INHIBITION OF PROTEOGLYCAN SYNTHESIS INDUCES AN INCREASE IN FOLLICLE-STIMULATING-HORMONE (FSH)-STIMULATED ESTRADIOL PRODUCTION BY IMMATURE RAT SERTOLI CELLS

In order to define the possible involvement of proteoglycans (PG) in t he regulation of Sertoli cell functions, we have examined the effect o f para-nitrophenyl-beta-D-xyloside (PNPX), a specific inhibitor of PG synthesis, on follicle stimulating hormone (FSH)-dependent estradiol p roduction by immature rat Sertoli cells. Addition of PNPX to the cultu re medium induced a dose-dependent inhibition of S-35-labeled PG synth esis in Sertoli cells both in the medium and the cell layer. Simultane ously there was a drastic increase in S-35- labeled secreted glycosami noglycans. By 1 mM PNPX, syntheses of chondroitin sulfate proteoglycan s released into culture medium and of heparan sulfate proteoglycans as sociated with the cell layer were 35% of values from untreated cells. Simultaneously, PNPX induced a twofold (mean of seven experiments, ran ge 17-250%) enhancement of FSH (100 ng/ml)-stimulated estradiol produc tion. In each individual experiment, there was an inverse relationship between the amplitude of PNPX-induced increase in FSH responsiveness and the FSH capability to stimulate basal estradiol production in cult ured rat Sertoli cells. The effect of PNPX on FSH-stimulated aromatase activity was not mimicked by para-nitrophenyl-beta-D-galactoside, a s tructural analog of PNPX that has no effect on PG synthesis. The (Bu)( 2)cAMP-stimulated estradiol synthesis was not modified in the presence of PNPX. Moreover, PNPX enhancement of FSH-stimulated estradiol synth esis disappeared when Sertoli cells were cultured in the presence of 1 -methyl-3-isobutylxanthine, an inhibitor of phosphodiesterase activity . These findings suggest that inhibition of PC synthesis under PNPX co nditions did not affect signal transduction steps distal to cAMP but r ather decreased the phosphodiesterase activity in Sertoli cells. These results strongly support the idea that PGs associated with the plasma membrane and/or extracellular matrix are involved in the repression o f FSH-dependent activities in prepubertal rat Sertoli cells.