Abstract P1-07-18: Loss of Rab1B promotes triple-negative breast cancer metastasis by activating TGF-β/Smad signaling

Abstract

Abstract Background: Triple-negative breast cancer (TNBC) is a highly aggressive tumor subtype associated with poor prognosis. The onset of metastasis in organs such as the lung,bone and brain is a major cause of mortality in TNBC patients. Thus, identification of novel targets for the treatment of triple-negative breastcancer is urgent for improved outcomes in patients with this disease. Methods and Results:Here we conducted quantitative proteomic analyses in breast cancer cell lines, which include a normal, primary tumor and a metastatic tumor that were isolated from a single patient. Stable isotope labeling of amino acid in cell culture followed by LC-MS/MS analysis was performed and deregulated proteins were identified using statistical analysis. We identified for the first time that Rab1B, a member of RAS oncogene family, was down-regulated in high metastatic human breast cancer cells. In a panel of breast tumor tissues, Immunohistochemical analysis demonstrated an inverse correlation between metastatic propensity and the expression of Rab1B. Compared with primary tumors, Rab1B expression was notably decreased in lymph node metastases. Low Rab1B expression also correlated with poorer survival in triple-negative breast cancer patients. Through in vitro assays, we confirmed that silencing of Rab1B expression by RNAi in MDA-MB-231 and MDA-MB-468 breast cancer cells, can potentiate the proclivity to metastasize in Transwell assay and enhance lung colonization by tail vain injection in mice. In a reverse-complimentary approach, we determined that elevated Rab1B expression in highly metastatic breast cancer cell lines (MDA-MB-231HM and MDA-MB-231Bo) can suppress the ability of invasion and metastasis in vitro and in vivo. Mechanistically, we establish that the metastatic behavior strongly correlates with increased phosphorylated Smad3 levels and overexpression of TGF-β type I receptor (TβRI). Conversely, restoration of Rab1B can inhibit the activation of this pathway in MDA-MB-231HM and MDA-MB-231Bo cells. Conclusion:By utilizing a series of mammary tumor cell lines, animal models, and clinically sourced tissues, we demonstrate that Rab1B acts as a metastasis suppressor in triple-negative breast cancer through regulating TGF-β/Smad signaling pathway. Citation Format: HongLin Jiang, Hefen Sun, Wei Jin. Loss of Rab1B promotes triple-negative breast cancer metastasis by activating TGF-β/Smad signaling [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P1-07-18.