
abstract: We recently reported an association between loss in T-cell receptor (TcR) zeta-chain expression and tumor-induced apoptosis of T lymphocytes. In this study, the possibility that zeta-chain serves as a direct substrate for activated caspases was investigated. Here, we report that two DXXD motifs, which are putative recognition sequences for caspase-3-related proteases and are present in the amino acid sequence of the zeta-chain, are cleaved in apoptotic Jurkat T lymphocytes. Cleavage of zeta-chain in Jurkat cells ligated by agonistic anti-Fas antibody was inhibited in the presence of peptide inhibitors of caspases, including the pan-caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone and N-benzyloxycarbonyl-Asp-Glu-Val-Asp-fluoromethyl ketone, an inhibitor of caspase-3-like activity. Fas-induced cleavage of zeta-chain was also inhibited in Jurkat cells overexpressing the intracellular inhibitors of caspase activity, Bcl-2 or cytokine response-modifier A. In vitro translated zeta-chain was cleaved in a similar fashion by recombinant caspase-3 or caspase-7 in a dose-dependent manner. In the presence of N-benzyloxycarbonyl-AspGlu-Val-Asp-fluoromethyl ketone, no cleavage of in vitro translated zeta-chain was observed. These results suggest that the loss of TcR zeta-chain, previously associated with tumor-induced immune dysfunction and more recently associated with tumor-induced apoptosis of T lymphocytes, is mediated by a direct degradation of the zeta-chain by activated caspases. This is the first report of involvement of caspases in degradation of the zeta protein.
authors: Department of Otolaryngology, University of Pittsburgh School of Medicine, Pennsylvania 15213, USA.
authors: B R
authors: BR
authors: Gastman
authors: D E
authors: DE
authors: Johnson
authors: T L
authors: TL
authors: Whiteside
authors: H
authors: H
authors: Rabinowich
mesh_terms: D000595:Amino Acid Sequence; D017209:Apoptosis; D020169:Caspases / Q000502:physiology*; D006801:Humans; D019169:Jurkat Cells; D008565:Membrane Proteins / Q000378:metabolism*; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism*; D011994:Recombinant Proteins / Q000494:pharmacology; D019014:fas Receptor / Q000502:physiology
chemical_list: D008565:Membrane Proteins; D011948:Receptors, Antigen, T-Cell; D011994:Recombinant Proteins; C054979:antigen T cell receptor, zeta chain; D019014:fas Receptor; D020169:Caspases