UC San Diego

Metastasis is a multistep process during which cancer cells gain the ability to invade through the extracellular matrix (ECM) to disseminate to distant organs. Cancer cells can degrade ECM by forming invasive structures called invadopodia which concentrate protease activities to areas of the cell in contact with the ECM. Twist1 is a key transcription factor known to promote the epithelial mesenchymal transition (EMT) and tumor metastasis. We find that Twist1 promotes local invasion in metastasis by inducing invadopodia formation via transcriptional regulation of platelet-derived growth factor [alpha] (PDGFR[alpha]) and a disintegrin and metalloprotease 12 (ADAM12). We find that Twist1 is both necessary and sufficient for invadopodia formation and ECM degradation in multiple cell lines. Twist1 induces PDGFR[alpha] expression, which in turn activates Src, to promote invadopodia formation. We demonstrate that Twist1 and PDGFR[alpha] are central mediators of invadopodia formation in response to various EMT-inducing signals. Induction of PDGFR[alpha] and invadopodia is essential for Twist1 to promote tumor metastasis. Consistent with PDGFR[alpha] being a direct transcriptional target of Twist1, co-expression of Twist1 and PDGFR[alpha] predicts poor survival in breast tumor patients. Therefore, invadopodia-mediated matrix degradation is a key function of Twist1 in promoting tumor metastasis. Moreover, we find that the transmembrane metalloprotease ADAM12 is strongly induced by Twist1 and localizes to both invadopodia and focal adhesions. Knockdown of ADAM12 reduces both migration and invasion while increasing adhesion and focal adhesion number. We show that ADAM12 is required for formation of invadopodia and gelatin degradation. Using a series of ADAM12 mutants, we find that the disintegrin domain of ADAM12 is involved in both regulation of focal adhesions and invadopodia while the metalloprotease domain is specifically required for efficient invadopodia formation. Functionally, ADAM12 is required for efficient metastasis of tumor cells to the lung in a human xenograft breast cancer metastasis model in mice. Our work defines a novel role for Twist1 in regulating ECM degradation during tumor invasion and metastasis. These results could lead to new biomarkers and targeted therapeutics for invasive and metastatic breast cancer