MicroRNA-33 and the SREBP host genes cooperate to control cholesterol homeostasis. Najafi-Shoushtari SH et al. Proper coordination of cholesterol biosynthesis and trafficking is essential to human health. The sterol regulatory element-binding proteins (SREBPs) are key transcription regulators of genes involved in cholesterol biosynthesis and uptake. We show here that microRNAs (miR-33a/b) embedded within introns of the SREBP genes target the adenosine triphosphate-binding cassette transporter A1 (ABCA1), an important regulator of high-density lipoprotein (HDL) synthesis and reverse cholesterol transport, for posttranscriptional repression. Antisense inhibition of miR-33 in mouse and human cell lines causes up-regulation of ABCA1 expression and increased cholesterol efflux, and injection of mice on a western-type diet with locked nucleic acid-antisense oligonucleotides results in elevated plasma HDL. Our findings indicate that miR-33 acts in concert with the SREBP host genes to control cholesterol homeostasis and suggest that miR-33 may represent a therapeutic target for ameliorating cardiometabolic diseases.
NCBI Summary:
This gene encodes a basic helix-loop-helix-leucine zipper (bHLH-Zip) transcription factor that binds to the sterol regulatory element-1 (SRE1), which is a motif that is found in the promoter of the low density lipoprotein receptor gene and other genes involved in sterol biosynthesis. The encoded protein is synthesized as a precursor that is initially attached to the nuclear membrane and endoplasmic reticulum. Following cleavage, the mature protein translocates to the nucleus and activates transcription. This cleaveage is inhibited by sterols. This gene is located within the Smith-Magenis syndrome region on chromosome 17. Alternative promoter usage and splicing result in multiple transcript variants, including SREBP-1a and SREBP-1c, which correspond to RefSeq transcript variants 2 and 3, respectively. [provided by RefSeq, Nov 2017]
General function
DNA binding, Transcription factor
Comment
Cellular localization
Nuclear
Comment
candidate123
Ovarian function
Steroid metabolism
Comment
Insulin and Human Chorionic Gonadotrophin Cause a Shift in the Balance of Sterol Regulatory Element-binding protein(SREBP) Isoforms Towards the SREBP-1c Isoform in Cultures of Human Granulosa Cells Richardson et al
The isoforms of SREBP (-1a, -1c and -2) are key transcriptional regulators of lipid biosynthesis. We examined their regulation by gonadotrophin and insulin in human granulosa cells. Following removal of leukocytes, granulosa cells were exposed to hormonal additions for 16 h starting on day 2 of culture. Progesterone, lactate and IGFBP-1 were measured in culture medium and cellular mRNA measured by competitive RT-PCR. Addition of hCG (100 ng/ml) stimulated progesterone production (7.0-fold, P < 0.001 vs. control), while lactate was increased by hCG (1.6-fold, P < 0.001) and insulin (1.4-fold, P < 0.001; 1000ng/ml). Insulin decreased IGFBP-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.
Expression regulated by
Comment
Ovarian localization
Granulosa
Comment
Genes in sterol/steroid and lipid biosynthetic pathways are targets of FSH and FOXO1 regulation in granulosa cells: evidence from cells expressing mutant forms of FOXO1. Liu Z et al. The forkhead box transcription factor FOXO1 is highly expressed in granulosa cells of growing follicles but is down-regulated by FSH in culture or by LH-induced luteinization in vivo. To analyze the function of FOXO1, we infected rat and mouse granulosa cells with adenoviral vectors expressing two FOXO1 mutants: a gain-of-function mutant FOXOA3 that has three serine residues mutated to alanines rendering this protein constitutively active and nuclear and FOXOA3-mDBD in which the DNA binding domain is mutated. The infected cells were then treated with vehicle or FSH for specific time intervals. Infection of the granulosa cells was highly efficient, caused only minimal apoptosis and maintained FOXO1 protein at levels of the endogenous protein observed in cells prior to exposure to FSH. RNA was prepared from control and adenoviral infected cells exposed to vehicle or FSH for 12 and 24h. Affymetrix microarray and data-base analyses identified, and real time RT-PCR verified, that genes within the lipid, sterol and steroidogenic biosynthetic pathways (Hmgcs1, Hmgcr, Mvk, Sqle, Lss, Cyp51, Tm7sf2, Dhcr24 and Star, Cyp11a1 and Cyp19), including two key transcriptional regulators Srebf1 and Srebf2 of cholesterol biosynthesis and steroidogenesis (Nr5a1, Nr5a2) were major targets induced by FSH and suppressed by FOXOA3 and FOXOA3-mDBD in the cultured granulosa cells. By contrast, FOXOA3 and FOXOA3-mDBD induced expression of Cyp27a1 mRNA that encodes an enzyme involved in cholesterol catabolism to oxysterols. The genes up-regulated by FSH in cultured granulosa cells were also induced in granulosa cells of preovulatory follicles and corpora lutea collected from immature mice primed with FSH (eCG) and LH (hCG), respectively. Conversely, Foxo1 and Cyp27a1 mRNAs were reduced by these same treatments. Collectively, these data provide novel evidence that FOXO1 may play a key role in granulosa cells to modulate lipid and sterol biosynthesis, thereby preventing elevated steroidogenesis during early stages of follicle development.
Follicle stages
Comment
Phenotypes
PCO (polycystic ovarian syndrome)
Mutations
1 mutations
Species: human
Mutation name: type: naturally occurring fertility: subfertile Comment: 54G/C polymorphism of SREBF-1 gene is associated with polycystic ovary syndrome. Li L et al. (2015) A sterol regulatory element-binding protein (SREBF-1) transcription factor is a major regulator of lipid metabolism, carbohydrate, and plays a key role in energy homeostasis. The 54(G/C) polymorphism of SREBF-1 gene was reported that it is related with metabolic diseases including obesity, type 2 diabetes, and dyslipidemia. Among these, polycystic ovary syndrome (PCOS) is known as a common metabolic-endocrine disorder of women in reproductive ages. Here, we performed a comparative study of 54(G/C) polymorphism of SREBF-1 gene with PCOS. The 54(G/C) polymorphism of SREBF-1 gene was analyzed by polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) of total 286 PCOS patients and 149 matched controls of healthy women. Statistical analysis was performed using HapAnalyzer. A p-value under 0.05 was considered statistically significant. There was a strong association between the 54(G/C) polymorphism of SREBF-1 gene and PCOS (OR: 0.65, 95% CI: 0.46-0.90, p: 0.0129). The genotype and allelic frequencies were in Hardy-Weinberg equilibrium (HWE). This is the first study on the genetic variation of SREBF-1 gene and PCOS. We concluded that 54(G/C) polymorphism of SREBF-1 gene is associated with PCOS. Therefore, our results suggest that SREBF-1 gene may play a role in genetic predisposition to PCOS, which is helpful in understanding the etiology of PCOS.//////////////////