Abstract 3097: Global transcript profiling for prolactin-stat5 dependent target genes in breast cancer

Abstract

Abstract Transcription factor Stat5 is a key mediator of prolactin receptor signaling and plays important roles in both normal mammary development and breast cancer. Although numerous studies support tumor-promoting roles for Stat5, accumulating evidence also points to a role of Stat5 in promoting cell differentiation in breast cancer cells. In fact, high levels of tyrosine phosphorylated Stat5 (pY-Stat5) in human breast cancer specimens are correlated with favorable prognosis. Identifying Stat5 target genes in human breast cancer may shed new light on the roles of Stat5 as well as provide new candidate prognostic biomarkers. This study was designed to identify candidate Stat5 target genes using tumor extracts of the breast cancer cell line T47D xenotransplanted into nude mice that were subsequently treated with or without human prolactin. Global transcript profiling on the Affymetrix U133 chip platform was employed. The analysis revealed 97 genes that were significantly modulated by prolactin, based on fold difference greater than 1.7 and a p-value less than 0.01. Among these, 61 genes were upregulated and 36 genes were downregulated by prolactin. A total of 18 transcripts were selected based on their relevance to breast cancer and these genes were further investigated using qRT-PCR analysis. Of the 18 candidate targets, 15 were regulated by prolactin in vivo. Of these, 13 were also regulated by prolactin in T47D cells in vitro. Given that prolactin signals through multiple pathways other than Stat5, we examined the ability of Stat5 to regulate the newly identified prolactin-dependent genes by over-expressing Stat5a or Stat5b in the T47D cells. Twelve of the 13 genes tested responded by increased degree of prolactin-modulation following ectopic over-expression of Stat5a or Stat5b, supporting the notion that these genes are downstream targets of Stat5. The identified candidate Stat5 target genes are known to have diverse functions that may critically impact breast cancer growth and progression. For instance, NTN4 is a transmembrane protein whose expression levels positively correlates with better prognosis in breast cancer. AREG and EREG are known to activate the ErbB receptors, whose functions are essential for breast cancer progression. FN1 is a known factor involved in breast cancer invasion. Lastly, PTHrP is well established as being functionally involved in breast cancer metastasis. Fluorescence-based quantitative immunohistochemistry revealed a highly positive correlation between levels of pY-Stat5 and PTHrP proteins in human clinical breast cancer specimens, providing proof-of-principle that the combination of global transcript profiling and quantitative immunohistochemistry analysis is valuable for identifying potential breast cancer biomarkers. Efforts are underway to examine the function of these and additional Stat5 target genes in order to further elucidate the roles of Stat5 in breast cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3097. doi:10.1158/1538-7445.AM2011-3097