Identification of androstenedione in a river containing paper mill effluent

Effluent from a paper mill discharging into the Fenholloway River, Taylor County, Florida, USA, contains chemicals that masculinize females of the resident population of eastern mosquitofish (Gambusia holbrooki), as evidenced in females by elongated anal fins, which is normally a male-specific trait. To identify androgenic components in the effluent, water collected from the Fenholloway River and a control tributary was fractionated using solid-phase extraction and reverse-phase high-performance-liquid chromatography. Two Fenholloway River fractions induced androgen receptor-dependent transcriptional activity in transient transfection cell culture assays. Of these, androstenedione was confirmed by liquid chromatography-mass spectrometry with multiple reaction monitoring.

A mechanism for androgen receptor-mediated prostate cancer recurrence after androgen deprivation therapy

The development and growth of prostate cancer depends on the androgen receptor and its high-affinity binding of dihydrotestosterone, which derives from testosterone. Most prostate tumors regress after therapy to prevent testosterone production by the testes, but the tumors eventually recur and cause death. A critical question is whether the androgen receptor mediates recurrent tumor growth after androgen deprivation therapy. Here we report that a majority of recurrent prostate cancers express high levels of the androgen receptor and two nuclear receptor coactivators, transcriptional intermediary factor 2 and steroid receptor coactivator 1. Overexpression of these coactivators increases androgen receptor transactivation at physiological concentrations of adrenal androgen. Furthermore, we provide a molecular basis for this activation and suggest a general mechanism for recurrent prostate cancer growth.

Androgen receptor stabilization in recurrent prostate cancer is associated with hypersensitivity to low androgen

The androgen receptor (AR) is highly expressed in androgen-dependent and recurrent prostate cancer (CaP) suggesting it has a role in the growth and progression of CaP. Previously proposed mechanisms for AR reactivation in recurrent CaP include altered growth factor signaling leading to protein phosphorylation and AR mutations that broaden ligand specificity. To further establish a role for AR in recurrent CaP, we compared several properties of AR in relation to the growth response to low levels of androgens in model systems of androgen-dependent and recurrent CaP. AR from all of the tumors and cell lines bound [3H]R1881 with similar high affinity (mean Kd, 0.12 nM). In the absence of androgen, AR in androgen-dependent LNCaP cells was unstable with a degradation half-time (t(1/2)) of 3 h at 37 degrees C. In contrast, AR was 2-4 times more stable in recurrent CWR22 tumors (t(1/2), >12 h) and CWR-R1 or LNCaP-C4-2 cell lines (t(1/2), 6-7 h) derived from recurrent prostate tumors. In the recurrent CWR22 tumor and its CWR-R1 cell line grown in the absence of androgen, AR immunostaining was entirely nuclear, whereas under the same conditions AR in LNCaP-C4-2 and LNCaP cells was predominantly nuclear but was also detected in the cytoplasm. High level expression, increased stability, and nuclear localization of AR in recurrent tumor cells were associated with an increased sensitivity to the growth-promoting effects of dihydrotestosterone in the femtomolar range. The concentration of dihydrotestosterone required for growth stimulation in CWR-R1 and LNCaP-C4-2 cells was four orders of magnitude lower than that required for androgen-dependent LNCaP cells. The results suggest that AR is transcriptionally active in recurrent CaP and can increase cell proliferation at the low circulating levels of androgen reported in castrated men.

A natural sequence consisting of overlapping glucocorticoid-responsive elements mediates glucocorticoid, but not androgen, regulation of gene expression

Cytosolic aspartate aminotransferase (cAspAT) is regulated by glucocorticoids in rat liver and kidney. Part of this regulation is mediated by an unusual glucocorticoid-responsive element (GRE)-like sequence called GRE A. GRE A is composed of two overlapping imperfect GREs, each comprising a conserved half-site (half-sites 1 and 4 respectively) and a poorly conserved half-site (half-sites 2 and 3 respectively). The sequence binds co-operatively two dimers of the glucocorticoid receptor (GR) and mediates efficient glucocorticoid regulation of gene expression. Analysis of deletions of the cAspAT gene promoter and subcloning of GRE A upstream of the thymidine kinase promoter indicate that this sequence is responsive to glucocorticoids, but not to androgens. Electrophoretic mobility shift assays indicate that the GRE A unit does not bind the androgen receptor (AR). The modification of three nucleotides in the poorly conserved half-sites 2 and 3, converting GRE A into two overlapping high-affinity GREs (ov-cGRE), resulted in co-operative binding of the AR. Furthermore, ov-cGRE efficiently mediated androgen regulation of the thymidine kinase promoter. A single base modification in half-site 2 or 3 in GRE A allowed the binding of the AR as one or two dimers respectively, and restored transcriptional activation by androgens only in the latter case. Thus the poor affinity of the AR for half-sites 2 and 3 prevented its binding to GRE A, indicating that the overlapping GRE A sequence of the cAspAT gene promoter discriminates a glucocorticoid-mediated from an androgen-mediated response.

FXXLF and WXXLF sequences mediate the NH2-terminal interaction with the ligand binding domain of the androgen receptor

The nuclear receptor superfamily members of eukaryotic transcriptional regulators contain a highly conserved activation function 2 (AF2) in the hormone binding carboxyl-terminal domain and, for some, an additional activation function 1 in the NH(2)-terminal region which is not conserved. Recent biochemical and crystallographic studies revealed the molecular basis of AF2 is hormone-dependent recruitment of LXXLL motif-containing coactivators, including the p160 family, to a hydrophobic cleft in the ligand binding domain. Our previous studies demonstrated that AF2 in the androgen receptor (AR) binds only weakly to LXXLL motif-containing coactivators and instead mediates an androgen-dependent interaction with the AR NH(2)-terminal domain required for its physiological function. Here we demonstrate in a mammalian two-hybrid assay, glutathione S-transferase fusion protein binding studies, and functional assays that two predicted alpha-helical regions that are similar, but functionally distinct from the p160 coactivator interaction sequence, mediate the androgen-dependent, NH(2)- and carboxyl-terminal interaction. FXXLF in the AR NH(2)-terminal domain with the sequence (23)FQNLF(27) mediates interaction with AF2 and is the predominant androgen-dependent interaction site. This FXXLF sequence and a second NH(2)-terminal WXXLF sequence (433)WHTLF(437) interact with different regions of the ligand binding domain to stabilize the hormone-receptor complex and may compete with AF2 recruitment of LXXLL motif-containing coactivators. The results suggest a unique mechanism for AR-mediated transcriptional activation.

Ligand-induced stabilization of PPARgamma monitored by NMR spectroscopy: implications for nuclear receptor activation

Nuclear receptors are ligand-dependent transcription factors that are mediators of the action of lipophilic hormones and other endogenous ligands and are the targets of drugs useful in a variety of therapeutic areas. Peroxisome proliferator-activated receptor (PPAR)gamma is a nuclear receptor that, acting as a heterodimer with RXR, mediates a variety of cellular effects including adipocyte-differentiation. Due to its role in modulating insulin sensitivity, it is the target of therapeutically active anti-diabetic agents such as rosiglitazone. We have assigned the chemical shifts of the backbone atoms of the 32 kDa ligand-binding domain of PPARgamma in the presence of bound rosiglitazone. Three-dimensional HNCO spectra of the apo ligand-binding domain (LBD) have less than half the expected number of cross-peaks. The missing cross-peaks are restored upon binding strong agonists such as rosiglitazone. The NMR results indicate that the apo-LBD of PPARgamma is in a conformationally mobile state, and that agonist binding is associated with a marked stabilization of the conformation. Mapping the missing peaks to the 3D X-ray crystallographic structure indicates the region of mobility is extensive and includes the ligand-binding region and the cofactor-binding site. This leads to the conclusion that activation of this nuclear receptor is a result of a population shift of a dynamic ensemble of conformations, rather than a two-state switch from an inactive to an active conformation. Our results have important implications for the mechanisms by which antagonists, partial agonists, and agonists of nuclear receptor function operate.

Activation function 2 in the human androgen receptor ligand binding domain mediates interdomain communication with the NH(2)-terminal domain

Activation function 2 in the ligand binding domain of nuclear receptors forms a hydrophobic cleft that binds the LXXLL motif of p160 transcriptional coactivators. Here we provide evidence that activation function 2 in the androgen receptor serves as the contact site for the androgen dependent NH(2)- and carboxyl-terminal interaction of the androgen receptor and only weakly interacts with p160 coactivators in an LXXLL-dependent manner. Mutagenesis studies indicate that it is the NH(2)-/carboxyl-terminal interaction that is required by activation function 2 to stabilize helix 12 and slow androgen dissociation critical for androgen receptor activity in vivo. The androgen receptor recruits p160 coactivators through its NH(2)-terminal and DNA binding domains in an LXXLL motif-independent manner. The results suggest a novel function for activation function 2 and a unique mechanism of nuclear receptor transactivation.

The forgotten copper 7 - a circus tale

A forgotten Gravigard intra-uterine contraceptive device, in a woman with an itinerant lifestyle, caused pelvic actinomycosis, mimicking ovarian malignancy. This case illustrates that although rare, this complication can still occur.

Development of a statewide protocol for the prehospital identification of DNR patients in Connecticut including new DNR regulations

This article describes the development and implementation of a standardized protocol for the prehospital identification of terminally ill "do-not-resuscitate" (DNR) patients. This pilot program was initiated by members of the Connecticut College of Emergency Physicians and instituted on a voluntary basis statewide in July 1991. Key components of the program are discussed, including developmental rationale, formation of a DNR Coalition, educational rollout, and implementation activities. The second phase of this initiative involved passage of state legislation and development of new DNR regulations, which went into effect in July 1997. The regulations successfully addressed the limitations and difficulties encountered in the pilot program. Major modifications included applicability of the bracelet program to a broader group of DNR patients, development of a uniform system for interfacility transfer of DNR patients, and mandatory compliance by health care personnel.

Redox-dependent DNA binding of the purified androgen receptor: evidence for disulfide-linked androgen receptor dimers

Full-length histidine-tagged, dihydrotestosterone-bound human androgen receptor (AR) was purified to homogeneity by affinity and gel-filtration chromatography for antibody production and analysis of AR dimerization and DNA binding properties. A monoclonal antibody was raised that recognized human and rat AR epitope (360)ArgAspTyrTyrAsnPheProLeuAla(368) in the NH(2)-terminal domain and slowed migration of AR-DNA complexes in mobility shift assays. AR binding to androgen response element DNA had a K(d) of 2.0 nM and a Hill coefficient of 2.1, indicating high-affinity, cooperative binding. AR solution dimerization was detected only at >/=0.2 microM AR, and DNA binding increased dimerization up to 30-fold. Slow- and fast-migrating AR-DNA complexes were detected under different reducing conditions that differed 5-fold in their dissociation rates from DNA. Treatment with the sulfhydryl oxidizing reagent diamide formed the faster migrating, slower dissociating complex, indicating it represents disulfide-linked AR dimers bound to DNA. The results indicate that high concentrations of purified AR are required for solution dimerization and that cooperative DNA binding stabilizes two dimer forms that differ in redox state.

Distinguishing androgen receptor agonists and antagonists: distinct mechanisms of activation by medroxyprogesterone acetate and dihydrotestosterone

Natural and pharmacological androgen receptor (AR) ligands were tested for their ability to induce the AR NH2-terminal and carboxyl-terminal (N/C) interaction in a two-hybrid protein assay to determine whether N/C complex formation distinguishes in vivo AR agonists from antagonists. High-affinity agonists such as dihydrotestosterone, mibolerone, testosterone, and methyltrienolone at concentrations between 0.1 and 1 nM induce the N/C interaction more than 40-fold. The lower affinity anabolic steroids, oxandrolone and fluoxymesterone, require concentrations of 10-100 nM for up to 23-fold induction of the N/C interaction. However no N/C interaction was detected in the presence of the antagonists, hydroxyflutamide, cyproterone acetate, or RU56187, at concentrations up to 1 microM, or with 1 microM estradiol, progesterone, or medroxyprogesterone acetate; each of these steroids at 1-500 nM inhibited the dihydrotestosterone-induced N/C interaction, with medroxyprogesterone acetate being the most effective. In transient and stable cotransfection assays using the mouse mammary tumor virus reporter vector, all ligands displayed concentration-dependent AR agonist activity that paralleled induction of the N/C interaction, with antagonists and weaker agonists failing to induce the N/C interaction. AR dimerization and DNA binding in mobility shift assays and AR stabilization reflected, but were not dependent on, the N/C interaction. The results indicate that the N/C interaction facilitates agonist potency at low physiological ligand concentrations as detected in transcription, dimerization/DNA binding, and stabilization assays. However the N/C interaction is not required for agonist activity at sufficiently high ligand concentrations, nor does its inhibition imply antagonist activity.

Binding properties and distribution of insulin-like growth factor binding protein-related protein 3 (IGFBP-rP3/NovH), an additional member of the IGFBP Superfamily

The protein product of the novH oncogene, a member of the CCN family, is structurally related to the insulin-like growth factor (IGF) binding proteins (IGFBPs). We have characterized aspects of structure, function, and distribution of this protein, which, as IGFBP-related protein 3 (IGFBP-rP3), is a proposed member of the IGFBP Superfamily. Affinity cross-linking experiments performed with baculovirus synthesized recombinant human IGFBP-rP3 established that rhIGFBP-rP3 binds IGF-I, IGF-II, and insulin with low affinity. Specificity of binding was shown by competitive cross-linking experiments; binding to IGF-I and -II was also demonstrated by nondenaturing Western ligand blots. Northern blot analysis indicated the presence of IGFBP-rP3 messenger RNA (mRNA) in a broad range of human tissues. Western immunoblotting studies, using a polyclonal rabbit anti-rhIGFBP-rP3 antibody, demonstrated that IGFBP-rP3 protein is synthesized in vitro by several breast and prostate cancer cell lines: Hs578T, PC3, P69, and LNCaP cells. Western immunoblotting studies of human biological fluids identified that IGFBP-rP3 was present in normal serum, pregnancy serum, serum from patients with growth hormone receptor deficiency, cerebrospinal fluid, amniotic fluid, peritoneal fluid, and follicular fluid, while IGFBP-rP3 fragments were identified in cerebrospinal fluid, amniotic fluid, and prepubertal and pubertal urine samples. Our studies demonstrate that IGFBP-rP3 exhibits IGF binding, albeit at low affinity, and IGFBP-rP3 thus merits inclusion in the IGFBP Superfamily. The low affinity IGF binding suggests that IGFBP-rP3 may act primarily independently of the IGFs. The synthesis of IGFBP-rP3 by several malignant cell lines and its presence in human biological fluids suggest that this protein possesses other interesting roles, potentially in cell growth regulation.

Characterization of insulin-like growth factor binding protein-3 (IGFBP-3) binding to human breast cancer cells: kinetics of IGFBP-3 binding and identification of receptor binding domain on the IGFBP-3 molecule

Insulin-like growth factor binding protein-3 (IGFBP-3) binds to specific membrane proteins located on human breast cancer cells, which may be responsible for mediating the IGF-independent growth inhibitory effects of IGFBP-3. In this study, we evaluated IGFBP-3 binding sites on breast cancer cell membranes by competitive binding studies with IGFBP-1 through -6 and various forms of IGFBP-3, including synthetic IGFBP-3 fragments. Scatchard analysis revealed the existence of high-affinity sites for IGFBP-3 in estrogen receptor-negative Hs578T human breast cancer cells (dissociation constant (Kd) = 8.19 +/- 0.97 x 10(-9) M and 4.92 +/- 1.51 x 10(5) binding sites/cell) and 30-fold fewer receptors in estrogen receptor-positive MCF-7 cells (Kd = 8.49 +/- 0.78 x 10(-9) M and 1.72 +/- 0.31 x 10(4) binding sites/cell), using a one-site model. These data demonstrate binding characteristics of typical receptor-ligand interactions, strongly suggesting an IGFBP-3:IGFBP-3 receptor interaction. Among IGFBPs, only IGFBP-5 showed weak competition, indicating that IGFBP-3 binding to breast cancer cell surfaces is specific and cannot be attributed to nonspecific interaction with glycosaminoglycans. This was confirmed by showing that synthetic IGFBP-3 peptides containing IGFBP-3 glycosaminoglycan-binding domains competed only weakly for IGFBP-3 binding to the cell surface. Rat IGFBP-3 was 20-fold less potent in its ability to compete with human IGFBP-3(Echerichia coli), as well as 10- to 20-fold less potent for cell growth inhibition than human IGFBP-3, suggesting the existence of species specificity in the interaction between IGFBP-3 and the IGFBP-3 receptor. When various IGFBP-3 fragments were evaluated for affinity for the IGFBP-3 receptor, only those fragments that contain the midregion of the IGFBP-3 molecule were able to inhibit 125I-IGFBP-3(Escherichia coli) binding, indicating that the midregion of the IGFBP-3 molecule is responsible for binding to its receptor. These observations demonstrate that specific, high-affinity IGFBP-3 receptors are located on breast cancer cell membranes. These receptors have properties that support the notion that they may mediate the IGF-independent inhibitory actions of IGFBP-3 in breast cancer cells.

Antiandrogens as environmental endocrine disruptors

Steroid hormone receptors control fundamental events in embryonic development and sex differentiation through their function as ligand-inducible transcription factors. The consequences of disrupting these processes can be especially profound during development due to the crucial role hormones play in controlling transient and irreversible developmental processes. Several environmental chemicals, including metabolites of the fungicide vinclozolin and the pesticide DDT, disrupt male reproductive development and function by inhibiting androgen receptor mediated events. A variety of in vitro and in vivo approaches have been used to determine the molecular basis of environmental antiandrogen toxicity. These chemicals commonly bind androgen receptor with moderate affinity and act as antagonists by inhibiting transcription of androgen dependent genes.

Evolution of the primate androgen receptor: a structural basis for disease

Androgen effects mediated by the androgen receptor (AR) are essential for male reproductive development and virilization. Comparison of AR DNA coding sequence from five primate species, Homo sapiens (human), Pan troglodytes (chimpanzee), Papio hamadryas (baboon), Macaca fascicularis (macaque), and Eulemur fulvus collaris (collared brown lemur), supports their phylogeny with complete conservation of the DNA and steroid binding domain protein sequence. A linear increase in trinucleotide repeat expansion of homologous CAG and GGC sequences occurs in the NH2-terminal transcriptional activation region and is proportional to the time of species divergence. A serine phosphate/glutamine repeat interaction is observed where increasing CAG repeat length is associated with an increased rate of serine 94 phosphorylation. Disparity in the calculated and apparent molecular weight with CAG repeat expansion of an AR NH2-terminal fragment suggests self-aggregation with increasing glutamine repeat length into the pathological range. These results suggest that a CAG/glutamine repeat expanded during divergence of the higher primate species, which may have a direct effect on AR structure and support a common pathway in CAG trigenic diseases in the pathophysiology of neurodegeneration observed in X-linked spinal bulbar and muscular atrophy.

Identification of glycosylated 38-kDa connective tissue growth factor (IGFBP-related protein 2) and proteolytic fragments in human biological fluids, and up-regulation of IGFBP-rP2 expression by TGF-beta in Hs578T human breast cancer cells

Connective Tissue Growth Factor (CTGF) is a cysteine-rich peptide involved in human atherosclerosis and fibrotic disorders such as scleroderma. CTGF has considerable N-terminal sequence similarity with the insulin-like growth factor binding proteins (IGFBPs), including preservation of cysteines, and has been postulated to be a member of the IGFBP superfamily. Indeed, recent studies have shown that baculovirus generated CTGF, a secreted 38-kDa protein, binds IGFs in a specific manner, leading to the provisional renaming of CTGF as IGFBP-8 (or IGFBP-rP2). With immunoprecipitation and immunoblotting, using polyclonal anti-IGFBP-rP2 antibody generated against recombinant human IGFBP-rP2bac, IGFBP-rP2 can be identified in the serum-free conditioned media of Hs578T human breast cancer cells, as well as in various human biological fluids, such as normal sera, pregnancy sera, and cerebrospinal, amniotic, follicular and peritoneal fluids. Glycosylation studies with endoglycosidase F reveal that endogenous human IGFBP-rP2 is a secreted, glycosylated, approximately 32-38-kDa protein with 2-8-kDa of N-linked sugars and a 30-kDa core. There are 18- and 24-kDa proteins that appear to be IGFBP-rP2 degradation products. In Hs578T human breast cancer cells, transforming growth factor (TGF)-beta 2, a potent growth inhibitor for these cells, upregulates IGFBP-rP2 mRNA and protein levels. Expression of Hs578T IGFBP-rP2 is significantly increased by TGF-beta 2 treatment in a dose-dependent manner, with 2.5- and 6-fold increases in mRNA and protein levels, respectively, at a TGF-beta 2 concentration of 10 ng/ml. Our studies indicate that IGFBP-rP2 appears to be an important endocrine factor, and one of the critical downstream effectors of the critical downstream effectors of TGF-beta, similar to the role of IGFBP-3 in TGF-beta-induced growth inhibition in human breast cancer cells.

EMS agenda for the future: where we are ... where we want to be. EMS Agenda for the Future Steering Committee

During the past 30 years, emergency medical services (EMS) in the United States have experienced explosive growth. The American health care system is now transforming, providing an opportune time to examine what we have learned over the past three decades in order to create a vision for the future of EMS. Over the course of several months, a multidisciplinary steering committee collaborated with hundreds of EMS-interested individuals, organizations, and agencies to develop the "EMS Agenda for the Future." Fourteen EMS attributes were identified as requiring continued development in order to realize the vision established within the Agenda. They are Integration of Health Services, EMS Research, Legislation and Regulation, System Finance, Human Resources, Medical Direction, Education Systems, Public Education, Prevention, Public Access, Communication Systems, Clinical Care, Information Systems, and Evaluation. Discussion of these attributes provides important guidance for achieving a vision for the future of EMS that emphasizes its critical role in American health care.

Intermolecular NH2-/carboxyl-terminal interactions in androgen receptor dimerization revealed by mutations that cause androgen insensitivity

Structural alignment of the human androgen receptor dimer was investigated by introducing steroid binding domain mutations that cause partial or complete androgen insensitivity into fusion proteins containing the full-length androgen receptor or the steroid binding domain. Most of the mutants had unchanged apparent equilibrium androgen binding affinity and increased dissociation rates of [3H]methyltrienolone and required increased dihydrotestosterone concentrations for transcriptional activation. In a 2-hybrid protein interaction assay in mammalian cells, the steroid binding domain interacts with an NH2-terminal-DNA binding domain fragment and with the full-length androgen receptor at physiological androgen concentrations in a dose-dependent manner. However, mutations at Val-889 and Arg-752 disrupt the NH2-/carboxyl-terminal interaction when introduced into the steroid binding domain fragment but not when present in the full-length androgen receptor. The N-C bimolecular interaction reduces the dissociation rate of bound androgen and slows the degradation rate of the carboxyl-terminal steroid binding domain fragment. The results suggest that steroid binding domain residues Val-889 and Arg-752 are critical to the NH2-/carboxyl-terminal interaction and that an intermolecular N-C interaction occurs during receptor dimerization that results in an antiparallel arrangement of androgen receptor monomers.

EMS Agenda for the Future: where we are...where we want to be

During the past 30 years, emergency medical services (EMS) in the United States have experienced explosive growth. The American health care system is now transforming, providing an opportune time to examine what we have learned over the past three decades in order to create a vision for the future of EMS. Over the course of several months, a multidisciplinary steering committee collaborated with hundreds of EMS-interested individuals, organizations, and agencies to develop the EMS Agenda for the Future. Fourteen EMS attributes were identified as requiring continued development in order to realize the vision established within the Agenda. They are integration of health services, EMS research, legislation and regulation, system finance, human resources, medical direction, education systems, public education, prevention, public access, communication systems, clinical care, information systems, and evaluation. Discussion of these attributes provides important guidance for achieving a vision for the future of EMS that emphasizes its critical role in American health care.

Inhibition of insulin receptor activation by insulin-like growth factor binding proteins

The insulin-like growth factors (IGFs) are transported by a family of high-affinity binding proteins (IGFBPs) that protect IGFs from degradation, limit their binding to IGF receptors, and modulate IGF actions. The six classical IGFBPs have been believed to have no affinity for insulin. We now demonstrate that IGFBP-7/mac25, a newly identified member of the IGFBP superfamily that binds IGFs specifically with low affinity is a high-affinity insulin binding protein. IGFBP-7 blocks insulin binding to the insulin receptor and thereby inhibiting the earliest steps in insulin action, such as autophosphorylation of the insulin receptor beta subunit and phosphorylation of IRS-1, indicating that IGFBP-7 is a functional insulin-binding protein. The affinity of other IGFBPs for insulin can be enhanced by modifications that disrupt disulfide bonds or remove the conserved COOH terminus. Like IGFBP-7, an NH2-terminal fragment of IGFBP-3 (IGFBP-3((1-87))), also binds insulin with high affinity and blocks insulin action. IGFBPs with enhanced affinity for insulin might contribute to the insulin resistance of pregnancy, type II diabetes mellitus, and other pathological conditions.

Transcriptional repression of the alpha-subunit gene by androgen receptor occurs independently of DNA binding but requires the DNA-binding and ligand-binding domains of the receptor

The pituitary glycoprotein hormones LH and FSH regulate the reproductive cycle and are sensitive to feedback by gonadal steroids. The common alpha-subunit shared by these hormones is transcriptionally repressed by androgen receptor (AR) in the presence of its ligand dihydrotestosterone. This identifies at least one mechanism that contributes to AR-dependent suppression of gonadotropin synthesis. Repression of alpha-subunit transcription by AR requires only the sequences within the first 480 bp of the promoter. While this region contains a high-affinity binding site for AR, this element does not mediate the suppressive effects of androgens. Instead, two other elements within the promoter-regulatory region (alpha-basal element and cAMP-regulatory element), which are important for expression of the alpha-subunit gene in gonadotropes, mediate the effects of AR. This suggests that AR inhibits activity of the alpha-subunit promoter by interfering with the transcriptional properties of the proteins that bind to alpha-basal element and the cAMP-regulatory elements. Furthermore, transfection analysis of various mutant ARs identified both the DNA-binding and ligand-binding domains of the receptor as critical for repression. Comparisons with the MMTV promoter revealed distinct structural requirements that underlie the transactivation and transrepression properties of AR.