Molecular pathologic analysis enhances the diagnosis and management of Muir-Torre syndrome and gives insight into its underlying molecular pathogenesis.

The Muir-Torre syndrome (MTS) is an autosomal dominantly inherited disorder, characterized by visceral malignancies and sebaceous skin lesions. In a subset of MTS families the disease is due to an underlying DNA mismatch-repair defect. We have identified a MTS family whose spectrum of reported neoplasia included adenocarcinomas of numerous gastrointestinal sites, carcinomas of the endometrium, ovary and breast, papillary transitional cell carcinoma of the ureter, a range of cutaneous tumors, as well as keratoacanthomas. All tumors were tested for microsatellite instability and immunohistochemically stained for expression of MLH1 and MSH2 proteins. All tumors were found to be microsatellite unstable and lacking in MSH2 protein expression. The subsequent mutation detection focused on hMSH2, and a germline mutation was identified (CAA-->TAA, Gln-->STOP, codon 337). This mutation was subsequently found in a family member with a single skin lesion only. We propose that the combination of immunohistologic and microsatellite instability analysis can be exploited to screen individuals with characteristic skin lesions even before development of visceral tumors and to direct the subsequent germline mutation search. The profile of microsatellite instability and the genes rendered dysfunctional differed between tumor samples, suggesting that the molecular pathogenesis varied between lesions, despite a common germline mutation.

Androgen receptor exon 1 CAG repeat length and breast cancer in women before age forty years.

BACKGROUND: We conducted a population-based, case-control-family study to determine whether androgen receptor (AR) exon 1 polymorphic CAG repeat length (CAGn) was a risk factor for early-onset breast cancer in the Australian population. METHODS: Case subjects under 40 years of age at diagnosis of a first primary breast cancer and age-matched control subjects were interviewed to assess family history and other risk factors. AR CAGn length was determined for 368 case subjects and 284 control subjects. Distributions in the two groups were compared by linear and logistic regression, allowing adjustment for measured risk factors. All statistical tests were two-tailed. RESULTS: When analyzed as either a continuous or a dichotomous variable, there was no association between CAG, length and breast cancer risk, before or after adjustment for risk factors. Mean (95% confidence interval [CI]) CAGn lengths were 22.0 (21.8-22.2) for case subjects and 22.0 (21.7-22.3) for control subjects (P = .9). The frequency (95% CI) of alleles with 22 or more CAGn repeats was 0.531 (0.494-0.568) for case subjects and 0.507 (0.465-0.549) for control subjects (P = .4). After adjustment, the average effect on log OR (odds ratio) per allele was 0.16 (95% CI = -0.03 to 0.40; P = .2), and the effect of any allele was equivalent to an OR of 1.40 (95% CI = 0.94-2.09; P = .1). Stratification by family history also failed to reveal any association. Similar results were obtained when alleles were defined by other cutoff points. CONCLUSION: We found no evidence for an association between AR exon 1 CAGn length and breast cancer risk in women under the age of 40, despite having 80% power to detect modest effects.

Distinct molecular pathogeneses of early-onset breast cancers in BRCA1 and BRCA2 mutation carriers: a population-based study.

Breast cancers arising in women with and without a germline mutation in the BRCA1 or BRCA2 gene display different histological features, which suggests unique mechanisms of molecular pathogenesis: We used a molecular pathological analysis to define the genetic abnormalities relevant to these specific pathogeneses. Tumor material was studied from 40 women with breast cancer diagnosed before 40 years of age, sampled from a population-based study and stratified by BRCA1 and BRCA2 germline mutation status. Cases were not selected for family history or ethnic origin, and none were known to be genetically related. Thus, germline mutation itself is likely to impact on the molecular pathogenesis of these tumors, with no substantial influence due to modifying genetic or environmental factors. Breast cancers occurring in BRCA1 mutation carriers had significantly higher levels of p53 expression, including the preinvasive (carcinoma in situ) stage of disease, compared with cancers occurring in BRCA2 mutation carriers or women with no detectable germline mutation. These cancers also had a higher proliferation rate as measured by Ki-67 antibody. Expression of the prognostic factors c-erbB-2, cyclin D1, and estrogen receptor was significantly less common in BRCA1 mutation carriers. Lower levels of cyclin D1 were also found in cancers from BRCA2 mutation carriers compared with non-mutation carriers. Direct p53 mutation analysis revealed mutations in 18% of all of the early-onset breast cancers within the study and included rare insertion and deletional mutations in cancers from BRCA1 mutation carriers. Our data indicate that a BRCA1 breast cancer phenotype may be recognized by an exceptionally high proliferation rate and early and frequent p53 overexpression but infrequent selection for overexpression of several other prognostic factor proteins known to be involved in breast oncogenesis. In contrast, breast cancers arising in BRCA2 mutation carriers have a more heterogeneous phenotypic profile.

Cyclin D1 and D3 associate with the SCF complex and are coordinately elevated in breast cancer.

D-type cyclins are important cell cycle regulators that promote cellular proliferation in response to growth factors by inactivation of the retinoblastoma protein (Rb). Cyclin D1 has been shown to be overexpressed in several cancer types and to act as an oncogene in breast cancers. As D-type cyclins are rate limiting for progression into S phase, the level at which they accumulate must be carefully regulated. Several mechanisms leading to overexpression of cyclin D1 have been reported including amplification, translocation and stabilization of the mRNA. Here, we present data showing elevated cyclin D1 protein in breast cancer samples in the absence of elevated mRNA level. Further, we found that in these cases, cyclin D3 protein also accumulates and that the coordinate increase in cyclin D1 and D3 occurs in 15% (7/47) of breast cancers. In addition we show that blocking the activity of the 26S proteosome results in the accumulation of cyclin D1 and D3, that both D-type cyclins are ubiquitinated and associate with Cul-1, a component of the SCF ubiquitin ligase complex. Finally, we show that the coordinated elevation of cyclin D1 and D3 is also observed in the breast cell line MCF-7 and demonstrate that the degradation of cyclin D1 and D3 is deficient in this cell line. These results indicate that cyclin D1 and cyclin D3 share a common mechanism of degradation and we propose that the coordinate increase of D-type cyclins observed in primary breast cancers reflects a defect in their proteolysis.

Expression of the human P2Y6 nucleotide receptor in normal placenta and gestational trophoblastic disease.

The P2Y family of purinergic receptors are members of the G-protein-coupled receptor superfamily. The P2Y6 subtype is expressed at particularly high levels in the placenta, suggesting that P2Y6 plays an important role in placental function. However, the cellular localization of P2Y6 within the placenta is unknown. This study examined the expression of P2Y6 in first-trimester and full-term placental tissues, as well as examples of gestational trophoblastic disease, by Northern blot analysis and in situ hybridization. P2Y6 message was present at similar levels in first-trimester and full-term placenta, and in situ hybridization revealed that message was most abundant in the cytotrophoblast of the villi and chorionic plate at both gestational stages. The syncytiotrophoblast harbored lower levels of P2Y6 in first-trimester placenta, and by full-term, the syncytiotrophoblast only focally expressed P2Y6 transcripts. Neither the intermediate trophoblast nor nontrophoblastic elements of the placenta expressed P2Y6. Molar disease expressed P2Y6 in the villous trophoblast but not in the proliferative intermediate trophoblast, recapitulating the pattern of first-trimester placenta. Neither choriocarcinoma nor the choriocarcinoma cell lines JEG-3 and JAr expressed P2Y6 transcript. These findings reveal that P2Y6 mRNA production is highly characteristic of the epithelial-like cytotrophoblast and syncytiotrophoblast, whereas expression is absent in the mesenchymal-like intermediate trophoblast. Thus, P2Y6 may play an important role in trophoblastic development, differentiation, and neoplasia.

Expression of the P2Y6 purinergic receptor in human T cells infiltrating inflammatory bowel disease.

The human P2Y6 receptor is a member of the G-protein-coupled P2Y purinergic receptor family that responds to extracellular uridine diphosphate (UDP). In previous work, we cloned the human P2Y6 receptor from an activated T-cell library, and others have shown that it is expressed as a 1.9-kb transcript in several lymphoid tissues. This suggests a role for P2Y6 in T-cell function. However, the precise cellular expression pattern and regulation of P2Y6 in immune cells have not yet been established. In this study, we have examined the expression of P2Y6 in a range of tissues containing leukocytes by a combination of in situ hybridization (ISH), Northern blot analysis, and RT-PCR. Northern hybridization revealed that activated peripheral T cells show increased levels of P2Y6 mRNA. Furthermore, RT-PCR analysis of CD4+ and CD8+ subsets illustrated strong expression in both activated CD4+ and CD8+ T cells. Stimulation of resting and activated T cells with the P2Y6 ligand UDP caused a rise in the intracellular free calcium concentration in only the activated subset, indicating the presence of functional receptor. By ISH, P2Y6 expression was detected in the T cells of the thymic medulla and spleen, whereas no signal was detected in the bone marrow, fetal liver, or lymph nodes. T cells are thought to play an important role in the pathogenesis of inflammatory bowel disease (IBD), and because a recent finding has suggested a role for extracellular nucleotides in mediating colonic epithelial cell damage in IBD, we speculated that the P2Y6 nucleotide receptor may be expressed in the T cells infiltrating IBD. ISH results reveal that P2Y6 is highly expressed in the T cells infiltrating active IBD, whereas P2Y6 expression was absent from the T cells of unaffected bowel. These results demonstrate expression and regulation of P2Y6 expression in T cells, and suggest a role for P2Y6 in the pathogenesis of IBD-mediated intestinal damage.