Shp2, an SH2-containing Protein-tyrosine Phosphatase, Positively Regulates Receptor Tyrosine Kinase Signaling by Dephosphorylating and Inactivating the Inhibitor Sprouty

Abstract

Src homology 2-containing phosphotyrosine phosphatase (Shp2) functions as a positive effector in receptor tyrosine kinase (RTK) signaling immediately proximal to activated receptors. However, neither its physiological substrate(s) nor its mechanism of action in RTK signaling has been defined. In this study, we demonstrate that Sprouty (Spry) is a possible target of Shp2. Spry acts as a conserved inhibitor of RTK signaling, and tyrosine phosphorylation of Spry is indispensable for its inhibitory activity. Shp2 was able to dephosphorylate fibroblast growth factor receptor-induced phosphotyrosines on Spry both in vivo and in vitro. Shp2-mediated dephosphorylation of Spry resulted in dissociation of Spry from Grb2. Furthermore, Shp2 could reverse the inhibitory effect of Spry on FGF-induced neurite outgrowth and MAP kinase activation. These findings suggest that Shp2 acts as a positive regulator in RTK signaling by dephosphorylating and inactivating Spry.Receptor tyrosine kinase signaling regulates a wide variety of biological processes in response to extracellular signals, including cellular growth, differentiation and metabolism (1-4). For example, fibroblast growth factor (FGF) 1 stimulates the receptor tyrosine kinase activity of the FGF receptor (FGFR), leading to tyrosine phosphorylation of the docking protein FRS2, consequent recruitment of multiple Grb2-Sos complexes, and activation of the Ras-mitogen-activated protein (MAP) kinase signaling pathway (5-7). Precise control of MAP kinase activation is critical for such cellular responses, and several molecules have been identified that serve to regulate the activation of MAP kinase either positively or negatively.Shp2 is a widely expressed protein-tyrosine phosphatase (PTPase) that seems to play a positive role in the activation of MAP kinase in response to growth factors (8 -14). In response to growth factor stimulation, Shp2 becomes tyrosine-phosphorylated and binds to Grb2, where it seems to act as an adaptor protein to recruit the Grb2-Sos complex to the plasma membrane. This, in turn, leads to Ras activation (6,9,(15)(16)(17). However, several studies have shown that mutation of Shp2 in the putative Grb2 binding site did not interfere with the function of Shp2 in mediating MAP kinase activation (12,18). In contrast, several lines of evidence indicate that the phosphatase catalytic activity of Shp2 is required for MAP kinase activation by FGF and other growth factors (12). Thus, two critical tasks are identifying the substrate for Shp2 and determining how dephosphorylation contributes to the activation of MAP kinase. Recently, it has been reported that a major binding protein of Shp2 is the multi-site docking protein Gab1 (Grb2-associated binder 1) and that this association is required for MAP kinase activation by several growth factors (19 -22). Interestingly, genetic analysis of Corkscrew (Csw), the Drosophila homologue of Shp2, has led to the identification of the Daughter of Sevenless (Dos) protein as a putative Csw substrate (23-25). The Dos protein...

Integrating signals from RTKs to ERK/MAPK

“…First, by dephosphorylating binding sites on some receptors and docking proteins that mediate binding of the Ras GTPase activating protein (RasGAP), Shp-2 prevents the localization of RasGAP to the plasma membrane and thereby, prolongs Ras activation (Klinghoffer and Kazlauskas, 1995;Agazie and Hayman, 2003;Montagner et al, 2005). Second, by dephosphorylating the negative signaling modulator Sprouty, Shp-2 prevents Sprouty from binding and blocking the membrane recruitment of Grb2/Sos (Hanafusa et al, 2004). Thus, the general underlying mechanism for the positive effects exerted by Shp-2 on Ras signaling is that Shp-2 antagonizes the ability of negative regulators to access and downregulate critical enzymes involved in Ras activation.…”

A Mass Action Model of a Fibroblast Growth Factor Signaling Pathway and Its Simplification

“…Also commonly noted is the binding of SOS to FRS2 via GRB2 and the subsequent activation of the RAS-MAP kinase pathway (ibid) together with CBL induced degradation (Dailey et al, 2005). It is also known that SHP2 can induce a dephosphorylation of SPRY (Jarvis et al, 2006;Hanafusa et al, 2004) and that SPRY associates with GRB2 (Thisse and Thisse, 2005) plus CBL (Wong et al, 2001). Signal attenuation due to SRC binding FRS2 has also been reported, along with the observation that SPRY is a direct physiological substrate for SRC (Li et al, 2004).…”

SHP2 is a downstream target of ZAP70 to regulate JAK1/STAT3 and ERK signaling pathways in mouse embryonic stem cells

“…Because Sprouty, which is a conserved inhibitor of the Ras-MAP kinase signaling pathway, is a known target of SHP2 [21], it will be important to elucidate whether SHP2 functions as a positive regulator of ERK1/2 pathway by inactivating Sprouty protein in mESCs. Fig.…”