Amino acids 1146-1148 of the integrin α1 tail control cell spreading, adhesion, and migration. (A) Schematic representation of the cytoplasmic truncation mutants of the human integrin α1 cDNA. (B) α1-null endothelial cells were transduced with either empty vector (α1KO) or the human integrin α1 mutant cDNAs indicated in panel A, and cell populations with equal levels of expression of the integrin α1 subunits were sorted by FACS using anti–human integrin α1 antibodies. (C) One millligram of total cell lysates of the cell populations indicated was immunoprecipitated with anti–human integrin α1 antibodies, subjected to SDS-PAGE, and immunoblotted with antibodies to either human integrin α1 or mouse β1 subunits. Equal loading was confirmed by analyzing the levels of total ERK in 40 μg total cell lysates. (D,E) Integrin α1KO endothelial cells expressing either the empty vector or cytoplasmic tail deletion mutants were plated in serum-free medium on 10 μg/mL collagen IV (D) or fibronectin (E). After 4 hours, the cells were fixed and stained with rhodamine-phalloidin. A representative cell is shown for each cell population. Bar represents 10 μm. (F,G) The cell populations were plated in serum-free medium on collagen IV at the concentrations indicated (F) or 10 μg/mL collagen IV with or without anti–human integrin α1 antibodies (10 μg/mL) (G) for 1 hour and their adhesion determined as described in “Cell adhesion.” Values are mean plus or minus SD of one representative experiment performed in quadruplicate. (H,I) The cell populations were plated on serum-free medium transwells coated with 10 μg/mL collagen IV with (▬) or without (▭) anti–human integrin α1 antibodies (10 μg/mL), and migration was evaluated 16 hours after plating. Values are mean plus or minus SD of one representative experiment performed in duplicate (5 fields/transwell were analyzed). Differences between α1KO and α1 mutant–expressing cells (*) and antibody-untreated versus-treated α1 mutant–expressing cells (**) were significant with P < .05.