Real-time, high-resolution microscopy of invasive cancer cells in the tumor microenvironment context

Tumor cell structures that have long been hypothesized as necessary for metastasis are invadopodia, invasive protrusions rich in structural and adhesion proteins, as well as metalloproteases. Using our unique intravital imaging approaches (Perrin et al, 2019 Canc Rep; Bayarmagnai et al, 2018 Meth Mol Biol.), we previously demonstrated that invadopodia in vivo are necessary for intravasation and consequent lung metastasis (Gligorijevic et al, Plos Bio 2014). In primary breast carcinoma, we found that cells which assemble invadopodia migrate at slow speeds, in perivascular niches where the ECM is cross-linked. Outside of these niches, no invadopodia were observed and cells migrated at high speeds, via contact guidance along collagen fibers. The invadopodia-driven motility can be switched to contact guidance by reducing the ECM cross-linking or by knocking down Tks5, which in turn reduces intravasation and metastasis. We next deduced that invadopodia-driven motility consists of two oscillating states: i. Invadopodia state, in which a cell is relatively sessile while it assembles invadopodia and degrades ECM; ii. Locomotion state. State balance is regulated by integrin Î(2)1 activation levels (Esmaeili et al 2018 Biophys J). 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. Using FUCCI markers (Esmaeili et al 2018 APL BioE), we next show that Invadopodia state occurs during the G1 phase of the cell cycle (Bayarmagnai et al, 2019 JCS). A close look at the regulators of G1 revealed that the cell cycle regulator p27kip1 localizes to the sites of invadopodia assembly and overexpression of p27kip1 causes faster turnover of invadopodia and increased ECM degradation. Taken together, these findings suggest that invadopodia assembly in the perivascular niche, is necessary for lung metastasis and function is controlled by the cell cycle.