Filamin A regulates focal adhesion disassembly and suppresses breast cancer cell migration and invasion

The actin cross-linking protein filamin A (FLNa) functions as a scaffolding protein and couples cell cytoskeleton to extracellular matrix and integrin receptor signaling. In this study, we report that FLNa suppresses invasion of breast cancer cells and regulates focal adhesion (FA) turnover. Two large progression tissue microarrays from breast cancer patients revealed a significant decrease of FLNa levels in tissues from invasive breast cancer compared with benign disease and in lymph node-positive compared with lymph node-negative breast cancer. In breast cancer cells and orthotopic mouse breast cancer models, down-regulation of FLNa stimulated cancer cell migration, invasion, and metastasis formation. Time-lapse microscopy and biochemical assays after FLNa silencing and rescue with wild-type or mutant protein resistant to calpain cleavage revealed that FLNa regulates FA disassembly at the leading edge of motile cells. Moreover, FLNa down-regulation enhanced calpain activity through the mitogen-activated protein kinase-extracellular signal-regulated kinase cascade and stimulated the cleavage of FA proteins. These results document a regulation of FA dynamics by FLNa in breast cancer cells.