Effects of mechanical stimulus on malignant-like behavior in breast epithelial cells

Abstract

Extracellular matrix (ECM) in the stromal compartment modulates the growth and differentiation of mammary epithelial cells during embryonic and postnatal development. ECM of high stiffness has been shown to induce normal breast epithelial cells to have malignant phenotype with enhanced focal adhesion formation and reorganized actin stress fibers. Since actin stress fibers are in charge of intracelluar tension, the internal tension built up by ECM stiffness is suggested as a key regulator that induced phenotypic changes in cells. To investigate the effects of externally applied mechanical tension on the phenotypic changes in normal breast epithelial cell line (MCF10A), we have developed a stimulator that applies cyclic uni-axial tensile stress on cells to induce internal tension build up inside cells. Upon 10%, 0.5Hz cyclic uni-axial tensile stimulation for 3 days, MCF10A showed significant increase in both mRNA and protein expression of matrix metalloproteinases-9(MMP-9), which is one of the key indicators for tumor invasion and metastasis. Using pharmacological inhibitor, Y-27632, Cytochalasin D and Latrunculin B, we show that actin polymerization is crucial for the uni-axial tensile stress induced regulation of MMP-9. We also observed significant increase in cellular motility, proliferation rate as well as irregular multilayer growth in cells that have been stimulated by uni-axial tensile stress. Our result may provide a key in understanding the role of cyclic tensile stress as an internal tension inducer, like in the case of stiff ECM, leading to malignant phenotypic changes in normal breast epithelial cells.