A Discrete Three-amino Acid Segment (LVI) at the C-terminal End of Kinase-impaired ErbB3 Is Required for Transactivation of ErbB2

Abstract

ErbB3 is unique among other members of the receptor tyrosine kinase family of growth factor receptors in that its kinase domain is enzymatically impaired. This renders it incapable of transducing a signal in response to ligand binding. However, in conjunction with ErbB2, ErbB3 is a potent mediator of signaling by the growth factor heregulin. Heregulin binding to ErbB3 induces formation of a heterodimeric complex with ErbB2, and this results in transactivation of the ErbB2 kinase. Although interaction between the extracellular domains of these receptors is an essential part of this process, it was not clear whether interaction between the cytoplasmic domains is also necessary for transactivation. By examining the abilities of a series of cytoplasmic domain mutants of ErbB3 to activate ErbB2, we have found a discrete sequence of three amino acid residues (LVI), located at the carboxyl-terminal end of the impaired ErbB3 kinase region, that is obligatory for transactivation. We conclude that formation of a functional ErbB2-ErbB3 signaling complex requires the presence of a specific structural feature within the ErbB3 cytoplasmic domain and suggest that ErbB2 transactivation results from a physical interaction between the cytoplasmic domains of these receptors.Receptor tyrosine kinases play a pivotal role in the transduction of extracellular signals into the cells. The binding of cognate growth factors to these cell-surface receptors results in receptor oligomerization and activation of the intrinsic kinase activity (1, 2). This leads to receptor phosphorylation and triggers a cascade of intracellular signaling events that ultimately elicit a variety of cellular responses such as proliferation, differentiation, survival, or migration.An extensively characterized subgroup of this receptor superfamily is the ErbB group of receptors, also known as the class I receptor tyrosine kinases. Members of this group include the epidermal growth factor receptor (EGFR 1 or ErbB1), ErbB2 (also termed HER2 or Neu), ErbB3 (HER3), and ErbB4 (HER4). EGFR binds several distinct ligands including EGF and transforming growth factor-␣ (3). ErbB3 and ErbB4 bind isoforms of the heregulin family (also designated neuregulin or Neu differentiation factor) (4, 5). A ligand that directly binds to ErbB2 has not been identified. Nevertheless, ErbB2 plays an important role in signaling. ErbB2 is transactivated by heterodimerization with ligand-occupied EGFR, ErbB3, or ErbB4 (6 -9).The extensive interreceptor associations that occur in the ErbB family serve to increase the repertoire of cellular responses to growth factor stimulation and to fine-tune growth factor signaling. At least 10 different homo-and heteromeric combinations of ErbB proteins have been reported (10, 11). However, these combinations are not equally favorable. The interreceptor interactions are hierarchically organized, where ErbB2 is the preferred heteromeric partner, and it favors interaction with ErbB3 (12, 13).Cross-talk between ErbB2 and ErbB3 is especially important as the ki...

The ERBB3 receptor in cancer and cancer gene therapy

“…(3) There are three sequential amino-acid residues in this region, Leu 957 , Val 958 and Ile 959 , that are required for transactivation of ERBB2 and that are conserved among EGFR, ERBB3 and ERBB4, whereas ERBB2 differs at the position equivalent to site 957. 61 (4) The same amino-acid substitutions at positions 931, 934 and 966 of ERBB3, relative to the other ERBBs, in three diverse species (human, rat and pufferfish) indicate potential functional significance. 41 (5) The carboxy terminal region of ERBB3 includes 13 tyrosines and the sequence Tyr-Glu-Tyr-Met is repeated three times.…”

“…Studies with transfected mutants of ERBB3 and ERBB2 appeared to rule out participation of ERBB3 as a kinase and of another cytoplasmic kinase. 61 It is most likely that allosteric interactions between lobes of the kinase regions of ERBB2 and ERBB3 result in activation of ERBB2. 8 (2) The C-terminal domain of ERBB3 is 30 to 50% longer than the comparable regions of EGFR and ERBB2.…”

Molecular requirements for the effect of neuregulin on cell spreading, motility and colony organization

“…We demonstrated that the combination of ErbB-3 with ErbB-2 was much more potent in the induction of cell spreading than ErbB-3/ErbB-1. ErbB-3 can eciently transactivate the kinase activity of the`orphan' receptor ErbB-2; a speci®c motif, LVI, localized at the impaired kinase domain of ErbB-3 is required for this transactivation (Schaefer et al, 1999). Truncated ErbB-3 receptors, preserving this LVI motif can transactivate ErbB-2, which in turn leads to phosphorylation of ErbB-3 receptor itself (Schaefer et al, 1999).…”

“…ErbB-3 can eciently transactivate the kinase activity of the`orphan' receptor ErbB-2; a speci®c motif, LVI, localized at the impaired kinase domain of ErbB-3 is required for this transactivation (Schaefer et al, 1999). Truncated ErbB-3 receptors, preserving this LVI motif can transactivate ErbB-2, which in turn leads to phosphorylation of ErbB-3 receptor itself (Schaefer et al, 1999). In our experiments we observed that the DCT-ErbB-3 receptor, lacking the C-terminal region downstream from the kinase domain but preserving LVI motif, can mediate some signaling eects, in particular, MAP kinase activation.…”

Structure of the Epidermal Growth Factor Receptor Kinase Domain Alone and in Complex with a 4-Anilinoquinazoline Inhibitor

“…This motif is necessary for ligand-independent dimerization of EGFR intracellular domains (12) and for transphosphorylation in ErbB2/ErbB3 heterodimers (13). Moreover, alanine substitutions in this region override mutations in the transmembrane segment of ErbB2 that would otherwise lead to constitutive signaling via non-ligand induced dimerization (14).…”