In Situ Estrogen Synthesized by Aromatase P450 in Uterine Leiomyoma Cells Promotes Cell Growth Probably Via an Autocrine/Intracrine Mechanism

Abstract

In the present study we characterized in detail the expression of aromatase P450 in leiomyomas to determine the role of in situ estrogen in the growth advantage of leiomyomas. The levels of aromatase P450 transcripts were determined by quantitative RT-PCR to be significantly higher in leiomyomas than in corresponding myometrium. The overexpression of aromatase P450 in leiomyomas was also confirmed by Western blot analysis. The estimated size of immunoreactive aromatase was 58 kDa, similar to that in placenta. To identify a cell type that express aromatase P450 in leiomyomas, histological specimens were stained for aromatase P450 using a polyclonal antibody. Strong immunoreactivity was detected in the cytoplasm of leiomyoma cells, whereas surrounding normal myometrium displayed weak or negative staining. Smooth muscle-like cells in culture obtained from leiomyomas, positive for actin D fiber, possessed immunoreactive granules of aromatase in the cytoplasm. Conversion of androgen to estrogen was effectively stimulated by phorbol myristate acetate and dexamethasone plus interleukin-1beta and was completely abolished by selective inhibitors of aromatase P450 (fadrozole and TZA-2209), but not by inhibitors of 5alpha-reductase (finasteride and flutamide). The apparent Km of androstenedione was 3 nM in the presence of dexamethasone and interleukin-1beta, corresponding to the plasma concentration of androstenedione in women of reproductive age. To determine whether endogenous aromatase P450 plays a role in the growth promotion of leiomyoma cells, we evaluated the cell growth of smooth muscle-like cells treated with various concentrations of estrogen and androgen using a WST-1 assay. Treatment with testosterone (10(-8) and 10(-7) M) and androstenedione (10(-8) and 10(-7) M) stimulated the growth of smooth muscle-like cells obtained from leiomyomas to the same extent as estradiol (10(-10)-10(-7) M), whereas dihydrotestosterone (10(-11)-10(-8) M) did not. The stimulatory effect of testosterone on cell growth was again abolished by cotreatment with fadrozole. The level of estradiol in the medium of testosterone (10(-8) M)-treated smooth muscle-like cells was 10(-11) M, which was 1 order lower than the minimum concentration of estradiol necessary to promote cell growth (10(-10) M). This indicates that estradiol synthesized in leiomyomas promotes their growth via an autocrine/intracrine mechanism. We conclude that myometrial cells of leiomyomas overexpress aromatase P450 and are able to synthesize sufficient estrogen to accelerate their own cell growth. Overexpression of aromatase P450 may play a role in the growth advantage of leiomyoma tissue over surrounding myometrium via an autocrine/intracrine mechanism.

Etiology and pathogenesis of uterine leiomyomas: a review.

“…The authors speculated that the higher levels of estradiol in the leiomyomas could be related to lower levels of the enzyme 17β-hydroxysteroid dehydrogenase, which accelerates the conversion of estradiol to estrone. Other investigators have also demonstrated higher estradiol concentrations (Folkerd et al 1984) and more frequent expression or overexpression of aromatase activity in leiomyomata than in matched myometrial samples (Folkerd et al 1984;Sumitani et al 2000;Yamamoto et al 1984), leading these authors to entertain the possibility that increased androgen to estrogen conversion in fibroids may potentiate their growth.…”

Medical Management of Uterine Fibroids

“…Aromatase mRNA is expressed in myoma but is not expressed in normal myometrial cells [30,31]. Further, estrogen concentration in myoma tissue is greater than in the surrounding myometrium.…”

“…Some studies have shown that leiomyoma tissues are a source of estrogen. Leiomyoma cells express an estrogen synthetase as well as aromatase and convert circulating androgens to estrogen [30,32,33]. Estrogen secreted by leiomyoma tissue may reach a sufficient concentration within the local compartment to support its own growth, allowing independence from ovarian estrogen [34,35].…”

The aromatase expression in myomas and myometriums of women in reproduction and perimenopausal age.

“…As compared to the surrounding myometrium, smooth muscle cell myomas contained eleveted levels of aromatase and were able to synthesize estrogen [10,11] while tissue concentrations of estrogen were augmented in smooth muscle cell myomas as compared to the surrounding myometrium [12,13]. In addition, in vitro experiments proved that estrogen synthesized in smooth muscle cells in a culture was sufficient to support proliferation in an intracrine manner, since stimulation of aromatase activity increased cell proliferation while an aromatase inhibitor reduced the proliferation [11].…”