Tyrosine phosphorylation of PDGF-Rα and downstream proteins in response to PDGF-CC. (A) Immunoprecipitation of equal amounts of PAEC/Rα extracts for PDGF-Rα and subsequent immunoblotting for pTyr, revealing a higher degree of PDGF-Rα tyrosine phosphorylation after 10-minute stimulation with PDGF-BB or -CC than with PDGF-AA. The lower panel shows an immunoblot of PDGF-Rα, displaying the amount of receptor present in each sample. (B) Immunoblotting of equal amounts of PAEC/Rα extracts for pTyr after stimulation with PDGF-AA, -BB, or -CC for 10 minutes, revealing that a similar set of proteins (judged on the basis of their molecular weight) was phosphorylated but that, in general, the phosphorylation signals were stronger in response to PDGF-BB and -CC than PDGF-AA. The lower panel shows an immunoblot of PDGF-Rα, displaying the amount of receptor present in each sample. For both A and B, though equal amounts of cell lysate were immunoprecipitated (A) and/or loaded (A and B), PDGF-Rα levels differed among the various lanes, presumably reflecting effects on receptor internalization and degradation. PDGF-Rα is present as a doublet due to differences in glycosylation.