Reduced functional activity in β1 integrin knockdown cells: (A): Adhesion assay of β1 integrin knockdown MCF-7-MT1 cells for Col I. (B): MDA-MB-231 cells were transfected with the indicated siRNAs. At appropriate time points, cell lysates were collected for analysis of β1 integrin levels by Western blot. (C): Collagen gel contraction by MDA-MB-231 cells after transfection with β1/4, β1/5, β1/6 and control siRNAs. 24 hours after transfection, collagen gels were made at 2 mg/ml and the cells resuspended to a final concentration of 4 × 105 cell/ml. Gels were polymerized and then the gels were released. The relaxed, floating gels were immersed in 1 ml medium with 10% FCS. The gel diameters were measured daily for 5 days. Collagen gel contractions were calculated as mean values in relation to the gel diameters before releasing, as shown in (D). Collagen gel contractions were performed in triplicate independently and mean percent of collagen gel contraction was compared using Student’s t-test.