THE ALPHA-1/BETA-1-INTEGRIN AND ALPHA-6/BETA-1-INTEGRIN HETERODIMERS MEDIATE CELL ATTACHMENT TO DISTINCT SITES ON LAMININ

This study was undertaken to determine the roles of individual α/β1 integrin heterodimers in promoting cellular interactions with the different attachment-promoting domains of laminin (LN). To do this, antibodies to the integrin β1 subunit or to specific integrin α subunits were tested for effects on cell attachment to LN, to elastase fragments E1-4 and E1, derived from the short arms and core of LN's cruciform structure, and to fragment E8 derived from the long arm of this structure. The human JAR choriocarcinoma cells used in this study attached to LN and to fragments E1 and E8. Attachment to E1-4 required a much higher substrate coating concentration, suggesting that it is a poor substrate for JAR cell attachment. The ability of cells to attach to different LN domains suggested the presence of more than one LN receptor. These multiple LN receptors were shown to be β1 integrin heterodimers because antibodies to the integrin β1 subunit inhibited attachment of JAR cells to LN and its three fragments. To identify the individual integrin α/β1 heterodimers that mediate interactions with these LN domains, mAbs specific for individual β1 heterodimers in human cells were used to study JAR cell interactions with LN and its fragments. An anti-α6/β1-specific mAb, GoH3, virtually eliminated cell attachment to E8 and partially inhibited attachment to E1 and intact LN. Thus the major α6/β1 attachment domain is present in fragment E8. An α1/ β1-specific mAb (S2G3) strongly inhibited cell attachment to collagen IV and partially inhibited JAR attachment to LN fragment E1. Thus, the α1/β1 heterodimer is a dual receptor for collagen IV and LN, interacting with LN at a site in fragment E1. In combination, the anti-α1- and anti-α6-specific antibodies completely inhibited JAR cell attachment to LN and fragment E1. Thus, the α1/β1 and α6/β1 integrin heterodimers each function as LN receptors and act together to mediate the interactions of human JAR choriocarcinoma cells with LN.