A Novel Regulatory Role of Ezrin in Promoting Breast Cancer Cell Invasion and Metastasis
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Metastasis is the leading cause of death for breast cancer patients and poses significant clinical challenges in the successful treatment of breast cancer. The cytoskeleton crosslinker protein ezrin, is frequently over-expressed in invasive cancers, including breast, and is correlated with disease progression and poor prognosis. Ezrin is often associated with an invasive and metastatic phenotype; however, the mechanisms by which ezrin regulates metastatic progression remain unclear. Thus, investigation of the functional role of ezrin in specific processes that promote tumour cell invasion, and the different stages of tumour cell dissemination, is key to understanding the biology of ezrin in cancer progression. Here, I demonstrate a regulatory role of ezrin in promoting focal adhesion and invadopodia turnover, two key structures that are necessary for effective cancer cell invasion. I also show that ezrin interacts with, and regulates the activity of the cysteine protease calpain, which cleaves several focal adhesion and invadopodia-associated proteins to promote their disassembly. Ezrin-mediated regulation of calpain requires the fully open and active conformation of ezrin, and is shown in this study to be specific for the calpain-1 isoform. In vivo assessment of ezrin function reveals that this protein is primarily required for late stage disease events, including organ seeding and colonization, but not primary tumour growth or intravasation, as measured by circulating tumour cell levels. Furthermore, ezrin is important for Src-induced lymph node metastasis, and correlates with high Src expression and the presence of lymphovascular invasion in a cohort of 63 primary invasive breast cancers. Collectively, these findings provide novel and much needed insight into the molecular and functional role of ezrin as a pro-metastatic regulator in breast cancer.