C114 is a Novel IL-11-inducible Nuclear Double-stranded RNA-binding Protein That Inhibits Protein Kinase R

We have identified a cDNA (named C114) that encodes novel transcripts induced by IL-11 in mouse 3T3 L1 cells. Northern analysis of RNAs from multiple mouse tissues detects two C114 transcripts of approximately 1.0 and approximately 2.0 kb with the highest expression in liver, testis, brain, and kidney. The C114 cDNA contains an open reading frame of 187 amino acids with a predicted mass of 21 kDa. Three putative nuclear localization signals are predicted at amino acids 83-88, 126-131, and 167-178. Using green fluorescent protein (GFP)-C114 fusion plasmids, amino acids 126-131 are shown to be essential for the nuclear localization of C114. An arginine-rich region (amino acids 98-143) spanning the nuclear localization signals (amino acids 126-131) exhibits a double-stranded RNA (dsRNA) binding activity. Competition experiments with different RNA homopolymers demonstrate that C114 preferentially binds to poly(I.C). Similar to other dsRNA-binding proteins, C114 binds to the dsRNA-activated protein kinase, protein kinase R (PKR), via dsRNA-binding domains of PKR and the N-terminal region of the C114 protein. In vitro kinase assays indicate that C114 inhibits PKR activation via a dsRNA-independent mechanism. Overexpression of C114 protein inhibits the induction of eIF-2alpha phosphorylation following poly(I.C) treatment. This is the first demonstration of a novel PKR modulator induced by a gp130 superfamily cytokine that may play a role in cytokine-mediated biological functions.