The selective pathway and a high-density lipoprotein receptor (SR-BI) in ovarian granulosa cells of the mouse

We recently reported that rat luteinized ovary tissue and primary cultures of rat ovarian granulosa cells reveal a remarkably tight functional correla tion between expressed selective uptake of lipoprotein cholesteryl esters a nd the expression of an HDL receptor protein, scavenger receptor, class B, type I (SR-BI). In the current study, we examine these same processes in C5 7 mouse granulosa cells and report a different correlation. Unlike the rat cells, non-hormone stimulated mouse granulosa cells are able to effectively carry out their selective pathway functions and secrete HDL-derived proges tins despite low levels of SR-BI and barely detectable levels of SR-BII (an isoform of SR-BI). Once stimulated with trophic hormones or Bt(2)cAMP, sma ll (30-40%) increases are observed in selective pathway functions, but majo r (similar to 20-fold) increases are seen in SR-BI and SR-BII expression: t hus, relatively little is gained in selective cholesteryl ester uptake by m ouse granulosa cells even though SR-BI and SR-BII levels are greatly increa sed. The importance of the HDL receptor proteins to the selective pathway r emains clear, however, since a significant portion of the selective process in both basal and stimulated granulosa cells is inhibitable by the use of blocking antibody. Another surface protein, caveolin, previously reported t o co-localize with SR-BI in mouse cells shows no change in expression durin g periods when SR-BI/BII levels are undergoing major shifts. (C) 1999 Elsev ier Science B.V. All rights reserved.