Effects of galectin-1 on regulation of progesterone production in granulosa cells from pig ovaries in vitro

The detection of galectin-1 (gal-1) in pig granulosa cell lysates by immunoblotting and its cytosolic as well as membrane-associated localization prompted us to study its effects on cell proliferation and regulation of progesterone synthesis. The lectin stimulated the proliferation of granulosa cells from pig ovaries cultured in serum-free medium. Gal-1 inhibited the FSH-stimulated progesterone synthesis of granulosa cells. This inhibitory effect was strongly reduced by the disaccharidic competitor lactose at 30 mM. The absence of inhibitory effects on dibutyryl-cAMP (db-cAMP), forskolin, and pregnenolone-enhanced cellular progesterone synthesis suggests that gal-1interferes with the receptor-dependent mechanism of FSH-stimulated progesterone production. In FSH-stimulated granulosa cells, western blot analysis revealed the gal-1-mediated suppression of the cytochrome P450-dependent cholesterol side chain cleavage enzyme (P450(SCC)) that catalyzes the conversion of cholesterol to pregnenolone. In the presence of 30 mM lactose, the gal-1-reduced P450(SCC) expression was prevented. Strongly reduced mRNA levels were recorded for P450(SCC) and 3beta-hydroxysteroid dehydrogenase/isomerase (3beta-HSD) when FSH-stimulated granulosa cells were cultured in the presence of gal-1. We conclude that gal-1 exerts its inhibitory effect on steroidogenic activity of granulosa cells by interfering the hormone-receptor interaction resulting in decreased responses to FSH stimulation.