THE ALPHA-6-BETA-4 INTEGRIN IS A RECEPTOR FOR BOTH LAMININ AND KALININ

Previously, we have established K562 transfectants that express either alpha 6A beta 1 or alpha 6B beta 1 (K alpha 6A or K alpha 6B) on thei r surface. Both cell lines bind to laminin and kalinin after treatment with the beta 1-stimulatory antibody TS2/16. Here we introduce the fu ll-length beta 4 cDNA into the alpha 6A- and alpha 6B-expressing K562 cells and selected stably transfected cells. The beta 4 subunit was ex pressed on the surface of both transfectants and it formed dimers with the alpha 6A or alpha 6B subunits. Immunoprecipitation and preclearin g analyses revealed that both transfectants expressed alpha 6 beta 1, in addition to alpha 6 beta 4. While K alpha 6A and K alpha 6B cells r equired TS2/16 stimulation for binding to laminin or kalinin, adhesion of the unstimulated beta 4-transfected K alpha 6A and K alpha 6B cell s to these matrix components was already substantial. This adhesion wa s mediated by both alpha 6 beta 1 and alpha 6 beta 4 since it was comp letely blocked by an alpha 6-specific antibody or by a combination of anti-beta 1 and anti-beta 4 antibodies, but only partially by either o f these latter two antibodies alone. Adhesion to laminin was completel y blocked by an antiserum to laminin fragment E8 as was the adhesion t o kalinin by an antibody to kalinin, demonstrating the specificity of adhesion. Both transfectants always adhered more strongly to kalinin t han to laminin. Furthermore, binding to kalinin was less well blocked by antibodies to beta 4 than binding to laminin, indicating that the a ffinity of alpha 6 beta 4 for kalinin is higher than that for laminin. The fact that alpha 6 beta 1 mediated adhesion without TS2/16 stimula tion on the beta 4-transfected K alpha 6A and K alpha 6B cells suggest s that some activation of alpha 6 beta 1 had occurred in these cells, even though binding was increased when they were actively stimulated b y the antibody TS2/16. Finally, we show that Mn2+ induced binding of s olubilized alpha 6 beta 4 to matrix containing kalinin, deposited by t he murine cell line RAC-11P/SD. This binding was inhibited by the anti -alpha 6 mAb GoH3. Together, these results indicate that both alpha 6 beta 1 and alpha 6 beta 4 are receptors for laminin and kalinin and th at there are no differences in ligand specificity between the A and B variants of the alpha 6 subunit when associated with either beta 1 or beta 4. (C) 1994 Academic Press, Inc.