Five carboxyl-terminal residues of neuregulin2 are critical for stimulation of signaling by the ErbB4 receptor tyrosine kinase

The neuregulins (NRGs) are members of the epidermal growth factor (EGF) family of peptide growth factors. These hormones are agonists for the ErbB family of receptor tyrosine kinases, a family that includes the epidermal growth factor receptor (EGFR/ErbB1), ErbB2/Neu/HER2, ErbB3/HER3, and ErbB4/HER4. We recently observed that the EGF family hormone NRG2 β is a potent agonist for ErbB4. In contrast, NRG2 α , a splicing isoform of the same gene that encodes NRG2 β , is a poor ErbB4 agonist. We hypothesized that carboxyl-terminal residues of NRG2 β are critical for stimulation of ErbB4 tyrosine phosphorylation and coupling to downstream signaling events. Here, we demonstrate that the substitution of a lysine residue for Phe45 in NRG2 β results in reduced ligand potency. We also demonstrate that substitution of a phenylalanine for Lys45 in NRG2 α results in increased ligand potency. Finally, analyses of the gain-of-function NRG2 α Chg5 mutant demonstrate that Gln43, Met47, Asn49, and Phe50 regulate ligand efficacy. Thus, these data indicate that carboxyl-terminal residues of NRG2 β are critical for activation of ErbB4 signaling. Moreover, these NRG2 α and NRG2 β mutants reveal new insights into models for ligand-induced ErbB family receptor tyrosine phosphorylation and coupling to downstream signaling events.