| Abstract: | We have examined the mechanism by which human epidermal keratinocytes adhere to the A/B1/B2 (α1β1γ1) form of laminin. Adhesion could be completely inhibited with an antibody to the β1 integrin subunit or a combination of antibodies recognising the α2β2 a3β1 and α6β4 integrins. Keratinocytes adhered in the presence of magnesium and manganese ions, but calcium ions did not support adhesion and inhibited adhesion when combined with magnesium and manganese. The effects of anti-integrin antibodies (including a stimulatory antibody to the β1 subunit) were not influenced by specific cations, with the exception that inhibition by an antibody to α2β1 was abrogated by the presence of manganese ions. The E3 and E8 proteolytic fragments of laminin did not support keratinocyte adhesion and heat inactivation of the E8 site in intact laminin did not reduce adhesion. Three laminin fragments that did support adhesion were P1, E4 and E1X-Nd, P1 activity being attributable at least in part to the RGD site; antibody blocking experiments suggested that adhesion to these fragments was primarily via α1β3. The synthetic peptide GD-6, derived from the carboxy terminus of the laminin A chain (included within E3) did support adhesion, but the significance of this observation is unclear, since a scrambled control peptide could also support adhesion. In conclusion, keratinocyte adhesion to A/B1/B2 laminin involves three integrins and multiple binding sites that are different from those defined previously. |
