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

Abstract

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 TyrXaa-Xaa-Met (YXXM) 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 YXXM motifs containing a Tyr 3 Phe substitution was unable to bind either the p85 regulatory or p110 catalytic subunit of PI 3-kinase. However, restoration of a single YXXM motif was sufficient to mediate association with the PI 3-kinase holoenzyme, although at a lower level than wild-type ErbB3. When ErbB3 YXXM 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.The type I subfamily of receptor protein-tyrosine kinases is composed of four members: the prototypical epidermal growth factor receptor (ErbB1/HER1), ErbB2 (HER2/Neu), ErbB3 (HER3), and ErbB4 (HER4). Interestingly, this family of receptors can generate a wide variety of cellular signals by mixing and matching to form various co-receptor signaling complexes (1-4). Of the various heterodimers and homodimers formed, the ErbB2/ErbB3 dimer constitutes a high affinity co-receptor for heregulin (5), which is capable of potent mitogenic signaling.In particular, ErbB3 has been characterized as a major mediator of heregulin-dependent activation of the phosphoinositide (PI) 1 3-kinase pathway (6 -14). One general mechanism of recruitment and activation of PI 3-kinase involves the binding of the tandem Src homology 2 (SH2) domains of its p85 regulatory subunit to phosphorylated YXXM motifs found in signaling proteins (15, 16). ErbB3 is particularly well adapted to mediate PI 3-kinase signaling, because it contains in its Cterminal phosphorylation domain six such consensus p85 binding motifs (17). Two previous studies have investigated the role of these YXXM motifs in ErbB3 signaling. One study showed that phosphopeptides containing the various ErbB3 YXXM motifs could inhibit p85 association with ErbB3 (9). Additionally, we have shown via the yeast two-hybrid system that these phosphorylated motifs can directly associate with th...

Involvement of Secretory and Endosomal Compartments in Presentation of an Exogenous Self-Glycolipid to Type II NKT Cells

“…These data further suggests that phosphorylation of the tyrosine motif plays an important role in trafficking of CD1d. Indeed, the phospho-tyrosine motif, pYXXM present in insulin receptor substrate-1, plateletderived growth factor receptor, and ErbB2, 3 receptors binds with the SH2 domain of the p85 subunit of PI 3-kinase (52)(53)(54)(55)(56)(57)(58). Additional studies in AP-3Ϫ/Ϫmice are needed to further clarify specific interaction of PI 3-kinase on trafficking of CD1d protein.…”

The ERBB3 receptor in cancer and cancer gene therapy

“…133 Each of the p85 sites contributes to ERBB3 signaling, as demonstrated by their one-at-a-time mutation and restoration, and cooperation among p85-binding sites was observed. 136 These interactions involve the N-terminal SH2 domain of p85, with the two phosphotyrosine-binding sites in this domain each interacting preferentially with certain phosphotyrosyl peptides from ERBB3. 137 For the three pairs of tyrosine residues separated by a glutamic acid, the first Tyr in each case binds p85.…”

“…ERBB3/PI3K/AKT-induced survival and proliferation pathways have been implicated in the malignancy of breast, ovarian, colon, gastric and lung cancer cells. Various approaches using ERBB3 mutants, 136,138 immunoprecipitations with antibody against ERBB3 139,140 or NRG, 141 ERBB3 antisense, 139 ERBB3 small interfering RNA (siRNA), 142 and use of the designer ERBB3 transcription inhibitor E3 in a variety of cells 143 have established the importance of this pathway. GRB7/GRB2-GRB7 was notable for its uniquely high-affinity binding with pY1197 in ERBB3 (Table 3).…”

Bone Microenvironment and Androgen Status Modulate Subcellular Localization of ErbB3 in Prostate Cancer Cells

“…In response to cognate ligands such as heregulin, ErbB-3 forms heterodimers with ErbB-2, and those heterodimeric ErbB-2/ErbB-3 complexes activate a phosphatidylinositol-3-kinase -dependent signaling pathway (2,3). Aberrant increases in ErbB-3 expression have been implicated in a variety of malignancies, including prostate cancer.…”