Heterogeneous nuclear ribonucleoprotein A1 and regulation of the xenobiotic-inducible gene Cyp2a5.

The heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1) functions in the packaging of nascent RNA polymerase II transcripts and participates in a variety of nuclear and cytoplasmic processes that modulate gene expression. The RNA binding characteristics of hnRNP A1 suggest that it can modulate the expression of specific genes, but little is known about its possible targets in vivo. In this article, we show that hnRNP A1 interacts with the transcript of a cytochrome P450 gene, Cyp2a5, induced by xenobiotics and during liver damage. Binding of the hnRNP A1 to CYP2A5 mRNA was demonstrated by immunoprecipitation of the xenobiotic-stimulated (37/39 kDa) CYP2A5 mRNA-protein complex with a monoclonal anti-hnRNP A1 antibody, by partial trypsin digestion of the complex, and by showing that the RNA-protein complex is not formed with protein extracts from cells lacking the hnRNP A1. We also show that a specific hepatotoxic inducer of the Cyp2a5 gene, pyrazole, increases the cytoplasmic levels of hnRNP A1 in vivo. Finally, we show that hnRNP A1 can be overexpressed in mouse primary hepatocytes, leading to an accumulation of the CYP2A5 mRNA. Collectively, these results indicate that the hnRNP A1 is an important regulator of the Cyp2a5 gene.