The effects of chronic EGF exposure on expression of the ␣ 2  1 collagen and ␣ 5  1 fibronectin receptor in a pair of human carcinoma cell lines (A431 and A549) with differential responses to EGF in a short-term ECM-cell adhesion assay were investigated. Treatment with EGF at 10 ng/ml for 24 hr increased on both cell lines the expression of the ␣ 2 -but not the  1 -or ␣ 5 -integrin sub-units, and concomitantly cellular adhesion was increased on collagen IV but not on fibronectin.
Increased collagen adhesion of A549 cells could be blocked by
␣ 2 -and  1 -integrin-sub-unit antibodies down to control levels, while it was blocked by ␣ 2 -integrin-sub-unit antibody only by 60% and completely by the  1 -integrin-sub-unit antibody on A431 cells. EGF induced disparate shifts in cell morphologies (dome-like structures, A431, vs. spindle-like fibroblastoid, A549) with concomitant opposite changes in the expression/ localization of E-cadherin in cell-cell contacts. This could be taken as an indication for cell-type-specific differential changes in the ratio of cell-ECM vs. cell-cell contacts. The EGFinduced up-regulation of the ␣ 2  1 integrin was instrumental in increasing collagen adhesion of A549 but only partly in the case of A431 cells, in which cells the ␣ 2  1 integrin may have additional functions besides serving as cell-ECM receptor. Int.