title: Interferon-gamma-induced dephosphorylation of STAT3 and apoptosis are dependent on the mTOR pathway.
abstract: Interferon-gamma (IFN-gamma) exhibits diverse biological activities, including control of cell growth and tumor suppression. Here, we report that the treatment of M12 cells, a human metastatic prostate cancer cell line, with IFN-gamma, resulted in marked inhibition of cell proliferation and induced apoptosis. These effects were not seen with either IFN-alpha or IFN-beta. M12 cells, like many other human cancer cells, contain constitutively activated signal transducer and activator of transcription 3 (STAT3). The basal levels of both Akt and ERK1/2 phosphorylation are also markedly elevated in M12 cells. Strikingly, IFN-gamma-induced apoptosis and growth inhibition of M12 cells were associated with persistent suppression of the constitutive tyrosine-phosphorylated STAT3 (pY-STAT3). The IFN-gamma-induced dephosphorylation of pY-STAT3, however, was inhibited when the mTOR pathway was specifically blocked by rapamycin. Inhibition of PI-3K with low-dose LY294002, or MAPK with PD98059 also suppressed the mTOR/p70 S6k pathway, and correlated with the blockage of IFN-gamma-induced dephosphorylation of pY-STAT3. Simultaneously, treatment with LY294002, PD98059, or rapamycin abolished IFN-gamma-induced apoptosis in M12 cells. The inhibition of the mTOR pathway, however, did not affect IFN-gamma-induced activation of STAT1 pathway, and suppression of STAT1 expression by siRNA had no effect on IFN-gamma-induced dephosphorylation of pY-STAT3. Taken together, these results demonstrate that an intact mTOR pathway is critical for IFN-gamma-induced suppression of pY-STAT3 and apoptosis. Our study thus provides novel insights into the contributions of signaling pathways other than the classical JAK/STAT1 pathway in the anti-proliferative, proapoptotic actions of IFN-gamma.
authors.affiliation: Department of Pediatrics, Oregon Health and Science University, Portland, OR 97239-3098, USA. fangp@ohsu.edu
authors.forename: Peng
authors.initials: P
authors.lastname: Fang
authors.forename: Vivian
authors.initials: V
authors.lastname: Hwa
authors.forename: Ron G
authors.initials: RG
authors.lastname: Rosenfeld
mesh_terms: D017209:Apoptosis / Q000502:physiology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects*; D002471:Cell Transformation, Neoplastic / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D015536:Down-Regulation / Q000187:drug effects / Q000235:genetics; D004791:Enzyme Inhibitors / Q000494:pharmacology; D025461:Feedback, Physiological / Q000187:drug effects / Q000502:physiology; D006801:Humans; D007166:Immunosuppressive Agents / Q000494:pharmacology; D007371:Interferon-gamma / Q000378:metabolism* / Q000494:pharmacology; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation / Q000187:drug effects; D011494:Protein Kinases / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D050794:STAT1 Transcription Factor / Q000235:genetics / Q000378:metabolism; D050796:STAT3 Transcription Factor / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases
chemical_list: D004791:Enzyme Inhibitors; D007166:Immunosuppressive Agents; D007371:Interferon-gamma; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011494:Protein Kinases; D034741:RNA, Small Interfering; D050794:STAT1 Transcription Factor; D050796:STAT3 Transcription Factor; D020123:Sirolimus; D058570:TOR Serine-Threonine Kinases; C494079:STAT1 protein, human; C494086:STAT3 protein, human; C546842:MTOR protein, human