Interaction of heterogeneous nuclear ribonucleoprotein A1 with cytochrome P450 2A6 mRNA: implications for post-transcriptional regulation of the CYP2A6 gene.
The human xenobiotic-metabolizing enzyme cytochrome P450, CYP2A6, catalyzes the bioactivation of a number of carcinogens and drugs and is overexpressed in cases of liver diseases, such as cirrhosis, viral hepatitis, and parasitic infestation, and in certain tumor cells. This suggests that CYP2A6 may be a major liver catalyst in pathological conditions. In the present study, we have addressed molecular mechanisms underlying the regulation of the CYP2A6 gene. We present evidence of several proteins present in human hepatocytes that interact specifically with the 3'-untranslated region (UTR) of CYP2A6 mRNA. Biochemical and immunological evidence show that the RNA-protein complex of highest intensity contains the heterogeneous nuclear ribonucleoprotein (hnRNP) A1 or a closely related protein. Mapping of the hnRNP A1 binding site within CYP2A6 3'-UTR reveals that the smallest portion of RNA supporting significant binding consists of 111 central nucleotides of the 3'-UTR. Our studies also indicate that hnRNPA1 from HepG2 cancer cells exhibits modified binding characteristics to the CYP2A6 3'-UTR compared with primary hepatocytes. We found that the level of CYP2A6 mRNA remains high in conditions of impaired transcription in primary human hepatocytes, showing that CYP2A6 expression can be affected post-transcriptionally in conditions of cellular stress. Our results indicate that the post-transcriptional regulation involves interaction of the hnRNP A1 protein with CYP2A6 mRNA. The present data suggest that hnRNPA1 is a critical regulator of expression of the human CYP2A6 gene and support the notion that this P450 isoform may be of particular significance in stressed human liver cells.
Christian
Kyle
K
Department of Pharmaceutical Biosciences, Division of Biochemistry, Uppsala University, Uppsala, Sweden.
Lang
Matti
M
Maurel
Patrick
P
Raffalli-Mathieu
Françoise
F
D020413:3' Untranslated Regions / Q000378:metabolism*; D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D006528:Carcinoma, Hepatocellular / Q000473:pathology; D065637:Cytochrome P-450 CYP2A6; D003609:Dactinomycin / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D022781:Hepatocytes / Q000201:enzymology; D000076245:Heterogeneous Nuclear Ribonucleoprotein A1; D034481:Heterogeneous-Nuclear Ribonucleoprotein Group A-B / Q000378:metabolism*; D006801:Humans; D051379:Mice; D006899:Mixed Function Oxygenases / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D008970:Molecular Weight; D011233:Precipitin Tests; D017433:Protein Structure, Secondary; D012333:RNA, Messenger / Q000187:drug effects / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects; D014407:Tumor Cells, Cultured
D020413:3' Untranslated Regions; D000076245:Heterogeneous Nuclear Ribonucleoprotein A1; D034481:Heterogeneous-Nuclear Ribonucleoprotein Group A-B; C000619657:Hnrnpa1 protein, mouse; D012333:RNA, Messenger; C000619656:hnRNPA1 protein, human; D003609:Dactinomycin; D006899:Mixed Function Oxygenases; D001189:Aryl Hydrocarbon Hydroxylases; C585710:CYP2A6 protein, human; D065637:Cytochrome P-450 CYP2A6