Double-stranded RNA decreases IGF-I gene expression in a protein kinase R-dependent, but type I interferon-independent, mechanism in C6 rat glioma cells.
We previously demonstrated that Poly (IC) decreased the growth of C6 cultures in association with reduced IGF-I synthesis and secretion. In this study we characterized the mechanism(s) by which Poly (IC) decreased IGF-I mRNA in C6 cells. Both Poly (IC) and type I interferon (IFN) decreased IGF-I mRNA. Cycloheximide and a blocking antibody against IFN did not alter the Poly (IC)-mediated inhibition of IGF-I mRNA, but prevented IFN from reducing IGF-I mRNA. Poly (IC) did not alter the stability of IGF-I mRNA. Poly (IC) decreased the abundance of IGF-I pre-mRNA in C6 nuclei, but did not inhibit proximal IGF-I exon 1 promoter/luciferase fusion constructs in transient transfection assays. Poly (IC) activated double-stranded RNA-activated protein kinase (PKR) at 5 min and increased PKR protein levels at 48 and 72 h. Exogenous IGF-I did not prevent Poly (IC) from activating PKR, but inhibited the Poly (IC)-mediated increase in PKR protein levels. The PKR inhibitor 2-aminopurine prevented the Poly (IC) stimulation of eIF2-alpha phosphorylation and the Poly (IC)-mediated decrease in IGF-I mRNA. We conclude that Poly (IC) decreases IGF-I gene transcription in a mechanism that requires the activation of preexisting PKR, but not the induction of IFN or PKR proteins in C6 cells.
Chacko
Maryanne S
MS
Department of Biochemistry, University of Texas Health Science Center, San Antonio, Texas 78229-3900, USA.
Adamo
Martin L
ML
D000199:Actins / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D001932:Brain Neoplasms / Q000235:genetics; D002467:Cell Nucleus / Q000737:chemistry; D005786:Gene Expression Regulation / Q000235:genetics*; D005910:Glioma / Q000235:genetics; D017403:In Situ Hybridization; D007334:Insulin-Like Growth Factor I / Q000096:biosynthesis* / Q000235:genetics; D007369:Interferon Inducers / Q000494:pharmacology; D007370:Interferon Type I / Q000502:physiology*; D023282:Nuclease Protection Assays; D011070:Poly I-C / Q000235:genetics / Q000494:pharmacology; D015347:RNA Probes; D012330:RNA, Double-Stranded / Q000235:genetics*; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D051381:Rats; D014162:Transfection; D014407:Tumor Cells, Cultured; D019892:eIF-2 Kinase / Q000235:genetics* / Q000378:metabolism*
D000199:Actins; D007369:Interferon Inducers; D007370:Interferon Type I; D015347:RNA Probes; D012330:RNA, Double-Stranded; D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I; D019892:eIF-2 Kinase; D011070:Poly I-C