Regulation of Sulfoprotein Synthesis by Rat Sertoli Cells in Culture*

In cultures of Sertoli cells, prepared from testesof 20-day-old rats, the incorporation of 35SO4= into sulfoproteins was increased by dibutyryl cAMP (dbcAMP) or FSH in the presence of isobutyl methylxanthine. Concentrations required for half-maximal stimulation of incorporation of 35SO4, measured 72 h after addition of the label, were 0.075 mM dbcAMP and 3.6 ng/ml partially purified ovine FSH. The protein nature of the 35SO4-labeled moiety released into the medium by Sertoli cells was indicated by the following criteria: 1) it was precipitatedby trichloroacetic acid; 2) when fractionated on a Sephadex G- 50 column, most of the material appeared in the void volume, and when subjected to polyacrylamide gel electrophoresis, 75% had a molecular weight greater than 100,000 daltons; and 3) after ronase digestion, only 1% of the material had a molecular eight greater than 100,000 daltons, whereas 57% had a molecular weight less than 39,000 daltons. Preliminary characterization of the 35SO4-labeled material indicated the presence of chondroitin sulfate-like compounds, assessed by the diminution of the S35 remaining in the trichloroacetic acid-precipitable fraction after digestion with chondroitinase ABC. In the labeled sulfoproteins released into the medium by Sertoli cells cultured under basal conditions, approximately 42% was sensitive to degradation by chondroitinase ABC. Compounds resistant to enzymatic attack included heparin-like materials, as indicated by the degradation of sulfo-labeled proteoglycans by nitrous acid digestion. The enhancement of incorporation of 35SO4 into sulfoproteins observed in cells stimulated by FSH or dbcAMP was associated with increased labeling of the chondroitinase-insensitive fraction, but not the chondroitin sulfate-like compounds. A comparison of possible functions of sulfoproteins synthesized by Sertoli cells and ovarian granulosa cells has been discussed.