PLG regulates hnRNP-L expression in the rat striatum and pre-frontal cortex: identification by ddPCR

Central dopaminergic systems are implicated in schizophrenia and Parkinson's disease, and are known to be modulated by the endogenous tripeptide Pro-Leu-Gly-NH(2) (PLG or MIF-1, melanocyte-stimulating hormone release inhibiting factor-1). Differential display polymerase chain reaction (ddPCR) was utilized to identify genes that are regulated by protracted PLG treatment (20 mg/kg, i.p. for 28 days) in male Sprague-Dawley rats. A total of 2400 genes were screened and 3 down-regulated bands were identified in the PLG-treated samples. Sequencing analysis revealed a total of six unique cDNA species. One fragment possessed a high degree of homology with Mus musculus hnRNP-L (protein L) mRNA (GenBank #AB009392) (termed PRG1: PLG regulated gene 1). Elongation of the PRG1 cDNA, by RACE-PCR, provided an 835 bp sequence with 95% homology to AB009392 over a 743 bp span. Open reading frame analysis provided a putative amino acid sequence consistent with the identity of PRG1 as rat hnRNP-L. Northern hybridization experiments with PRG1 revealed a 2.3 kb mRNA species that was decreased by 65% in the PLG-treated tissue. Western blot analysis revealed significantly decreased hnRNP-L levels in the striatum and pre-frontal cortex (but not the nucleus accumbens) by 71 and 61%, respectively of PLG-treated animals. The identification of altered expression of hnRNP-L following PLG treatment provides insight into the long-term effects of PLG and may provide insight into its molecular mechanism of action.