Granzyme B-mediated degradation of T-cell receptor ζ chain

• Published in: Cancer research (Chicago, Ill.) Vol. 62; no. 17; pp. 4884 - 4889
• Main Authors: WIECKOWSKI, Eva, WANG, Gui-Oiang, GASTMAN, Brian R, GOLDSTEIN, Leslie A, RABINOWICH, Hannah
• Format: Journal Article
• Language: English
• Published: Philadelphia, PA American Association for Cancer Research 01-09-2002
• Subjects: Amino Acid Chloromethyl Ketones - pharmacology; Antibiotics. Antiinfectious agents. Antiparasitic agents; Antiviral agents; Apoptosis - drug effects; Apoptosis - physiology; Biological and medical sciences; Caspase 3; Caspase Inhibitors; Caspases - metabolism; Cysteine Proteinase Inhibitors - pharmacology; Granzymes; Humans; Jurkat Cells - drug effects; Jurkat Cells - metabolism; Jurkat Cells - pathology; Medical sciences; Membrane Proteins - metabolism; Pharmacology. Drug treatments; Receptors, Antigen, T-Cell - metabolism; Serine Endopeptidases - metabolism; Serine Endopeptidases - pharmacology; Human; T cell receptor; Serine endopeptidases; Enzyme; Caspase; In vitro; Biological activity; Serine enzyme; Peptidases; Signal transduction; Granzyme B; Zéta-Peptide chain; Established cell line; T-Lymphocyte; Enzymatic digestion; Hydrolases; Antiviral; Mechanism of action
• ISSN: 0008-5472; 1538-7445

We recently reported that the T-cell receptor (TCR)-zeta chain is cleaved by caspase-3 and -7 in apoptotic T lymphocytes or in a cell-free system. We report here that the zeta chain is also a direct substrate for granzyme B (GrB) proteolytic activity. Loss in expression of TCR-zeta was observed in Jurkat T leukemic cells treated by a combination of GrB and a replication-deficient adenovirus. Although the apoptosis initiated in these cells by GrB was significantly reduced by the pancaspase inhibitor Z-VAD-FMK, TCR-zeta degradation was not prevented. These findings suggest that the GrB-mediated degradation of TCR-zeta chain can proceed despite the efficient inhibition of caspase activity. An in vitro translated TCR-zeta product was efficiently cleaved by GrB, which suggests that the TCR-zeta protein is a direct substrate for GrB. As assessed by site-directed mutagenesis, the activity of GrB was directed toward aspartic acid residues that were different from those of recombinant caspase-3. Whereas caspase-3 cleavage products appear to accumulate, the GrB-generated products seem to undergo further degradation, which suggests the presence of multiple GrB-specific cleavage sites within the TCR-zeta protein. These findings suggest that the TCR-zeta protein in target T lymphocytes serves as a substrate for the proteolytic activities that are featured by the two major mechanisms of cytotoxicity: death receptor pathways mediated by caspases and granule exocytosis mediated by direct GrB activity or GrB-activated caspases. TCR-zeta protein degradation may be of significance in cytotoxic mechanisms directed against T cells infected with viruses, such as HIV-1, in which the TCR-zeta protein is used for viral pathogenesis.