Annexin II binds to SHP2 and this interaction is regulated by HSP70 levels

The protein tyrosine phosphatase SHP2 is a positive effector of EGFR signaling. To improve our understanding of SHP2's function, we searched for additional binding proteins of SHP2. We found that Annexin II is an SHP2-binding protein. Physical interactions of SHP2 with Annexin II were confirmed in vivo. Furthermore, binding of SHP2 with Annexin II was regulated somewhat by EGF treatment and the extracellular Ca2+ chelator, EGTA. Previously, we reported that HSP70 levels can influence the binding of SHP2 with EGFR. Interestingly, increased HSP70 levels also inhibited the binding of SHP2 with Annexin II after EGF treatment in vivo. In addition, immunostaining experiments indicated that a fraction of SHP2 and Annexin II co-localized in the cell membrane region after EGF treatment. Our findings indicate that Annexin II is binding partner of SHP2 and the binding of SHP2 with Annexin II is affected by EGF stimulation, extracellular calcium levels, and the levels of HSP70.     

Flow activates ERK1/2 and endothelial nitric oxide synthase via a pathway involving PECAM1, SHP2, and Tie2

Blood flow modulates endothelial cell (EC) functions through specific signaling events. Previous data show that flow stimulates SHP2 translocation to cell membranes and binding to phosphotyrosine proteins. Flow-induced ERK1/2 phosphorylation depends on SHP2 phosphatase activity and SHP2 binding to phospho-PECAM1 (platelet endothelial adhesion molecule 1), suggesting that SHP2 forms a signaling module with PECAM1. We hypothesized that flow induces assembly of the multi-protein complexes with SHP2 that are required for downstream signaling. ECs were exposed to flow for 10 min, and endogenous SHP2 was immunoprecipitated. SHP2-associated proteins were analyzed by SDS-PAGE and identified by mass spectrometry. Tie2 and several known SHP2-binding proteins were identified in flow-induced SHP2 complexes. Flow significantly increased tyrosine phosphorylation of both Tie2 and PECAM1 and their association with SHP2. To evaluate their functional roles, ECs were treated with Tie2 or PECAM1 small interfering RNA (siRNA). Tie2 and PECAM1 expression decreased >80% after siRNA treatment, and flow-stimulated phosphorylation of ERK1/2, Akt, and endothelial nitric oxide synthase was significantly inhibited by Tie2 and PECAM1 siRNA. Tie2 phosphorylation by flow was significantly inhibited by PECAM1 siRNA treatment. These results establish Tie2 transactivation via PECAM1 as an early event in flow-mediated mechanotransduction and suggest an important role for a PECAM1-SHP2-Tie2 pathway in flow-mediated signal transduction.     

SHP2 and SOCS3 contribute to Tyr-759-dependent attenuation of interleukin-6 signaling through gp130

Interleukin-6 (IL-6) activates the Jak/STAT pathway as well as the mitogen-activated protein kinase cascade. Tyrosine 759 of the IL-6 signal-transducing receptor subunit gp130 has been identified as being involved in negative regulation of IL-6-induced gene induction and activation of the Jak/STAT pathway. Because this site is known to be a recruitment motif for the protein-tyrosine phosphatase SHP2, it has been suggested that SHP2 is the mediator of tyrosine 759-dependent signal attenuation. We recently observed that the suppressor of cytokine-signaling SOCS3 also acts through the tyrosine motif 759 of gp130. However, the relative contributions of SHP2 and SOCS3 to the repression of IL-6 signaling are not understood. Therefore, we designed experiments allowing the independent recruitment of each of these proteins to the IL-6-receptor complex. We show that receptor- and membrane-targeted SHP2 counteracts IL-6 signaling independent of SOCS3 binding to gp130. On the other hand, SOCS3 inhibits signaling in cells expressing a truncated SHP2 protein, which is not recruited to gp130. These data suggest, that there are two, largely distinct modes of negative regulation of gp130 activity, despite the fact that both SOCS3 and SHP2 are recruited to the same site within gp130.     

Molecular mechanism for a role of SHP2 in epidermal growth factor receptor signaling

The Src homology 2-containing phosphotyrosine phosphatase (SHP2) is primarily a positive effector of receptor tyrosine kinase signaling. However, the molecular mechanism by which SHP2 effects its biological function is unknown. In this report, we provide evidence that defines the molecular mechanism and site of action of SHP2 in the epidermal growth factor-induced mitogenic pathway. We demonstrate that SHP2 acts upstream of Ras and functions by increasing the half-life of activated Ras (GTP-Ras) in the cell by interfering with the process of Ras inactivation catalyzed by Ras GTPase-activating protein (RasGAP). It does so by inhibition of tyrosine phosphorylation-dependent translocation of RasGAP to the plasma membrane, to its substrate (GTP-Ras) microdomain. Inhibition is achieved through the dephosphorylation of RasGAP binding sites at the level of the plasma membrane. We have identified Tyr992 of the epidermal growth factor receptor (EGFR) to be one such site, since its mutation to Phe renders the EGFR refractory to the effect of dominant-negative SHP2. To our knowledge, this is the first report to outline the site and molecular mechanism of action of SHP2 in EGFR signaling, which may also serve as a model to describe its role in other receptor tyrosine kinase signaling pathways.     

Requirement of Tyr-992 and Tyr-1173 in phosphorylation of the epidermal growth factor receptor by ionizing radiation and modulation by SHP2

The epidermal growth factor receptor (EGFR) is activated by ionizing radiation (IR) in many human carcinomas, mediating a cytoprotective response and subsequent radioresistance. The underlying molecular mechanisms remain to be understood, and we propose here a specific role for the Tyr-992 residue of EGFR and examine its regulation by the phosphatase, SHP2. The -fold increase in phosphorylation of Tyr-992 in response to IR is twice that seen with ligand (EGF) binding. Mutation of Tyr-992 blocked completely IR-induced EGFR phosphorylation and reduced activation of the downstream signaling molecule, phospholipase Cgamma. IR has previously been demonstrated to inhibit activity of protein-tyrosine phosphatases. Following protein-tyrosine phosphatase inhibition by sodium vanadate both EGFR expressing Chinese hamster ovary (CHO) and A431 exhibited up to an 8-fold increase in the basal level of Tyr-992 phosphorylation, significantly higher than that seen with Tyr-1173, Tyr-1068, and total EGFR Tyr. CHO cells expressing a SHP2 mutant also demonstrated up to an 8-fold increase in the basal level of Tyr-992 phosphorylation. In this study we show the unique association of SHP2 with EGFR in response to IR, with up to a 2.5-fold increase in the direct association of endogenous SHP2 with EGFR-wt in response to 2 gray of IR in both CHO and A431 cells. Mutation of Tyr-992 abolished this response. In conclusion we have identified several differentially activated Tyr residues, one of which is not only more sensitive to activation by IR, translating into differential activation of downstream signaling, but uniquely modulated by the phosphatase SHP2.     

Inhibition of SHP2 leads to mesenchymal to epithelial transition in breast cancer cells

The Src homology phosphotyrosyl phosphatase 2 (SHP2) is an essential transducer of mitogenic and cell survival signaling in the epidermal growth factor receptor (EGFR) signaling pathway. However, the role of SHP2 in aberrant EGFR and human EGFR2 (HER2) signaling and cancer, particularly in breast cancer, has not been investigated. Here, we report that SHP2 is required for mitogenic and cell survival signaling and for sustaining the transformation phenotypes of breast cancer cell lines that overexpress EGFR and HER2. Inhibition of SHP2 suppressed EGF-induced activation of the Ras-ERK and the phosphatidylinositol 3 kinase-Akt signaling pathways, abolished anchorage-independent growth, induced epithelial cell morphology and led to reversion to a normal breast epithelial phenotype. Furthermore, inhibition of SHP2 led to upregulation of E-cadherin (epithelial marker) and downregulation of fibronectin and vimentin (mesenchymal markers). These results indicate that SHP2 promotes breast cancer cell phenotypes by positively modulating mitogenic and cell survival signaling, by suppressing E-cadherin expression which is known to play a tumor suppressor role and by sustaining the mesenchymal state as evidenced by the positive impact on fibronectin and vimentin expression. Therefore, SHP2 promotes epithelial to mesenchymal transition, whereas its inhibition leads to mesenchymal to epithelial transition. On the basis of these premises, we propose that interference with SHP2 function might help treat breast cancer.     

Requirement of SHP2 binding to Grb2-associated binder-1 for mitogen-activated protein kinase activation in response to lysophosphatidic acid and epidermal growth factor

Grb2-associated binder-1 (Gab1) is a multisite docking protein containing a pleckstrin homology (PH) domain, multiple potential tyrosine phosphorylation sites, and several proline-rich sequences. Gab1 becomes tyrosine-phosphorylated in cells stimulated with growth factors, cytokines, and ligands for G protein-coupled receptors. A major Gab1-binding protein detected in cells treated with extracellular stimuli is the tyrosine phosphatase, SHP2. Although the role of SHP2-Gab1 interaction in cell signaling has not yet been characterized, SHP2 is known to mediate mitogen-activated protein (MAP) kinase activation induced by the epidermal growth factor (EGF). However, the mechanism by which the SHP2 phosphatase exerts a positive signaling role remains obscure. In this study, we prepared Gab1 mutants lacking the SHP2 binding site (Gab1Y627F), the phosphatidylinositol 3-kinase (PI3K) binding sites (Gab1DeltaPI3K), and the PH domain (Gab1DeltaPH). Expression of Gab1Y627F blocked the extracellular signal-regulated kinase-2 (ERK2) activation by lysophosphatidic acid (LPA) and EGF. Conversely, expression of the wild-type Gab1 in HEK293 cells augmented the LPA receptor Edg2-mediated ERK2 activation. Whereas the PH domain was required for Gab1 mediation of ERK2 activation by LPA, it was not essential for EGF-induced ERK2 activation. Expression of Gab1DeltaPI3K had no apparent effect on ERK2 activation by LPA and EGF in the cells that we have examined. These results establish a role for Gab1 in the LPA-induced MAP kinase pathway and clearly demonstrate that Gab1-SHP2 interaction is essential for ERK2 activation by LPA and EGF. These findings also suggest that the positive role of SHP2 in the MAP kinase pathway depends on its interaction with Gab1.     

Targeting SHP2 for EGFR inhibitor resistant non-small cell lung carcinoma

Targeted therapy with inhibitors of epidermal growth factor receptor (EGFR) has produced a noticeable benefit to non-small cell lung cancer (NSCLC) patients whose tumors carry activating mutations (e.g. L858R) in EGFR. Unfortunately, these patients develop drug resistance after treatment, due to acquired secondary gatekeeper mutations in EGFR (e.g. T790M). Given the critical role of SHP2 in growth factor receptor signaling, we sought to determine whether targeting SHP2 could have therapeutic value for EGFR inhibitor resistant NSCLC. We show that SHP2 is required for EGF-stimulated ERK1/2 phosphorylation and proliferation in EGFR inhibitor resistant NSCLC cell line H1975, which harbors the EGFR T790M/L858R double-mutant. We demonstrate that treatment of H1975 cells with II-B08, a specific SHP2 inhibitor, phenocopies the observed growth inhibition and reduced ERK1/2 activation seen in cells treated with SHP2 siRNA. Importantly, we also find that II-B08 exhibits marked anti-tumor activity in H1975 xenograft mice. Finally, we observe that combined inhibition of SHP2 and PI3K impairs both the ERK1/2 and PI3K/AKT signaling axes and produces significantly greater effects on repressing H1975 cell growth than inhibition of either protein individually. Collectively, these results suggest that targeting SHP2 may represent an effective strategy for treatment of EGFR inhibitor resistant NSCLCs.     

A critical role for phosphoinositide 3-kinase upstream of Gab1 and SHP2 in the activation of ras and mitogen-activated protein kinases by epidermal growth factor

Although the mechanisms involved in the activation of mitogen-activated protein kinases (MAPK) by receptor tyrosine kinases do not display an obvious role for phosphoinositide 3-kinases (PI3Ks), we have observed in the nontransformed cell line Vero stimulated with epidermal growth factor (EGF) that wortmannin and LY294002 nearly abolished MAPK activation. The effect was observed under strong stimulation and was independent of EGF concentration. In addition, three mutants of class Ia PI3Ks were found to inhibit MAPK activation to an extent similar to their effect on Akt/protein kinase B activation. To determine the importance of PI3K lipid kinase activity in MAPK activation, we have used the phosphatase PTEN and the pleckstrin homology domain of Tec kinase. Overexpression of these proteins, but not control mutants, was found to inhibit MAPK activation, suggesting that the lipid products of class Ia PI3K are necessary for MAPK signaling. We next investigated the location of PI3K in the MAPK cascade. Pharmacological inhibitors and dominant negative forms of PI3K were found to block the activation of Ras induced by EGF. Upstream from Ras, although association of Grb2 with its conventional effectors was independent of PI3K, we have observed that the recruitment of the tyrosine phosphatase SHP2 required PI3K. Because SHP2 was also essential for Ras activation, this suggested the existence of a PI3K/SHP2 pathway leading to the activation of Ras. In addition, we have observed that the docking protein Gab1, which is involved in PI3K activation during EGF stimulation, is also implicated in this pathway downstream of PI3K. Indeed, the association of Gab1 with SHP2 was blocked by PI3K inhibitors, and expression of Gab1 mutant deficient for binding to SHP2 was found to inhibit Ras stimulation without interfering with PI3K activation. These results show that, in addition to Shc and Grb2, a PI3K-dependent pathway involving Gab1 and SHP2 is essential for Ras activation under EGF stimulation.     

Sprouty-related Ena/vasodilator-stimulated phosphoprotein homology 1-domain-containing protein (SPRED1), a tyrosine-protein phosphatase non-receptor type 11 (SHP2) substrate in the Ras/extracellular signal-regulated kinase (ERK) pathway

SHP2 is a tyrosine phosphatase involved in the activation of the Ras/ERK signaling pathway downstream of a number of receptor tyrosine kinases. One of the proposed mechanisms involving SHP2 in this context is to dephosphorylate and inactivate inhibitors of the Ras/ERK pathway. Two protein families bearing a unique, common domain, Sprouty and SPRED proteins, are possible candidates because they have been reported to inhibit the Ras/ERK pathway upon FGF activation. We tested whether any of these proteins are likely substrates of SHP2. Our findings indicate that Sprouty2 binds to the C-terminal tail of SHP2, which is an unlikely substrate binding site, whereas SPRED proteins bind to the tyrosine phosphatase domain that is known to be the binding site for its substrates. Overexpressed SHP2 was able to dephosphorylate SPREDs but not Sprouty2. Finally, we found two tyrosine residues on SPRED1 that are required, when phosphorylated, to inhibit Ras/ERK activation and identified Tyr-420 as a specific dephosphorylation target of SHP2. The evidence obtained indicates that SPRED1 is a likely substrate of SHP2, whose tyrosine dephosphorylation is required to attenuate the inhibitory action of SPRED1 in the Ras/ERK pathway.     

Small molecule inhibitors of SHP2 tyrosine phosphatase discovered by virtual screening

SHP2, encoded by PTPN11, is a non-receptor protein tyrosine phosphatase (PTP) containing two tandem Src homology-2 (SH2) domains. It is expressed ubiquitously and plays critical roles in growth factor mediated processes, primarily by promoting the activation of the RAS/ERK signaling pathway. Genetic and biochemical studies have identified SHP2 as the first bona fide oncoprotein in the PTP superfamily, and a promising target for anti-cancer and anti-leukemia therapy. Here, we report a structure-based approach to identify SHP2 inhibitors with a novel scaffold. Through sequential virtual screenings and in vitro inhibition assays, a reversible competitive SHP2 inhibitor (C21) was identified. C21 is structurally distinct from all known SHP2 inhibitors. Combining molecular dynamics simulation and binding free energy calculation, a most likely binding mode of C21 with SHP2 is proposed, and further validated by site-directed mutagenesis and structure-activity relationship studies. This binding mode is consistent with the observed potency and specificity of C21, and reveals the molecular determinants for further optimization based on the new scaffold.     

The neurite outgrowth multiadaptor RhoGAP, NOMA-GAP, regulates neurite extension through SHP2 and Cdc42

Neuronal differentiation involves the formation and extension of neuronal processes. We have identified a novel regulator of neurite formation and extension, the neurite outgrowth multiadaptor, NOMA-GAP, which belongs to a new family of multiadaptor proteins with RhoGAP activity. We show that NOMA-GAP is essential for NGF-stimulated neuronal differentiation and for the regulation of the ERK5 MAP kinase and the Cdc42 signaling pathways downstream of NGF. NOMA-GAP binds directly to the NGF receptor, TrkA, and becomes tyrosine phosphorylated upon receptor activation, thus enabling recruitment and activation of the tyrosine phosphatase SHP2. Recruitment of SHP2 is required for the stimulation of neuronal process extension and for sustained activation of ERK5 downstream of NOMA-GAP. In addition, we show that NOMA-GAP promotes neurite outgrowth by tempering activation of the Cdc42/PAK signaling pathway in response to NGF. NOMA-GAP, through its dual function as a multiadaptor and RhoGAP protein, thus plays an essential role downstream of NGF in promoting neurite outgrowth and extension.     

An autoregulatory feedback loop between Mdm2 and SHP that fine tunes Mdm2 and SHP stability

Mdm2 is a crucial negative regulator of the tumor suppressor function of p53. However, little is known about Mdm2 protein stability regulation by other tumor suppressors. Nuclear receptor small heterodimer partner (SHP, NROB2) functions as a tumor suppressor in liver cancer. We show here a surprising finding of a feedback regulatory loop between SHP and Mdm2. SHP stabilizes Mdm2 protein by abrogating Mdm2 self-ubiquitination, and Mdm2 in turn attenuates SHP protein levels under p53-deficient conditions. Such cross-regulation critically depends on the physical interaction of SHP with Mdm2 through the SHP K170 residue. The Mdm2-SHP interplay represents a novel component of Mdm2 signaling that is likely to dictate Mdm2 activity and function.     

SOCS3 exerts its inhibitory function on interleukin-6 signal transduction through the SHP2 recruitment site of gp130

Interleukin-6 is involved in the regulation of many biological activities such as gene expression, cell proliferation, and differentiation. The control of the termination of cytokine signaling is as important as the regulation of initiation of signal transduction pathways. Three families of proteins involved in the down-regulation of cytokine signaling have been described recently: (i) SH2 domain-containing protein-tyrosine phosphatases (SHP), (ii) suppressors of cytokine signaling (SOCS), and (iii) protein inhibitors of activated STATs (PIAS). We have analyzed the interplay of two inhibitors in the signal transduction pathway of interleukin-6 and demonstrate that the tyrosine phosphatase SHP2 and SOCS3 do not act independently but are functionally linked. The activation of one inhibitor modulates the activity of the other; Inhibition of SHP2 activation leads to increased SOCS3-mRNA levels, whereas increased expression of SOCS3 results in a reduction of SHP2 phosphorylation after activation of the interleukin-6 signal transduction pathway. Furthermore, we show that tyrosine 759 in gp130 is essential for both SHP2 and SOCS3 but not for SOCS1 to exert their inhibitory activities on interleukin-6 signal transduction. Besides SHP2, SOCS3 also interacts with the Tyr(P)-759 peptide of gp130. Taken together, our results suggest differences in the function of SOCS1 and SOCS3 and a link between SHP2 and SOCS3.     

Phosphoproteomics identified Endofin, DCBLD2, and KIAA0582 as novel tyrosine phosphorylation targets of EGF signaling and Iressa in human cancer cells

With the completion of the human genome project, analysis of enriched phosphotyrosyl proteins from epidermal growth factor (EGF)-induced phosphotyrosine proteome permits the identification of novel downstream substrates of the EGF receptor (EGFR). Using cICAT-based LC-MS/MS method, we identified and relatively quantified the tyrosine phosphorylation levels of 21 proteins between control and EGF-treated A431 human cervical cancer cells. Of these, Endofin, DCBLD2, and KIAA0582 were validated to be novel tyrosine-phosphorylation targets of EGF signaling and Iressa, a highly selective inhibitor of EGFR. In addition, EGFR activity was shown to be necessary for EGF-induced localization of Endofin, an FYVE domain-containing protein regulated by phosphoinositol lipid and engaged in endosome-mediated receptor modulation. Although several groups have conducted phosphoproteomics of EGF signaling in recent years, our study is the first to identify and validate Endofin, DCBLD2, and KIAA0582 as part of a complex EGF phosphotyrosine signaling network. These novel data will provide new insights into the complex EGF signaling and may have implications on target-directed cancer therapeutics.     

Roles of Gab1 and SHP2 in paxillin tyrosine dephosphorylation and Src activation in response to epidermal growth factor

Epidermal growth factor (EGF) induces paxillin tyrosine dephosphorylation and Src activation, but the signaling pathways that mediate these responses were largely undefined. We found that Gab1, a docking protein for the SHP2 protein-tyrosine phosphatase in EGF-stimulated cells, was associated with paxillin. SHP2 dephosphorylated paxillin and caused dissociation of Csk, a negative regulator of Src, from paxillin but had no effect on paxillin-Src association. A lower level of Src Tyr-530 phosphorylation was detected in paxillin-associated Src in EGF-stimulated cells. Expression of an SHP2 binding defective mutant of Gab1 (Gab1FF) or a catalytically inactive mutant of SHP2 (SHP2DN) prevented paxillin tyrosine dephosphorylation and Src activation induced by EGF. Importantly, Gab1FF blocked paxillin-SHP2 complex formation, Src Tyr-530 dephosphorylation, Erk activation, and cell migration induced by EGF. Inhibition of Src tyrosine kinase activity abrogated EGF-stimulated Erk activation and cell migration. Together, these results reveal that Gab1 recruits SHP2 to dephosphorylate paxillin, leading to dissociation of Csk from the paxillin-Src complex and Src activation and that Src is an SHP2 effector involved in EGF-stimulated Erk activation and cell migration.     

Beta-chemokine receptor CCR5 signals through SHP1, SHP2, and Syk

The beta-chemokine receptor CCR5 has been shown to modulate cell migration, proliferation, and immune functions and to serve as a co-receptor for the human immunodeficiency virus. We and others have shown that CCR5 activates related adhesion focal tyrosine kinase (RAFTK)/Pyk2/CAK-beta. In this study, we further characterize the signaling molecules activated by CCR5 upon binding to its cognate ligand, macrophage inflammatory protein-1beta (MIP1beta). We observed enhanced tyrosine phosphorylation of the phosphatases SHP1 and SHP2 upon MIP1beta stimulation of CCR5 L1.2 transfectants and T-cells derived from peripheral blood mononuclear cells. Furthermore, we observed that SHP1 associated with RAFTK. However, using a dominant-negative phosphatase-binding mutant of RAFTK (RAFTK(m906)), we found that RAFTK does not mediate SHP1 or SHP2 phosphorylation. SHP1 and SHP2 also associated with the adaptor protein Grb2 and the Src-related kinase Syk. Pretreatment of CCR5 L1.2 transfectants or T-cells with the phosphatase inhibitor orthovanadate markedly abolished MIP1beta-induced chemotaxis. Syk was also activated upon MIP1beta stimulation of CCR5 L1.2 transfectants or T-cells and associated with RAFTK. Overexpression of a dominant-negative Src-binding mutant of RAFTK (RAFTK(m402)) significantly attenuated Syk activation, whereas overexpression of wild-type RAFTK enhanced Syk activity, indicating that RAFTK acts upstream of CCR5-mediated Syk activation. Taken together, these results suggest that MIP1beta stimulation mediated by CCR5 induces the formation of a signaling complex consisting of RAFTK, Syk, SHP1, and Grb2.     

Probing the acting mode and advantages of RMC-4550 as an Src-homology 2 domain-containing protein tyrosine phosphatase (SHP2) inhibitor at molecular level through molecular docking and molecular dynamics

Abstract

The over-activation of Ras/mitogen-activated protein kinase (MAPK) signaling pathway associated with a variety of cancers is usually related with abnormal activation of Src-homology 2 domain-containing protein tyrosine phosphatase (SHP2). For this purpose, SHP2 has attracted extensive interest as a potential target for cancer treatment. RMC-4550, as a newly developed selective inhibitor of SHP2, possesses an overwhelming advantage over the previous generation inhibitor SHP099 in terms of in vitro activity. However, the binding mode of SHP2 with RMC-4550 and the reason for the high efficiency of RMC-4550 as SHP2 inhibitor at molecular level are still unclear. Therefore, in this study, the binding mode of RMC-4550 with SHP2 and the superiorities of RMC-4550 as inhibitor at binding affinity and dynamic interactive behavior with SHP2 were probed by molecular docking and molecular dynamics (MD) simulations. By comparing the results of molecular docking, it was found that SHP2 formed more tight interaction with RMC-4550 than that with SHP099. Subsequently, a series of post-dynamic analyses on three simulation trajectories (SHP2^WT, SHP2^SHP099 and SHP2^RMC-4550) were performed and found that the SHP2 protein bound with RMC-4550 maintained a firmer interaction between N-Src-homology 2 (N-SH2) and PTP domain throughout the MD simulation, leading to a more stable protein conformation. The finding here provides new clues for the design of SHP2 inhibitor against the over-activation of Ras/MAPK pathway.

Communicated by Ramaswamy H. Sarma     

The Protein-tyrosine-phosphatase SHP2 is phosphorylated on serine residues 576 and 591 by protein kinase C isoforms alpha, beta 1, beta 2, and eta.

To study whether protein kinase C (PKC) isoforms can interact with protein-tyrosine-phosphatases (PTPs) which are connected to the insulin signaling pathway, we co-overexpressed PKC isoforms together with insulin receptor, docking proteins, and the PTPs SHP1 and SHP2 in human embryonic kidney (HEK) 293 cells. After phorbol ester induced activation of PKC isoforms alpha, beta 1, beta 2, and eta, we could show a defined gel mobility shift of SHP2, indicating phosphorylation on serine/threonine residues. This phosphorylation was not dependent on insulin receptor or insulin receptor substrate-1 (IRS-1) overexpression and did not occur for the closely related phosphatase SHP1. Furthermore, PKC phosphorylation of SHP2 was completely blocked by the PKC inhibitor bisindolylmaleimide and was not detectable when SHP2 was co-overexpressed with kinase negative mutants of PKC beta 1 and -beta 2. The phosphorylation also occurred on endogenous SHP2 in Chinese hamster ovary (CHO) cells stably overexpressing PKC beta 2. Using point mutants of SHP2, we identified serine residues 576 and 591 as phosphorylation sites for PKC. However, no change of phosphatase activity by TPA treatment was detected in an in vitro assay. In summary, SHP2 is phosphorylated on serine residues 576 and 591 by PKC isoforms alpha, beta 1, beta 2, and eta.