title: Roles of mitogen-activated protein kinase and phosphoinositide 3'-kinase in ErbB2/ErbB3 coreceptor-mediated heregulin signaling.
abstract: ErbB2/HER2 and ErbB3/HER3, two members of the ErbB/HER family, together constitute a heregulin coreceptor complex that elicits a potent mitogenic and transforming signal. Among known intracellular effectors of the ErbB2/ErbB3 heregulin coreceptor are mitogen-activated protein kinase (MAPK) and phosphoinositide (PI) 3-kinase. Activation of the distinct MAPK and PI 3-kinase signaling pathways by the ErbB2/ErbB3 coreceptor in response to heregulin and their relative contributions to the mitogenic and transformation potentials of the activated coreceptor were investigated here. To this end, cDNAs encoding the wild-type ErbB3 protein (ErbB3-WT) and ErbB3 proteins with amino acid substitutions in either the Shc-binding site (ErbB3-Y1325F), the six putative PI 3-kinase-binding sites (ErbB3-6F), or both (ErbB3-7F) were generated and expressed in NIH-3T3 cells to form functional ErbB2/ErbB3 heregulin coreceptors. While the coreceptor incorporating ErbB3-WT activated both the MAPK and the PI 3-kinase signaling pathways, those incorporating ErbB3-Y1325F or ErbB3-6F activated either PI 3-kinase or MAPK, respectively. The ErbB2/ErbB3-7F coreceptor activated neither. Elimination of either signaling pathway lowered basal and eliminated heregulin-dependent expression of cyclin D1, which was in each case accompanied by an attenuated mitogenic response. Selective elimination of the PI 3-kinase pathway severely impaired the ability of heregulin to transform cells expressing the coreceptor, whereas attenuation of the MAPK pathway had a lesser effect. Thus, while both pathways contributed in a roughly additive manner to the mitogenic response elicited by the activated ErbB2/ErbB3 coreceptor, the PI 3-kinase pathway predominated in the induction of cellular transformation.
authors.affiliation: Department of Pharmacology, The University of Iowa, College of Medicine, Iowa City, IA 52242-1109, USA.
authors.forename: Ulka
authors.initials: U
authors.lastname: Vijapurkar
authors.forename: Myong-Soo
authors.initials: MS
authors.lastname: Kim
authors.forename: John G
authors.initials: JG
authors.lastname: Koland
mesh_terms: D016475:3T3 Cells; D000818:Animals; D002471:Cell Transformation, Neoplastic / Q000235:genetics; D019938:Cyclin D1 / Q000378:metabolism; D005057:Eukaryotic Cells / Q000201:enzymology*; D020935:MAP Kinase Signaling System / Q000235:genetics*; D051379:Mice; D008938:Mitosis / Q000235:genetics; D009154:Mutation / Q000235:genetics; D020890:Neuregulin-1 / Q000235:genetics / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism*; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D020893:Receptor, ErbB-3 / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000235:genetics*
chemical_list: D019938:Cyclin D1; D020890:Neuregulin-1; D019869:Phosphatidylinositol 3-Kinases; D018719:Erb-b2 Receptor Tyrosine Kinases; D020893:Receptor, ErbB-3