An invasion-related complex of cortactin, paxillin and PKC mu associates with invadopodia at sites of extracellular matrix degradation

Invasive breast cancer cells have the ability to extend membrane protrusion s, invadopodia, into the extracellular matrix (EC). These structures are as sociated with sites of active matrix degradation. The amount of matrix degr adation associated with the activity of these membrane protrusions has been shown to directly correlate with invasive potential. We demonstrate here t hat microinjection of polyclonal anti-cortactin antibodies blocks matrix de gradation at invadopodia supporting the hypothesis that cortactin has a dir ect role in invasive behavior. MDA-MB-231, invasive breast cancer cells wer e sheared from the surface of a gelatin matrix to isolate invadopodia. Cort actin, paxillin and protein kinase C (PKC) mu, a serine kinase, were co-imm unoprecipitated as a complex from invadopodia-enriched membranes. We confir med the subcellular distribution of these proteins by immunolocalization an d Western blotting. We also determined that, in contrast to its presence in invasive cells, this complex of proteins was not detected in lysates from non-invasive cells that do not form invadopodia. Taken together, these data suggest that the formation of this cortactin-containing complex correlates ,vith cellular invasiveness. We hypothesize that this complex of molecules has a role in the formation and function of invadopodia during cellular inv asion.