The microstructure of laminin-111 compensates for dystroglycan loss in functional differentiation of mammary epithelial cells

Abstract: Laminin-111, an extracellular matrix (ECM) glycoprotein found in the basement membrane of mammary gland epithelia, is essential for lactation. In mammary epithelial cells, dystroglycan (Dg) is believed to be necessary for polymerization of laminin-111 into networks, thus we asked whether correct polymerization could compensate for Dg loss. Artificially polymerized laminin-111 and the laminin-glycoprotein mix Matrigel, both formed branching, spread networks with fractal dimensions from 1.7-1.8, whereas laminin-111 in media formed small aggregates without fractal properties (a fractal dimension of 2). In Dg knockout cells, either polymerized laminin-111 or Matrigel readily attached to the cell surface, whereas aggregated laminin-111 did not. In contrast, polymerized and aggregated laminin-111 bound similarly to Dg knock-ins. Both polymerized laminin-111 and Matrigel promoted cell rounding, clustering, formation of tight junctions, and expression of milk proteins, whereas aggregated Ln-1 did not attach to cells or promote functional differentiation. Highlights Laminin assembles into a fractal network when in presence of either the cell surface receptor dystroglycan or acidic glycoproteins or an acidic buffer. When this microstructure is recreated with an acidic treatment, laminin binds readily to dystroglycan null cells and induces functional differentiation of mammary epithelial cells.