The role of cyclic AMP response element binding protein in transactivation of scavenger receptor class B type I promoter in transfected cells and in primary cultures of rat theca-interstitial cells

SR-BI as a target of natural products and its significance in cancer

Scavenger receptor class B type I (SR-BI) protein is an integral membrane glycoprotein. SR-BI is emerging as a multifunctional protein, which regulates autophagy, efferocytosis, cell survival and inflammation. It is well known that SR-BI plays a critical role in lipoprotein metabolism by mediating cholesteryl esters selective uptake and the bi-directional flux of free cholesterol. Recently, SR-BI has also been identified as a potential marker for cancer diagnosis, prognosis, or even a treatment target. Natural products are a promising source for the discovery of new drug leads. Multiple natural products were identified to regulate SR-BI protein expression. There are still a number of challenges in modulating SR-BI expression in cancer and in using natural products for modulation of such protein expression. In this review, our purpose is to discuss the relationship between SR-BI protein and cancer, and the molecular mechanisms regulating SR-BI expression, as well as to provide an overview of natural products that regulate SR-BI expression.

4-Bromodiphenyl Ether Causes Adrenal Gland Dysfunction in Rats during Puberty

Polybrominated diphenyl ethers (PBDEs) are a group of flame retardants with two or more bromines attached. They are endocrine disruptors. PBDEs photodegrade into 4-bromodiphenyl ether (BDE3). Whether BDE3 impairs adrenal cortical cell function during postnatal development still remains unknown. The aim of the current study was to investigate the influence of BDE3 on adrenal cortical cell function. Sprague-Dawley rats (35 days of age, male) were orally administered with BDE3 (0, 50, 100, and 200 mg/kg/day body weight) for 21 days. BDE3 significantly increased serum aldosterone and corticosterone levels at 200 mg/kg without affecting adrenocorticotropic hormone level. Further study showed that BDE3 up-regulated Cyp11b1 at 100 and 200 mg/kg and Scarb1, Star, Cyp11b2, Cyp21, and Nr5a1 mRNA levels in the 200 mg/kg group. BDE3 also decreased the phosphorylation of AMP-activated protein kinase (AMPK) at 200 mg/kg and increased PGC-1α and phosphorylated cyclic AMP-responsive element-binding protein (CREB)/CREB at 200 mg/kg. Taken together, these findings demonstrate that BDE3 stimulates adrenal cell function likely through decreasing phosphorylation of AMPK and increasing phosphorylation of CREB.

PKA-site phosphorylation of importin13 regulates its subcellular localization and nuclear transport function

Importin 13 (IPO13) is a key member of the importin β superfamily, which can transport cargoes both into and out of the nucleus to contribute to a variety of important cellular processes. IPO13 is known to undergo phosphorylation, but the impact of this on function has not been investigated. Here, we show for the first time that IPO13 is phosphorylated by cAMP-dependent protein kinase A specifically at serine 193. Results from fluorescence recovery after photobleaching and fluorescence loss in photobleaching approaches establish that negative charge at serine 193 through phosphorylation or point mutation both reduces IPO13 nuclear import and increases its nuclear export. Importantly, phosphorylation also appears to enhance cargo interaction on the part of IPO13, with significant impact on localization, as shown for the Pax6 homeobox-containing transcription partner. This is the first report that IPO13 can be phosphorylated at Ser193 and that this modification regulates IPO13 subcellular localization and nucleocytoplasmic transport function, with important implications for IPO13's role in development and other processes.

SR-BI: Linking Cholesterol and Lipoprotein Metabolism with Breast and Prostate Cancer

Studies have demonstrated the significant role of cholesterol and lipoprotein metabolism in the progression of cancer. The SCARB1 gene encodes the scavenger receptor class B type I (SR-BI), which is an 82-kDa glycoprotein with two transmembrane domains separated by a large extracellular loop. SR-BI plays an important role in the regulation of cholesterol exchange between cells and high-density lipoproteins. Accordingly, hepatic SR-BI has been shown to play an essential role in the regulation of the reverse cholesterol transport pathway, which promotes the removal and excretion of excess body cholesterol. In the context of atherosclerosis, SR-BI has been implicated in the regulation of intracellular signaling, lipid accumulation, foam cell formation, and cellular apoptosis. Furthermore, since lipid metabolism is a relevant target for cancer treatment, recent studies have focused on examining the role of SR-BI in this pathology. While signaling pathways have initially been explored in non-tumoral cells, studies with cancer cells have now demonstrated SR-BI's function in tumor progression. In this review, we will discuss the role of SR-BI during tumor development and malignant progression. In addition, we will provide insights into the transcriptional and post-transcriptional regulation of the SCARB1 gene. Overall, studying the role of SR-BI in tumor development and progression should allow us to gain useful information for the development of new therapeutic strategies.

Loss of PKBβ/Akt2 predisposes mice to ovarian cyst formation and increases the severity of polycystic ovary formation in vivo

Ovarian cysts affect women of all ages and decrease fertility. In particular, polycystic ovarian syndrome (PCOS), in which multiple follicular cysts develop, affects 5–10% of women of reproductive age and can result in infertility. Current non-invasive treatments for PCOS can resolve cysts and restore fertility, but unresponsive patients must undergo severe ovarian wedge resection and resort to in vitro fertilization. PCOS is related to the deregulation of leutinizing hormone (LH) signaling at various levels of the hypothalamic-pituitary-ovarian axis and resultant hyperproduction of androgens. Because insulin resistance and compensatory hyperinsulinemia are observed in 50–70% of individuals with PCOS, deregulated insulin signaling in the ovary is considered an important factor in the disease. Here we report that aged mice specifically lacking the PKBβ (also known as Akt2) isoform that is crucial for insulin signaling develop increased testosterone levels and ovarian cysts, both of which are also observed in insulin-resistant PCOS patients. Young PKBβ knockout mice were used to model PCOS by treatment with LH and exhibited a cyst area that was threefold greater than in controls, but without hyperinsulinemia. Thus, loss of PKBβ might predispose mice to ovarian cysts independently of hyperactive insulin signaling. Targeted therapeutic augmentation of specific PKBβ signaling could therefore provide a new avenue for the treatment and management of ovarian cysts.

Mechanistic profiling of the cAMP-dependent steroidogenic pathway in the H295R endocrine disrupter screening system: new endpoints for toxicity testing

The need for implementation of effects on steroid synthesis and hormone processing in screening batteries of endocrine disruptive compounds is widely acknowledged. In this perspective, hormone profiling in the H295R adrenocortical cell system is extensively examined and recently OECD validated (TG 456) as a replacement of the minced testis assay. To further elucidate the complete mechanisms and endocrine responsiveness of this cell system, microarray-based gene expression profiling of the cAMP response pathway, one of the major pathways in steroidogenesis regulation, was examined in H295R cells. Next to the steroid synthesis pathway, a broader lipid metabolic pathway, including cholesterol uptake/biosynthesis, hormone metabolization and many hormone and nuclear receptors, are sensitive towards cAMP stimulation in this cell system. Moreover, these pathways were clearly dose and time responsive, indicating early regulation (10 h) of cholesterol uptake and mobilization genes and later expression (24-48 h) of cholesterol biosynthesis and steroid synthesis. Transcription network analysis suggested several important transcription factors that could be involved in regulation of the steroid hormone pathway, of which HNF4α, a broader lipid metabolism related transcription factor, might indicate some new transcription regulation patterns in this cell line. Overall we can conclude that the time dependent gene expression patterns of the strongly coordinated cholesterol supply and steroidogenesis pathways in the H295R cell system seem to reflect well the in vivo ACTH/cAMP signalling cascade in adrenal cells. Moreover, the completeness of the steroidogenic related pathways in terms of gene expression sensitivity, indicates the H295R cell line as a promising cell line in omics-based endocrine disruption screening.

Inhibitory effect of valproic acid on ovarian androgen biosynthesis in rat theca-interstitial cells

The objective of the study was to evaluate the effect of valproic acid (VPA) on ovarian androgen biosynthesis in primary cultures of theca-interstitial (T-I) cells isolated from rat ovaries. Ovarian T-I cells were cultured with VPA in the presence or absence of hCG. VPA did not increase basal or hCG-stimulated androgen synthesis when added to primary cultures of T-I cells. However, the addition of VPA caused a marked concentration-dependent inhibitory effect on hCG-stimulated androstendione synthesis. Treatment of T-I cells with 8-Bromo-cAMP resulted in a marked increase in the production of androstenedione, and VPA inhibited this stimulatory effect, suggesting that the mechanism of VPA's inhibitory effect on androstenedione production occurs at a step after second messenger activation. Treatment of T-I cells with hCG resulted in a significant increase in the mRNA expression of steroidogenic enzymes CYP17A1 and 17β-hydroxysteroid dehydrogenase. Addition of VPA sharply blunted the stimulatory effect of hCG, reducing the mRNA expression of the steroidogenic enzymes to basal levels. In conclusion, VPA exerts an inhibitory effect on hCG-stimulated androgen synthesis in rat T-I cells.

Regulation of sterol regulatory element-binding transcription factor 1a by human chorionic gonadotropin and insulin in cultured rat theca-interstitial cells

Theca-interstitial (T-I) cells of the ovary synthesize androgens in response to luteinizing hormone (LH). In pathological conditions such as polycystic ovarian syndrome, T-I cells are hyperactive in androgen production in response to LH and insulin. Because cholesterol is an essential substrate for androgen production, we examined the effect of human chorionic gonadotropin (hCG) and insulin on signaling pathways that are known to increase cholesterol accumulation in steroidogenic cells. Specifically, the effect of hCG and insulin on sterol regulatory element-binding transcription factor 1a (SREBF1a) required for cholesterol biosynthesis and uptake was examined. Primary cultures of T-I cells isolated from 25-day-old rat ovaries responded to hCG and insulin to increase the active/processed form of SREBF1a. The hCG and insulin significantly reduced insulin-induced gene 1 (INSIG1) protein, a negative regulator of SREBF processing. Furthermore, an increase in the expression of selected SREBF target genes, 3-hydroxy-3-methylglutaryl-coenzyme A reductase (Hmgcr) and mevalonate kinase (Mvk), was also observed. Protein kinase A (PRKA) inhibitor completely abolished the hCG-induced increase in SREBF1a, while increasing INSIG1. Although the hCG-induced depletion of total and free cholesterol was abolished by aminoglutethimide, the stimulatory effect on SREBF1a was not totally suppressed. Treatment with 25-hydroxycholesterol abrogated the effect of hCG on SREBF1a. Inhibition of the phosphatidylinositol 3-kinase pathway did not block the insulin-induced increase in SREBF1a, whereas mitogen-activated protein kinase inhibition reduced the insulin response. These results suggest that the increased androgen biosynthesis by T-I cells in response to hCG and insulin is regulated, at least in part, by increasing the expression of sterol response element-responsive genes by increasing SREBF1a.