Expression regulation and genomic organization of human polynucleotide phosphorylase, hPNPaseold-35, a Type I interferon inducible early response gene

Abstract An overlapping pathway screening (OPS) approach designed to identify and clone genes displaying parallel expression profiles as a function of induction of terminal differentiation and cellular senescence in human cells identified a novel gene old-35 . Sequence and functional analysis indicates that old-35 encodes human polynucleotide phosphorylase, hPNPase old-35 . Polynucleotide phosphorylases comprise a family of phosphate dependent 3′–5′ RNA exonucleases implicated in RNA regulation. Treatment of HO-1 human melanoma and additional diverse normal and tumor-derived human cell types with Type I interferon (IFN), IFN-β or IFN-α, induces hPNPase old-35 expression. To provide insights into the regulation of hPNPase old-35 , we cloned and analyzed the promoter region of this gene. These studies demonstrate that IFN-β controls hPNPase old-35 expression by transcriptional modulation rather than by altering mRNA stability. Transcriptional activation of hPNPase old-35 by IFN-β is primarily mediated by the interferon stimulatory response element (ISRE) present in its promoter. Analysis of hPNPase old-35 expression in cell lines defective in various IFN signaling molecules confirms that hPNPase old-35 expression is dependent upon the Janus activated kinase (JAK)/signal transducers and activators of transcription (STAT) pathway. Furthermore, gel shift analyses document that hPNPase old-35 is a direct target of the interferon stimulated gene factor 3 (ISGF3) complex. The hPNPase old-35 gene spans ∼54 kb of genomic DNA and is distributed on 28 exons and 27 introns. hPNPase old-35 maps to 2p15–2p16.1, a region implicated in hereditary nonpolyposis colorectal cancer, Carney complex, Doyne′s honeycomb retinal dystrophy and several other diseases. To provide insights into PNPase function in vivo , we have also cloned the mouse PNPase old-35 cDNA, mPNPase old-35 . Induction of hPNPase old-35 by IFN treatment as well as during differentiation and senescence suggest that this gene may play a significant role in regulating cellular growth and that overlapping gene expression changes, also induced by IFN, may contribute to these important physiological processes.