LAMININ-INDUCED RETINOBLASTOMA CELL-DIFFERENTIATION - POSSIBLE INVOLVEMENT OF A 100-KDA CELL-SURFACE LAMININ-BINDING PROTEIN

Gene and protein expression of Y-79 retinoblastoma cells growing on poly(D-lysine) is switched from a photoreceptor-like to a conventional neuron-like pathway by the basement membrane glycoprotein laminin. Unlike other cell systems where laminin influences differentiation, Y-79 cells can neither attach to nor chemotactically respond to laminin. However, laminin increases attachment to poly(D-lysine). The laminin effects therefore seem to occur via an adhesion- and chemotaxis-independent mechanism. Moreover, these tumor cells do not exhibit high-affinity laminin binding, having only a single binding site of intermediate affinity. Laminin-Sepharose affinity chromatography of Y-79 cell surface proteins labeled with I-125 revealed a single major radiolabeled 100-kDa protein eluted by 20 mM EDTA, with an electrophoretic behavior different from that of integrins. No other proteins were eluted under more stringent conditions. This material, which we call LBM-100 (100-kDa laminin-binding molecule), may be a "differentiative" laminin-binding protein through which laminin influences gene expression and development independently of attachment.