Insulin and human chorionic gonadotropin cause a shift in the balance of sterol regulatory element-binding protein (SREBP) isoforms toward the SREBP-1c isoform in cultures of human granulosa cells.
The isoforms of sterol regulatory element-binding proteins (SREBP) (1a, 1c, and 2) are key transcriptional regulators of lipid biosynthesis. We examined their regulation by gonadotropin and insulin in human granulosa cells. After removal of leukocytes, granulosa cells were exposed to hormonal additions for 16 h starting on d 2 of culture. Progesterone, lactate, and IGF binding protein-1 were measured in culture medium and cellular mRNA measured by competitive RT-PCR. Addition of human chorionic gonadotropin (hCG) (100 ng/ml) stimulated progesterone production (7.0-fold, P < 0.001 vs. control), whereas lactate was increased by hCG (1.6-fold, P < 0.001) and insulin (1.4-fold, P < 0.001; 1000 ng/ml). Insulin decreased IGF binding protein-1 production by 85% (P < 0.001). There were no significant effects on the expression of SREBP-1a but significant increases in mRNA for SREBP-1c with insulin (6.3-fold), hCG (10.4-fold) and in combination (15.2-fold; P < 0.01 for all comparisons). No consistent effects on SREBP-2 were observed. The expression of mRNA for fatty acid synthase, a target gene for SREBP-1c, was increased by hCG (24-fold, P = 0.006) and insulin (19-fold, P = 0.024), which also increased the level of cellular, total fatty acid (1.34-fold; P = 0.03). Thus, hCG and insulin cause a switch toward expression of the SREBP-1c isoform with consequent effects on fatty acid synthesis. We suggest that high circulating insulin, associated with clinically defined insulin resistance, may up-regulate SREBP-1c expression in the ovary.
Richardson
Malcolm C
MC
Developmental Origins of Health and Disease Research Division, University of Southampton, Level F, Princess Anne Hospital, Coxford Road, Southampton SO16 5YA, United Kingdom. mcr2@soton.ac.uk
Cameron
Iain T
IT
Simonis
Chantal D
CD
Das
Madhab C
MC
Hodge
Tessa E
TE
Zhang
Junlong
J
Byrne
Christopher D
CD
D022762:CCAAT-Enhancer-Binding Proteins / Q000187:drug effects / Q000235:genetics*; D002478:Cells, Cultured; D006063:Chorionic Gonadotropin / Q000494:pharmacology*; D017931:DNA Primers; D018076:DNA, Complementary / Q000235:genetics; D004268:DNA-Binding Proteins / Q000187:drug effects / Q000235:genetics*; D064429:Fatty Acid Synthases / Q000235:genetics; D005230:Fatty Acids, Nonesterified / Q000378:metabolism; D005260:Female; D005307:Fertilization in Vitro; D006107:Granulosa Cells / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000494:pharmacology*; D018970:Insulin-Like Growth Factor Binding Protein 1 / Q000378:metabolism; D011374:Progesterone / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D051780:Sterol Regulatory Element Binding Protein 1; D051782:Sterol Regulatory Element Binding Protein 2; D014157:Transcription Factors / Q000187:drug effects / Q000235:genetics*
D022762:CCAAT-Enhancer-Binding Proteins; D006063:Chorionic Gonadotropin; D017931:DNA Primers; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D005230:Fatty Acids, Nonesterified; D007328:Insulin; D018970:Insulin-Like Growth Factor Binding Protein 1; D012333:RNA, Messenger; C497387:SREBF1 protein, human; C497390:SREBF2 protein, human; D051780:Sterol Regulatory Element Binding Protein 1; D051782:Sterol Regulatory Element Binding Protein 2; D014157:Transcription Factors; D011374:Progesterone; D064429:Fatty Acid Synthases