The Role of miR-194-2-192 Cluster and Metadherin in Breast Cancer Metastasis

Abstract

In the first section of my dissertation, we evaluated the role of miR-194-2-192 cluster in the regulation of the multifaceted epithelial-mesenchymal transition (EMT) and breast cancer metastasis. As the initiating step of cancer metastasis, EMT has been implicated in giving rise to the dissemination of migratory and invasive mesenchymal carcinoma cells from the primary epithelial tumors. EMT is a multifaceted cellular process involving not only cell morphology change but also resistance to cell death and senescence. In this study, we demonstrate that the miRNA-194-2-192 cluster is endowed with the ability to inhibit EMT by concomitantly regulating multiple aspects of EMT, including epithelial traits, cell cycle and apoptosis, through epigenetic-based regulation of various genes by targeting Mecp2. Consistent with the cluster's role in inhibiting EMT, in vivo delivery of miRs-194/192 decreased metastatic burden of 4T1 cells. In addition, both miR-192 and miR-194 expression correlates inversely with metastatic recurrence in a cohort of human breast tumors. These results suggest that miRs-194/192 hinder many aspects of EMT, indicating a potential miRNA-based therapeutics for breast cancer patients.

In the second section of my dissertation, we studied a dual-function protein in breast cancer metastasis, named Metadherin (MTDH). Suggested to be a plasma membrane localized protein, MTDH plays dual roles in promoting tumor progression by enhancing cancer cell adhesion to vascular endothelium and chemoresistance. Therefore, molecular targeting of MTDH may not only prevent the metastasis of breast cancer cells but also sensitize cancer cells to chemotherapy, hampering the deadly spread of breast cancer. In this study, we applied genetic and biochemical methods to identify MTDH-interacting proteins. Furthermore, interaction domains were mapped out for MTDH-NCL and MTDH-MTDH interactions, which would be important for generation of neutralizing monoclonal antibodies to block the interaction and eventually inhibit the dual roles of MTDH in breast cancer metastasis. However, in contrast to previous findings, follow up studies using two distinct approaches independently showed that MTDH is not plasma membrane localized under normal or suspension conditions in various cancer types. In addition, all the evidences supporting MTDH to be an important factor for tumorigenesis and metastasis were derived from in vitro assays or in vivo studies using xenograft models, but mammary tumor progression is a highly complex process that cannot be fully recapitulated by these methods alone. Therefore, two MMTV-Mtdh transgenic mice lines were successfully generated and characterized for better understanding of MTDH's functions in mammary gland development and tumor progression.