ALTERNATIVE SPLICING OF CYP2D MESSENGER-RNA IN HUMAN BREAST-TISSUE

The human cytochrome P450 (CYP) 2D subfamily comprises the CYP2D6 gene and four pseudogenes, CYP2D7P1 and 2 and CYP2D8P1 and 2. The CYP2D6 g ene product is a prominent drug-metabolizing enzyme, which is probably constitutive and has no known inducing agents. Alternative splicing o f the pre-mRNAs of these genes has been detected in human liver and br east tissue. RNA-PCR, competitive RNA-PCR, Southern blotting, cDNA seq uencing, and gene-specific PCR have been used to fully characterize th e alternatively spliced forms of CYP2D mRNA in human breast tissue in the region of exon 5 to 8, Such alternative splicing could regulate th e expression of CYP2D6 protein. A full-length mRNA (exons 5 to 8), and variants c (exon 6 deleted), b' (3' portion of exon 6 deleted), e (3' portion of exon 6 deleted, 3' 57-bp portion of intron 6 included), d (3' 57-bp portion of intron 6 included), and b (intron 6 included) wer e characterized and quantitated. Variant c was derived from CYP2D6, va riants d, e, and b were from CYP2D7P, and variant b' and full-length m RNA were derived from both CYP2D6 and 2D7P. Full-length mRNA was a min or form in human breast tissue where variants b' and c predominated, H uman breast tumor MCF-7 cells had CYP2D mRNA splice variant patterns s imilar to those of human breast tissue, while human liver tumor HepG2 cells had wild-type mRNA predominating. These results suggest that CYP 2D6 could be regulated tissue specifically using tissue-specific alter native mRNA splicing. (C) 1997 Academic Press