Molecular Basis of Distinct Interactions Between Dok1 PTB Domain and Tyrosine-phosphorylated EGF Receptor

Integrated transcriptomics and metabolomics study of embryonic breast muscle of Jiaji ducks

Because number of matured muscle fibers in poultry does not increase after birth, the meat yield is mainly determined during embryogenesis. We previously indicated breast muscle grew rapidly from 18th day after hatching (E18) to E27, and almost stopped from E27 to E34 of Jiaji ducks, while the mechanism is unclear. This study utilized RNA-seq to explore the related genes of muscle development and their relationship with small molecule metabolites at E18, E27 and E34 of Jiaji ducks. Several thousand differentially expressed genes (DEGs) were detected among E18, E27 and E34. DEGs expression profiles included 8 trend maps, among which trend 1 was opposite to and trend 6 was consistent with breast muscle development trend of Jiaji ducks. Through joint analysis between trend 1 of DEGs and trend 1 of differential metabolites (DEMs), protein digestion and absorption pathway stood out. The decrease of COL8A2 gene expression will lead to the decrease of arginine content, which will inhibit the development of breast muscle in embryonic Jiaji duck. Similarly, joint analysis between trend 6 of DEGs and trend 6 of DEMs indicated the increase of GAMT gene expression will cause the increase of proline content, and then promote the development of breast muscle of Jiaji duck in embryonic period. These results will be helpful for further understanding the mechanism of muscle yields of Jiaji ducks.

Evolutionary conservation of Ebola virus proteins predicts important functions at residue level

MOTIVATION

The recent outbreak of Ebola virus disease (EVD) resulted in a large number of human deaths. Due to this devastation, the Ebola virus has attracted renewed interest as model for virus evolution. Recent literature on Ebola virus (EBOV) has contributed substantially to our understanding of the underlying genetics and its scope with reference to the 2014 outbreak. But no study yet, has focused on the conservation patterns of EBOV proteins.

RESULTS

We analyzed the evolution of functional regions of EBOV and highlight the function of conserved residues in protein activities. We apply an array of computational tools to dissect the functions of EBOV proteins in detail: (i) protein sequence conservation, (ii) protein-protein interactome analysis, (iii) structural modeling and (iv) kinase prediction. Our results suggest the presence of novel post-translational modifications in EBOV proteins and their role in the modulation of protein functions and protein interactions. Moreover, on the basis of the presence of ATM recognition motifs in all EBOV proteins we postulate a role of DNA damage response pathways and ATM kinase in EVD. The ATM kinase is put forward, for further evaluation, as novel potential therapeutic target.

AVAILABILITY AND IMPLEMENTATION

http://www.biw.kuleuven.be/CSB/EBOV-PTMs CONTACT: vera.vannoort@biw.kuleuven.beSupplementary information: Supplementary data are available at Bioinformatics online.

Subcellular compartmentalization of docking protein-1 contributes to progression in colorectal cancer

Full-length (FL) docking protein-1 (DOK1) is an adapter protein which inhibits growth factor and immune response pathways in normal tissues, but is frequently lost in human cancers. Small DOK1 variants remain in cells of solid tumors and leukemias, albeit, their functions are elusive. To assess the so far unknown role of DOK1 in colorectal cancer (CRC), we generated DOK1 mutants which mimic the domain structure and subcellular distribution of DOK1 protein variants in leukemia patients. We found that cytoplasmic DOK1 activated peroxisome-proliferator-activated-receptor-gamma (PPARγ) resulting in inhibition of the c-FOS promoter and cell proliferation, whereas nuclear DOK1 was inactive. PPARγ-agonist increased expression of endogenous DOK1 and interaction with PPARγ. Forward translation of this cell-based signaling model predicted compartmentalization of DOK1 in patients. In a large series of CRC patients, loss of DOK1 protein was associated with poor prognosis at early tumor stages (*p = 0.001; n = 1492). In tumors with cytoplasmic expression of DOK1, survival was improved, whereas nuclear localization of DOK1 correlated with poor outcome, indicating that compartmentalization of DOK1 is critical for CRC progression. Thus, DOK1 was identified as a prognostic factor for non-metastatic CRC, and, via its drugability by PPARγ-agonist, may constitute a potential target for future cancer treatments.

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Forward translation of a cell-based signaling model predicted clinical relevance for DOK1 in colorectal cancer (CRC).

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DOK1 is an independent prognostic factor in CRC patients, and its loss associated with poor survival.

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Cancer cell growth inhibition by DOK1 was increased (“drugable”) by PPARγ-agonist.

Poor survival due to failure to respond to clinical therapies prevents effective treatment of cancer. Thus, there is a high medical need for novel drug targets and biomarkers. DOK1 blocks pro-cancer signaling in the healthy body, but is often lost in tumors. We show that colorectal cancer patients who are positive for DOK1 have a better survival outcome than patients who are negative. Anti-diabetic drugs up-regulated DOK1 and promoted its protective actions against tumor cells. Our study therefore suggests DOK1 as a marker for good prognosis and as a potential drug target for therapy of colorectal cancer.

DOK2 inhibits EGFR-mutated lung adenocarcinoma

Somatic mutations in the EGFR proto-oncogene occur in ~15% of human lung adenocarcinomas and the importance of EGFR mutations for the initiation and maintenance of lung cancer is well established from mouse models and cancer therapy trials in human lung cancer patients. Recently, we identified DOK2 as a lung adenocarcinoma tumor suppressor gene. Here we show that genomic loss of DOK2 is associated with EGFR mutations in human lung adenocarcinoma, and we hypothesized that loss of DOK2 might therefore cooperate with EGFR mutations to promote lung tumorigenesis. We tested this hypothesis using genetically engineered mouse models and find that loss of Dok2 in the mouse accelerates lung tumorigenesis initiated by oncogenic EGFR, but not that initiated by mutated Kras. Moreover, we find that DOK2 participates in a negative feedback loop that opposes mutated EGFR; EGFR mutation leads to recruitment of DOK2 to EGFR and DOK2-mediated inhibition of downstream activation of RAS. These data identify DOK2 as a tumor suppressor in EGFR-mutant lung adenocarcinoma.

TROY interacts with Rho guanine nucleotide dissociation inhibitor α (RhoGDIα) to mediate Nogo-induced inhibition of neurite outgrowth

TROY can functionally substitute p75 to comprise the Nogo receptor complex, which transduces the inhibitory signal of myelin-associated inhibitory factors on axon regeneration following CNS injury. The inhibition of neurite extension relies on TROY-dependent RhoA activation, but how TROY activates RhoA remains unclear. Here, we firstly identified Rho guanine nucleotide dissociation inhibitor α (RhoGDIα) as a binding partner of TROY using GST pull-down combined with two-dimensional gel electrophoresis and mass spectra analysis. The interaction was further confirmed by coimmunoprecipitation in vitro and in vivo. Deletion mutagenesis revealed that two regions of the TROY intracellular domain (amino acids 234-256 and 321-350) were essential for the interaction with RhoGDIα. Secondly, TROY and RhoGDIα were coexpressed in postnatal dorsal root ganglion neurons, cortex neurons, and cerebellar granule neurons (CGNs). Thirdly, TROY/RhoGDIα association was potentiated by Nogo-66 and was independent of p75/RhoGDIα interaction. Fourthly, TROY/RhoGDIα interaction was still able to activate RhoA when p75 was deficient. Furthermore, RhoA activation was decreased dramatically when TROY was knocked down in p75-deficient CGNs cells. Finally, RhoGDIα overexpression abolished RhoA activation and following neurite outgrowth inhibition by Nogo-66 in both wild-type and p75-deficient CGNs. These results showed that the association of RhoGDIα with TROY contributed to TROY-dependent RhoA activation and neurite outgrowth inhibition after Nogo-66 stimulation.

DOK2 as a marker of poor prognosis of patients with gastric adenocarcinoma after curative resection

BACKGROUND

DOK2 is known as the substrate of chmeric p210bcr/abl oncoprotein characterizing chronic myelogenous leukemia with Philadelphia chromosome. Reduced DOK2 expression was recently reported in lung adenocarcinoma, suggesting that this protein acts as a tumor suppressor in solid tumors. The purpose of this study was to determine the significance of DOK2 in gastric cancer.

METHODS

The study subjects were 118 patients who underwent curative surgery for gastric cancer, as well as 7 gastric cancer cell lines. The tissues and cell lines were analyzed for DOK2 gene and protein expressions by histopathology and immunohistochemistry, and also using a microsatellite marker for loss of heterozygosity. Correlation of survival with clinicopathological parameters was investigated by univariate and multivariate analyses.

RESULTS

DOK2 expression was confirmed in the normal gastric mucosa. Considerable differences in the gene expression were noted among the gastric cell lines. Positive DOK2 expression was noted in the noncancerous regions of all pathological specimens, whereas 59 (50.0%) specimens of 118 patients were negatively stained in the tumor. Loss of heterozygosity was observed in 54.5% of DOK2(-) cases. DOK2(-) patients were more likely to develop recurrence than DOK2(+) and showed poorer 5-year overall survival (59.1%) than DOK2(+) (76.4%, P = .0403). Multivariate analysis identified pT (hazard ratio [HR] = 2.748, 95% confidence interval [95% CI] = 1.061-8.927, P = .0361), pN (HR = 2.486, 95% CI = 1.264-4.932, P = .0086), and DOK2(-) (HR = 2.343, 95% CI = 1.211-4.727, P = .0112) as significant and independent determinants of poor survival.

CONCLUSIONS

Our data suggest the potential usefulness of DOK2 as a marker of poor prognosis in patients with gastric cancer after curative resection.

Oncogenic tyrosine kinases target Dok-1 for ubiquitin-mediated proteasomal degradation to promote cell transformation

Cellular transformation induced by oncogenic tyrosine kinases is a multistep process involving activation of growth-promoting signaling pathways and inactivation of suppressor molecules. Dok-1 is an adaptor protein that acts as a negative regulator of tyrosine kinase-initiated signaling and opposes oncogenic tyrosine kinase-mediated cell transformation. Findings that its loss facilitates transformation induced by oncogenic tyrosine kinases suggest that Dok-1 inactivation could constitute an intermediate step in oncogenesis driven by these oncoproteins. However, whether Dok-1 is subject to regulation by oncogenic tyrosine kinases remained unknown. In this study, we show that oncogenic tyrosine kinases, including p210(bcr-abl) and oncogenic forms of Src, downregulate Dok-1 by targeting it for degradation through the ubiquitin-proteasome pathway. This process is dependent on the tyrosine kinase activity of the oncoproteins and is mediated primarily by lysine-dependent polyubiquitination of Dok-1. Importantly, restoration of Dok-1 levels strongly suppresses transformation of cells expressing oncogenic tyrosine kinases, and this suppression is more pronounced in the context of a Dok-1 mutant that is largely refractory to oncogenic tyrosine kinase-induced degradation. Our findings suggest that proteasome-mediated downregulation of Dok-1 is a key mechanism by which oncogenic tyrosine kinases overcome the inhibitory effect of Dok-1 on cellular transformation and tumor progression.

Mass spectrometry mapping of epidermal growth factor receptor phosphorylation related to oncogenic mutations and tyrosine kinase inhibitor sensitivity

The epidermal growth factor receptor (EGFR) plays an important role in cancer by activating downstream signals important in growth and survival. Inhibitors of EGFR are frequently selected as treatment for cancer including lung cancer. We performed an unbiased and comprehensive search for EGFR phosphorylation events related to somatic activating mutations and EGFR inhibitor (erlotinib) sensitivity. EGFR immunoprecipitation combined with high resolution liquid chromatography-mass spectrometry and label free quantitation characterized EGFR phosphorylation. Thirty (30) phosphorylation sites were identified including 12 tyrosine (pY), 12 serine (pS), and 6 threonine (pT). Site-specific phosphorylation was monitored by comparing ion signals from the corresponding unmodified peptide. Phosphorylation sites related to activating mutations in EGFR as well as sensitivity to erlotinib were identified using 31 lung cancer cell lines. We identified three sites (pY1092, pY1110, pY1172) correlated with activating mutations and three sites (pY1110, pY1172, pY1197) correlated with erlotinib sensitivity. Five sites (pT693, pY1092, pY1110, pY1172, and pY1197) were inhibited by erlotinib in concentration-dependent manner. Erlotinib sensitivity was confirmed using liquid chromatography coupled to multiple reaction monitoring (LC-MRM) and quantitative Western blotting. This LC-MS/MS strategy can quantitatively assess site-specific EGFR phosphorylation and can identify relationships between somatic mutations or drug sensitivity and protein phosphorylation.

Antibody effector mechanisms in myasthenia gravis-pathogenesis at the neuromuscular junction

Myasthenia gravis (MG) is an autoimmune disorder caused by autoantibodies that are either directed to the muscle nicotinic acetylcholine receptor (AChR) or to the muscle-specific tyrosine kinase (MuSK). These autoantibodies define two distinct subforms of the disease-AChR-MG and MuSK-MG. Both AChR and MuSK are expressed on the postsynaptic membrane of the neuromuscular junction (NMJ), which is a highly specialized region of the muscle dedicated to receive and process signals from the motor nerve. Autoantibody binding to proteins of the postsynaptic membrane leads to impaired neuromuscular transmission and muscle weakness. Pro-inflammatory antibodies of the human IgG1 and IgG3 subclass modulate the AChR, cause complement activation, and attract lymphocytes; together acting to decrease levels of the AChR and AChR-associated proteins and to reduce postsynaptic folding. In patients with anti-MuSK antibodies, there is no evidence of loss of junctional folds and no apparent loss of AChR density. Anti-MuSK antibodies are predominantly of the IgG4 isotype, which functionally differs from other IgG subclasses in its anti-inflammatory activity. Moreover, IgG4 undergoes a posttranslational modification termed Fab arm exchange that prevents cross-linking of antigens. These findings suggest that MuSK-MG may be different in etiological and pathological mechanisms from AChR-MG. The effector functions of IgG subclasses on synapse structure and function are discussed in this review.

Rap1GAP interacts with RET and suppresses GDNF-induced neurite outgrowth

Glial cell line-derived neurotrophic factor (GDNF) was originally recognized for its ability to promote survival of midbrain dopaminergic neurons, but it has since been demonstrated to be crucial for the survival and differentiation of many neuronal subpopulations, including motor neurons, sympathetic neurons, sensory neurons and enteric neurons. To identify possible effectors or regulators of GDNF signaling, we performed a yeast two-hybrid screen using the intracellular domain of RET, the common signaling receptor of the GDNF family, as bait. Using this approach, we identified Rap1GAP, a GTPase-activating protein (GAP) for Rap1, as a novel RET-binding protein. Endogenous Rap1GAP co-immunoprecipitated with RET in neural tissues, and RET and Rap1GAP were co-expressed in dopaminergic neurons of the mesencephalon. In addition, overexpression of Rap1GAP attenuated GDNF-induced neurite outgrowth, whereas suppressing the expression of endogenous Rap1GAP by RNAi enhanced neurite outgrowth. Furthermore, using co-immunoprecipitation analyses, we found that the interaction between RET and Rap1GAP was enhanced following GDNF treatment. Mutagenesis analysis revealed that Tyr981 in the intracellular domain of RET was crucial for the interaction with Rap1GAP. Moreover, we found that Rap1GAP negatively regulated GNDF-induced ERK activation and neurite outgrowth. Taken together, our results suggest the involvement of a novel interaction of RET with Rap1GAP in the regulation of GDNF-mediated neurite outgrowth.

Adapters in the organization of mast cell signaling

Mast cells are pivotal in innate immunity and play an important role in amplifying adaptive immunity. Nonetheless, they have long been known to be central to the initiation of allergic disorders. This results from the dysregulation of the immune response whereby normally innocuous substances are recognized as non-self, resulting in the production of IgE antibodies to these 'allergens'. Preformed and newly synthesized inflammatory (allergic) mediators are released from the mast cell following allergen-mediated aggregation of allergen-specific IgE bound to the high-affinity receptors for IgE (FcepsilonRI). Thus, the process by which the mast cell is able to interpret the engagement of FcepsilonRI into the molecular events necessary for release of their allergic mediators is of considerable therapeutic interest. Unraveling these molecular events has led to the discovery of a functional class of proteins that are essential in organizing activated signaling molecules and in coordinating and compartmentalizing their activity. These so-called 'adapters' bind multiple signaling proteins and localize them to specific cellular compartments, such as the plasma membrane. This organization is essential for normal mast cell responses. Here, we summarize the role of adapter proteins in mast cells focusing on the most recent advances toward understanding how these molecules work upon FcepsilonRI engagement.

The roles of Dok family adapters in immunoreceptor signaling

The mammalian Dok protein family has seven members (Dok-1-Dok-7). The Dok proteins share structural similarities characterized by the NH2-terminal pleckstrin homology and phosphotyrosine-binding domains followed by SH2 target motifs in the COOH-terminal moiety, indicating an adapter function. Indeed, Dok-1 was originally identified as a 62 kDa protein that binds with p120 rasGAP, a potent inhibitor of Ras, upon tyrosine phosphorylation by a variety of protein tyrosine kinases. Among the Dok family, only Dok-1, Dok-2, and Dok-3 are preferentially expressed in hematopoietic/immune cells. Dok-1 and its closest relative Dok-2 act as negative regulators of the Ras-Erk pathway downstream of many immunoreceptor-mediated signaling systems, and it is believed that recruitment of p120 rasGAP by Dok-1 and Dok-2 is critical to their negative regulation. By contrast, Dok-3 does not bind with p120 rasGAP. However, accumulating evidence has demonstrated that Dok-3 is a negative regulator of the activation of JNK and mobilization of Ca2+ in B-cell receptor-mediated signaling, where the interaction of Dok-3 with SHIP-1 and Grb2 appears to be important. Here, we review the physiological roles and underlying mechanisms of Dok family proteins.

Analysis of DOK-6 function in downstream signaling of RET in human neuroblastoma cells

Point mutations and structural alterations of the RET tyrosine kinase gene cause multiple endocrine neoplasia type 2 (MEN 2) and papillary thyroid carcinoma, respectively. RET activation by glial cell line-derived neurotrophic factor (GDNF) is essential for the development of the enteric nervous system and the kidney. The signal through RET tyrosine kinase requires several adaptor proteins including the DOK (downstream of kinase) family of proteins. Of the seven members of the DOK protein family, DOK-1, -4, -5, and -6 have been reported to play roles in the GDNF-RET signaling pathway. Although DOK-6 has been shown to bind to RET and promote GDNF-induced neurite outgrowth in mouse Neuro2A cells, DOK-6 function in human cells remains unclear. In the present study, we investigated the role of DOK-6 in GDNF-RET signaling in human cells including neuroblastoma cells. DOK-6 was constitutively localized to the plasma membrane via its pleckstrin homology (PH) domain, and was phosphorylated following RET activation via a MEN2A mutation or GDNF stimulation. However, DOK-6 could not significantly affect downstream signaling and neurite outgrowth in human neuroblastoma cells. The binding affinity of the DOK-6 phosphotyrosine-binding (PTB) domain to RET was much lower than that of the DOK-1, DOK-4, and SHC PTB domains to RET. These findings indicate that DOK-6 is involved in RET signaling with less influence when compared with DOK-1, DOK-4, and SHC.

LINGO-1 interacts with WNK1 to regulate nogo-induced inhibition of neurite extension

LINGO-1 is a component of the tripartite receptor complexes, which act as a convergent mediator of the intracellular signaling in response to myelin-associated inhibitors and lead to collapse of growth cone and inhibition of neurite extension. Although the function of LINGO-1 has been intensively studied, its downstream signaling remains elusive. In the present study, a novel interaction between LINGO-1 and a serine-threonine kinase WNK1 was identified by yeast two-hybrid screen. The interaction was further validated by fluorescence resonance energy transfer and co-immunoprecipitation, and this interaction was intensified by Nogo66 treatment. Morphological evidences showed that WNK1 and LINGO-1 were co-localized in cortical neurons. Furthermore, either suppressing WNK1 expression by RNA interference or overexpression of WNK1-(123-510) attenuated Nogo66-induced inhibition of neurite extension and inhibited the activation of RhoA. Moreover, WNK1 was identified to interact with Rho-GDI1, and this interaction was attenuated by Nogo66 treatment, further indicating its regulatory effect on RhoA activation. Taken together, our results suggest that WNK1 is a novel signaling molecule involved in regulation of LINGO-1 mediated inhibition of neurite extension.

Interaction of Mint2 with TrkA is involved in regulation of nerve growth factor-induced neurite outgrowth

TrkA receptor signaling is essential for nerve growth factor (NGF)-induced survival and differentiation of sensory neurons. To identify possible effectors or regulators of TrkA signaling, yeast two-hybrid screening was performed using the intracellular domain of TrkA as bait. We identified muc18-1-interacting protein 2 (Mint2) as a novel TrkA-binding protein and found that the phosphotyrosine binding domain of Mint2 interacted with TrkA in a phosphorylation- and ligand-independent fashion. Coimmunoprecipitation assays showed that endogenous TrkA interacted with Mint2 in rat tissue homogenates, and immunohistochemical evidence revealed that Mint2 and TrkA colocalized in rat dorsal root ganglion neurons. Furthermore, Mint2 overexpression inhibited NGF-induced neurite outgrowth in both PC12 and cultured dorsal root ganglion neurons, whereas inhibition of Mint2 expression by RNA interference facilitated NGF-induced neurite outgrowth. Moreover, Mint2 was found to promote the retention of TrkA in the Golgi apparatus and inhibit its surface sorting. Taken together, our data provide evidence that Mint2 is a novel TrkA-regulating protein that affects NGF-induced neurite outgrowth, possibly through a mechanism involving retention of TrkA in the Golgi apparatus.

Constitutive plasma membrane targeting and microdomain localization of Dok5 studied by single-molecule microscopy

In the present study, single-molecule fluorescence microscopy was used to examine the characteristics of plasma membrane targeting and microdomain localization of enhanced yellow fluorescent protein (eYFP)-tagged wild-type Dok5 and its variants in living Chinese hamster ovary (CHO) cells. We found that Dok5 can target constitutively to the plasma membrane, and the PH domain is essential for this process. Furthermore, single-molecule trajectories analysis revealed that Dok5 can constitutively partition into microdomain on the plasma membrane. Finally, the potential mechanism of microdomain localization of Dok5 was discussed. This study provided insights into the characteristics of plasma membrane targeting and microdomain localization of Dok5 in living CHO cells.

Phosphoproteomic analysis of Her2/neu signaling and inhibition

Her2/neu (Her2) is a tyrosine kinase belonging to the EGF receptor (EGFR)/ErbB family and is overexpressed in 20-30% of human breast cancers. We sought to characterize Her2 signal transduction pathways further by using MS-based quantitative proteomics. Stably transfected cell lines overexpressing Her2 or empty vector were generated, and the effect of an EGFR and Her2 selective tyrosine kinase inhibitor, PD168393, on these cells was characterized. Quantitative measurements were obtained on 462 proteins by using the SILAC (stable isotope labeling with amino acids in cell culture) method to monitor three conditions simultaneously. Of these proteins, 198 showed a significant increase in tyrosine phosphorylation in Her2-overexpressing cells, and 81 showed a significant decrease in phosphorylation. Treatment of Her2-overexpressing cells with PD168393 showed rapid reversibility of the majority of the Her2-triggered phosphorylation events. Phosphoproteins that were identified included many known Her2 signaling molecules as well as known EGFR signaling proteins that had not been previously linked to Her2, such as Stat1, Dok1, and delta-catenin. Importantly, several previously uncharacterized Her2 signaling proteins were identified, including Axl tyrosine kinase, the adaptor protein Fyb, and the calcium-binding protein Pdcd-6/Alg-2. We also identified a phosphorylation site in Her2, Y877, which is located in the activation loop of the kinase domain, is distinct from the known C-terminal tail autophosphorylation sites, and may have important implications for regulation of Her2 signaling. Network modeling, which combined phosphoproteomic results with literature-curated protein-protein interaction data, was used to suggest roles for some of the previously unidentified Her2 signaling proteins.

Interaction of SH2-Bbeta with RET is involved in signaling of GDNF-induced neurite outgrowth

RET receptor signalling is essential for glial-cell-line-derived neurotrophic factor (GDNF)-induced survival and differentiation of various neurons such as mesencephalic neurons. To identify proteins that mediate RET-dependent signaling, yeast two-hybrid screening was performed with the intracellular domain of RET as bait. We identified a new interaction between RET and the adapter protein SH2-Bbeta. Upon GDNF stimulation of PC12-GFRalpha1-RET cells (that stably overexpress GDNF receptor alpha1 and RET), wild-type SH2-Bbeta co-immunoprecipitated with RET, whereas the dominant-negative SH2-Bbeta mutant R555E did not. RET interacted with endogenous SH2-Bbeta both in PC12-GFRalpha1-RET cells and in rat tissues. Mutagenesis analysis revealed that Tyr981 within the intracellular domain of RET was crucial for the interaction with SH2-Bbeta. Morphological evidence showed that SH2-Bbeta and RET colocalized in mesencephalic neurons. Furthermore, functional analysis indicated that overexpression of SH2-Bbeta facilitated GDNF-induced neurite outgrowth in both PC12-GFRalpha1-RET cells and cultured mesencephalic neurons, whereas the mutant R555E inhibited the effect. Moreover, inhibition of SH2-Bbeta expression by RNA interference caused a significant decrease of GDNF-induced neuronal differentiation in PC12-GFRalpha1-RET cells. Taken together, our results suggest that SH2-Bbeta is a new signaling molecule involved in GDNF-induced neurite outgrowth.