Fig. 4. PTP1B is essential for effective fibronectin-induced CrkII dephosphorylation. (A) 293-EBNA cells were co-transfected with siRNA (2x10^-11 or 2x10^-10 mol) for either PTP1B or ß-actin and pRK-GFP and pcDNA3 plasmids. The cells were homogenized at 36 hours after transfection and immunoblotted with anti-PTP1B (Blot: PTP1B) or anti-actin (Blot: actin) antibodies. (B) 293-EBNA cells were co-transfected with siRNA for PTP1B, and pRK-GFP and pcDNA3 plasmids. At 36 hours after transfection, cells were trypsinized, kept in suspension for 20 minutes, and replated onto culture dishes coated with 10 µg/ml fibronectin for 30 or 120 minutes. The cells were homogenized and immunoblotted with anti-PTP1B (Blot: PTP1B), anti-Crk (Blot: Crk) or anti-GFP (Blot: GFP) antibodies.