Interleukin 3 stimulates protein synthesis by regulating double-stranded RNA-dependent protein kinase.
In a murine interleukin 3 (IL-3)-dependent cell line, IL-3 deprivation resulted in increased autophosphorylation of double-stranded RNA-dependent protein kinase (PKR) that has been reported to inhibit protein synthesis by phosphorylating the alpha subunit of eukaryotic initiation factor 2 (eIF-2 alpha). Autophosphorylation was characterized by a shift up in mobility of PKR on SDS/PAGE gels from a 60- to a 64-kDa form. In vitro kinase studies comparing the autophosphorylated 64-kDa PKR with the nonphosphorylated 60-kDa PKR confirmed that only the 64-kDa form was active for eIF-2 alpha phosphorylation. PKR activation in vivo was associated with phosphorylation of eIF-2 alpha and inhibition of protein synthesis. Addition of IL-3 to deprived cells elicited a reciprocal response characterized by the rapid dephosphorylation of PKR and eIF-2 alpha, indicating inactivation of PKR. This was rapidly followed by the full recovery of protein synthesis. Furthermore, upon IL-3 addition, a 97-kDa phosphotyrosine-containing protein becomes rapidly and transiently associated with PKR prior to dephosphorylation of PKR and eIF-2 alpha. Genistein, a tyrosine kinase inhibitor, blocks both phosphorylation of the 97-kDa phosphoprotein and protein synthesis after IL-3 addition, suggesting a role for the 97-kDa phosphoprotein in the mechanism of inactivation of PKR and stimulation of protein synthesis. Thus, IL-3 appears to positively regulate protein synthesis by inducing the inactivation of PKR in a growth factor signaling pathway.
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Johns Hopkins Oncology Center, Baltimore, MD 21231.
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May
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D000818:Animals; D002478:Cells, Cultured; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects*; D019833:Genistein; D007377:Interleukin-3 / Q000494:pharmacology*; D007529:Isoflavones / Q000494:pharmacology; D051379:Mice; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D019000:Phosphotyrosine; D014176:Protein Biosynthesis / Q000187:drug effects*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D014443:Tyrosine / Q000031:analogs & derivatives / Q000378:metabolism; D019892:eIF-2 Kinase
D015852:Eukaryotic Initiation Factor-2; D007377:Interleukin-3; D007529:Isoflavones; D010750:Phosphoproteins; D019000:Phosphotyrosine; D014443:Tyrosine; D019833:Genistein; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D019892:eIF-2 Kinase