LDL and cAMP cooperate to regulate the functional expression of the LRP in rat ovarian granulosa cells

Salman Azhar¹^,*^,, Satyanarayana Medicherla²^,*, Wen-Jun Shen^*, Yoshio Fujioka, Loren G. Fong³^,, Eve Reaven^* and Allen D. Cooper

^* Geriatric Research, Education, and Clinical Center, Department of Veterans Affairs Palo Alto Health Care System, Palo Alto, CA
Division of Gastroenterology and Hepatology, Stanford University School of Medicine, Stanford, CA

Published, JLR Papers in Press, August 23, 2006.

^² Present address of S. Medicherla: Scios, Inc., 6500 Paseo PadrePark, Fremont, CA 94557.

^³ Present address of L. G. Fong: Department of Medicine/Divisionof Cardiology, David Geffen School of Medicine, University ofCalifornia, Los Angeles, CA 90095.

^¹ To whom correspondence should be addressed. e-mail: salman.azhar{at}va.gov

Rat ovarian granulosa rely heavily on lipoprotein-derived cholesterolfor steroidogenesis, which is principally supplied by the LDLreceptor- and scavenger receptor class B type I (SR-BI)-mediatedpathways. In this study, we characterized the hormonal and cholesterolregulation of another member of the LDL receptor superfamily,low density lipoprotein receptor-related protein (LRP), andits role in granulosa cell steroidogenesis. Coincubation ofcultured granulosa cells with LDL and N⁶,O^2'-dibutyryl adenosine3',5'-cyclic monophosphate (Bt₂cAMP) greatly increased the mRNA/proteinlevels of LRP. Bt₂cAMP and Bt₂cAMP plus human (h)LDL also enhancedSR-BI mRNA levels. However, there was no change in the expressionof receptor-associated protein, a chaperone for LRP, or anotherlipoprotein receptor, LRP8/apoER2, in response to Bt₂cAMP plushLDL, whereas the mRNA expression of LDL receptor was reducedsignificantly. The induced LRP was fully functional, mediatingincreased uptake of its ligand, ${alpha}$ ₂-macroglobulin. The level ofbinding of another LRP ligand, chylomicron remnants, did notincrease, although the extent of remnant degradation that couldbe attributed to the LRP doubled in cells with increased levelsof LRP. The addition of lipoprotein-type LRP ligands such aschylomicron remnants and VLDL to the incubation medium significantlyincreased the progestin production under both basal and stimulatedconditions. In summary, our studies demonstrate a role for LRPin lipoprotein-supported ovarian granulosa cell steroidogenesis.

Supplementary key words low density lipoprotein • adenosine 3',5'-cyclic monophosphate • low density lipoprotein receptor-related protein

Abbreviations: apoE, apolipoprotein E; Bt₂cAMP, N⁶,O^2'-dibutyryl adenosine 3',5'-cyclic monophosphate; CE, cholesteryl ester; DRB, 5,6-dichloro-1-ß-D-ribofuranosylbenzimidazole; GST, glutathione S-transferase; LRP, low density lipoprotein receptor-related protein; RAP, receptor-associated protein; RPA, RNase protection assay; SR-BI, scavenger receptor class B type I

Add to CiteULike CiteULike Add to Complore Complore Add to Connotea Connotea Add to Del.icio.us Del.icio.us Add to Digg Digg Add to Reddit Reddit Add to Technorati Technorati What's this?