Fibronectin fragments induce MMP activity in mouse mammary epithelial cells: evidence for a role in mammary tissue remodeling

Abstract

Mammary gland form and function are regulated by interactions between epithelium and extracellular matrix. Major glycoprotein components of extracellular matrix have been identified that give survival, proliferation and differentiation signals to mammary epithelial cells. We provide evidence that proteolytic fragments of the extracellular matrix glycoprotein, fibronectin, suppress growth and can promote apoptosis of mouse mammary epithelial cells. During mammary gland involution, total fibronectin and fibronectin fragment levels are increased. The peak levels of fibronectin protein and fragments are observed 4–6 days post-weaning, coincident with the peak in epithelial cell death. Using a model for hormone withdrawal-induced death of mammary epithelium, elevated levels of fibronectin proteolytic fragments were associated with apoptosis in TM-6 cells, a tumorigenic mouse mammary epithelial cell line. Treatment of TM-6 cells with exogenous fibronectin fragments (FN120) reduced cell number, and induced apoptosis and matrix degrading protease activity. Inhibition of matrix protease activity rescued TM-6 cell viability, indicating that FN120-induced cell loss is mediated through matrix protease activity. In a three-dimensional model for mammary gland development, FN120 reduced alveolar-like and promoted ductal-like development by a matrix protease-dependent mechanism. These data suggest that during post-lactational involution, fibronectin fragments may contribute to epithelial cell loss and dissolution of mammary alveoli by inducing matrix degrading proteinases.

Activation and Inhibition of Human Matrix Metalloproteinase-9 (MMP9) by HOCl, Myeloperoxidase and Chloramines

“…HOCl-modified HSA also modulates immune-cell function (reviewed [ 3 , 6 , 70 ]), with exposure to the modified protein reported to elevate oxidant formation by stimulating neutrophil activation and degranulation at sites of inflammation [ 71 , 72 ]. Other studies have reported that fibronectin fragments (potentially arising from oxidant or enzymatic degradation) and cryptic domains in the α1-chain of laminin-1 exposed by structural changes can induce cellular MMP expression [ 73 , 74 ]. Thus, oxidant formation can result in a feed-forward loop (“vicious cycle”) of increasing MMP expression, release, activation, ECM damage and further activation cycles, with this driven by the synergistic effects of oxidant formation, MMP activation and the further proteolysis of additional proMMP by the oxidant-activated enzyme ( Figure 12 ).…”

Identification of a gene regulatory network associated with prion replication

“…Transmembrane receptor proteins of the integrin family mechanically couple the actin cytoskeleton to the ECM by binding to Fn1 and other adhesion molecules, such as collagen and vitronectin. A convincing body of evidence suggests that MMP activation and expression is triggered by interaction of the cell adhesion molecule Fn1 or its proteolytic fragments with integrins (Esparza et al, 1999;Schedin et al, 2000;Yan et al, 2000;Thant et al, 2001;Forsyth et al, 2002;Loeser et al, 2003;Jin et al, 2011). This interaction can be inhibited by the RGD peptide (Koivunen et al, 1995), a tripeptide domain located in the 10th type-III module of Fn1 and site of cell attachment via b1 integrins.…”

Rat Mammary Extracellular Matrix Composition and Response to Ibuprofen Treatment During Postpartum Involution by Differential GeLC–MS/MS Analysis

“…During postpartum involution, significant remodeling occurs in the ECM. , Differential ECM protein synthesis occurs in various cells within the organ and several secreted proteases become activated resulting in active matrix remodeling. ,, ECM can be biochemically isolated from the mammary gland and utilized both in vitro and in vivo to assess effects on tumor cell behavior . ECM isolated from actively involuting mammary glands consistently promotes an invasive tumor cell phenotype in 3D culture assays and tumor growth and metastasis in xenograft tumor models when compared to ECM isolated from nulliparous rats. ,, However, ECM isolated from mammary glands of rats treated with ibuprofen during involution demonstrated reduced tumor promoting attributes; phenocopying mammary ECM from the nulliparous rather than the involuting gland .…”

“…20,21 Differential ECM protein synthesis occurs in various cells within the organ and several secreted proteases become activated resulting in active matrix remodeling. 15,22,23 ECM can be biochemically isolated from the mammary gland and utilized both in vitro and in vivo to assess effects on tumor cell behavior. 24 ECM isolated from actively involuting mammary glands consistently promotes an invasive tumor cell phenotype in 3D culture assays and tumor growth and metastasis in xenograft tumor models when compared to ECM isolated from nulliparous rats.…”