MRTF promotes breast cancer cell motility through SRF-dependent upregulation of DIAPH3 expression.

Dysregulated actin cytoskeleton gives rise to aberrant cell motility and metastatic spread of tumor cells. The MRTF-SRF transcriptional complex plays a key role in regulating the expressions of actin cytoskeleton-modulatory genes. In this study, we demonstrate that MRTF's interaction with SRF is critical for migration and invasion of breast cancer cells. Disruption of the MRTF-SRF interaction suppresses membrane dynamics affecting the frequency and the effectiveness of membrane protrusion during cell motility. Consistent with these phenotypic changes, we further show that MRTF promotes actin polymerization at the leading edge, a key aspect of membrane protrusion, and migration of breast cancer cells through upregulating the expression of formin-family actin nucleating/elongating protein encoding gene DIAPH3 in an SRF-dependent manner. In support of these findings, multiplexed quantitative immunohistochemistry and transcriptome analyses of clinical specimens of breast cancer further demonstrate a positive correlation between nuclear localization of MRTF with malignant traits of cancer cells as well as enrichment of MRTF/SRF gene signature in distant metastases relative to primary tumors. In conclusion, this study for the first time links the MRTF/SRF signaling axis to cell migration through the regulation of a specific actin-binding protein, and provides evidence for an association between MRTF/SRF activity and malignancy in human breast cancer.