Signal transduction by epidermal growth factor and heregulin via the kinase-deficient ErbB3 protein

Abstract

The role of protein tyrosine kinase activity in ErbB3-mediated signal transduction was investigated. ErbB3 was phosphorylated in vivo in response to either heregulin (HRG) in cells expressing both ErbB3 and ErbB2, or epidermal growth factor (EGF) in cells expressing both ErbB3 and EGF receptor. A recombinant receptor protein (ErbB3-K/M, in which K/M stands for Lys-->Met amino acid substitution) containing an inactivating mutation in the putative ATP-binding site was also phosphorylated in response to HRG and EGF. Both the wild-type ErbB3 and mutant ErbB3-K/M proteins transduced signals to phosphatidylinositol 3-kinase, Shc and mitogen-activated protein kinases. Separate kinase-inactivating mutations in the EGF receptor and ErbB2 proteins abolished ErbB3 phosphorylation and signal transduction activated by EGF and HRG respectively. Hence the protein tyrosine kinase activity necessary for growth factor signalling via the ErbB3 protein seems to be provided by coexpressed EGF and ErbB2 receptor proteins.

The ERBB3 receptor in cancer and cancer gene therapy

“…Signal transduction to SHC from ERBB3 occurs after NRG or EGF exposure in NIH 3T3 cells. 106 Site-directed mutagenesis studies in these cells indicated that NRG stimulation of mitogenesis involved both MAPK and PI3K pathways from ERBB3, with the ERBB3 SHC-binding site at rat Tyr1325 essential for the MAPK pathway stimulation. 147,148 In MDA-MB-468 human mammary cancer cells, NRG1β preferentially stimulated ERBB3, resulting in recruitment of SHC.…”

“…104,109 However, in five human mammary and ovarian carcinoma cell lines expressing both receptors no EGFR tyrosine phosphorylation occurred after NRG treatment. 86 Interaction of ERBB3 with the ligand-less ERBB2 results in a complex with enhanced affinity for NRG and increased ERBB3 phosphorylation, 106,110,111 and these receptors, as noted below, contribute synergistically to cell transformation and to malignant properties of cancer cells. ERBB2 is more likely to heterodimerize with ERBB3 than to homodimerize.…”

“…[101][102][103] In several different types of transfected cells, the expression of the EGFR was sufficient to allow activation of ERBB3 in response to EGF. [104][105][106] ERBB3 was a highly receptive substrate for EGFR tyrosine kinase activity. 107 Activity of purified EGFR toward tyrosine-containing peptides from the C-terminal region of ERBB3 was measured in vitro.…”

Critical role for the docking-protein FRS2α in FGF receptor-mediated signal transduction pathways

“…On the basis of these observation we have considered the possibility that recruitment of Gab1 in response to FGF stimulation depends on FRS2␣. Because PI-3 kinase is one of the effectors of Gab1 (13,18), this could provide a mechanism for FGF-induced activation of PI-3 kinase. Moreover, it raises an intriguing possibility that FRS2␣ functions not only as a platform for recruitment of signaling proteins, but also as a signal for coordinated assembly of docking proteins that recruit an additional complement of effector proteins (Fig.…”

“…If FRS2␣ is required for tyrosine phosphorylation of Gab1, it is expected that FRS2␣ might play a role in activation of PI-3 kinase, because PI-3 kinase is one of the effectors that is recruited by Gab1 (13,18). To test this hypothesis, wild-type or FRS2␣-deficient fibroblasts were stimulated with FGF, and lysates from stimulated or unstimulated cells were subjected to immunoprecipitation with anti-Gab1 antibodies, followed by analysis of PI-3 kinase activity in anti-Gab1 immunoprecipitates (see Methods).…”