Breast cancer cell migration is potentiated by associated fibroblasts through a laminin-511-Integrin α6β1-transduced Arp2/3 localization

Invading cancer cells are intermingled with fibroblasts that interact with them to regulate their migration, although the precise motility-driving signaling mechanisms initiated upon such interactions remain ill-understood. We constitute time-lapse-tractable 3D pathotypic cultures with breast cancer cell lines with fibroblasts enriched from invasive ductal carcinoma biopsies. Herein, cancer-associated fibroblasts (CAFs) enhanced breast cancer migration relative to non-cancerous fibroblasts (NFs), also observed through greater infiltration of orthotopically injected cancer cells within murine inguinal lymph nodes. The enhancement was also seen in cancer cells exposed to CAF-secreted medium. CAFs phenocopied laminin-rich matrix in compacting cancer cell clusters. A subsequent immunocytochemical screen identified laminins α5, -β1, and -γ1 to be highly expressed in enriched CAFs populations as well as in stromal areas of breast cancer sections. Depleting laminin-α5, -β1, and -γ1 in CAFs downregulated 3D cancer cell migration. Cancer cells cultivated on Laminin-511 substrata showed increased adhesion, faster and persistent migration, enhanced shape polarization, and deformability of cancer cells relative to Laminin-211 controls. Observation of higher invadopodial F-actin dynamics on Laminin-511 led us to assay for and demonstrate anisotropically corticalized Arp 2/3 in cancer cells. An integrin antibody screen showed Integrin α6β1 inhibition specifically nullified Laminin-511-driven enhancement of morphomigrational traits of cancer cells, similar to Arp2/3 inhibition. Moreover, cells on Laminin-511 showed enhanced Integrin α6 localization to their invadopodia. We propose that activated fibroblasts use Laminin-511 to localize cognate integrin receptors, and Arp2/3 of cancer cells to their invadopodia, resulting in higher Arp2/3-driven actin remodeling and enhanced cell migration.