Abstract A58: Cell motility in a basement membrane gel concentrates ECM around breast epithelial cells, a feature lost in malignant cells

Introduction: The basement membrane (BM) underlying epithelial cells plays a key role in regulating cell function and suppressing malignancy; loss of this layer of ECM proteins is a hallmark of invasive cancer. Using 3D extracellular matrix (ECM) gels, we sought to understand how this structure develops by comparing nonmalignant breast epithelial cells (BEC), which develop into polarized, growth arrested structures to malignant breast cancer cells (BCC), which form disorganized masses under the same conditions. These two cell types show different movement patterns in the ECM gels: BEC rotate around their center of mass in a process termed coherent angular motion, whereas BCC migrate randomly, with unknown consequences for assembly of ECM into a basement membrane-like layer. We investigated whether coherent angular motion could concentrate exogenous ECM into a BM like structure, and whether these changes were due to the physical forces applied by the cells on their microenvironment. Methods: To determine if cells undergoing coherent angular motion were better able to concentrate exogenous ECM at their surface compared to malignant cells, single human BEC and BCC from the HMT3522 breast cancer progression series were cultured in fluorescent laminin rich ECM gels (LrECM; using BD Matrigel), and ECM density at the cell surface was measured during growth with confocal microscopy. To determine how motility translated into forces on the microenvironment, cells were embedded in lrECM labeled with a dilute suspension of fluorescent microbeads. Confocal microscopy was performed over the first several days of culture, and traction force microscopy was used to determine the magnitude and spatial pattern of forces applied by the cells. After 5-6 days of culture, cells stained to determine whether cells had developed into polarized structures. Results: Over the first several days of culture, non-malignant BEC rotated as a coherent mass. At 24 hours, labeled ECM proteins were observed to concentrate in a spherical shell on surface of rotating clusters of BEC, whereas malignant, non-rotating cell masses had lower levels of ECM at the surface of the mass and higher levels of ECM proteins between the cells. Traction patterns between rotating and non-rotating cell masses were observed to differ- cells undergoing random motility applied strains to the ECM along the line of invasion, whereas cells undergoing coherent angular motion showed shear strains at the cell surface and even inward tractions. Conclusions: Coherent angular motion appears to affect concentration of exogenous ECM by physically pulling ECM proteins into an organized shell at the cell surface as an early aspect of formation of a basement membrane-like ECM structure in mammary epithelial cells in culture whereas this process is defective in malignant cells undergoing random motility. Further investigation will determine whether this process of motility, physically altering ECM density, is seen during normal development. Citation Format: Claire Robertson, Mina J. Bissell. Cell motility in a basement membrane gel concentrates ECM around breast epithelial cells, a feature lost in malignant cells. [abstract]. In: Proceedings of the AACR Special Conference on Engineering and Physical Sciences in Oncology; 2016 Jun 25-28; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2017;77(2 Suppl):Abstract nr A58.