Invasive carcinoma cells use specialized actin polymerization-driven protrusions called invadopodia to degrade and possibly invade through the extracellular matrix (ECM) during metastasis. Phosphorylation of the invadopodium protein cortactin is a master switch that activates invadopodium maturation and function. Cortactin was originally identified as a hyperphosphorylated protein in v-Src-transformed cells, but the kinase or kinases that are directly responsible for cortactin phosphorylation in invadopodia remain unknown. In this study, we provide evidence that the Abl-related nonreceptor tyrosine kinase Arg mediates epidermal growth factor (EGF)-induced cortactin phosphorylation, triggering actin polymerization in invadopodia, ECM degradation, and matrix proteolysis-dependent tumor cell invasion. Both Src and Arg localize to invadopodia and are required for EGF-induced actin polymerization. Notably, Arg overexpression in Src knockdown cells can partially rescue actin polymerization in invadopodia while Src overexpression cannot compensate for loss of Arg, arguing that Src indirectly regulates invadopodium maturation through Arg activation. Our findings suggest a novel mechanism by which an EGFR-Src-Arg-cortactin pathway mediates functional maturation of invadopodia and breast cancer cell invasion. Furthermore, they identify Arg as a novel mediator of invadopodia function and a candidate therapeutic target to inhibit tumor invasion in vivo. Cancer Res; 71(5); 1730-41. Ó2011 AACR.

The protein tyrosine kinase Pyk2 is highly expressed in osteoclasts, where it is primarily localized in podosomes. Deletion of Pyk2 in mice leads to mild osteopetrosis due to impairment in osteoclast function. Pyk2-null osteoclasts were unable to transform podosome clusters into a podosome belt at the cell periphery; instead of a sealing zone only small actin rings were formed, resulting in impaired bone resorption. Furthermore, in Pyk2-null osteoclasts, Rho activity was enhanced while microtubule acetylation and stability were significantly reduced. Rescue experiments by ectopic expression of wild-type or a variety of Pyk2 mutants in osteoclasts from Pyk2−/− mice have shown that the FAT domain of Pyk2 is essential for podosome belt and sealing zone formation as well as for bone resorption. These experiments underscore an important role of Pyk2 in microtubule-dependent podosome organization, bone resorption, and other osteoclast functions.

Cortactin phosphorylation induces recruitment of the sodium-hydrogen exchanger NHE1 to invadopodia, resulting in pH changes that regulate cortactin-cofilin binding and invadopodium dynamics.