Growth Hormone-Induced Tyrosine Phosphorylation of EGF Receptor as an Essential Element Leading to MAP Kinase Activation and Gene Expression

Abstract

Abstract. GH binding to its receptor, which belongs to the cytokine receptor superfamily, activates Janus kinase (JAK) 2 tyrosine kinase, thereby activating a number of intracellular key proteins such as STAT (signal transducers and activators of transcription) proteins and mitogen-activated protein (MAP) kinases, which finally lead to GH's biological actions including gene expression. In contrast to receptor tyrosine kinases, the signalling pathways leading to MAP kinase activation by GH are poorly understood but appear to involve Grb2 and Shc. We now show that GH stimulated tyrosine phosphorylation of epidermal growth factor receptor (EGFR) and its association with Grb2, and concomitantly stimulated MAP kinase activity in liver, a major target tissue. Expression of EGFR and its mutants into CHO-GH receptor (GHR) cells revealed that GH-induced full activation of MAP kinase and c-fos expression required tyrosine phosphorylation sites of EGFR but not its intrinsic tyrosine kinase activity. Moreover, by also using dominant negative JAK2 and in vitro kinase assay, we demonstrated that tyrosine 1068 of EGFR was evidently one of the major phosphorylation and Grb2 binding sites stimulated by GH via JAK2. These data suggest that the role of EGFR in GH signalling is to be phosphorylated by JAK2, thereby providing docking sites for Grb2 and activating MAP kinases and gene expression. This novel cross talk pathway may provide the first example of the hormone and cytokine receptor superfamily transducing signals via associated nonreceptor tyrosine kinase by phosphorylating growth factor receptor and utilizing it as a docking protein independent of its receptor tyrosine kinase activity.

Prolactin modulates phosphorylation, signaling and trafficking of epidermal growth factor receptor in human T47D breast cancer cells

“…It is increasingly appreciated that interactions and crosstalk among signaling pathways allow both integration and diversity in responses to cellular stimuli. EGFR and cytokine receptor family member signaling pathways can interrelate in various ways (Johnson et al, 1996;Fenton and Sheffield, 1997;Wiepz et al, 1997;Yamauchi et al, 1997Yamauchi et al, , 1998Yamauchi et al, , 2000Qiu et al, 1998;Quijano and Sheffield, 1998;Kim et al, 1999;Maus et al, 1999;Badache and Hynes, 2001;Huang et al, 2003;Eisenberg et al, 2004). We previously focused on interactions between GH/GHR signaling and signaling mediated by intrinsic tyrosine kinase growth factor receptors, including EGFR and ErbB-2, in murine preadipocytes (Kim et al, 1999;Huang et al, 2003Huang et al, , 2004a.…”

“…Recent studies suggest that PRL, growth hormone (GH) and other cytokines may use multiple mechanisms to crosstalk with EGFR and/or ErbB-2 (Johnson et al, 1996;Fenton and Sheffield, 1997;Wiepz et al, 1997;Yamauchi et al, 1997Yamauchi et al, , 1998Yamauchi et al, , 2000Qiu et al, 1998;Quijano and Sheffield, 1998;Kim et al, 1999;Maus et al, 1999;Badache and Hynes, 2001;Huang et al, 2003). For example, GH causes EGFR tyrosine phosphorylation without the activation of EGFR kinase activity (Yamauchi et al, 1997;Kim et al, 1999).…”

Growth hormone (GH) modulation of Epidermal growth factor (EGF) signalling in human mammary epithelial cells

“…As mentioned above, the ErbB-receptors can also be phosphorylated by GH and PRL, a protein related to GH (Yamauchi et al, 1997(Yamauchi et al, , 1998(Yamauchi et al, , 2000. GH was first described to induce Tyr1068 phosphorylation at EGFR in vitro and in vivo (Yamauchi et al, 1997, exogenous GH administration this expression deficit can be reversed (Jansson et al, 1988;Johansson et al, 1989).…”

“…ErbB-receptors are not only activated by specific ligands, they can also be activated indirectly by Growth hormone (GH) or Prolactin (PRL) and other growth factors through the JAK-2/STAT pathway (Yamauchi et al 1997(Yamauchi et al , 1998(Yamauchi et al , 2000. EGFR can also be phosphorylated at sites in the intracellular domain as serine and threonine residues (Li et al, 2008).…”

Signaling Pathways Coupled to Activation of the Kinin B1 Receptor

“…The GRB2 adaptor protein binds activated EGFR at phospho-Tyr1068 (Rojas et al, 1996). Interestingly, Yamauchi et al,(1998) demonstrated that binding of growth hormone to its receptor, which belongs to the cytokine receptor superfamily, activates Janus kinase tyrosine kinase, STAT proteins and MAPK that regulate expression of c-fos. This activation depends on phosphorylation of Tyr1068 by Janus kinase tyrosine kinase 2, providing docking sites for Grb2 and Shc protein adaptor and activating MAPK and gene expression.…”