Tyrosine phosphorylation of the SH2-containing proteins PLCγ, Shc and p89/90 (FRS2) and associated proteins following activation of PFR1, -3, and -4 by PDGF. (A) Tyrosine phosphorylation of immunoprecipitated PLCγ before (−) and after (+) stimulation at 37°C for 10 min with PDGF (30 ng/ml). Upper, immunoblot with anti-phosphotyrosine (αPY); Lower, immunoblot, after stripping and reprobing, with an anti-PLCγ. (B) Tyrosine phosphorylation of immunoprecipitated Shc and its association with Sos and Grb2 after stimulation of PC12 cells at 37°C for 5 min with PDGF (30 ng/ml). Top, immunoblot with anti-Sos; Middle, immunoblot with anti-phosphotyrosine; Bottom, immunoblot with anti-Grb2. (C) Tyrosine phosphorylation of p89/90 (FRS2) and its association with Sos and Grb2 after stimulation of PC12 cells at 37°C for 5 min with PDGF (30 ng/ml). Lysates (PFR1 and PFR3, 2 mg, and PFR4, 3 mg) were treated with recombinant p13Suc agarose to precipitate the proteins. Top, immunoblot with anti-Sos; Middle, immunoblot with anti-phosphotyrosine; Bottom, immunoblot with anti-Grb2. The arrows indicate the tyrosine-phosphorylated polypeptides of 110, 66, 64, and 43 kDa, which coprecipitate with the FRS2-phosphorylated protein.