Invadopodia are actin-rich structures that are present at the basal surfaces of cells that are capable of crossing extracellular barriers, such as cancer cells. The primary function of invadopodia appears to be the focal degradation of the extracellular matrix (ECM) through the secretion of matrix metalloproteinases (MMPs) [1, 2]. The formation and function of Invadopodia can be described over defined steps that include initiation, extension, ECM degradation and disassembly. 

Figure 1. Structure of an invadopodium

The basic structure of an invadopodium consists of a F-actin core similar to that found in podosomes. Microtubules and intermediate filaments have also been detected in mature invadopodia [5]. Actin filament nucleators and their regulators such as the Arp2/3 complex, N-WASP (neuronal Wiskott-Aldrich syndrome protein), WASP-interacting protein (WIP) and cortactin [3] are also found localized to this structure. In addition to the podosome-like structure at their base, invadopodia contain a substantial number of actin filaments arranged as parallel bundles, akin to those observed in filopodia. Cross-linking proteins such as fascin are abundant in invadopodia, and indeed there is a strong correlation between cancer cell invasive potential and fascin expression ([4], as reviewed in [6]).

Unlike podosomes which can be found in cells under normal physiological conditions, invadopodia are found only in pathological states, most commonly in invasive cancer cells. To this end, invadopodia serve to enhance tumor metastasis by inducing basement membrane disruption through local matrix degradation [9]. To achieve this, the targeted release of surface-exposed proteases (including MMPs) is required [10]. Invadopodia mark the first steps of tumor cell invasion [11].