Rose Lumbroso

The Androgen Receptor Gene Mutations Database

The current version of the androgen receptor (AR) gene mutations database is described. The total number of reported mutations has risen from 212 to 272. We have expanded the database: (i) by adding a large amount of new data on somatic mutations in prostatic cancer tissue; (ii) by defining a new constitutional phenotype, mild androgen insensitivity (MAI); (iii) by placing additional relevant information on an internet site (http://www.mcgill.ca/androgendb/ ). The database has allowed us to examine the contribution of CpG sites to the multiplicity of reports of the same mutation in different families. The database is also available from EMBL (ftp.ebi.ac.uk/pub/databases/androgen) or as a Macintosh Filemaker Pro or Word file (MC33@musica,mcgill.ca)

Oligospermic infertility associated with an androgen receptor mutation that disrupts interdomain and coactivator (TIF2) interactions

Structural changes in the androgen receptor (AR) are one of the causes of defective spermatogenesis. We screened the AR gene of 173 infertile men with impaired spermatogenesis and identified 3 of them, unrelated, who each had a single adenine-->guanine transition that changed codon 886 in exon 8 from methionine to valine. This mutation was significantly associated with the severely oligospermic phenotype and was not detected in 400 control AR alleles. Despite the location of this substitution in the ligand-binding domain (LBD) of the AR, neither the genital skin fibroblasts of the subjects nor transfected cell types expressing the mutant receptor had any androgen-binding abnormality. However, the mutant receptor had a consistently (approximately 50%) reduced capacity to transactivate each of 2 different androgen-inducible reporter genes in 3 different cell lines. Deficient transactivation correlated with reduced binding of mutant AR complexes to androgen response elements. Coexpression of AR domain fragments in mammalian and yeast two-hybrid studies suggests that the mutation disrupts interactions of the LBD with another LBD, with the NH2-terminal transactivation domain, and with the transcriptional intermediary factor TIF2. These data suggest that a functional element centered around M886 has a role, not for ligand binding, but for interdomain and coactivator interactions culminating in the formation of a normal transcription complex.

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.

The polymorphic CAG repeat of the androgen receptor gene: a potential role in breast cancer in women over 40

Previous investigations into the relationship of CAG-repeat lengths in the androgen receptor (AR) gene to female breast cancer (BC) have yielded somewhat confusing results. Decreased AR transactivational activity lowers androgen:estrogen balance, and may thereby effect functional hyperestrogenicity. This may promote the pathogenesis of BC. To elucidate whether longer CAG repeats of the AR gene (AR), which correlate with lower transactivational activity of the AR, are associated with BC in women over 40, we examined the distribution of CAG-repeat lengths in BC tissue from this population. The BC tissue was histologically graded as: Grade 1, well differentiated (WD); Grade 2, moderately differentiated (MD); and Grade 3, poorly-differentiated (PD). Analysis showed significant differences as compared to controls when CAG lengths greater than 21 were examined, and that alleles with ≥26 repeats were 2.4-fold more frequent in BC samples than in constitutional samples from a normal population. A significant shift to greater CAG-repeat lengths, appeared in WD and MD tumors only. Our results give some indication as to the progression of BC by suggesting that hypotransactive ARs with long polyglutamine (polyGln) tracts may have a role in the initiation and/or progression of BC. PD tumors tended to have shorter than normal CAG-repeat lengths. In this case it is hypothesized that the ARs have now become hypertransactive, possibly coinciding with the estrogen resistance that is associated with PD tumors. Whether this shift is of germline or somatic origin was not clear, though the appearance in 14% of the BC samples of a third CAG-repeat length indicates that it may be somatic.

Codon-usage variants in the polymorphic (GGN)n trinucleotide repeat of the human androgen receptor gene.

Abstract The human androgen receptor gene (hAR) has a long, polymorphic trinucleotide (GGN; glycine)n repeat in the 3′ portion of its first exon, with n = 10–31. Owing to technical difficulties that have precluded routine sequencing of this region, it is widely unknown that N represents T, G or C, and that the usual sense codon sequence of the GGN tract is (GGT)3GGG(GGT)2(GGC)4–25. Furthermore, on 4 of 61 X chromosomes, we observed that the internal GGT sequence was present three or four times instead of twice. Strikingly, each of the three alleles with an internal (GGT)3, and only these three, also had a (GGC)20 repeat. The size or composition of a (GGN)n repeat was not correlated with the length of the accompanying (CAG)nCAA repeat in the 5′ portion of exon one. Hence, codon-usage variants of the GGN tract may be used to seek associations with particular diseases, as diagnostic aids in families with androgen insensitivity whose AR mutations have not yet been identified, or as internal controls for observations on intergenerational contractions or expansions of the (CAG)nCAA tract in a given hAR allele.

An investigation into CAG repeat length variation and N/C terminal interactions in the T877A mutant androgen receptor found in prostate cancer

Prostate cancer may progress by circumventing ablation therapy due to mutations in the androgen receptor (AR) gene. The most intensively studied is the T877A mutation in the ligand binding domain (LBD), which causes the AR to become promiscuous, i.e., respond to a number of different ligands. Our investigations have shown that the T877A mutation alters the inverse relationship between CAG repeat length and transactivation in a noticeable albeit minor manner, while increasing N/C terminal interactions. In the presence of beta-catenin, a coactivator over-expressed in prostate cancer, the inverse relationship between CAG repeat length and transactivation is reversed for the wild type (wt) AR as well. We have also used molecular modeling with the AR and FXXLF and LXXLL peptides to investigate N/C terminal and coactivator interactions. In T877A, this approach revealed an increase in the flexibility of amino acid residues in the activation function 2 (AF-2) domain in the LBD, and a larger solvent accessible surface in T877A compared to the wt AR AF-2 domain. Thus, the improved induced fit of the AR N-terminal domain FXXLF-containing peptide into the T877A LBD could be due to the increased flexibility and solvent accessibility of the AF-2 domain. These new observations suggest that the AR CAG effect can be overridden by prostate cancer mutations, and also further our understanding of hormone-refractory prostate cancer by helping to explain the promiscuity of the T877A mutation.