Invadopodia

Invadopodia or invasive feet are protrusions in the cell membrane of some cells that are rich in actin and extend into the extracellular matrix (ECM). Researchers have reported that invadopodia formation is initiated with the assembly of actin core structures, followed by the accumulation of mtrix metalloproteinase for ECM degradation. They are associated with high levels of proteolysis and cell signaling and are frequently seen in metastatic cancer cells that are invading surrounding tissues. These structures are very similar to the podosomes formed by normal cells that need to cross tissue barriers, such as macrophages and monocytes, or cells such as osteoclasts that remodel tissue. However, podosomes are short-lived and do not cause major degradation of the ECM.

In the case of breast cancer cell lines, the ability to form invadopodia is closely related to their invasive and metastatic properties. Additionally, during intravasation, invadopodia-like protrusions in tumor cells have been observed in vivo by intravital imaging. Therefore, invadopodia are proposed to function in local ECM degradation during cancer invasion and metastasis, although the in vivo relevance of invadopodia has yet to be determined.