α₅β₁ primarily mediates cell adhesion in MigR1 and MigP210^BCR-ABL cells, though α₅β₁ and α₄β₁ are present at similar levels on 32D cells. (A) Three populations of 32D cells expressing MigR1 and 2 populations of MigP210^BCR-ABL cells were assessed for the level of integrin expression. Cell populations were transduced independently and subsequently stained in triplicate without selection. Cells stained with the secondary phycoerythrin-conjugated antibody alone are shown as negative controls. Representative histograms are shown for a single population, and the average mean fluorescence index (MFI)¹³  for all populations and standard deviations determined by a propagation of error are also indicated. Significant differences in α₄ expression are observed neither between MigP210^BCR-ABL GFP⁺ and MigR1 GFP⁺ cells (P = .13) nor between MigP210^BCR-ABL GFP^– and GFP⁺ cells (P = .26, not shown). Likewise, significant differences in α₅ expression are observed neither between MigP210^BCR-ABL GFP⁺ and MigR1 GFP⁺ cells (P = .13) nor between MigP210^BCR-ABL GFP^– and GFP⁺ cells (P = .09, not shown). (B) The ability of MigR1 cells to bind fibronectin was determined by leaving cells untreated (No treatment) or treating cells with a control Rat immunoglobulin G (IgG) antibody, a monoclonal antibody directed against the fibronectin-binding region of α₄β₁ (anti-α₄), a monoclonal antibody directed against the fibronectin-binding region of α₅β₁ (anti-α₅), both antibodies (anti-α₄ + α₅), or untreated cells incubated on coverslips coated without fibronectin (BSA only). The percentage change in critical shear stress is relative to that of untreated cells. (C) MigP210^BCR-ABL 32D cells were treated with the same anti-integrin antibodies as in panel B. Additionally, MigP210^BCR-ABL cells were treated with 1 μM cytochalasin D (CyD), which abrogates cell adhesion to levels that are comparable to coverslips coated with BSA only. NSD indicates not significantly different.