Faculty Bibliography

p23 is a heat shock protein 90 (Hsp90) cochaperone located in both the cytoplasm and nucleus that stabilizes unliganded steroid receptors, controls the catalytic activity of certain kinases, regulates protein-DNA dynamics, and is upregulated in several cancers. We had previously shown that p23-overexpressing MCF-7 cells (MCF-7+p23) exhibit increased invasion without affecting the estrogen-dependent proliferative response, which suggests that p23 differentially regulates genes controlling processes linked to breast tumor metastasis. To gain a comprehensive view of the effects of p23 on estrogen receptor (ER)-dependent and -independent gene expression, we profiled mRNA expression from control versus MCF-7+p23 cells in the absence and presence of estrogen. A number of p23-sensitive target genes involved in metastasis and drug resistance were identified. Most striking is that many of these genes are also misregulated in invasive breast cancers, including PMP22, ABCC3, AGR2, Sox3, TM4SF1, and p8 (NUPR1). Upregulation of the ATP-dependent transporter ABCC3 by p23 conferred resistance to the chemotherapeutic agents etoposide and doxorubicin in MCF-7+p23 cells. MCF-7+p23 cells also displayed higher levels of activated Akt and an expanded phosphoproteome relative to control cells, suggesting that elevated p23 also enhances cytoplasmic signaling pathways. For breast cancer patients, tumor stage together with high cytoplasmic p23 expression more accurately predicted disease recurrence and mortality than did stage alone. High nuclear p23 was found to be associated with high cytoplasmic p23, therefore both may promote tumor progression and poor prognosis by increasing metastatic potential and drug resistance in breast cancer patients

Hormones and their receptors play an important role in the development and progression of breast carcinoma. Although the primary focus has been on oestrogen and oestrogen receptor (ER), androgen, androgen receptor (AR) and its coactivator(s) have been implicated in tumorigenesis of breast carcinoma and warrant further investigation. AR coactivator p44/Mep50 is identified as a subunit of methylosome complex and lately characterized as an AR coactivator that enhances AR mediated transcription activity in a ligand dependent manner. In prostate cancer, p44 is expressed in the nucleus of benign epithelia and translocated into the cytoplasm in cancer cells. Furthermore, nuclear expression of p44 inhibits prostate cancer growth. In this report, we examined the expression and function of p44 in breast cancer. In addition to being an AR coactivator, p44 also functions as an ER coactivator. In contrast to findings in prostate cancer, the expression of p44 shows strong cytoplasmic expression in morphologically normal terminal ductal lobular units, while nuclear p44 is observed in both ductal carcinoma in situ and invasive carcinoma. Further, overexpression of nuclear-localized p44 stimulates proliferation and invasion in MCF7 breast cancer cells in the presence of oestrogen and the process is ERalpha dependent. These findings strongly suggest that p44 plays a role in mediating the effects of hormones during tumorigenesis in breast

A major obstacle in treating prostate cancer is the development of androgen-independent disease. In this study, we examined LEF1 expression in androgen-independent cancer as well as its regulation of androgen receptor (AR) expression, prostate cancer growth, and invasion in androgen-independent prostate cancer cells. Affymetrix microarray analysis of LNCaP and LNCaP-AI (androgen-independent variant LNCaP) cells revealed 100-fold increases in LEF1 expression in LNCaP-AI cells. We showed that LEF1 overexpression in LNCaP cells resulted in increased AR expression and consequently enhanced growth and invasion ability, whereas LEF1 knockdown in LNCaP-AI cells decreased AR expression and, subsequently, growth and invasion capacity. Chromatin immunoprecipitation, gel shift, and luciferase assays confirmed LEF1 occupancy and regulation of the AR promoter. Thus, we identified LEF1 as a potential marker for androgen-independent disease and as a key regulator of AR expression and prostate cancer growth and invasion. LEF1 is highly expressed in androgen-independent prostate cancer, potentially serving as a marker for androgen-independent disease

Protein phosphorylation is a versatile posttranslational modification that can regulate nuclear receptor function. Although the precise role of receptor phosphorylation is not fully understood, it appears that it functions to direct or refine receptor activity in response to particular physiological requirements. Identifying and characterizing specific nuclear receptor phosphorylation sites is an important step in elucidating the role(s) receptor phosphorylation plays in function. Although traditional methods of metabolic labeling and in vitro protein phosphorylation have been informative, receptor phosphorylation site-specific antibodies are simple and reliable tools to study receptor phosphorylation. This chapter will discuss how to develop nuclear receptor phosphorylation site-specific antibodies to elucidate function

The glucocorticoid steroid hormone cortisol is released by the adrenal glands in response to stress and serves as a messenger in circadian rhythms. Transcriptional responses to this hormonal signal are mediated by the glucocorticoid receptor (GR). We determined GR binding throughout the human genome by using chromatin immunoprecipitation followed by next-generation DNA sequencing, and measured related changes in gene expression with mRNA sequencing in response to the glucocorticoid dexamethasone (DEX). We identified 4392 genomic positions occupied by the GR and 234 genes with significant changes in expression in response to DEX. This genomic census revealed striking differences between gene activation and repression by the GR. While genes activated with DEX treatment have GR bound within a median distance of 11 kb from the transcriptional start site (TSS), the nearest GR binding for genes repressed with DEX treatment is a median of 146 kb from the TSS, suggesting that DEX-mediated repression occurs independently of promoter-proximal GR binding. In addition to the dramatic differences in proximity of GR binding, we found differences in the kinetics of gene expression response for induced and repressed genes, with repression occurring substantially after induction. We also found that the GR can respond to different levels of corticosteroids in a gene-specific manner. For example, low doses of DEX selectively induced PER1, a transcription factor involved in regulating circadian rhythms. Overall, the genome-wide determination and analysis of GR:DNA binding and transcriptional response to hormone reveals new insights into the complexities of gene regulatory activities managed by GR

The androgen receptor (AR) directs diverse biological processes through interaction with coregulators such as AR trapped clone-27 (ART-27). Our results show that ART-27 is recruited to AR-binding sites by chromatin immunoprecipitation analysis. In addition, the effect of ART-27 on genome-wide transcription was examined. The studies indicate that loss of ART-27 enhances expression of many androgen-regulated genes, suggesting that ART-27 inhibits gene expression. Surprisingly, classes of genes that are up-regulated upon ART-27 depletion include regulators of DNA damage checkpoint and cell cycle progression, suggesting that ART-27 functions to keep expression levels of these genes low. Consistent with this idea, stable reduction of ART-27 by short-hairpin RNA enhances LNCaP cell proliferation compared with control cells. The effect of ART-27 loss was also examined in response to the antiandrogen bicalutamide. Unexpectedly, cells treated with ART-27 siRNA no longer exhibited gene repression in response to bicalutamide. To examine ART-27 loss in prostate cancer progression, immunohistochemistry was conducted on a tissue array containing samples from primary tumors of individuals who were clinically followed and later shown to have either recurrent or nonrecurrent disease. Comparison of ART-27 and AR staining indicated that nuclear ART-27 expression was lost in the majority of AR-positive recurrent prostate cancers. Our studies show that reduction of ART-27 protein levels in prostate cancer may facilitate antiandrogen-resistant disease