Mammary epithelial cell interactions with fibronectin stimulate epithelial-mesenchymal transition

Abstract

In the mammary gland, the stromal extracellular matrix (ECM) undergoes dramatic changes during development and in tumorigenesis. For example, normal adult breast tissue is largely devoid of the ECM protein fibronectin (FN) whereas high FN levels have been detected in the stroma of breast tumors. FN is an established marker for epithelial-mesenchymal transition (EMT), which occurs during development and has been linked to cancer. During EMT, epithelial cell adhesion switches from cell-cell contacts to mainly cell-ECM interactions raising the possibility that FN may have a role in promoting this transition. Using MCF-10A mammary epithelial cells, we show that exposure to exogenous FN induces an EMT response including up-regulation of the EMT markers FN, Snail, N-cadherin, vimentin, the matrix metalloprotease MMP2, α-smooth muscle actin, and phospho-Smad2 as well as acquisition of cell migratory behavior. FN-induced EMT depends on Src kinase and ERK/MAP kinase signaling but not on the immediate early gene EGR-1. FN initiates EMT under serum-free conditions; this response is partially reversed by a TGFβ neutralizing antibody suggesting that FN enhances the effect of endogenous TGFβ. EMT marker expression is up-regulated in cells on a fragment of FN containing the integrin-binding domain but not other domains. Differences in gene expression between FN and MG are maintained with addition of a sub-threshold level of TGFβ1. Together, these results show that cells interacting with FN are primed to respond to TGFβ. The ability of FN to induce EMT shows an active role for the stromal ECM in this process and supports the notion that the increased levels of FN observed in breast tumors facilitate tumorigenesis.

Molecular alterations that drive breast cancer metastasis to bone

“…In addition, exogenous fibronectin is able to induce EMT under serum-free conditions; this process could be reversed following addition of a TGF-b-neutralising antibody. 45 These data suggest that fibronectin can induce EMT in breast cancers by enhancing the activity of endogenous TGF-b.…”

CD151 represses mammary gland development by maintaining the niches of progenitor cells

“…1-3), we evaluated the impact of CD151 removal on integrin-mediated cell-ECM interactions, as they are consistently implicated in driving the formation of lobuloalveolar structures during mammary gland development. 35,36 As shown in Figure 4A, expression of fibronectin, and to a lesser extent, tenascin C, exhibited a marked increase in mammary tissues upon CD151 removal. Also, the expression of fibronectin in TEBs was markedly elevated (Fig.…”

“…[36][37][38] We therefore evaluated changes in the expression of EMTinducing transcription factors upon CD151 removal, particularly Snail and Slug, which have been previously linked to CD151 function as well as the dynamics of mammary epithelial stem/ progenitor cells or mammary gland development. 39,40 As shown in Figure 6A, expression of Slug, but not Snail, increased more than 3-fold at the protein level in the absence of CD151.…”

Function of cancer cell-derived extracellular matrix in tumor progression

“…[8,17] Fibronectin, a marker of epithelialmesenchymal transition, enhances cancer metastasis through Src kinase and extracellular signal-regulated kinase/mitogen-activated protein kinase pathway. [55] Hyaluronan expression is upregulated in breast cancer, lung cancer, pancreatic cancer, melanoma cancer, and myeloma cancer. [22,23,27] Upregulation of hyaluronan is also associated with tumor progression and poor prognosis.…”