Mechanostimulation of integrin αvβ6 and fibronectin in DCISmyoepithelial cells
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Alterations to the tumour microenvironment is a common feature of many cancers, including breast cancer, and there is increasing evidence that alterations to the microenvironment, including; increased integrin expression, ECM deposition and protease activity, promote cancer progression. Most invasive breast cancers arise from a preinvasive stage, ductal carcinoma in situ (DCIS). Previous work in our laboratory has shown the microenvironment of DCIS is altered, such that myoepithelial cells (MECs) switch to a tumour-promoting phenotype, associated with upregulation of integrin αvβ6 and fibronectin (FN) expression. Mechanisms by which integrin αvβ6 and FN expression are regulated is unclear. We show DCIS progression into invasion is accompanied by an increase in MEC expression of integrin αvβ6 and periductal FN deposition, and their expression were associated in DCIS. These findings were modelled in isolated primary DCIS-MECs, primary normal MECs and MEC lines, with and without integrin αvβ6 expression, where integrin αvβ6-positive MECs upregulating FN expression. We identified integrin αvβ6-positive DCIS ducts were larger than integrin αvβ6-negative DCIS ducts, and mechanical stretching of primary normal MECs and a normal MEC line led to upregulation of integrin αvβ6 expression and FN deposition in a TGFβ-dependent manner. We further show upregulation of integrin αvβ6 and FN by MECs mediate TGFβ-dependent upregulation of MMP13 which promotes breast cancer cell invasion in vitro. These data show altered tissue mechanics in DCIS and MEC expression of integrin αvβ6 and FN deposition are linked, and implicate TGFβ in their activation. These findings suggest integrin αvβ6 and FN may be used as markers to stratify DCIS patients.
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