Glucocorticoids inhibit the apoptotic actions of UV-C but not Fas ligand in hepatoma cells: direct evidence for a critical role of Bcl-xL.
Our laboratory has shown that glucocorticoids can inhibit apoptosis in rat hepatoma cells; however, the mechanisms are incompletely understood. To address this issue we sought to determine if glucocorticoid inhibition is effective when death is induced by stimuli that more selectively activate either the intrinsic (UV-C) or extrinsic (FasL) apoptotic pathways. Using flow cytometric analysis, we show that pretreatment of HTC cells with dexamethasone (Dex) inhibits UV-C- but not FasL-induced apoptosis. This inhibition requires Dex pretreatment and can be abrogated by the glucocorticoid antagonist RU486 indicating glucocorticoid receptor-mediated action. Dex increases anti-apoptotic Bcl-x(L) at both mRNA and protein levels. The Bcl-x(L) protein level remains elevated even after apoptosis induction with either UV-C or FasL although only UV-C-induced cell death is inhibited. Repression of Bcl-x(L) protein with siRNA abrogates the anti-apoptotic effect of glucocorticoids. Together these data provide direct evidence that Bcl-x(L) mediates glucocorticoid inhibition of UV-C induced apoptosis.
Scoltock
A B
AB
Laboratory of Signal Transduction, National Institute of Environmental Health Sciences, National Institutes of Health, Department of Health and Human Services, Research Triangle Park, NC 27709, USA.
Heimlich
G
G
Cidlowski
J A
JA
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D006528:Carcinoma, Hepatocellular / Q000188:drug therapy / Q000378:metabolism*; D003907:Dexamethasone / Q000494:pharmacology*; D053222:Fas Ligand Protein / Q000187:drug effects / Q000378:metabolism*; D005938:Glucocorticoids / Q000494:pharmacology*; D007155:Immunologic Factors; D034741:RNA, Small Interfering; D051381:Rats; D014407:Tumor Cells, Cultured; D014466:Ultraviolet Rays; D051020:bcl-X Protein / Q000378:metabolism*; D019014:fas Receptor / Q000378:metabolism
D053222:Fas Ligand Protein; D005938:Glucocorticoids; D007155:Immunologic Factors; D034741:RNA, Small Interfering; D051020:bcl-X Protein; D019014:fas Receptor; D003907:Dexamethasone