Regulation of transferrin receptor cycling by protein kinase C is independent of receptor phosphorylation at serine 24 in Swiss 3T3 fibroblasts.
Treatment of Swiss 3T3 fibroblasts with tumor-promoting phorbol diester or with platelet-derived growth factor caused the phosphorylation of the transferrin receptor by protein kinase C (Ca2+/phospholipid-dependent enzyme) at serine 24 and increased the cell surface expression of the transferrin receptor. The hypothesis that the regulation of transferrin receptor cycling by protein kinase C is causally related to the phosphorylation of the receptor at serine 24 was critically tested. Site-directed mutagenesis of the human transferrin receptor cDNA was used to substitute serine 24 with threonine or alanine residues in order to create phosphorylation defective receptors. Wild-type and mutated transferrin receptors were expressed in Swiss 3T3 fibroblasts using the retrovirus vector pZipNeoSV (X). These receptors were functionally active and caused the receptor-mediated endocytosis of diferric transferrin. Incubation of the fibroblasts with phorbol diester caused the phosphorylation of the wild-type (Ser-24) human transferrin receptor, but this treatment did not result in the phosphorylation of the mutated (Ala-24 and Thr-24) receptors. The cycling of the phosphorylation defective receptors was regulated by phorbol diester and platelet-derived growth factor in a manner similar to that observed for the wild-type receptor. We conclude that the regulation of transferrin receptor cycling by protein kinase C is independent of receptor phosphorylation at serine 24 in Swiss 3T3 fibroblasts.
D000818:Animals; D002478:Cells, Cultured; D002999:Clone Cells; D005347:Fibroblasts / Q000378:metabolism; D006706:Homeostasis; D006801:Humans; D007700:Kinetics; D051379:Mice; D009154:Mutation; D010766:Phosphorylation; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism*; D011990:Receptors, Transferrin / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D012694:Serine; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D010982:Platelet-Derived Growth Factor; D011990:Receptors, Transferrin; D012694:Serine; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate