Identification of a cell-surface protein involved in PC12 cell-substratum adhesion and neurite outgrowth on laminin and collagen.

On substrata coated with laminin or native collagen (Types I/III), PC12 cells employ an active adhesion mechanism (i.e., one inhibited at low temperature, by azide or in the absence of divalent cations) to attach and extend neurites; on substrata coated with wheat germ agglutinin (WGA) or polylysine, by contrast, PC12 cells attach via a passive mechanism and fail to extend neurites (Turner et al., 1987). This paper reports the isolation of 2 monoclonal antibodies (3A3 and 1B1) that promote retraction of neurites extended on laminin and collagen. In studies of initial cell attachment, 3A3 inhibited active attachment to laminin or collagen but not passive attachment to WGA or polylysine, whereas 1B1 inhibited both active and passive attachment. The more potent of the antibodies, 3A3, precipitates 2 radioactive protein bands (of approximately 185 and 125 kDa) from 1% Nonidet P-40 extracts of metabolically labeled PC12 cells. The properties of these proteins suggest that the antigen recognized by 3A3 is a member of the integrin family of matrix receptors. The other monoclonal antibody, 1B1, reacts with many PC12 proteins, including both bands precipitated by 3A3. The available data strongly suggest that an integrin with specificity for both laminin and collagen mediates PC12 adhesion to the substratum at both the cell body and the neurite growth cone.