JAK-mediated signaling inhibits Fas ligand-induced apoptosis independent of de novo protein synthesis.
There is a growing appreciation for how cells integrate and appropriately respond to competing signals for proliferation and apoptosis. The studies described in this report examined the effects of exposure to the cytokine IFN-alpha (IFN-alpha-2a) on sensitivity of the human cell lines H9 and SKW6.4 to Fas ligand (FasL)-induced apoptosis. In a concentration-dependent manner, FasL induced apoptosis, as shown by Western blot analysis of procaspase 8 and poly(ADP-ribose) polymerase cleavage after 3-h exposure and by cytofluorometric analysis of sub-G(0)-G(1) cellular DNA content after 24-h exposure. H9 and SKW6.4 cell lines responded to 10,000 IU/ml IFN-alpha-2a, as evidenced by decreased cell proliferation and tyrosine phosphorylation of Stat1 and Stat3 proteins without significant cytotoxicity. The effects of cytokine exposure on apoptosis were examined; incubation in medium containing 10,000 IU/ml IFN-alpha-2a for 1 h before FasL treatment significantly reduced all above-mentioned hallmarks of apoptosis. Surprisingly, these antiapoptotic effects of IFN-alpha-2a were independent of de novo protein synthesis, because they occurred in both the absence and the presence of cycloheximide. However, chemical inhibitors of JAK completely abrogated the effects of IFN-alpha-2a on FasL-induced apoptosis, indicating a direct role for JAK-mediated protein phosphorylation in modulating sensitivity to apoptosis. Together, these data suggest a novel mechanism, independent of protein synthesis, by which cytokine signals through JAKs can interact with and attenuate this receptor-mediated apoptotic process.
Cousens
Leslie P
LP
Department of Medicine, Division of Medical Oncology, Brown University and Rhode Island Hospital, 593 Eddy Street, Providence, RI 02903, USA. lcousens@lifespan.org
Goulette
Frederick A
FA
Darnowski
James W
JW
D017209:Apoptosis / Q000187:drug effects* / Q000276:immunology; D015153:Blotting, Western; D049109:Cell Proliferation / Q000187:drug effects; D003513:Cycloheximide / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D053222:Fas Ligand Protein; D006801:Humans; D016898:Interferon-alpha / Q000276:immunology / Q000494:pharmacology; D053613:Janus Kinase 1; D008562:Membrane Glycoproteins / Q000276:immunology / Q000494:pharmacology*; D010766:Phosphorylation; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D011505:Protein-Tyrosine Kinases / Q000276:immunology / Q000378:metabolism*; D050794:STAT1 Transcription Factor; D050796:STAT3 Transcription Factor; D015398:Signal Transduction / Q000502:physiology*; D015534:Trans-Activators / Q000187:drug effects / Q000378:metabolism; D014407:Tumor Cells, Cultured; D014443:Tyrosine / Q000187:drug effects / Q000378:metabolism
D004268:DNA-Binding Proteins; C505661:FASLG protein, human; D053222:Fas Ligand Protein; D016898:Interferon-alpha; D008562:Membrane Glycoproteins; D011500:Protein Synthesis Inhibitors; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; D015534:Trans-Activators; D014443:Tyrosine; D003513:Cycloheximide; D011505:Protein-Tyrosine Kinases; C507904:JAK1 protein, human; D053613:Janus Kinase 1