FIGURE 4. Acute effect of Grb2 knock-down on basal cell growth rate.

COS7^WT and COS7^shControl versus COS7^shGrb2, proliferation curve and response to EGF. A, COS7^shControl and COS7^shGrb2 were plated in the presence of 1 mg/ml neomycin at a density of 1-5 cells/well. Cell number was monitored during the indicated times by counting at least 3 different colonies in 6 different wells in the 100X field. When COS7^shControl cells reached confluency, neomycin was withdrawn from three of the six wells of COS7^shGrb2 (indicated by an upside down vertical arrow). Results are expressed as cell number directly counted in 3-6 100X fields ± SEM. B, [³H] thymidine incorporation. De novo DNA synthesis in COS7^WT, COS7^shControl and COS7^shGrb2 (in the presence or absence of neomycin, or transfected with pcDNA-XGrb2^SiL) was estimated under basal conditions. Cells were incubated with 1 μCi/ml overnight. TCA-precipitable [³H]-DNA was counted (%controls)