A 110-KD NUCLEAR SHUTTLING PROTEIN, NUCLEOLIN, BINDS TO THE NEURITE-PROMOTING IKVAV SITE OF LAMININ-1

The basement membrane protein laminin and the IKVAV-containing sequenc e from the laminin al chain have been found to promote the differentia tion of primary neurons and a variety of neural cell lines, We previou sly reported that a 110-kd IKVAV-binding protein (LBP110) isolated fro m brain appears to be a member of the beta-amyloid precursor protein ( APP) family by immunologic and functional studies, which showed that L BP110/APP is also important in neurite outgrowth (Kibbey et al.: Proc Natl Acad Sci USA 90:10150-10153, 1993), In the preparation of this bi nding protein, a contaminating IKVAV-binding protein of identical mole cular weight, nucleolin, was also identified, Here we have studied the relationship between these binding proteins, We find that nucleolin b inds specifically to the IKVAV sequence independently of LBP110/APP, W e have also demonstrated significant levels of nucleolin in mature bra in and in differentiating neural cells, suggesting that nucleolin func tions not only in cell proliferation and in ribosome biogenesis as was previously reported, but also in the differentiation and maintenance of neural tissue, Our identification of cytoplasmic and cell-surface n ucleolin, an IKVAV-binding protein, suggests that this protein may fun ction in signalling by extracellular matrix. (C) 1995 Wiley-Liss, Inc.