Activation of STAT1 is required for interferon-alpha-mediated cell death

Interferon-alpha (IFN alpha)-Induced cell death of tumor cells is likely mediated through several signaling pathways We previously demonstrated that blocking the activation of phosphomosinde-3-kinase PI3K or mammalian target of rapamycin mTOR, partially inhibited apoptosis induced by IFN alpha Here we postulate using pharmacological inhibition and dominant negative mutants that activation of signal transducer and activator of transcription-1 STAT1 is also required for the cell death induced by IFN alpha Inhibition of STAT1 tyrosine phosphorylation and DNA binding by a naturally occurring rotenoid deguelin also rescued U266 myeloma cell lines from IFN alpha-induced apoptosis Deguelin had no effect on upstream Jak kinases or STAT2 phosphorylation suggesting the involvement of a yet unknown mechanism Inhibition of STAT1 tyrosine phosphorylation and activity was independent of the known effects of deguelin on PI3K Ala or mTOR as shown using selective pharmacological inhibitors against these kinases The combination of deguelin and PI3K or mTOR antagonists further inhibited apoptosis suggesting that both the Jak-STAT and the PI3K/mTOR pathways contribute to the induction of apoptosis by IFN alpha in these cells Over-expression of STAT1-Y701A or K410/413A mutants in Rhek-1 keratinocytes largely inhibited apoptosis further supporting the Importance of STAT1 phosphorylation and activity for IFN alpha-induced cell death Thus at least two signaling pathways one of which requires STAT1 activation cooperate to mediate IFN alpha-induced apoptosis (C) 2010 Elsevier Inc All rights reserved