There is emerging evidence that the balance between estrogen receptor-A (ERA) and androgen receptor (AR) signaling is a critical determinant of growth in the normal and malignant breast. In this study, we assessed AR status in a cohort of 215 invasive ductal breast carcinomas. AR and ERA were coexpressed in the majority (80-90%) of breast tumor cells. KaplanMeier product limit analysis and multivariate Cox regression showed that AR is an independent prognostic factor in ERApositive disease, with a low level of AR (less than median of 75% positive cells) conferring a 4.6-fold increased risk of cancer-related death (P = 0.002). Consistent with a role for AR in breast cancer outcome, AR potently inhibited ERA transactivation activity and 17B-estradiol-stimulated growth of breast cancer cells. Transfection of MDA-MB-231 breast cancer cells with either functionally impaired AR variants or the DNA-binding domain of the AR indicated that the latter is both necessary and sufficient for inhibition of ERA signaling. Consistent with molecular modeling, electrophoretic mobility shift assays showed binding of the AR to an estrogenresponsive element (ERE). Evidence for a functional interaction of the AR with an ERE in vivo was provided by chromatin immunoprecipitation data, revealing recruitment of the AR to the progesterone receptor promoter in T-47D breast cancer cells. We conclude that, by binding to a subset of EREs, the AR can prevent activation of target genes that mediate the stimulatory effects of 17B-estradiol on breast cancer cells. [Cancer Res 2009;69(15):6131-40]

The complete cDNA for a human mitochondrial protein designated P1, which was previously identified as a microtubule-related protein, has been cloned and sequenced. The deduced amino acid sequence of P1 shows strong homology (40 to 50% identical residues and an additional 20% conservative replacements) to the 65-kilodalton major antigen of mycobacteria, to the GroEL protein of Escherichia coli, and to the ribulose 1,5-bisphosphate carboxylase-oxygenase (rubisco) subunit binding protein of plant chloroplasts. Similar to the case with the latter two proteins, which have been shown to act as chaperonins in the posttranslational assembly of oligomeric protein structures, it is suggested that P1 may play a similar role in mammalian cells. The observed high degree of homology between human P1 and mycobacterial antigen also suggests the possible involvement of this protein in certain autoimmune diseases.Our earlier studies with mutants of Chinese hamster ovary (CHO) cells selected for resistance to the microtubule (MT) inhibitor podophyllotoxin showed that a large number of these mutants involved specific electrophoretic alteration in a major protein designated P1 (Mr, 63 kilodaltons [kDa]) (6, 7). The genetic lesion in these mutants appears to be related to the cellular action of the drug, since podophyllotoxinresistant mutants exhibit highly specific cross-resistance and collateral sensitivity to other MT inhibitors, such as colchicine, nocodazole, and taxol, and show reduced binding of the drug in cell extracts (6, 7). Immunofluorescence studies show that in interphase cells of vertebrate and invertebrate species, P1 antibody stains mitochondria, which show specific association with MTs (5, 7). Subfractionation of rat mitochondria has localized P1 to the matrix compartment (4). To help understand the cellular function of P1, cloning and sequencing of P1 cDNA from human cells was undertaken. The P1 sequence reported here shows extensive sequence and structural homology to a family of bacterial and plant proteins, termed chaperonins (8), which are involved in facilitating the posttranslational assembly of oligomeric protein complexes (1,3,8), as well as to the 65-kDa major antigenic protein of mycobacterial species (15,(18)(19)(20). The observed high degree of sequence and structural similarity between these proteins strongly indicates that P1 is the human homolog of this evolutionarily highly conserved group of proteins.Isolation of Pl-specific clones from kgtll libraries. We have previously demonstrated that our antibodies to P1 crossreact only with the P1 protein in one-and two-dimensional immunoblots of proteins from CHO and human cells (5, 7).

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Stress proteins are frequently the target of humoral and cell-mediated immune responses to infection. These proteins belong to highly conserved gene families and there is substantial sequence homology between antigens produced by pathogenic organisms and the corresponding proteins from mammalian cells. Human T cells from sites of infectious and autoimmune lesions proliferate in response to stress proteins, and mapping of antigenic determinants on a mycobacterial stress protein shows that both species specific and highly conserved, 'self-like', regions of the molecule can take part in immune recognition. It is proposed that the lymphocyte population induced in response to stress proteins of pathogens during infection includes cells capable of autoimmune recognition of the corresponding self protein. Local accumulation of self stress proteins--in response to viral infection, for example--may subsequently provide a stimulus for proliferation of such autoreactive lymphocytes, thereby triggering a cycle of events which may contribute to the pathological damage associated with autoimmune disease.