ENHANCED EXPRESSION OF GRANULOSA-CELL LOW-DENSITY-LIPOPROTEIN RECEPTOR ACTIVITY IN RESPONSE TO IN-VITRO CULTURE CONDITIONS

Previous studies have shown that the B/E (low density lipoprotein [LDF ]) receptor pathway plays a minor role in cholesterol uptake in the in tact rat ovary, but when granulosa cells are isolated and maintained i n culture, the cells develop a fully functional B/E receptor system. I n the current study we examined the development of the B/E receptor ov er time (96 h) in culture and compared its physiological function, exp ression of mRNA and protein levels, and morphological events to the up regulation induced in 24 h by hormone (human chorionic gonadotropin [h CG] or Bt(2)cAMP). With both protocols, increased progestin production occurs and is associated With elevated binding, uptake, and degradati on of LDL in the medium although the impact of Bt(2)cAMP stimulation o n all these measurements is several times that observed with time alon e. Only the hormone-stimulated LDL receptor response was associated wi th an increase in receptor protein (Western blot) or mRNA levels (RNas e protection assay). We conclude that unstimulated granulosa cells sho w posttranslational increases in BIE receptor activity with time in cu lture, but transcriptional changes in BIE receptor follow stimulation with trophic hormone or its second messenger, cAMP. (C) 1994 Wiley-Lis s, Inc.