Heregulin-dependent Activation of Phosphoinositide 3-Kinase and Akt via the ErbB2/ErbB3 Co-receptor

• Published in: The Journal of biological chemistry 2001-11, Vol.276 (45), p.42153-42161
• Main Authors: Hellyer, Nathan J., Kim, Myong-Soo, Koland, John G.
• Format: Article
• Language: English
• Subjects: 3T3 Cells; Akt protein; Amino Acid Motifs; Animals; Binding Sites; Biological Transport; COS Cells; Enzyme Activation; ErbB2 protein; heregulin; Mice; Neu protein; Neuregulin-1 - physiology; Phosphatidylinositol 3-Kinases - metabolism; Phosphorylation; Precipitin Tests; Protein-Serine-Threonine Kinases; Proto-Oncogene Proteins - metabolism; Proto-Oncogene Proteins c-akt; Receptor, ErbB-2 - physiology; Receptor, ErbB-3 - physiology
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M102079200

The ErbB2/ErbB3 heregulin co-receptor has been shown to couple to phosphoinositide (PI) 3-kinase in a heregulin-dependent manner. The recruitment and activation of PI 3-kinase by this co-receptor is presumed to occur via its interaction with phosphorylated Tyr-Xaa-Xaa-Met (Y XXM) motifs occurring in the ErbB3 C terminus. In this study, mutant ErbB3 receptor proteins expressed in COS7 cells were used to investigate PI 3-kinase-dependent signaling pathways activated by the ErbB2/ErbB3 co-receptor. We observed that a mutant ErbB3 protein with each of its six Y XXM motifs containing a Tyr → Phe substitution was unable to bind either the p85 regulatory or p110 catalytic subunit of PI 3-kinase. However, restoration of a single Y XXM motif was sufficient to mediate association with the PI 3-kinase holoenzyme, although at a lower level than wild-type ErbB3. When ErbB3 Y XXM motifs were restored in pairs, evidence for cooperativity between two, those incorporating Tyr-1273 and Tyr-1286, was observed. Interestingly, we have shown that an apparent association of PI 3-kinase activity with ErbB2/Neu was due to the residual presence of ErbB3 in ErbB2 immunoprecipitates. The necessity of ErbB3 association with PI 3-kinase for downstream signaling to the effector kinase Akt was also investigated. Here, the heregulin-dependent translocation of Akt to the plasma membrane and its subsequent activation was observed in intact NIH-3T3 fibroblasts. Recruitment of PI 3-kinase to ErbB3 was required for both activities, and it appeared that ErbB2 activation alone was not sufficient to activate PI 3-kinase signaling in these cells.