EXPRESSION OF 17-BETA-HYDROXYSTEROID DEHYDROGENASE IN HUMAN GRANULOSA-CELLS - CORRELATION WITH FOLLICULAR SIZE, CYTOCHROME-P450 AROMATASE-ACTIVITY AND ESTRADIOL PRODUCTION

The aim of this study was to examine the expression and regulation of type 1 17 beta-hydroxysteroid dehydrogenase (type 1 17-HSD) enzyme pro tein and mRNA, and 17-HSD activity in human granulosa cells. The cells were obtained from patients taking part in an in vitro fertilization programme. The cells from each patient were divided into two groups: c ells obtained from preovulatory follicles (LGC = granulosa cells from large follicles greater than or equal to 18 mm in diameter), and cells from other visible follicles (SGC = granulosa cells from small follic les, less than 15 mm in diameter). The identity of 17-HSD enzyme prote in expressed in human granulosa cells with placental cytosolic 17-HSD (type 1 17-HSD) was assessed by immunoblot analysis using polyclonal a ntibodies, and the enzyme was immunolocalized in the cytoplasm of gran ulosa cells. Type 1 17-HSD protein concentration, 17-HSD and cytochrom e P450 aromatase (P450arom) activities and oestradiol (OE(2)) producti on in cells from LGC were significantly lower than the corresponding v alues obtained in SGC in the same patient (paired t-test). The type 1 17-HSD protein concentration, 17-HSD activity and P450arom activity we re 140 +/- 16% (mean +/- S.E.M.), 121 +/- 22% and 113 +/- 26% higher i n cells from SGC, which was also reflected in a 70 +/- 12% higher OE(2 ) production in these cells. In freshly isolated cells from LGC or SGC , a high correlation between 17-HSD and P450arom activities was observ ed (r = 0.93, P < 0.001). In long-term cultured cells, type 1 17-HSD w as stably expressed at least until day 9, while P450arom expression de creased. In addition, treatments with gonadotrophins did not affect ty pe 1 17-HSD protein concentration and 17-HSD activity. In contrast to this, both P450arom activity and OE(2) production were significantly i ncreased (P < 0.05). The data, therefore, suggest that type 1 17-HSD a nd P450arom are expressed in parallel during the latest stages of foll icular maturation but, in cultured granulosa-luteal cells, the enzymes are regulated by distinct mechanisms.