Fig. 4. Gab1 tyrosine phosphorylation and association with SHP2 and Grb2 correlate with the enhanced growth phenotype. SHP2 (A) or Gab1 (B) was immunoprecipitated (IP) from lysates of HDFs expressing no (control) or the indicated viral oncoprotein. Immunoprecipitates were subjected to immunoblotting for Gab1, SHP2, Grb2 or phosphotyrosine (PY) as indicated. For the graphs shown below representative blots, the relative band intensities for the Gab1 and Grb2 blots in A, and the PY and Grb2 blots in B were quantitated using the Image J program and normalized for SHP2 (A) or total Gab1 (B) amounts. These normalized values are expressed as a percentage relative to the amount of co-immunoprecipitation or PY-Gab1 observed in the wild-type E5-expressing HDFs. The mean values from two different experiments with standard error are shown.