title: Interferons block protein kinase C-dependent but not-independent activation of Raf-1 and mitogen-activated protein kinases and mitogenesis in NIH 3T3 cells.
abstract: Interferons (IFNs) exert antiproliferative effects on many types of cells. The underlying molecular mechanism, however, is unclear. One possibility is that IFNs block growth factor-induced mitogenic signaling, which involves activation of Ras/Raf-1/MEK/mitogen-activated protein kinase. We have tested this hypothesis by using HER14 cells (NIH 3T3 cell expressing both platelet-derived growth factor [PDGF] and epidermal growth factor [EGF] receptors) as a model system. Our studies showed that IFNs (alpha/beta and gamma) blocked PDGF-and phorbol ester- but not EGF-stimulated DNA synthesis and cell proliferation. While the ligand-stimulated receptor tyrosine phosphorylation and interaction with downstream signaling molecules, such as GRB2, were not affected, IFNs specifically blocked PDGF- and phorbol ester- but not EGF-stimulated activation of Raf-1, mitogen-activated protein kinases, and tyrosine phosphorylation of an unidentified 34-kDa protein. This inhibition could be detected as early as 5 min after IFN treatments and was insensitive to cycloheximide, indicating that de novo protein synthesis is not required. The IFN-induced inhibition acted upstream of Raf-1 kinase and downstream of diacyl glycerol/phorbol ester, suggesting that protein kinase C (PKC) is the potential primary target. Consistently, downregulation of PKC by chronic phorbol myristate acetate treatment or inhibition of PKC by H7 and staurosporine blocked PDGF- and phorbol myristate acetate- but not EGF-induced signaling and DNA synthesis. Moreover, incubating cells with antisense oligodeoxyribonucleotides of PKC delta eliminated production of PKC delta protein and specifically blocked PDGF- but not EGF-stimulated mitogenesis in these cells. Thus, these studies have elucidated a major difference in the early events of EGF-and PDGF-stimulated signal transduction and, more importantly, revealed a novel mechanism by which IFNs may execute their antiproliferative function.
authors.affiliation: Ben May Institute, University of Chicago, Illinois 60637.
authors.forename: J
authors.initials: J
authors.lastname: Xu
authors.forename: S
authors.initials: S
authors.lastname: Rockow
authors.forename: S
authors.initials: S
authors.lastname: Kim
authors.forename: W
authors.initials: W
authors.lastname: Xiong
authors.forename: W
authors.initials: W
authors.lastname: Li
mesh_terms: D016475:3T3 Cells; D000818:Animals; D001483:Base Sequence; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D004247:DNA / Q000096:biosynthesis; D004789:Enzyme Activation; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D006131:Growth Inhibitors / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D007372:Interferons / Q000494:pharmacology*; D007527:Isoenzymes / Q000502:physiology; D051379:Mice; D008969:Molecular Sequence Data; D015345:Oligonucleotide Probes / Q000737:chemistry; D010703:Phorbol Esters / Q000494:pharmacology; D019000:Phosphotyrosine; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*; D011493:Protein Kinase C / Q000502:physiology*; D051745:Protein Kinase C-delta; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism; D017978:Receptors, Growth Factor / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects*; D014443:Tyrosine / Q000031:analogs & derivatives / Q000378:metabolism
chemical_list: D006131:Growth Inhibitors; D007527:Isoenzymes; D015345:Oligonucleotide Probes; D010703:Phorbol Esters; D010982:Platelet-Derived Growth Factor; D011518:Proto-Oncogene Proteins; D017978:Receptors, Growth Factor; D019000:Phosphotyrosine; D014443:Tyrosine; D004815:Epidermal Growth Factor; D004247:DNA; D007372:Interferons; C497259:Prkcd protein, mouse; D020794:Receptor Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; C497258:PRKCD protein, human; D011493:Protein Kinase C; D051745:Protein Kinase C-delta; D017871:Calcium-Calmodulin-Dependent Protein Kinases