HnRNPK and lysine specific histone demethylase-1 regulates IP-10 mRNA stability in monocytes

Altered mRNA metabolism is a feature of many inflammatory diseases. Post transcriptional regulation of interferon-γ-inducible protein (IP)-10 has been uncharacterized in diabetes conditions. RNA-affinity capture method and RNA immuno-precipitation revealed S100b treatment increased the binding of heterogeneous nuclear ribonucleoprotein (hnRNP)K to the IP-10 3'UTR and increased IP-10 mRNA accumulation. Luciferase activity assay using reporter plasmids showed involvement of IP-10 3'UTR. Knocking down of hnRNPK destabilized S100b induced IP-10 mRNA accumulation. S100b promoted the translocation of hnRNPK from nucleus to the cytoplasm and this was confirmed by phosphomimetic S284/353D mutant and non-phosphatable S284/353A hnRNPK mutant. S100b treatment demethylates hnRNPK at Lys219 by Lysine Specific Demethylase (LSD)-1. HnRNPK^K219I, a demethylation defective mutant increased IP-10 mRNA stability. Apparently, triple mutant hnRNPK^{K219I/S284D/353D} promoted IP-10 mRNA stability. Interestingly, knocking down LSD-1 abolished S100b induced IP-10 mRNA accumulation. These observations show for the first time that IP-10 mRNA stability is dynamically regulated by Lysine demethylation of hnRNPK by LSD-1. These results indicate that hnRNPK plays an important role in IP-10 mRNA stability induced by S100b which could exacerbate monocyte activation, relevant to the pathogenesis of diabetic complications like atherosclerosis.