Invadopodia Dynamics is Regulated by ECM Cross-Linking

Tumor cell structures that have long been hypothesized as necessary for metastasis are invadopodia, invasive protrusions rich in structural proteins (Tks5, actin), adhesion proteins (eg. integrin β1), and metalloproteases, known to degrade the ECM proteins. By time-lapse microscopy, we observe that the Slow phenotype consists of temporal integration of two oscillating states: i. Invadopodia state, in which a cell is relatively sessile while it assembles invadopodia and degrades ECM; ii. Locomotion state. Importantly, the Invadopodia state only occurs in early G1, whereas the Locomotion state can be seen throughout the entire cell cycle, suggesting that the cell cycle controls invadopodia assembly. Towards elucidating the mechanism of state oscillations, we devised a mathematical model and engineered different levels of ECM cross-linking in 2D or 3D environments, discovering that state oscillation frequencies show a biphasic trend to linearly increasing levels of ECM cross-linking. We further show that in our model and experimentally, the oscillation dynamics between the states depend on ECM interactions with its major cellular receptor, integrin β1. Partial inhibition of the integrin β1 activity not only lowers the invadopodia-mediated ECM degradation, but can also eliminate Invadopodia state. In turn, cells spend more time in Locomotion state, increasing the net distance of cell migration. Our latest data demonstrates that an ECM degradation product, 60kDa fragment of laminin which binds integrin β1, can also act as a modulator of Locomotion-Invadopodia state balance. When released from the laminin network into the media, this fragment decreases invadopodia by 5-fold, simultaneously increasing both the speed and the time spent in cell migration. Overall, our data shows that invadopodia assembly is regulated by ECM components and ECM degradation products via integrin β1 activity, implying that breast cancer metastasis may be prevented by modulating integrin β1 activity levels.