Abstract 3167: Estrogenic regulation of S6 kinase 1 expression creates a positive feed-forward loop in control of breast cancer cell proliferation

Abstract

Abstract The 40S ribosomal S6 kinase 1 (S6K1) acts downstream of the mammalian Target of Rapamycin (mTOR), and is sensitive to inhibition by rapamycin. Chromosomal region 17q23 containing the RPS6KB1 gene is frequently amplified in breast cancer cells, and S6K1 is overexpressed in about 30% of cases. Overexpression of S6K1 correlates with increased rapamycin sensitivity. The role of S6K1 in disease development and progression is supported by the observation that S6K1 overexpression is associated with poor prognosis in breast cancer patients. However, the reason for high-level amplification of the RPS6KB1 gene specifically in breast cancer, and not other cancer types is not well understood. We have previously reported that S6K1 regulates growth of breast cancer cells by phosphorylating Estrogen Receptor α (ERα), and co-expression of S6K1 and ERα in breast cancer cells renders them sensitive to combination therapy with rapamycin and tamoxifen. In this study, we demonstrate that in response to estrogen activation, ERα activates expression of S6K1 by upregulating transcription of the RPS6KB1 gene. Increased levels of S6K1 promote further phosphorylation and activation of ERα, creating a positive feed-forward loop. We hypothesize that this relationship promotes breast cancer cell growth, thus providing a selective advantage to S6K1- and ERα-overexpressing cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3167.