Regulation of apolipoprotein E synthesis in rat ovarian granulosa cells.
Apoprotein E (apo-E) is a surface component of several classes of plasma lipoproteins. It functions as a ligand for receptor-mediated uptake of lipoproteins. Granulosa cells from ovaries of diethylstilbestrol-stimulated hypophysectomized immature rats cultured in serum-free medium with [35S]methionine secretes a 34-kDa protein which reacts with a monospecific anti-rat apo-E antibody and represents 0.2% of total secreted protein. Protease mapping confirms that this protein is apoprotein E. The secreted apoprotein E may be complexed with lipid since it floats in the ultracentrifuge at density less than 1.21 micrograms/ml. Freshly isolated granulosa cells contain receptors for follicle stimulating hormone (FSH) but not for human chorionic gonadotropin (hCG) or prolactin. Apoprotein E secretion is stimulated 2-fold by FSH, but hCG and prolactin have no effect. When granulosa cells develop hCG and prolactin receptors after 48 h of culture with FSH, apoprotein E secretion is not stimulated by addition of FSH, hCG, or prolactin although steroidogenesis is induced. The addition of 10(-7) M androgen plus FSH stimulates a marked increase in progestin synthesis over FSH alone, but androgen has little added effect on apoprotein E secretion. Cholera toxin (1.25 micrograms/ml) and dibutyryl cAMP (5 mg/ml), both of which increase intracellular cAMP, stimulate apo-E secretion 9-fold and 12-fold, respectively. The dibutyryl cAMP effect is dependent on both dose (greater than or equal to 0.5 mg/ml required) and time (onset at 24 h, maximum at 48 h, and back to near baseline at 96 h). Isobutylmethylxanthine, a phosphodiesterase inhibitor, augments FSH-stimulated apoprotein E synthesis 2.5-fold, supporting a role for cAMP in mediating the FSH effect. This is the first demonstration of the hormonal regulation of apoprotein E synthesis in an extrahepatic tissue.
D M
DM
Driscoll
J R
JR
Schreiber
V M
VM
Schmit
G S
GS
Getz
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000818:Animals; D001057:Apolipoproteins E / Q000096:biosynthesis* / Q000378:metabolism; D003994:Bucladesine / Q000494:pharmacology; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000502:physiology; D005260:Female; D005640:Follicle Stimulating Hormone / Q000494:pharmacology; D012739:Gonadal Steroid Hormones / Q000096:biosynthesis; D006107:Granulosa Cells / Q000378:metabolism*; D051381:Rats; D011973:Receptors, LDL / Q000502:physiology
D001057:Apolipoproteins E; D012739:Gonadal Steroid Hormones; D011973:Receptors, LDL; D003994:Bucladesine; D005640:Follicle Stimulating Hormone; D000242:Cyclic AMP; D015056:1-Methyl-3-isobutylxanthine