Figure 6.

Cell adhesion to ECM proteins is not required for β₁ effect on β₃ mRNA steady-state level. GD25-β₁TR and GD25-β₁COM cells were cultured to confluence in complete culture medium. Cells were then resuspended in serum-free medium containing 1 μM monensin and allowed to attach and spread on polylysine- (PL), FN-, or vitronectin (VN)-coated tissue culture dishes for 2 h at 37°C before lysis. Total RNA was isolated as described in MATERIALS AND METHODS, and equal amounts (25 μg/lane) were analyzed for β₃ mRNA steady-state level by Northern blot hybridization with the use of ³²P-labeled mouse integrin β₃ cDNA fragments as probe. Equal loading was confirmed by hybridization of the same blot with a ³²P-labeled probe for β-actin. The positions of 28s and 18s rRNAs are indicated as markers for RNA sizes. Notice that the β₃ mRNA steady-state level is constitutively low in GD25-β₁COM compared with that of GD25-β₁TR cells.