Human polynucleotide phosphorylase (hPNPase old-35): an RNA degradation enzyme with pleiotrophic biological effects.

Identification of small inhibitory RNAs and microRNA established that regulation of RNA metabolism plays an essential role in controlling intracellular biochemical processes. Interferons induce a number of RNA degradation enzymes involved in innate immunity by degrading viral RNAs. We cloned human polynucleotide phosphorylase (hPNPase(old-35)), a type I interferon-inducible 3'-5' exoribonuclease, as a transcript induced during terminal differentiation and senescence, two physiological processes marked by irreversible growth arrest. Our studies in the last four years show that hPNPase(old-35) plays an essential role in mediating IFN-mediated growth inhibition and its upregulation might mediate chronic inflammatory pathological processes during aging. The present review recaps these findings and provides a framework for the future understanding of the versatile functions of this interesting molecule.