Single base mutations in the human androgen receptor gene causing complete androgen insensitivity: rapid detection by a modified denaturing gradient gel electrophoresis technique

Complete androgen insensitivity syndrome in a 13-year-old Lebanese child, reared as female, with bilateral inguinal hernia: a case report

Background

Androgen insensitivity syndrome is a rare X-linked disorder of sex development, caused by mutations in the androgen receptor. In this case, a 13-year-old child, reared as female, presenting for primary amenorrhea, was diagnosed with complete androgen insensitivity syndrome.

Case presentation

A 13-year-old Caucasian child, reared as female, presents with primary amenorrhea. Physical examination revealed female appearance and a short vagina with blind-ended pouch. Laboratory examination showed high levels of testosterone and anti-Müllerian hormone; uterus and ovaries were absent. Karyotype confirmed a 46,XY pattern. Deoxyribonucleic acid analysis of the androgen receptor gene revealed a homozygous mutation p.R856C in exon 7. Gender was assigned as female, and she was started on hormonal therapy and underwent gonadectomy.

Conclusion

Androgen insensitivity syndrome comprises a large spectrum of presentations. High index of suspicion is needed. Investigation of girls with bilateral inguinal hernia is critical.

Novel missense mutation in ligand binding domain of AR gene identified in patient with androgen insensitivity syndrome from Ukraine

To improve diagnostic informativity of AR gene mutation analysis in patients with AIS, we recommend to include novel identified missense mutation c.2507T>G in the list of AIS-causing mutations.

Phenotypic and molecular characteristics of androgen insensitivity syndrome patients

Androgen insensitivity syndrome (AIS), an X-linked recessive genetic disorder of sex development, is caused by mutations in the androgen receptor (AR) gene, and is characterized by partial or complete inability of specific tissues to respond to androgens in individuals with the 46, XY karyotype. This study aimed to investigate AR gene mutations and to characterize genotype–phenotype correlations. Ten patients from unrelated families, aged 2–31 years, were recruited in the study. Based on karyotype, altered hormone profile, and clinical manifestations, nine patients were preliminarily diagnosed with complete AIS and one with partial AIS. Genetic analysis of AR gene revealed the existence of 10 different mutations, of which five were novel (c.2112 C>G[p.S704R], c.2290T>A[p.Y764N], c.2626C>T[p.Q876X], c.933dupC[p.K313Qfs*28], and c.1067delC[p.A356Efs*123]); the other five were previously reported (c.1789G>A[p.A597T], c.2566C>T[p.R856C], c.2668G>A[p.V890M], c.2679C>T[p.P893L], and c.1605C>G[p.Y535X]). Regarding the distribution of these mutations, 60.0% were clustered in the ligand-binding domain of AR gene. Exons 1 and 8 of AR gene each accounted for 30.0% (3/10) of all mutations. Most of the truncation mutations were in exon 1 and missense mutations were mainly located in exons 4–8. Our study expands the spectrum of AR gene mutations and confirms the usefulness of AR gene sequencing to support a diagnosis of AIS and to enable prenatal or antenatal screening.

Melanoma antigen-A11 (MAGE-A11) enhances transcriptional activity by linking androgen receptor dimers

Prostate cancer growth and progression depend on androgen receptor (AR) signaling through transcriptional mechanisms that require interactions with coregulatory proteins, one of which is the primate-specific steroid receptor coregulator melanoma antigen-A11 (MAGE-A11). In this report, we provide evidence how increased expression of MAGE-A11 during prostate cancer progression enhances AR signaling and prostate cancer growth. MAGE-A11 protein levels were highest in castration-recurrent prostate cancer. The cyclic AMP-induced increase in androgen-dependent and androgen-independent AR transcriptional activity correlated with an increase in MAGE-A11 and was inhibited by silencing MAGE-A11 expression. MAGE-A11 mediated synergistic AR transcriptional activity in LAPC-4 prostate cancer cells. The ability of MAGE-A11 to rescue transcriptional activity of complementary inactive AR mutants and promote coimmunoprecipitation between unlike forms of AR suggests that MAGE-A11 links transcriptionally active AR dimers. A model for the AR·MAGE-A11 multidimeric complex is proposed in which one AR FXXLF motif of the AR dimer engages in the androgen-dependent AR NH(2)- and carboxyl-terminal interaction, whereas the second FXXLF motif region of the AR dimer interacts with dimeric MAGE-A11. The AR·MAGE-A11 multidimeric complex accounts for the dual functions of the AR FXXLF motif in the androgen-dependent AR NH(2)- and carboxyl-terminal interaction and binding MAGE-A11 and for synergy between reported AR splice variants and full-length AR. We conclude that the increased expression of MAGE-A11 in castration-recurrent prostate cancer, which is enhanced by cyclic AMP signaling, increases AR-dependent growth of prostate cancer by MAGE-A11 forming a molecular bridge between transcriptionally active AR dimers.

Characterization of androgen receptor structure and nucleocytoplasmic shuttling of the rice field eel

Androgen receptor (AR) plays a critical role in prostate cancer and male sexual differentiation. We have identified AR from a primitive vertebrate with a sex reversal characteristic, the rice field eel. AR of this species (eAR) is distinct from human AR, especially in the ligand binding domain (LBD), and its expression in gonads shows an increasing tendency during gonadal transformation from ovary via ovotestis to testis. eAR has a restricted androgen-dependent transactivation function after a nuclear translocation upon dihydrotestosterone exposure. A functional nuclear localization signal was further identified in the DNA binding domain and hinge region. Although nuclear export is CRM1-independent, eAR has a novel nuclear export signal, which is negatively charged, indicating that a nuclear export pathway may be mediated by electrostatic interaction. Further, our studies have identified critical sequences for ligand binding in the C terminus. A structure of three α-helices in the LBD has been conserved from eels to humans during vertebrate evolution, despite a distinct amino acid sequence. Mutation analysis confirmed that the LBD is essential for dihydrotestosterone-induced nuclear import of eAR and following transactivation function in the nucleus. In addition, eAR interacts with both Sox9a1 and Sox9a2, and their interaction regulates transactivation of eAR. Our data suggest that the primitive species conserves and especially acquires key novel domains, the nuclear export signal and LBD, for the eAR function in spite of a rapid sequence evolution.

Comparison of crystal structures of human androgen receptor ligand-binding domain complexed with various agonists reveals molecular determinants responsible for binding affinity

Androgens exert their effects by binding to the highly specific androgen receptor (AR). In addition to natural potent androgens, AR binds a variety of synthetic agonist or antagonist molecules with different affinities. To identify molecular determinants responsible for this selectivity, we have determined the crystal structure of the human androgen receptor ligand-binding domain (hARLBD) in complex with two natural androgens, testosterone (Testo) and dihydrotestosterone (DHT), and with an androgenic steroid used in sport doping, tetrahydrogestrinone (THG), at 1.64, 1.90, and 1.75 A resolution, respectively. Comparison of these structures first highlights the flexibility of several residues buried in the ligand-binding pocket that can accommodate a variety of ligand structures. As expected, the ligand structure itself (dimension, presence, and position of unsaturated bonds that influence the geometry of the steroidal nucleus or the electronic properties of the neighboring atoms, etc.) determines the number of interactions it can make with the hARLBD. Indeed, THG--which possesses the highest affinity--establishes more van der Waals contacts with the receptor than the other steroids, whereas the geometry of the atoms forming electrostatic interactions at both extremities of the steroid nucleus seems mainly responsible for the higher affinity measured experimentally for DHT over Testo. Moreover, estimation of the ligand-receptor interaction energy through modeling confirms that even minor modifications in ligand structure have a great impact on the strength of these interactions. Our crystallographic data combined with those obtained by modeling will be helpful in the design of novel molecules with stronger affinity for the AR.

A novel missense mutation in the amino-terminal domain of the human androgen receptor gene in a family with partial androgen insensitivity syndrome causes reduced efficiency of protein translation

The role of the androgen receptor (AR) in male sexual differentiation is revealed in part by the analysis of naturally occurring mutations in families with androgen insensitivity syndrome (AIS). We have investigated a family with partial AIS affecting three generations and have identified a G to A substitution in the AR gene at the fourth position 3' from the A of the ATG initiation codon changing the second amino acid residue from glutamic acid to lysine (EK2). Transient expression of the mutant EK2-pCMVhAR expression vector in COS cells revealed decreased translation with a 20-50% reduction in mutant protein relative to wild type AR by immunoblot analysis. The rate of dissociation of [3H]methyltrienolone from the EK2 mutant (half-time [t1/2] = 1.7 +/- 0.08 SE h) was increased compared with wild type AR (t1/2 = 2.4 +/- 0.11 h). Cotransfection studies using an androgen responsive luciferase reporter vector demonstrated a 50% reduction in transcriptional activation by EK2. These functional alterations are consistent with the partial AIS phenotype in affected males, corroborate the AR amino-terminal domain effect on kinetics of androgen binding, and provide physiological evidence for earlier translation experiments identifying the nucleotide sequence for optimal translation initiation.

Genes involved in testicular development and function

The development of the testis requires the highly regulated expression of a series of genes. Many of the genes involved are transcription factors, such as steroid hormone receptors and growth factors. Investigators have used gene cloning, mutation analysis, transgenic mice, and gene-deletion studies to define the role of specific genes in testicular development and function. In the past 5 years, investigators have defined a gene on the Y chromosome, SRY, thought to be required for testis determination. This protein is a member of a larger family of related transcription factors. Expression of this gene triggers a cascade of events that leads to the development of the Sertoli cell, Leydig cells, and the testis. The development of the male phenotype is dependent on the presence and action of androgens, which exert their effect after combining with a receptor in the nucleus of the target cell that stimulates gene transcription. Defects in the androgen receptor gene lead to a full spectrum of morphological defects in the male. Interestingly, mutations in other members of the steroid receptor superfamily, such as the estrogen receptor gene, also affect male fertility. A number of "orphan" receptors (i.e., receptors whose ligans have not been identified) are also required for normal testicular development and function, as are several genes normally thought to be tumor-suppressor genes (e.g., Wilms' tumor-suppressor gene). In contrast, alpha-inhibin has been thought to be an endocrine hormone, yet it functions as a tumor-suppressor gene in the testis. Testicular development and normal spermatogenesis require the proper function and coordination of a large number of transcription factors, steroid hormone and orphan receptors, and growth factors. There are likely to be a large number of other, as yet unidentified genes that are necessary for male gonadal development.

Substitution of arginine-839 by cysteine or histidine in the androgen receptor causes different receptor phenotypes in cultured cells and coordinate degrees of clinical androgen resistance

We aim to correlate point mutations in the androgen receptor gene with receptor phenotypes and with clinical phenotypes of androgen resistance. In two families, the external genitalia were predominantly female at birth, and sex-of-rearing has been female. Their androgen receptor mutation changed arginine-839 to histidine. In a third family, the external genitalia were predominantly male at birth, and sex-of-rearing has been male: their codon 839 has mutated to cysteine. In genital skin fibroblasts, both mutant receptors have a normal androgen-binding capacity, but they differ in selected indices of decreased affinity for 5 alpha-dihydrotestosterone or two synthetic androgens. In transiently cotransfected androgen-treated COS-1 cells, both mutant receptors transactivate a reporter gene subnormally. The His-839 mutant is less active than its partner, primarily because its androgen-binding activity is more unstable during prolonged exposure to androgen. Adoption of a nonbinding state explains a part of this instability. In four other steroid receptors, another dibasic amino acid, lysine, occupies the position of arginine-839 in the androgen receptor. Androgen receptors with histidine or cysteine at position 839 are distinctively dysfunctional and appear to cause different clinical degrees of androgen resistance.

Identical mutations in unrelated families with generalized resistance to thyroid hormone occur in cytosine-guanine-rich areas of the thyroid hormone receptor beta gene. Analysis of 15 families

Generalized resistance to thyroid hormone (GRTH) is a syndrome of variable reduction of tissue responsiveness to thyroid hormone. 28 different point mutations in the human thyroid hormone receptor beta (TR beta) gene have been associated with GRTH. These mutations are clustered in two regions of the T3 binding domain of the TR beta (codons 310-347 and 417-453). We now report point mutations in the TR beta gene of six additional families with GRTH and show that three mutations occurred each in three families with GRTH, and that three other mutations were each present in two families. In 11 of these 15 families, lack of a common ancestor could be confirmed by genetic analysis. 28 of the 38 point mutations so far identified, including all those occurring in more than one family, are located in cytosine-guanine-rich areas of the TR beta gene. Differences in clinical and laboratory findings in unrelated families harboring the same TR beta mutation suggest that genetic variability of other factors modulate the expression of thyroid hormone action.