Perivascular tenascin C triggers sequential activation of macrophages and endothelial cells to generate a pro-metastatic vascular niche in the lungs

When cancers progress to metastasis, disseminated cancer cells frequently lodge near vasculature in secondary organs. However, our understanding of the cellular crosstalk evoked at perivascular sites is still rudimentary. In this study, we identify intercellular machinery governing formation of a pro-metastatic vascular niche during breast cancer colonization in lungs. We show that four secreted factors, INHBB, SCGB3A1, OPG and LAMA1, induced in metastasis-associated endothelial cells (ECs), are essential components of the vascular niche and promote metastasis in mice by enhancing stem cell properties and survival ability of cancer cells. Notably, blocking VEGF, a key regulator of EC behavior, dramatically suppressed EC proliferation, whereas no impact was observed on the expression of the four vascular niche factors in lung ECs. However, perivascular macrophages, activated via the TNC-TLR4 axis, were shown to be crucial for EC-mediated production of niche components. Together, our findings provide mechanistic insights into the formation of vascular niches in metastasis.