Decoupling chemical and mechanical signaling in colorectal cancer cell migration.

Colorectal cancer metastasis is governed by a variety of chemical and mechanical signaling that are largely influenced by cancer-associated fibroblasts (CAFs) in the tumor microenvironment. Here, we deconvolute the chemical from mechanical signaling in the case of the colon cancer cell line HCT-116 and CAFs. We examined three chemoattractants (CXCL12, TGF-β, and activin A) which allegedly are secreted by CAFs and induce HCT-116 cell migration. None of the chemoattractants tested resulted in enhanced migration of HCT-116 in a 2D transwell assay, at low cell density. Similarly, CAF-conditioned media also did not lead to enhanced HCT-116 migration, while CAFs co-cultured in the transwell assay did lead to increased HCT-116 migration. This result suggests that either high cell densities are required for chemotaxis, and/or a reciprocal two-way signaling network between CAFs and HCT-116 is necessary to induce chemotaxis. Surprisingly, we find that HCT-116 cells exhibit enhanced migration along the axis of mechanical stress in a 3D collagen matrix, at very high cell densities. This migration is independent of whether the strain is induced mechanically or by CAFs. By comparing purely mechanical and purely chemical migration to a 3D co-culture of CAFs and HCT-116 containing both chemical and mechanical cues, it is concluded that HCT-116 migration is dominated by mechanical signaling, while chemical cues are less influential.