Mechanism of interferon action: phosphorylation of protein synthesis initiation factor eIF-2 in interferon-treated human cells by a ribosome-associated kinase processing site specificity similar to hemin-regulated rabbit reticulocyte kinase.
The phosphorylation of purified protein synthesis factors catalyzed by protein kinase preparations isolated from interferon-treated human amnion cells was examined. Ribosomal salt-wash fractions prepared from interferon-treated human cells contained a protein kinase that catalyzed the [gamma-(32)P]ATP-mediated phosphorylation of the 38,000-dalton subunit of eukaryotic initiation factor 2 (eIF-2alpha); this kinase activity was significantly enhanced in interferon-treated as compared to untreated cells. The tryptic [(32)P]phosphopeptide pattern obtained for eIF-2alpha phosphorylated by the interferon-mediated human kinase was indistinguishable from the pattern obtained for eIF-2alpha phosphorylated by the hemin-regulated rabbit reticulocyte kinase when analyzed by thin-layer chromatography with three different solvent systems and by high-voltage electrophoresis. O-[(32)P]Phosphoserine was liberated by partial acid hydrolysis from eIF-2alpha phosphorylated by either the human or the rabbit kinase. In addition to the phosphorylation of eIF-2alpha, interferon treatment of human cells enhanced the phosphorylation of two additional ribosome-associated proteins designated P(1) and P(f). The major phosphoester linkage observed for the human, as well as murine, phosphoprotein P(1) was O-phosphoserine. The interferon-mediated phosphorylation of both eIF-2alpha and protein P(1) was dependent upon the presence of RNA with double-stranded character; P(f) phosphorylation was not affected by double-stranded RNA. These results suggest that the interferon-mediated ribosome-associated human protein kinase catalyzes the phosphorylation of eIF-2alpha in a site-specific manner that is apparently identical with the reaction catalyzed by the hemin-regulated rabbit reticulocyte kinase; hence, the phosphorylation of eIF-2 may play a role in regulating the initiation of translation in interferon-treated cells.
D002478:Cells, Cultured; D006427:Hemin / Q000494:pharmacology; D006801:Humans; D007372:Interferons / Q000494:pharmacology*; D010442:Peptide Chain Initiation, Translational / Q000187:drug effects*; D010448:Peptide Initiation Factors / Q000378:metabolism*; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D012313:RNA / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D012367:RNA, Viral / Q000378:metabolism; D012156:Reticulocytes / Q000201:enzymology; D012270:Ribosomes / Q000201:enzymology*
D010448:Peptide Initiation Factors; D012333:RNA, Messenger; D012367:RNA, Viral; D012313:RNA; D006427:Hemin; D007372:Interferons; D011494:Protein Kinases