mibolerone and Androgen-Insensitivity-Syndrome

Five mutations in the ligand-binding domain (LBD) of the human androgen receptor (hAR) found in patients with varying degrees of androgen insensitivity syndrome (AIS) were investigated for their effects on receptor dynamics. These were Arg(871)Gly (mild), Ser(814)Asn (partial), Glu(772)Ala (partial), Val(866)Met (complete), and Arg(774)Cys (complete). Previous analysis showed that the mutant receptors exhibited near-normal kinetics, except Arg(774)Cys, which had severely reduced androgen binding, and Val(866)Met, which showed increased equilibrium dissociation constant (K(d)) and elevated dissociation rate (k) values. Ser(814)Asn exhibited ligand-selective k values, i.e. increased for dihydrotestosterone and mibolerone, but normal for methyltrenolene. Using mammalian two-hybrid assays, hAR amino/carboxyl (N/C)-terminal interactions of the mutant receptors were analyzed in the presence and absence of the hAR coactivator transcription intermediary factor 2 (TIF2). The mutations conferred decreased hAR N/C-terminal interaction, i.e. mild (approximately 1.5-fold), partial (2-fold), and complete (10-fold), that mirrored the degree of AIS. All mutant LBDs showed a 2- to 3-fold increase in N/C-terminal interactions when TIF2 was cotransfected, although of a magnitude still less than that of wild-type LBD with TIF2. The ligand-selective properties of the Ser(814)Asn mutant were also clearly reflected by the N/C-terminal interactions. Thus, measurement of N/C-terminal interactions may assist in the molecular analysis of mutant hARs associated with AIS.

Topics: Adolescent; Adult; Androgen-Insensitivity Syndrome; Androgens; Animals; Binding Sites; Cell Line; Cells, Cultured; Child; Child, Preschool; COS Cells; Dihydrotestosterone; Female; Gene Expression; Humans; Kinetics; Male; Models, Molecular; Mutation; Nandrolone; Nuclear Receptor Coactivator 2; Peptide Fragments; Point Mutation; Protein Structure, Secondary; Receptors, Androgen; Structure-Activity Relationship; Transcription Factors; Transcriptional Activation; Transfection

Androgen insensitivity syndrome (AIS) is an X-linked recessive disorder. The molecular mechanism of AIS is reduction or absence of androgen signalling caused by androgen receptor (AR) malfunction or absence. The phenotype of AIS varies from a complete female phenotype (complete AIS, CAIS) to male genitalia with mild hypospadias (partial AIS, PAIS). In the current study, we characterize a novel point mutation in the ligand binding domain of the AR gene in a 50-year-old Japanese CAIS patient. Sequence analysis showed a single point mutation at nucleotide 3359 (Genbank, NM 000044), T to C, in exon E in the AR gene. This mutation led to the conversion of codon 739 tyrosine into aspartic acid in the ligand binding domain. No specific androgen binding was detected in genital fibroblasts isolated from the patient. Transcriptional activating activity of the mutant AR was examined by transient DNA transfection into COS-1 cells. Wild-type AR successfully activated androgen inducible MMTV promoter dose-dependently. In contrast, the mutant AR did not activate MMTV promoter. Thus, we demonstrated the molecular characteristics of the novel point mutation in the ligand binding domain of the AR gene associated with CAIS. This information will provide a further understanding of the structure and function of the AR gene.

Topics: Amino Acid Substitution; Androgen-Insensitivity Syndrome; Animals; Binding Sites; COS Cells; Female; Humans; Male; Middle Aged; Nandrolone; Point Mutation; Protein Structure, Tertiary; Receptors, Androgen; Reverse Transcriptase Polymerase Chain Reaction; RNA; Sequence Analysis, DNA; Testosterone; Transfection

We have characterized two different mutations of the human androgen receptor (hAR) found in two unrelated subjects with androgen insensitivity syndrome (AIS): in one, the external genitalia were ambiguous (partial, PAIS); in the other, they were male, but small (mild, MAIS). Single base substitutions have been found in both individuals: E772A in the PAIS subject, and R871G in the MAIS patient. In COS-1 cells transfected with the E772A and R871G hARs, the apparent equilibrium dissociation constants (Kd) for mibolerone (MB) and methyltrienolone are normal. Nonetheless, the mutant hAR from the PAIS subject (E772A) has elevated nonequilibrium dissociation rate constants (k(diss)) for both androgens. In contrast, the MAIS subject's hAR (R871G) has k(diss) values that are apparently normal for MB and methyltrienolone; in addition, the R871G hAR's ability to bind MB resists thermal stress better than the hAR from the PAIS subject. The E772A and R871G hARs, therefore, confer the same pattern of discordant androgen-binding parameters in transfected COS-1 cells as observed previously in the subjects' genital skin fibroblasts. This proves their pathogenicity and correlates with the relative severity of the clinical phenotype. In COS-1 cells transfected with an androgen-responsive reporter gene, trans-activation was 50% of normal in cells containing either mutant hAR. However, mutant hAR-MB binding is unstable during prolonged incubation with MB, whereas normal hAR-MB binding increases. Thus, normal equilibrium dissociation constants alone, as determined by Scatchard analysis, may not be indicative of normal hAR function. An increased k(diss) despite a normal Kd for a given androgen suggests that it not only has increased egress from a mutant ligand-binding pocket, but also increased access to it. This hypothesis has certain implications in terms of the three-dimensional model of the ligand-binding domain of the nuclear receptor superfamily.

Topics: Amino Acid Sequence; Androgen-Insensitivity Syndrome; Androgens; Animals; COS Cells; Drug Stability; Female; Hot Temperature; Humans; Male; Metribolone; Molecular Sequence Data; Mutagenesis, Site-Directed; Nandrolone; Point Mutation; Receptors, Androgen; Testosterone Congeners; Transcriptional Activation; Transfection

We have investigated the basis of androgen resistance in seven unrelated individuals with complete testicular feminization or Reifenstein syndrome caused by single amino acid substitutions in the hormone-binding domain of the androgen receptor. Monolayer-binding assays of cultured genital skin fibroblasts demonstrated absent ligand binding, qualitative abnormalities of androgen binding, or a decreased amount of qualitatively normal receptor. The consequences of these mutations were examined by introducing the mutations by site-directed mutagenesis into the androgen receptor cDNA sequence and expressing the mutant cDNAs in mammalian cells. The effects of the amino acid substitutions on the binding of different androgens and on the capacity of the ligand-bound receptors to activate a reporter gene were investigated. Substantial differences were found in the responses of the mutant androgen receptors to incubation with testosterone, 5 alpha-dihydrotestosterone, and mibolerone. In several instances, increased doses of hormone or increased frequency of hormone addition to the incubation medium resulted in normal or near normal activation of a reporter gene by cells expressing the mutant androgen receptors. These studies suggest that the stability of the hormone receptor complex is a major determinant of receptor function in vivo.

Topics: Androgen-Insensitivity Syndrome; Animals; Binding, Competitive; Cells, Cultured; CHO Cells; Cricetinae; Dihydrotestosterone; Fibroblasts; Gene Expression; Genitalia; Humans; Male; Mutation; Nandrolone; Receptors, Androgen; Recombinant Fusion Proteins; Testosterone; Testosterone Congeners; Transcription, Genetic

We have identified two different single nucleotide missense substitutions at valine-865 in exon 7 of the human androgen receptor (AR) gene in two families with androgen resistance. Val-->methionine is associated with the complete syndrome; Val-->leucine is associated with the partial form. In genital skin fibroblasts, both alterations yield a normal maximum binding capacity, but an increased apparent equilibrium dissociation constant for all androgens tested. In genital skin fibroblasts, Val865-Met A-R complexes have increased rate constants of dissociation with 5 alpha-dihydrotestosterone, and the nonmetabolized ligands methyltrienolone or mibolerone (MB); their Val865-Leu counterparts have increased rates with methyltrienolone and MB, but not with 5 alpha-dihydrotestosterone. In transiently transfected COS-1 or PC-3 cells, Met865 AR is more severely impaired than Leu865 AR in transactivating two different androgen-responsive reporter constructs, thereby correlating with clinical phenotype. In COS-1 cells exposed to MB for 74 h, this relative impairment correlates with the relative instability of the MB-binding activity of each mutant AR, suggesting that their respective intrinsic transcriptional regulatory competence is normal. Notably, these mutant ARs lose significantly more MB-binding activity than immunoreactivity, suggesting that prolonged MB exposure induces them to adopt a nonbinding state. The position homologous to Val865 in the AR is occupied by Leu or Met in the three steroid receptors closely related to the AR. This indicates the structural subtlety that underlies the steroid-binding activity of different steroid receptors.

Topics: Amino Acid Sequence; Androgen-Insensitivity Syndrome; Animals; Base Sequence; Cells, Cultured; Chlorocebus aethiops; Dihydrotestosterone; Exons; Fibroblasts; Genes; Genitalia, Male; Humans; Male; Molecular Sequence Data; Mutation; Nandrolone; Phenotype; Polymerase Chain Reaction; Receptors, Androgen; Receptors, Steroid; Recombinant Proteins; Sequence Homology, Amino Acid; Skin