title: Characterization of a naturally occurring ErbB4 isoform that does not bind or activate phosphatidyl inositol 3-kinase.
abstract: Receptor tyrosine kinases regulate cell behavior by activating specific signal transduction cascades. Epidermal growth factor (EGF) receptor tyrosine kinases include ErbB1, ErbB2, ErbB3 and ErbB4. ErbB4 is a tyrosine kinase receptor that binds neuregulins (NRG) and several other EGF family members. Reverse transcriptase polymerase chain reaction (RT-PCR) analysis identified two isoforms of ErbB4 that differed in their cytoplasmic domain sequences. Specifically, RT-PCR using primers flanking the putative phosphatidyl inositol 3-kinase (PI3-K) binding site of ErbB4 generated two specific bands when human and mouse heart and kidney tissues were analysed. Cloning and sequencing of these RT-PCR products revealed that one of the ErbB4 isoforms (ErbB4 CYT-2) lacked a 16 amino acid sequence including a putative PI3-K binding site, that was present in the other isoform (ErbB4 CYT-1). RT-PCR analysis of mouse tissues suggested that the expression of ErbB4 CYT-1 and ErbB4 CYT-2 was tissue-specific. Heart, breast and abdominal aorta expressed predominantly ErbB4 CYT-1 whereas neural tissues and kidney expressed predominantly ErbB4 CYT-2. To ascertain whether the absence of the putative PI3-K binding site in ErbB4 CYT-2 also resulted in the loss of PI3-K activity, NIH3T3 cell lines overexpressing ErbB4 CYT-1 or ErbB4 CYT-2 were produced. NRG-1 bound to and stimulated equivalent tyrosine phosphorylation of both isoforms. However, unlike ErbB4 CYT-1, the ErbB4 CYT-2 isoform was unable to bind the p85 subunit of PI3-K and to stimulate PI3-K activity in these cells. Furthermore, tyrosine phosphorylation of p85 or association of PI3-K activity with phosphotyrosine was not induced in NRG-1 treated cells expressing ErbB4 CYT-2, indicating that this isoform was incapable of activating PI3-K even indirectly. It was concluded that a novel naturally occurring ErbB4 isoform exists with a deletion of the cytoplasmic domain sequence required for the activation of the PI3-K intracellular signal transduction pathway and that this is the only PI3-K binding site in ErbB4.
authors.affiliation: Department of Surgery, Children's Hospital and Harvard Medical School, Boston, MA 02115, USA.
authors.forename: K
authors.initials: K
authors.lastname: Elenius
authors.forename: C J
authors.initials: CJ
authors.lastname: Choi
authors.forename: S
authors.initials: S
authors.lastname: Paul
authors.forename: E
authors.initials: E
authors.lastname: Santiestevan
authors.forename: E
authors.initials: E
authors.lastname: Nishi
authors.forename: M
authors.initials: M
authors.lastname: Klagsbrun
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003593:Cytoplasm / Q000201:enzymology; D004789:Enzyme Activation; D066246:ErbB Receptors / Q000378:metabolism*; D006801:Humans; D051379:Mice; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D011485:Protein Binding; D020033:Protein Isoforms / Q000378:metabolism; D066247:Receptor, ErbB-4; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid
chemical_list: D020033:Protein Isoforms; D019869:Phosphatidylinositol 3-Kinases; C587689:ERBB4 protein, human; D066246:ErbB Receptors; C587690:Erbb4 protein, mouse; D066247:Receptor, ErbB-4