EXPRESSION OF THE CYP19 GENE AND ITS PRODUCT AROMATASE CYTOCHROME-P450 IN HUMAN UTERINE LEIOMYOMA TISSUES AND CELLS IN CULTURE

The conversion of C-19 steroids to estrogens occurs in a number of tis sues and is catalyzed by a specific form of cytochrome P450, namely ar omatase cytochrome P450 (P450arom). Previously, conversion of radiolab eled androstenedione to estrone has been demonstrated in uterine leiom yomas. By use of reverse transcription followed by polymerase chain re action amplification of total RNA together with a rat cRNA as an inter nal standard, we detected and quantified P450arom transcripts in total RNA isolated from 32 of the 35 leiomyoma (91%) and from 18 of the 24 adjacent myometrial (75%) tissue samples from 26 women. P450arom trans cripts were not detectable in myometrial tissues from disease-free ute ri (n = 8). P450arom transcript levels in leiomyomas were similar to t hose in adipose tissue (normalized to total RNA) and were 1.5- to 25-f old higher than those in adjacent myometrial tissues. We did not find any correlation between P450arom transcript levels and leiomyoma size, histopathology, uterine weight, or patient age. In leiomyoma smooth m uscle cells in culture (n = 4) and tissue explants (n = 4), aromatase activity was stimulated by dibutyryl cAMP, and this effect was potenti ated by a phorbol ester. These increases in aromatase expression were accompanied by comparable increases in the levels of translatable P450 arom mRNA. Treatment with dexamethasone or platelet-derived growth fac tor did not stimulate aromatase expression. Consistently higher levels of aromatase activity and P450arom transcripts were found in the leio myoma tissues than in smooth muscle cells in culture (2- to 20-fold). Reverse transcription-polymerase chain reaction analysis of untranslat ed 5'-termini of mRNA species in leiomyomas revealed the use of primar ily promoter II (the ovarian-type promoter) for CYP19 gene transcripti on. Leiomyomas also contain some transcripts with untranslated exon I. 4 (previously found in adipose stromal cells and skin fibroblasts). Pl acental-type promoter-specific 5'-ends were not present in leiomyomas. We conclude that aromatase expression in leiomyomas is regulated by t he rate of CYP19 gene transcription, which is, in turn, regulated by t he use of tissue-specific promoters. These findings are consistent wit h the hypothesis that localized estrogen biosynthesis may be of pathol ogical significance in the promotion of leiomyoma growth.