Figure. 1.

β₁ integrin expression is essential for prostate tumor growth. A (left panel), PC3, PC3-β₁-shRNA or PC3-vector cells were injected s.c. in nude mice. Two groups of mice were also injected with PC3-β₁-shRNA or PC3-vector cells in the presence of Matrigel. The graph shows kinetics of tumor growth. Tumor growth was measured up to 26 days and is expressed as tumor volume in mm³. The difference in tumor volume between cells transfected with vector or β₁ shRNA from 14 to 26 days after injection are statistically significant (*p≤0.0001). A (right panel), PC3-β₁-shRNA or PC3-vector cells were lysed and immunoblotted using Ab to β₁ or ERK1. These experiments were repeated twice with similar results. B-C, PC3 transfectants expressing chimeric exogenous (exo) β_1A (chicken extracellular and human intracellular) were transfected with β₁ siRNA (siRNA sequence R2), to downregulate endogenous (endo) β₁, or with control siRNA (100 nM). Cells were cultured in the presence or in the absence of tet and injected s.c. in nude mice. Cells express one of the following four combinations of β₁: both endo and exo (Cont-siRNA, -tet); endo only (Cont-siRNA, +tet); exo only (β₁-siRNA, -tet); none of the two (β₁-siRNA, +tet). The graphs show kinetics of tumor growth, measured as described above. *p≤0.0001 from 14 to 26 days after injection (B). Data are the mean ± SEM obtained using 11 animals (A) or 5 animals (B). Cells transfected with β_1A siRNA (siRNA sequence R2) or control siRNA were cultured in the absence of tet. Cells were processed for FACS analysis to determine the expression of endo (human) and exo (chimera) β₁ using Ab to human β₁ (TS2/16, thin black line), to chicken β₁ (W1B10, thick black line) or as a negative control, 12CA5 (filled grey) (C).