No abstract

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 > or = 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.

The death of cells by apoptosis is a fundamental event in development and the maintenance of cell homoeostasis. The other side of the coin, however, is that excessive cell death by apoptosis or the lack of apoptosis is often the driving force of many diseases. Whereas reduced apoptosis sensitivity is a basic characteristic of many tumour cells, accelerated tissue cell death and loss of tissue functions is the underlying cause of many auto-immune and inflammatory diseases.

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.

The length of the CAG repeat polymorphism of the androgen receptor gene may be important for prostate cancer recurrence among patients who are otherwise at low risk for recurrence after radical prostatectomy. These findings have potential implications for patient selection for adjuvant treatment, and for the development of novel treatments.

The hereditary breast and ovarian cancer syndrome is associated with a high frequency of BRCA1 mutations. However, the widespread use of BRCA1 testing has been limited to date by three principal concerns: the fear of loss of health and life insurance, the uncertain clinical value of a positive test result, and the current lack of an inexpensive and sensitive screening test for BRCA1 mutations. We have developed an inexpensive system for gene mutational scanning, based on a combination of extensive multiplex PCR amplification and two dimensional electrophoresis. The eYciency of this system, as a screening test for BRCA1 mutations, was evaluated in a panel of 60 samples from high risk women, 14 of which contained a previously identified mutation in BRCA1. All 14 mutations were identified, as well as an additional five that had previously escaped detection. In addition to the 19 mutations, a total of 15 diVerent polymorphic variants were scored, most of which were recurring. All were confirmed by nucleotide sequencing. The cost of screening per sample was calculated to be approximately US$70 for the manual technique used in this study, and may be reduced to approximately US$10 with the introduction of commercially available PCR robotics and fluorescent imaging. Implementation of this method of mutation screening in the research and clinical setting should permit rapid accrual of quantitative data on genotype-phenotype associations for the evaluation of diagnostic testing. (J Med Genet 1999;36:747-753)

Structural studies of the ligand-binding domain (LBD) of several steroid receptors have revealed that the dynamic properties of the C-terminal helix 12 (H12) are the major determinant of the activation mode of these receptors. H12 exhibits high mobility and different conformations in the absence of ligand. Upon ligand binding, H12 is stabilized in a precise position to seal the ligand-binding pocket and finalize the assembly of the activation function (AF-2) domain. In this study, we investigated the role of the conserved proline 892 of the androgen receptor (AR) in directing the dynamic location and orientation of the AR-H12. We used a combined approach including kinetic and biochemical assays with molecular dynamic simulations to analyze two substitutions (P892A and P892L) identified in individuals with complete androgen insensitivity syndrome. Our analyses revealed distinct mechanisms by which these substitutions impair H12 function resulting in severely defective receptors. The AR-P892A receptor exhibited reduced ligand binding and transactivational potential because of an increased flexibility in H12. The AR-P892L substitution renders the receptor inactive due to a distorted, unstructured and misplaced H12. To confirm the mutants' inability to stabilize H12 in an active position, we have developed a novel in vivo assay to evaluate the accessibility of the H12-docking site on the AR-LBD surface. An extrinsic AR-H12 peptide was able to interact with wild-type and mutant LBDs in the absence of ligand. Ligand-induced proper positioning of the intrinsic H12 of wild-type AR prevented these interactions, whereas the misplacement of the mutants' H12 did not. Proline at this position may be critical for H12 dynamics not only in the AR, but also in other nuclear receptors where this proline is conserved.

Background: Punctate palmoplantar keratoderma type 1 (PPPK1) presents in late childhood to adulthood with multiple small discrete hyperkeratotic papules on palms and soles. PPPK1 is an autosomal dominant skin disease caused by AAGAB mutations. It has been suggested that PPPK1 may be associated with an increased predisposition to systemic malignancies. Objectives: To evaluate the presence of AAGAB mutations in Canadian families with PPPK1 and the possible increased predisposition to systemic malignancies. Methods: Eighteen unrelated Canadian families with PPPK1 were recruited for this study. Genomic DNA was extracted from saliva and PCR amplification was performed for all AAGAB exons and exon/intron junctions. PCR products were sequenced and analyzed for mutations. A family history of malignancy was obtained from the index case and, when possible, from other family members. Results: We have identified 5 heterozygous AAGAB loss of function mutations in 11 families. The mutation c.370 C>T, p.Arg124* was the most prevalent and was identified in 6 families. A splice site mutation, c.451+3delAAGT, was identified in 2 families. The other mutations c.473delG, p.Gly158Glufs*0; c.550-551insAAT, p.Gly183*; and c.505-506 dupAA, p.Asn169Lysfs*6 were each identified in 1 family. Different cancers were reported in 11 families (Table 1 and Supplemental Figure S1). Conclusions: AAGAB mutations were found in 11 of 18 families with PPPK1. In some families there appears to be an association with cancer.