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Originally published In Press as doi:10.1194/jlr.M600349-JLR200 on August 23, 2006

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Journal of Lipid Research, Vol. 47, 2538-2550, November 2006
Copyright © 2006 by American Society for Biochemistry and Molecular Biology

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

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

* Geriatric Research, Education, and Clinical Center, Department of Veterans Affairs Palo Alto Health Care System, Palo Alto, CA
{dagger} 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 Padre Park, Fremont, CA 94557.

3 Present address of L. G. Fong: Department of Medicine/Division of Cardiology, David Geffen School of Medicine, University of California, 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 cholesterol for steroidogenesis, which is principally supplied by the LDL receptor- and scavenger receptor class B type I (SR-BI)-mediated pathways. In this study, we characterized the hormonal and cholesterol regulation of another member of the LDL receptor superfamily, low density lipoprotein receptor-related protein (LRP), and its role in granulosa cell steroidogenesis. Coincubation of cultured granulosa cells with LDL and N6,O2'-dibutyryl adenosine 3',5'-cyclic monophosphate (Bt2cAMP) greatly increased the mRNA/protein levels of LRP. Bt2cAMP and Bt2cAMP plus human (h)LDL also enhanced SR-BI mRNA levels. However, there was no change in the expression of receptor-associated protein, a chaperone for LRP, or another lipoprotein receptor, LRP8/apoER2, in response to Bt2cAMP plus hLDL, whereas the mRNA expression of LDL receptor was reduced significantly. The induced LRP was fully functional, mediating increased uptake of its ligand, {alpha}2-macroglobulin. The level of binding of another LRP ligand, chylomicron remnants, did not increase, although the extent of remnant degradation that could be attributed to the LRP doubled in cells with increased levels of LRP. The addition of lipoprotein-type LRP ligands such as chylomicron remnants and VLDL to the incubation medium significantly increased the progestin production under both basal and stimulated conditions. In summary, our studies demonstrate a role for LRP in 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,O2'-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


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