The basement membrane protein laminin (LM)-511 is highly expressed in triple negative breast cancers (TNBC) and its expression correlates with disease progression in patients. It promotes adhesion and migration through ligation of α3β1 and α6β4 integrin receptors, however, direct evidence of its functional contribution to metastasis in vivo is lacking. Here we use a gene knockdown approach to stably suppress LM-511 expression in the highly metastatic MDA-MB-231HM human carcinoma cells and demonstrate for the first time that the loss of tumour LM-511 dramatically impairs spontaneous metastasis to lung and bone and significantly reduces the incidence of circulating tumour cells (CTCs). Moreover, we show that cells lacking LM-511 lose cell-matrix interactions and are more susceptible to anoikis. Additionally, down regulation of the β4 integrin significantly reduced 4T1BM2 spontaneous and experimental metastasis to bone and invasion and colony formation in vitro, indicating that LM511/β4 interactions may be required for invasion and survival in bone.
Suppression of LM-511 expression in 4T1BM2 or MDA-MB-231HM cells induced morphological and functional changes suggestive of a Mesenchymal to Epithelial Plasticity (MEP). Using western blot analysis, we show that loss of LM-511 is associated with classical features of Mesenchymal to Epithelial Plasticity (MEP), including increased E-cadherin and reduced N-cadherin, SNAIL1, Vimentin, ZEB1, ZEB2, and TWIST1.
Furthermore, we demonstrate that blockade of integrin signaling using a disintegrin (Lebein-1) results in increased chemosensitivity to standard therapies by 10-fold. Collectively, our data demonstrates that LM-511 and its integrin β4 receptor are potential therapeutic targets for the treatment of advanced TNBC patients.