In this study, we used clone A, a human colon
carcinoma cell line, to characterize those
integrins that mediate colon
carcinoma adhesion to
laminin.
Monoclonal antibodies specific for the human beta 1 subunit inhibited clone A adhesion to
laminin. They also precipitated a complex of
surface proteins that exhibited an electrophoretic behavior characteristic of alpha 2 beta 1 and alpha 3 beta 1. A
monoclonal antibody specific for alpha 2 (PIH5) blocked clone A adhesion to
laminin, as well as to
collagen I. An alpha 3-specific antibody (P1B5) had no effect on clone A adhesion to
laminin, even though it can block the adhesion of other cell types to
laminin. Thus, the alpha 2 beta 1
integrin can function as both a
laminin and
collagen I receptor on clone A cells. Although these cells express alpha 3 beta 1, an established
laminin receptor, they do not appear to use it to mediate
laminin adhesion. In addition, the
monoclonal antibody GoH3, which recognizes the
alpha 6 integrin subunit, also inhibited
carcinoma adhesion to
laminin but not to
fibronectin or
collagen I. This antibody precipitated the alpha 6 subunit in association with the beta 4 subunit. There was no evidence of alpha 6 beta 1 association on these cells. In summary, the results obtained in this study indicate that multiple
integrin alpha subunits, in association with two distinct beta subunits, are involved in colon
carcinoma adhesion to
laminin. Based on the behavior of alpha 3 beta 1 and alpha 2 beta 1, the results also suggest that cells can regulate the ability of a specific
integrin to mediate adhesion.