DISTINCT AND OVERLAPPING LIGAND SPECIFICITIES OF THE ALPHA-3A-BETA-1 AND ALPHA-6A-BETA-1 INTEGRINS - RECOGNITION OF LAMININ ISOFORMS

The ligand specificity of the alpha3Abeta1 integrin was analyzed using K562 cells transfected with full-length alpha3A cDNA and was compared with that of alpha6Abeta1 in similarly transfected K562 cells. Clones were obtained that showed comparable surface expression of either alp ha3Abeta1 or alpha6Abeta1 integrins. Those expressing alpha3Abeta1 att ached to and spread on immunopurified human kalinin and cellular matri ces containing human kalinin, which is a particular isoform of laminin . In addition, alpha3A transfectants adhered to bovine kidney laminins possessing a novel A chain variant. Binding to kalinin was blocked by a monoclonal antibody against the A chain constituent of kalinin and adhesion to both kalinin and kidney laminins by anti-alpha3 and beta1 monoclonal antibodies. The alpha3A transfected cells bound more strong ly to kalinin and bovine kidney laminins after treatment with the beta 1 stimulatory antibody TS2/16. A distinctly weaker and activation-depe ndent adhesion of alpha3A transfectants was observed on human placenta l laminins possessing the Am chain variant (merosin), and no adhesion occurred on bovine heart laminins and murine EHS tumor laminin. Furthe r inactive substrates were fibronectin, nidogen, and collagen types IV and VI, indicating that the alpha3Abeta1 integrin is a much less prom iscuous receptor than thought before. By contrast, alpha6A transfected cells adhered to all laminin isoforms when stimulated with TS2/16. Ad hesion also occurred only on bovine kidney laminins in the absence of TS2/16. These results demonstrate that both alpha3Abeta1 and alpha6Abe ta1 integrins are typical laminin receptors but that their affinity an d activation dependence for binding to various laminin isoforms differ considerably.