An in vitro correlation of metastatic capacity, substrate rigidity, and ECM composition.

The process of metastasis requires a metastatic cancer cell to invade a variety of micro-environments of variable stiffnesses. Unlike metastatic cells, normal cell function and viability is dependent on the stiffness of the environment and used as a cue to maintain cell health and proper tissue organization. In this study we have asked if metastatic cells can ignore the parameter of stiffness and if this ability is gradually acquired and if so, through what mechanism. Using a panel of mouse mammary tumor cells derived from the same parental tumor, but possessing different metastatic abilities, we cultured the cells on hard and soft substrates conjugated with collagen or fibronectin. Normal and non-metastatic tumor cells responded to changes in stiffness on fibronectin, but not collagen. However, the more metastatic cells ignored the change in stiffness on fibronectin-coated substrates. This lack of response on fibronectin correlated with a change in the expression level of the α3 integrin subunit, activation of the β1 subunit, and phosphorylation of FAKpY397. We conclude that through fibronectin, changes in the activation and tethering of the beta-1 integrin provides a mechanism for metastatic cells to disregard changes in compliance to survive and navigate in environments of different stiffness.