Research Grants Awarded
Identification of biomarker for activator form of estrogen-related receptor alpha in breast cancer
Tumor Cell Biology II
Many breast tumors initially respond to treatment with antiestrogens, but progress to a hormone-resistant phenotype. E strogen-related receptor alpha (ERRalpha) shares significant sequence identity with ERalpha, but does not bind estrogen or tamoxifen. It can modulate expression of estrogen-responsive genes by competing with ERalpha for binding estrogen response elements (EREs). It can also bind ERREs that ERalpha can not. It is the main member of the ER/ERR family present in ER(-) tumors. Forty percent of patients with ERRalpha(+) breast cancers have poor clinical outcomes. ERRalpha can function as either a repressor, down-modulating ERalpha-regulated transcription, or a ligand-independent activator, with its activities determined, in part, by phosphorylations occurring via the EGFR/ErbB2(HER2) signaling pathways, a target treated with Herceptin or Iressa. Our working hypothesis is the activator form of ERRalpha (ERRalpha-act) plays a major role in the etiology and progression of a subset of breast cancers , especially ERalpha(-), ErbB2(+), and tamoxifen-resistant ones, by activating expression of ERE-regulated genes regardless of the presence of estrogens, anti-estrogens, or ERalpha, while the repressor form of ERRalpha (ERRalpha-rep) is a good prognosticator unless ERalpha is over-expressed. Thus, a better biomarker than ERRalpha would be one for ERRalpha-act. Our aims are: (i) to identify genes that are direct targets of ERRalpha-act, but not ERalpha, by performing chromatin immunoprecipitation (ChIP) with antisera specific to ERRalpha, ERalpha, and RNA polymerase II followed by hybridization to human promoter microarray chips; (ii) to validate expression of a few of these genes being truly indicative of ERRalpha-act by performing standard ChIP, Northern blot, and immunoblot assays with well-characterized breast carcinoma cell lines under a variety of growth conditions; and (iii) to perform immunohistochemistry on sections of approximately 400 primary breast carcinomas with antibodies to these ERRalpha-act-specific biomarkers to begin to look for correlations between ERRalpha’s functional status, currently assayed biomarkers, therapeutic treatment, and clinical outcome. If successful, our studies would (i) identify a new, independent biomarker for prognosis and prediction of therapeutic benefit from currently available treatment options, and (ii) suggest ERRalpha-act is a new therapeutic target for some currently hard-to-treat breast cancers.
Testing breast tumors for estrogen receptor alpha (ERalpha) is routinely done to select patients for treatment with anti-estrogens such as tamoxifen and aromatase inhibitors. Progesterone receptor (PgR) is also tested to determine whether ERalpha is active. Most breast cancer patients whose tumors contain both ERalpha and PgR initially respond to these drugs. Unfortunately, they usually stop responding within a few years and some never respond. Estrogen-related receptor alpha (ERRalpha) exhibits some of the same properties as ERalpha. ERRalpha can modify estrogen responsiveness by competing with E r alpha for binding DNA sites in target genes, but does not bind estrogens or tamoxifen. Instead, its ability to turn on expression of estrogen-responsive genes is controlled, in part, by changes induced via the ErbB2(HER2) pathway. ErbB2 is now also routinely tested for, with ErbB2-positive tumors being treated with Herceptin or Iressa. A pproximately 40 percent of patients with ERRalpha-positive breast cancers have poor clinical outcomes, with resistance to tamoxifen therapy. Thus, ERRalpha probably plays important roles in the origin and progression of some breast cancers, especially ERalpha-negative, PgR-negative, tamoxifen-resistant, and ErbB2-positive ones. However, whereas presence of the turned-on form of ERRalpha may be “bad”, contributing to loss of proper control of genes and, thus, growth of the cells, presence of the turned-off form of ERRalpha may be “good”, helping to properly control gene expression. Thus, a better biomarker than ERRalpha may be one specific for the turned-on form of ERRalpha. Our specific aims are: (i) to identify genes that are direct targets of the turned-on form of ERRalpha, but not ERalpha; (ii) to show that expression of some of these genes is truly specifically indicative of the turned-on form of ERRalpha; and (iii) to use antibodies to the proteins made from these validated genes as biomarkers for the turned-on form of ERRalpha to begin to look for correlations between ERRalpha’s functional status in breast tumors, currently assayed biomarkers, therapeutic treatment, and clinical outcome. These studies may lead to discovery of a new, independent biomarker for prognosis and prediction of benefit from current treatment options, especially for currently hard-to-treat breast cancers. The findings may also indicate that the turned-on form of ERRalpha is a good target for the development of new drugs for these specific cancers.