Acute regulation of the bovine gene for the steroidogenic acute regulatory protein in ovarian theca and adrenocortical cells (original) (raw)
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Regulation of Transcription by Steroid Hormones
Annals of the New York Academy of Sciences, 1994
Steroid hormones bind to their corresponding receptors in the cytoplasm of responsive cells, and this complex is translocated to the nucleus where the hormonereceptor complex binds to specific DNA sequences located in the regulatory regions of the target gene. These specific DNA sequences are referred to as hormoneresponsive elements (HRE) and act as enhancer elements, such that when the receptor complex binds, transcription is induced. In the absence of ligand, the hormone receptor is maintained in an inactive form by association with other cellular proteins.
Steroids, 2003
The rate-limiting, committed, and regulatable step in steroid hormone biosynthesis is the transport of cholesterol from the outer to the inner mitochondrial membrane, a process that is mediated by the steroidogenic acute regulatory (StAR) protein. In steroidogenic cells, the StAR protein is regulated by cAMP-dependent mechanisms. However, the StAR promoter lacks a consensus cAMP response-element (CRE), suggesting the involvement of alternate regulatory factor(s) in cAMP responsiveness. These regulatory elements are found to be located in a transcription factor-binding site-rich region (consisting of approximately 150 nucleotides upstream of the transcription start site) of the StAR promoter, and appears to be the most important region in regulating transcription of the StAR gene. The StAR promoter sequences in mouse, rat and human are highly homologous, and in the absence of a canonical CRE, multiple cis-elements have been shown to be instrumental in the regulation of StAR gene expression. Nevertheless, it has become apparent that functional cooperation, interaction, and alteration of different transcription factors are involved in the fine-tuning of the regulatory events associated with StAR gene transcription.
Regulation of steroidogenic acute regulatory protein (StAR) gene expression in hamster adrenals
Endocrine Research, 1998
The regulation of steroidogenic acute regulatory protein (StAR) in vitro by gonadotropins was investigated in granulosa cells from prehierarchal and preovulatory hen follicles. Basal levels of StAR messenger RNA (mRNA) in undifferentiated granulosa cells from prehierarchal (6- to 8-mm) follicles were consistently low, but detectable, and were significantly increased by treatment with 8-bromo-cAMP and FSH (but not LH) within 3-6 h of culture. After 20 h of culture, 8-bromo-cAMP, FSH, and LH each increased StAR mRNA levels above those in control cultured cells, and the delayed response to LH treatment was associated with increased levels of LH receptor (LH-R) mRNA. On the other hand, inhibition of mitogen-activated protein (MAP) kinase signaling, using the MAP kinase kinase inhibitors U0126 and PD98059, in the presence of FSH further increased StAR mRNA and protein levels, LH-R mRNA levels, and progesterone synthesis compared with those in cells cultured with FSH alone. The highest basal expression of StAR mRNA during follicle development was found in granulosa from the largest (F1) preovulatory follicle, with comparatively lower levels in granulosa from less mature (F2 plus F3) preovulatory follicles. Treatment with LH rapidly increased StAR mRNA and protein (but not LH-R mRNA) expression in cultures of F1 granulosa and in combined F2 plus F3 granulosa within 3 h, although the magnitude of stimulation was greater in F2 plus F3 granulosa. Compared with results from granulosa cells from prehierarchal follicles cultured for 20 h, inhibition of MAP kinase signaling in the presence of LH for 1 h failed to further enhance levels of StAR or LH-R expression or progesterone production in F2 plus F3 follicle granulosa compared with the effect of LH treatment alone. These results demonstrate that StAR expression in the hen ovary is up-regulated by gonadotropins at least in part via cAMP signaling. The ability of MAP kinase kinase inhibitors to potentiate gonadotropin-induced StAR and LH-R expression plus progesterone synthesis in prehierarchal follicle granulosa cells in vitro suggests that inhibition of paracrine or autocrine factor-mediated MAP kinase signaling in vivo may be a prerequisite for the full potentiation of granulosa cell steroidogenesis that occurs after recruitment into the preovulatory hierarchy. Finally, these results fail to support a role for MAP kinase signaling in acutely modulating LH-mediated StAR expression or progesterone production in hierarchal follicles, such as occurs during the preovulatory surge of progesterone.
The steroidogenic acute regulatory (StAR) protein two years later
Endocrine, 1997
It has now been approx 2 yr since the purification, cloning, sequencing, and expression of the Steroidogenic Acute Regulatory (STAR) protein. This article will attempt to not only catalog the earlier studies that have been performed on this steroidogenic tissue-specific, trophic hormone-induced protein, but also to update what has recently been found. The intention of this article is, therefore, to summarize the available data and then integrate this data into what is thought to be its role in the acute regulation of steroid hormone biosynthesis. A number of review articles and commentaries on this subject have also recently appeared (1-8). In several of those articles, a much wider scope of the field of the acute regulation of steroidogenesis was included. Many of those observations will not again be presented here. Rather, the subject of this review will be confined to what has been learned in the past and what is currently known about the StAR protein. As in any ongoing scientific endeavour, much of which has been observed, and which will be described herein, is fact and much of that which will be discussed, especially with regard to the mechanism of action of STAR, is more speculative.
Nucleic Acids Research, 1989
Normalized dose response-curves for transcriptional activation of reporter genes were obtained by co-transfecting them with increasing amounts of wild-type (wt) progesterone (PR), glucocorticoid (GR) and oestrogen (ER) expression vectors. Marked differences in both shape and magnitude of the stimulation were observed depending on whether HeLa or CV1 cells were transfected. In HeLa cells the transcriptional stimulation from a reporter gene containing the hormone responsive element (RE) present in the mouse mammary tumour virus (MMTV) long terminal repeat (LTR) increased as increasing amounts (from 0.05 to 7.5 pg) of PR expression vector were transfected, whereas no such increase was observed in CV1 cells above 1 pg of the same vector. In contrast, a PR mutant lacking the hormone binding domain (HBD, region E), exhibited increasing constitutive activity with increasing amounts of PR expression vector, such that in CV1 cells, but not in HeLa cells, similar activities were measured for the mutant and wt PR when 5 pg expression vectors were transfected. Western blot analyses indicated that the differences between the two cell lines were not due to differences in the amount of receptor proteins. Using the same MMTV LTR-based reporter gene, cell-specific differences were also detected between the dose-response curves obtained for the human GR and a mutant which lacks the HBD. A PR mutant in which the N-terminal A/B region was deleted exhibited no (CV1 cells) or less than 5% (HeLa cells) of the wt-activity, whereas the corresponding GR mutant stimulated efficiently transcription in both cell lines. Identical studies with the wt human ER or a mutant truncated for the N-terminal A/B region resulted in bell-shaped dose-response curves in both HeLa and CV1 cells, whereas an ER mutant lacking the HBD was weakly active in either cell line.
Control of Transcription by Steroid Hormones
Annals of the New York Academy of Sciences, 1996
All members of the superfamily are organized according to a modular pattern and include at least three structural and functional domains able to act relatively a The experimental work summarized in this review was supported by grants from the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie. 93 94 ANNALS NEW YORK ACADEMY OF SCIENCES BEAT0 ef at.: TRANSREGULATION 95
Molecular Endocrinology, 2004
cAMP-dependent mechanisms regulate the steroidogenic acute regulatory (StAR) protein even though its promoter lacks a consensus cAMP response-element (CRE, TGACGTCA). Transcriptional regulation of the StAR gene has been demonstrated to involve combinations of DNA sequences that provide recognition motifs for sequence-specific transcription factors. We recently identified and characterized three canonical 5′-CRE half-sites within the cAMP-responsive region (−151/−1 bp) of the mouse StAR gene. Among these CRE elements, the CRE2 half-site is analogous (TGACTGA) to an activator protein-1 (AP-1) sequence [TGA(C/G)TCA]; therefore, the role of the AP-1 transcription factor was explored in StAR gene transcription. Mutation in the AP-1 element demonstrated an approximately 50% decrease in StAR reporter activity. Using EMSA, oligonucleotide probes containing an AP-1 binding site were found to specifically bind to nuclear proteins obtained from mouse MA-10 Leydig and Y-1 adrenocortical tumor c...
Transcriptional regulation by steroid hormones
Steroids, 1996
Steroid hormones influence the transcription of a large number of genes by virtue of their interaction with intracellular receptors, which are modular proteins composed of a ligand binding domain, a DNA binding domain, and several transactivation functions distributed along the molecule. The DNA binding domain is organized around two zinc ions and allows the receptors to bind as homodimers to palindromic DNA sequences, the hormone responsive elements (HRE), in such a way that each homodimer contacts one half of the palindrome. Since the two halves are separated by three base pairs, the two homodimers contact the same face of the double helix. Before hormone binding, the receptors are part of a complex with multiple chaperones which maintain the receptor in its steroid binding conformation. Following hormone binding, the complex dissociates and the receptors bind to HREs in chromatin.