Mutation of a protein kinase C phosphorylation site in the erbB protein of avian erythroblastosis virus

Tumor promoter-stimulated phosphorylation of threonine 98 of the erbB protein of avian erythroblastosis virus (AEV) correlates with inhibition of erbB-dependent mitogenesis. To more clearly define the role of phosphorylation of this residue in regulation of the activity of the erbB protein, the authors have constructed erbB mutations which encode alanine (Ala-98), tyrosine (Tyr-98), or serine (Ser-98) at position 98. The biosynthesis and stability of the three mutant proteins were similar to those of the wild-type erbB protein, and all three retained the ability to transform chicken embryo fibroblasts. Treatment of transformed CEF with 12-tetradecanoylphorbol-13-acetate (TPA) stimulated incorporation of 32P/sub i/ into wild-type and mutant erbB proteins and resulted in a slight decrease in the electrophoretic mobilities of all the erbB proteins. Cells transformed by wild-type and mutant AEV were equally sensitive to TPA-dependent inhibition of growth in soft agar and TPA-dependent inhibition of [3H]thymidine incorporation. These data indicate that phosphorylation of threonine 98 of the erbB protein is not responsible for TPA-dependent inhibition of growth of AEV-transformed cells or TPA-induced inhibition of erbB-dependent tyrosine phosphorylation. TPA-stimulated phosphorylation of the erbB protein at any other sites may mediate these effects. The data also show that subtle changes in a phosphorylation site drastically alter recognition by protein kinases