Extracellular Matrix Rigidity Promotes Invadopodia Activity

Abstract

Summary Invadopodia are actin-rich subcellular protrusions with associated proteases used by cancer cells to degrade extracellular matrix (ECM) [1]. Molecular components of invadopodia include branched actin assembly proteins, membrane trafficking proteins, signaling proteins and transmembrane proteinases[1]. Similar structures exist in nontransformed cells, such as osteoclasts and dendritic cells, but are generally called podosomes and are thought to be more involved in cell-matrix adhesion than invadopodia [2–4]. Despite intimate contact with their ECM substrates, it is unknown whether physical or chemical ECM signals regulate invadopodia function. Here, we report that ECM rigidity directly increases both the number and activity of invadopodia. Transduction of ECM rigidity signals depends on the cellular contractile apparatus [5–7], as inhibition of nonmuscle myosin II, myosin light chain kinase, and Rho kinase all abrogate invadopodia-associated ECM degradation. Whereas myosin IIA, IIB, and phosphorylated myosin light chain do not localize to invadopodia puncta, active phosphorylated forms of the mechanosensing proteins p130Cas (Cas) and focal adhesion kinase (FAK) are present in actively degrading invadopodia and the levels of phospho-Cas and phospho-FAK in invadopodia are sensitive to myosin inhibitors. Overexpression of Cas or FAK further enhances invadopodia activity in cells plated on rigid polyacrylamide substrates. Thus, in invasive cells, ECM rigidity signals lead to increased matrix-degrading activity at invadopodia, via a myosin II-FAK/Cas pathway. These data suggest a potential mechanism, via invadopodia, for the reported correlation of tissue density with cancer aggressiveness.

Invadosomes at a glance

“…Src, in particular, seems to be a master switch for invadosome formation (Cortesio et al, 2008;Destaing et al, 2008;Oikawa et al, 2008), and inhibition of Src-family proteins using inhibitors such as PP2 (Linder et al, 2000a) has proven to be a useful tool for their manipulation. FAK and its hematopoietic homolog Pyk2 bind to both β1 and β3 integrins as well as to Src, and have been shown to localize to invadopodia (Alexander et al, 2008) and the ring structure of podosomes (Pfaff and Jurdic, 2001). Interestingly, FAK was found to function upstream of Src as a negative regulator of invadopodium formation in adenocarcinoma cells (Chan et al, 2009).…”

“…Myosin II has been detected around some active invadopodia, but myosin is mostly absent from these structures. Still, invadopodial localization of other proteins involved in mechanotransduction, such as Cas or FAK, is sensitive to myosin inhibition (Alexander et al, 2008). Clearly, this is an area that needs further exploration.…”

The Novel Adaptor Protein Tks4 (SH3PXD2B) Is Required for Functional Podosome Formation

“…This leaves open the possibility that differences in culture conditions may influence podosome/invadopodia architecture and function. Indeed, a recent article reported that extracellular matrix rigidity influences both the number and activity of invadopodia (Alexander et al, 2008). Our understanding of the protein components of podosomes and invadopodia has deepened in recent years, and we are also beginning to learn the signals that promote the formation and turnover of these structures.…”

Contribution of Bone Tissue Modulus to Breast Cancer Metastasis to Bone

“…Many studies investigating the effects of the rigidity of the matrix on cell migration, differentiation, and invasion have used 2D cell culture on hydrogel substrates, including Matrigel™ [77], crosslinked gelatin [78], and synthetic hydrogels [79]. Similarly, the invasiveness of cancer cells has been reported to increase with matrix rigidity when cultured on hydrogels [51,52,78,80].…”

“…Similarly, the invasiveness of cancer cells has been reported to increase with matrix rigidity when cultured on hydrogels [51,52,78,80]. However, considering that the elastic modulus of hydrogel substrates is generally <100 nN/μm 2 , their applicability to the bone microenvironment, where the modulus of the mineralized extracellular matrix ranges from 17,100,000-28,900,000 nN/μm 2 [50], may be limited.…”