Epithelial cells maintain intercellular communication directly by cell-cell, cell-ECM interaction and indirectly by paracrine secretion of extracellular messengers either as free molecules or via exosomes. The vesicular trafficking machinery is an integral part of such communication, paralleling digital cables that transmit the information bytes to the correct hub. During the process of EMT, derailing of the trafficking machinery leads to a systemic breakdown of intra and inter-cellular communication pathways. The purpose of the current study is to elucidate the functional role of Rab25, a key member of the vesicular trafficking machinery in mediating EMT-MET processes during breast cancer progression.

Aberrant endocytosis is a new hallmark of cancer. Rab GTPases are the primary regulators of endocytosis. Many members of this large family are implicated in a wide array of cancers including breast cancer. Specifically, Rab25, a GTPase associated with the recycling endosomes, is deregulated in most epithelial cancers. Rab25 appears to function both as a tumor suppressor and an oncogene in a context dependent manner.

We found that Rab25 is lost in Claudin Low tumors as well as in representative cell lines such as the MDA MB231. Rab25 is a robust and sufficient marker of breast cancers and cell lines with an increased EMT signature. Additionally, in immortalized human mammary epithelial cell lines (HMLE), induction of EMT by overexpression of Snail1 completely obliterates Rab25 protein. Exogenous re-expression of Rab25 dramatically rescues these cells from Snail driven invasion through Matrigel. However this Snail dependent regulation is unique only to TN and Claudin Low tumors and does not hold true for hormone receptor positive tumors. Further, analysis of RNA Seq data from a MMTV mouse model showed that tumors enriched in EMT markers and by corollary with low CDH and claudins, also lost Rab25 transcripts.

Snail mediated transcriptional repression targets recycling endosomal proteins such as Rab25 to decrease delivery of junction proteins that facilitate cell-cell communication to the appropriate compartment. In parallel, it potentially enhances paracrine regulation by secreted exosomes. Overall, our study shows presence and absence of Rab25 markedly alters cell-cell communication, which is essential for maintenance of epithelial features of cells. Rab25 could be a prognostic marker and a therapeutic target for a subset of patients with increased risk of metastatic disease.

Citation Format: Shreya Mitra, Lorenzo Federico, Gordon B. Mills. Transcription factor Snail mediates EMT by altering vesicular trafficking protein Rab25. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research; Oct 17-20, 2015; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(2_Suppl):Abstract nr B40.