Neu-mediated phosphorylation of protein tyrosine phosphatase epsilon is critical for activation of Src in mammary tumor cells.
The receptor-type protein tyrosine phosphatase epsilon (RPTPepsilon) activates c-Src in mammary tumor cells induced in vivo by Neu. Tumor cells lacking RPTPepsilon exhibit reduced c-Src activity, appear less transformed morphologically and proliferate slower in vitro and in vivo. Expression of Src rescues most of these phenotypes, indicating that c-Src activity is important for maintaining the transformed phenotype. However, the molecular mechanisms that control activation of c-Src by RPTPepsilon are unknown. We show that Neu induces phosphorylation of RPTPepsilon exclusively at its C-terminal Y695, and that this phosphorylation is required for activation of c-Src by RPTPepsilon. Phosphorylation of RPTPepsilon does not affect its activity toward another substrate, the voltage-gated potassium channel Kv2.1, suggesting that phosphorylation directs RPTPepsilon activity toward c-Src. Phosphorylation of RPTPepsilon reduces its dimerization at the cell membrane, although this does not affect its activity significantly. RPTPepsilon is subject to strong auto- and trans-dephosphorylation, suggesting that dephosphorylation limits the activation of c-Src downstream of Neu. We conclude that an Neu-RPTPepsilon-Src signaling pathway exists in mammary tumor cells, in which phosphorylation of RPTPepsilon by Neu directs RPTPepsilon to activate c-Src. Reversible phosphorylation of RPTPepsilon at Y695 may thus function as a 'molecular switch', which affects the substrate specificity of the phosphatase.
Berman-Golan
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D
Department of Molecular Genetics, The Weizmann Institute of Science, Rehovot, Israel.
Elson
A
A
D000818:Animals; D005260:Female; D005455:Fluorescent Antibody Technique; D047468:Immunoprecipitation; D008325:Mammary Neoplasms, Experimental / Q000201:enzymology / Q000209:etiology* / Q000473:pathology; D008324:Mammary Tumor Virus, Mouse / Q000235:genetics; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D010446:Peptide Fragments / Q000276:immunology; D010641:Phenotype; D010766:Phosphorylation; D017027:Protein Tyrosine Phosphatases / Q000502:physiology*; D051076:Proto-Oncogene Proteins c-fyn / Q000235:genetics / Q000502:physiology; D051575:Proto-Oncogene Proteins c-yes / Q000235:genetics / Q000502:physiology; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000235:genetics / Q000502:physiology*; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000235:genetics*; D054630:Receptor-Like Protein Tyrosine Phosphatases, Class 4 / Q000235:genetics / Q000378:metabolism*
D010446:Peptide Fragments; D017027:Protein Tyrosine Phosphatases; D051076:Proto-Oncogene Proteins c-fyn; D051575:Proto-Oncogene Proteins c-yes; D016392:Proto-Oncogene Proteins pp60(c-src); D018719:Erb-b2 Receptor Tyrosine Kinases; D054630:Receptor-Like Protein Tyrosine Phosphatases, Class 4; C524056:Erbb2 protein, mouse