Analysis of the promoter of the luteinizing hormone/human chorionic gonadotropin receptor gene in neuroendocrine cells

Involvement of Luteinizing Hormone in Alzheimer Disease Development in Elderly Women

Alzheimer disease (AD) is a slow progressive neurodegenerative disease that affects more elderly women than elderly men. It impairs memory, typically progresses into multidomain cognitive decline that destroys the quality of life, and ultimately leads to death. About 5.3 million older Americans are now living with this disease, and this number is projected to rise to 14 million by 2050. Annual health-care costs in the United States alone are projected to increase to about US$1.1 trillion by 2050. The initial theory that decreasing estrogen levels leads to AD development in postmenopausal women has been proven inconclusive. For example, Women's Health Research Initiative Memory Study and the population-based nested case-control study have failed to demonstrate that estrogen/progesterone (hormone replacement therapy [HRT]) or estrogen replacement therapy could prevent the cognitive decline or reduce the risk of AD. This led to the realization that AD development could be due to a progressive increase in luteinizing hormone (LH) levels in postmenopausal women. Accordingly, a large number of studies have demonstrated that an increase in LH levels is positively correlated with neuropathological, behavioral, and cognitive changes in AD. In addition, LH has been shown to promote amyloidogenic pathway of precursor protein metabolism and deposition of amyloid β plaques in the hippocampus, a region involved in AD. Cognate receptors that mediate LH effects are abundantly expressed in the hippocampus. Reducing the LH levels by treatment with gonadotropin-releasing hormone agonists could provide therapeutic benefits. Despite these advances, many questions remain and require further research.

Pituitary cell lines and their endocrine applications

The pituitary gland is an important component of the endocrine system, and together with the hypothalamus, exerts considerable influence over the functions of other endocrine glands. The hypothalamus either positively or negatively regulates hormonal productions in the pituitary through its release of various trophic hormones which act on specific cell types in the pituitary to secrete a variety of pituitary hormones that are important for growth and development, metabolism, reproductive and nervous system functions. The pituitary is divided into three sections-the anterior lobe which constitute the majority of the pituitary mass and is composed primarily of five hormone-producing cell types (thyrotropes, lactotropes, corticotropes, somatotropes and gonadotropes) each secreting thyrotropin, prolactin, ACTH, growth hormone and gonadotropins (FSH and LH) respectively. There is also a sixth cell type in the anterior lobe-the non-endocrine, agranular, folliculostellate cells. The intermediate lobe produces melanocyte-stimulating hormone and endorphins, whereas the posterior lobe secretes anti-diuretic hormone (vasopressin) and oxytocin. Representative cell lines of all the six cell types of the anterior pituitary have been established and have provided valuable information on genealogy of the various cell lineages, endocrine feedback control of hormone synthesis and secretions, intrapituitary interactions between the various cell types, as well as the role of specific transcription factors that determine each differentiated cell phenotype. In this review, we will discuss the morphology and function of the cell types that make up the anterior pituitary, and the characteristics of the various functional anterior pituitary cell systems that have been established to be representative of each anterior pituitary cell lineage.

Transgenic mice harboring murine luteinizing hormone receptor promoter/beta-galactosidase fusion genes: different structural and hormonal requirements of expression in the testis, ovary, and adrenal gland

In vivo regulation of the LH receptor (LHR) promoter was studied using transgenic (TG) mice harboring fusion genes containing three different lengths of the LHR promoter (7.4 kb, 2.1 kb, and 173 bp), fused with coding sequence of the Escherichia coli beta-galactosidase (beta-GAL) reporter gene. The length of the LHR promoter significantly affected the pattern of beta-GAL expression. In the testis the shortest promoter directed expression primarily of the full-length beta-GAL mRNA, but mainly truncated messages were transcribed from the longer LHR promoter/beta-GAL constructs. The case was reversed in the ovary and adrenal gland. Furthermore, we have recently detected strong LHR expression in the adrenal gland of female mice with chronically elevated serum LH. Therefore, the regulation of the adrenal LHR expression was addressed in the present study using the LHR/beta-GAL TG mice. Elevated LH levels were achieved in the LHR/beta-GAL mice either by gonadectomy or cross-breeding them with TG mice overexpressing a chimeric protein of bovine LH beta-subunit and the C-terminal fragment of human chorionic gonadotropin-beta. In both models, beta-GAL mRNA was found in the adrenal cortex when the 7.4-kb LHR promoter was applied but not in mice carrying the 173-bp LHR promoter. The 7.4-kb construct was activated also in the ovaries in the double TG LHR(beta-GAL)/bovine LH beta-subunit/C-terminal fragment of human chorionic gonadotropin-betamice in some theca-interstitial cells surrounding the follicles. Hence, the LHR promoter elements essential for directing beta-GAL expression to the adrenal gland and ovary (7.4 kb) are different from those recently shown to be essential for the testicular expression (173 bp). In conclusion, elevated serum LH concentrations were found seminal for the LHR promoter activation in the ovaries and adrenals, and different lengths of the promoter are responsible for reporter gene expression in the testis, ovary, and adrenal gland.

Determinants of Transcription of the Chorionic Gonadotropin /Luteinizing Hormone Receptor Gene in Human Breast Cells

Epidemiological evidence suggests that the earlier in life a woman becomes pregnant, the lower her chances for developing breast cancer later in life. This protective effect appears to be due to pregnancy hormone hCG inducing the nonreversible differentiation of proliferative terminal end buds into secretory type lobules. Perhaps this and other actions of hCG are mediated by newly discovered hCG/LH receptors in human breast cells. Thus the hCG actions in breast are potentially important for breast cancer prevention. Because of this importance, we investigated the cis-acting elements and trans-acting proteins that determine the transcription of human chorionic gonadotropin (hCG)/luteinizing hormone (LH) receptor gene in MCF-7, MDA-MB-231, and normal human breast epithelial HMEC cells. These cells contained major-4.8 and 1.8 kb-and minor-9.0, 6.0, and 1.2 kb-hCG/LH receptor transcripts with significantly higher levels in MCF-7 cells. Nuclear run-on transcription, as well as transfection with a fusion construct of luciferase gene and the -2056 to -1 bp of the 5'-flanking region of hCG/LH receptor gene, revealed that MCF-7 cells were transcriptionally more active than the other breast cells. Sequential deletion of the 5'-flanking region revealed that breast cells contained a promoter at -184 to -1 bp. Electrophoretic gel mobility shift assays demonstrated that breast cell nuclear extracts contained Ap2 and Egr promoter binding proteins. Sp1 was also present, but it could not bind because of competition with Egr for binding to a partially overlapping Egr/Sp1 site. The higher levels of Ap2 and Egr binding proteins may explain higher transcription of hCG/LH receptor gene in MCF-7 cells than in the other breast cells.

Ectopic and abnormal hormone receptors in adrenal Cushing's syndrome

The mechanism by which cortisol is produced in adrenal Cushing's syndrome, when ACTH is suppressed, was previously unknown and was referred to as being "autonomous." More recently, several investigators have shown that some cortisol and other steroid-producing adrenal tumors or hyperplasias are under the control of ectopic (or aberrant, illicit, inappropriate) membrane hormone receptors. These include ectopic receptors for gastric inhibitory polypeptide (GIP), beta-adrenergic agonists, or LH/hCG; a similar outcome can result from altered activity of eutopic receptors, such as those for vasopressin (V1-AVPR), serotonin (5-HT4), or possibly leptin. The presence of aberrant receptors places adrenal cells under stimulation by a trophic factor not negatively regulated by glucocorticoids, leading to increased steroidogenesis and possibly to the proliferative phenotype. The molecular mechanisms responsible for the abnormal expression and function of membrane hormone receptors are still largely unknown. Identification of the presence of these illicit receptors can eventually lead to new pharmacological therapies as alternatives to adrenalectomy, now demonstrated by the long-term control of ectopic P-AR- and LH/hCGR-dependent Cushing's syndrome by propanolol and leuprolide acetate. Further studies will potentially identify a larger diversity of hormone receptors capable of coupling to G proteins, adenylyl cyclase, and steroidogenesis in functional adrenal tumors and probably in other endocrine and nonendocrine tumors.

Immortalized hippocampal cells contain functional luteinizing hormone/human chorionic gonadotropin receptors

We used immortalized HN33p cells as surrogates for hippocampal neurons to investigate the functional importance of luteinizing hormone (LH)/human chorionic gonadotropin (hCG) receptors. The use of various detection techniques demonstrated that HN33p cells contain LH/hCG receptor transcripts and receptor protein that can bind 125I-hCG. Culturing them with highly purified hCG resulted in a significant, although modest, dose-and time-dependent and hormone specific increase in steady state 5-lipoxygenase (5-LO) mRNA and protein levels. The studies on signaling revealed that treatment of HN33p cells with hCG resulted in a robust dose- and a time-dependent significant increase in media cyclic AMP levels. In addition, treatment with a protein kinase (PK)A inhibitor, isoquinolinesulfonamide (H-89), but not with a PKC inhibitor, bisindolylmaleimide (Bis), prevented hCG from increasing the 5-LO protein levels. Pretreatment of HN33p cells for 48 hrs with 2 microM antisense, but not sense, phosphorothioate oligodeoxy-nucleotides (ODN) synthesized from mouse LH/hCG receptor sequence resulted in a dramatic decrease in LH/hCG receptor protein levels. In the antisense, but not in sense, ODN-treated cells, hCG was unable to increase cyclic AMP and 5-LO protein levels, suggesting that receptors are required for hCG to work in HN33p cells.