The Bcl-2 transgene protects T cells from renal cell carcinoma-mediated apoptosis.
OBJECTIVE
Tumors induce T-cell apoptosis as a mechanism of inhibiting antitumor immunity. Using coculture experiments, it has been shown that tumor lines stimulate T-cell apoptosis by a pathway involving a mitochondrial permeability transition and cytochrome c release. Activated T cells express abundant levels of Bcl-2, an antiapoptotic molecule that would be expected to confer resistance to such tumor-mediated killing. We examined the mechanism by which Bcl-2 is dysregulated in T cells exposed to the renal tumor line SK-RC-45, and we determined whether overexpressing Bcl-2 protects T cells from tumor-mediated apoptosis.


METHODS
Activated T lymphocytes and Jurkat cells transfected or not transfected with Bcl-2 were exposed to SK-RC-45 for 48-72 h. After coculture, lymphocytes were analyzed for Bcl-2 expression using Western analysis and for tumor-induced apoptosis by terminal deoxynucleotidyl transferase-mediated nick end labeling. The role of SK-RC-45-stimulated caspase activation in degrading T-cell Bcl-2 was assessed using a pan-caspase inhibitor, as well as a specific inhibitor of caspase-9.


RESULTS
The renal cell carcinoma cell line SK-RC-45 sensitizes peripheral blood activated T lymphocytes and Jurkat cells to apoptosis by a mechanism that involves degradation of the antiapoptotic protein Bcl-2. The SK-RC-45-induced modulation of lymphocyte Bcl-2 levels was largely caspase independent because pretreatment of T cells with pan-caspase inhibitor III or an inhibitor of caspase-9 had minimal or no effect on stabilizing the protein, although it did provide protection against apoptosis. Overexpression of Bcl-2 protected Jurkat cells from tumor-mediated killing.


CONCLUSIONS
Bcl-2 inhibition is a mechanism by which tumors may render lymphocytes sensitive to other tumor-derived, proapoptotic stimuli.
D017209:Apoptosis / Q000235:genetics*; D002292:Carcinoma, Renal Cell / Q000235:genetics / Q000473:pathology*; D053453:Caspase 9; D061945:Caspase Inhibitors; D002460:Cell Line; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation; D019254:Genes, bcl-2 / Q000235:genetics*; D006801:Humans; D019169:Jurkat Cells; D007680:Kidney Neoplasms / Q000235:genetics / Q000473:pathology*; D008213:Lymphocyte Activation; D013601:T-Lymphocytes / Q000276:immunology / Q000502:physiology*; D014162:Transfection
D061945:Caspase Inhibitors; D015853:Cysteine Proteinase Inhibitors; C506433:CASP9 protein, human; D053453:Caspase 9