Invasive
carcinoma cells form actin-rich matrix-degrading protrusions called invadopodia. These structures resemble podosomes produced by some normal cells and play a crucial role in extracellular matrix remodeling. In
cancer, formation of invadopodia is strongly associated with invasive potential. Although deregulated signals from the
receptor tyrosine kinase Met (also known as
hepatocyte growth factor are linked to
cancer metastasis and poor prognosis, its role in invadopodia formation is not known. Here we show that stimulation of
breast cancer cells with the
ligand for Met,
hepatocyte growth factor, promotes invadopodia formation, and in aggressive gastric
tumor cells where Met is amplified, invadopodia formation is dependent on Met activity. Using both GRB2-associated-
binding protein 1 (Gab1)-null fibroblasts and specific knockdown of Gab1 in
tumor cells we show that Met-mediated invadopodia formation and cell invasion requires the scaffold
protein Gab1. By a structure-function approach, we demonstrate that two
proline-rich motifs (P4/5) within Gab1 are essential for invadopodia formation. We identify the actin regulatory
protein,
cortactin, as a direct interaction partner for Gab1 and show that a Gab1-
cortactin interaction is dependent on the SH3 domain of
cortactin and the integrity of the P4/5 region of Gab1. Both
cortactin and Gab1 localize to invadopodia rosettes in Met-transformed cells and the specific uncoupling of
cortactin from Gab1 abrogates invadopodia biogenesis and cell invasion downstream from the
Met receptor tyrosine kinase. Met localizes to invadopodia along with
cortactin and promotes phosphorylation of
cortactin. These findings provide insights into the molecular mechanisms of invadopodia formation and identify Gab1 as a scaffold
protein involved in this process.