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Sensitization of immunoresistant prostate carcinoma cell lines to Fas/Fas ligand‐mediated killing by cytotoxic lymphocytes: Independence of de novo protein synthesis
Author(s) -
Frost Patrick J.,
Belldegrun Arie,
Bonavida Benjamin
Publication year - 1999
Publication title -
the prostate
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.295
H-Index - 123
eISSN - 1097-0045
pISSN - 0270-4137
DOI - 10.1002/(sici)1097-0045(19990915)41:1<20::aid-pros4>3.0.co;2-w
Subject(s) - du145 , cytotoxic t cell , fas ligand , tumor necrosis factor alpha , sensitization , cancer research , fas receptor , immunology , pharmacology , medicine , biology , apoptosis , programmed cell death , prostate , biochemistry , in vitro , cancer , lncap
BACKGROUND We recently reported that drug‐resistant prostate tumor cells (DU145, PC‐3) are resistant to Fas‐mediated killing by cytotoxic lymphocytes, and that this resistance can be overcome by treatment with subtoxic concentrations of chemotherapeutic drugs. Fas belongs to the tumor necrosis factor (TNF) family of receptors. Since resistance to TNF‐α‐mediated killing has been shown to be due, in part, to the presence of protective factors and that inhibitors of protein synthesis can sensitize cells to TNF‐α killing, we hypothesized that resistance to Fas‐mediated killing may be due to similar mechanisms. Since sensitization is achieved with chemotherapeutic drugs, and some chemotherapeutic drugs can also inhibit protein synthesis, we tested whether sensitization of prostate tumor cells to Fas ligand (Fas‐L) occurred through inhibition of protein synthesis in a manner analogous to that of TNF‐α. METHODS The effect of chemotherapeutic drugs on protein synthesis in DU145 and PC‐3 cells was characterized by 3 H‐leucine incorporation assays. We also determined the ability of inhibitors of protein synthesis and chemotherapeutic drugs to sensitize Fas and TNF‐resistant DU145 cells to killing. The ability of RNA (actinomycin‐D, Act‐D) and protein synthesis inhibitors (cyclohexamide (CHX), emetine) to block drug‐mediated sensitization to Fas‐L killing was analyzed. Sensitivity to Fas‐L killing was determined by the 51 Cr‐release assay using human lymphokine‐activated killer cells (LAK) and tumor‐infiltrating lymphocyte (TIL) effector cells and the murine Fas‐L‐expressing PMMI cells. RESULTS The drugs cis ‐diamminedichloroplatinum (II) (CDDP), adriamycin (ADR), and etoposide (VP‐16) sensitized DU145 and PC‐3 cells to Fas killing. CDDP and ADR, which sensitized DU145 and PC‐3 cells to Fas‐L‐ and TNF‐mediated killing, inhibited de novo protein synthesis in both cell lines, while VP‐16 only inhibited protein synthesis in DU145 cells. Further, neither CHX nor emetine sensitized DU145 or PC‐3 cells to Fas‐L‐mediated killing, despite blocking >90% de novo protein synthesis. In contrast, CDDP, VP‐16, and the protein synthesis inhibitors, Act‐D and CHX sensitized DU145 cells to TNF‐α killing. Finally, pretreating cells with protein synthesis inhibitors (CHX, emetine) did not abrogate drug‐mediated sensitization to Fas‐mediated killing. CONCLUSIONS These findings demonstrate that downregulation of protective factors by protein synthesis inhibition may not be the primary mechanism of drug‐mediated sensitization to Fas‐L killing in prostate cell lines. These findings also suggest that drug‐mediated sensitization to Fas‐L killing may be due to modifications of preexisting gene products that participate in Fas‐L‐mediated apoptosis. Prostate 41:20–30, 1999. © 1999 Wiley‐Liss, Inc.