SHP-1 tyrosine phosphatase binding to c-Src kinase phosphor-dependent conformations: A comparative structural framework.

SHP-1 is a cytosolic tyrosine phosphatase that is primarily expressed in hematopoietic cells. It acts as a negative regulator of numerous signaling pathways and controls multiple cellular functions involved in cancer pathogenesis. This study describes the binding preferences of SHP-1 (pY536) to c-Srcopen (pY416) and c-Srcclose (pY527) through in silico approaches. Molecular dynamics simulation analysis revealed more conformational changes in c-Srcclose upon binding to SHP-1, as compared to its active/open conformation that is stabilized by the cooperative binding of the C-SH2 domain and C-terminal tail of SHP-1 to c-Src SH2 and KD. In contrast, c-Srcclose and SHP-1 interaction is mediated by PTP domain-specific WPD-loop (WPDXGXP) and Q-loop (QTXXQYXF) binding to c-Srcclose C-terminal tail residues. The dynamic correlation analysis demonstrated a positive correlation for SHP-1 PTP with KD, SH3, and the C-terminal tail of c-Srcclose. In the case of the c-Srcopen-SHP-1 complex, SH3 and SH2 domains of c-Srcopen were correlated to C-SH2 and the C-terminal tail of SHP-1. Our findings reveal that SHP1-dependent c-Src activation through dephosphorylation relies on the conformational shift in the inhibitory C-terminal tail that may ease the recruitment of the N-SH2 domain to phosphotyrosine residue, resulting in the relieving of the PTP domain. Collectively, this study delineates the intermolecular interaction paradigm and underlying conformational readjustments in SHP-1 due to binding with the c-Src active and inactive state. This study will largely help in devising novel therapeutic strategies for targeting cancer development.

A novel approach of recombinant laterosporulin production using the N-SH2 domain of SHP-2.

BACKGROUND: The current study was aimed at evaluating the role of the N-SH2 domain of SHP-2 as a partner protein in the expression of a toxic peptide, laterosporulin (LTS). We also investigated its effects on the formation of the disulfide bond and functional folding of the peptide in vitro. The N-SH2-LTS protein was expressed as a His-tagged fusion protein, capable of undergoing enzymatic cleavage. RESULTS: Based on the data presented herein, the total yield of the folded fusion protein from inclusion bodies was found to be about 105 mg/l, demonstrating a high-level of heterologous expression. After enzymatic cleavage, 1.5 mg of the folded recombinant laterosporulin was obtained from each 10 mg of the fusion protein. The purity of the recombinant laterosporulin was analyzed by RP-HPLC, to yield peptides with suitable purity (85%). CONCLUSIONS: Our findings indicated the advantages of using the N-SH2 domain of SHP-2 as a rapid and easy approach not only in producing easy target proteins but also in its function as a chaperone. N-SH2 domain of SHP-2 can influence on the purification of laterosporulin at reasonable yield and in a cost-effective fashion. The N-SH2 domain of SHP-2 as a protein chaperone may be potentially favorable to produce other proteins with disulfide bonds.

Druggable cancer phosphatases.

The phosphorylation status of oncoproteins is regulated by both kinases and phosphatases. Kinase inhibitors are rarely sufficient for successful cancer treatment, and phosphatases have been considered undruggable targets for cancer drug development. However, innovative pharmacological approaches for targeting phosphatases have recently emerged. Here, we review progress in the therapeutic targeting of oncogenic Src homology region 2 domain-containing phosphatase-2 (SHP2) and tumor suppressor protein phosphatase 2A (PP2A) and select other druggable oncogenic and tumor suppressor phosphatases. We describe the modes of action for currently available small molecules that target phosphatases, their use in drug combinations, and advances in clinical development toward future cancer therapies.

Determination of the molecular reach of the protein tyrosine phosphatase SHP-1.

Immune receptors signal by recruiting (or tethering) enzymes to their cytoplasmic tails to catalyze reactions on substrates within reach. This is the case for the phosphatase SHP-1, which, upon tethering to inhibitory receptors, dephosphorylates diverse substrates to control T cell activation. Precisely how tethering regulates SHP-1 activity is incompletely understood. Here, we measure binding, catalysis, and molecular reach for tethered SHP-1 reactions. We determine the molecular reach of SHP-1 to be 13.0 nm, which is longer than the estimate from the allosterically active structure (5.3 nm), suggesting that SHP-1 can achieve a longer reach by exploring multiple active conformations. Using modeling, we show that when uniformly distributed, receptor-SHP-1 complexes can only reach 15% of substrates, but this increases to 90% when they are coclustered. When within reach, we show that membrane recruitment increases the activity of SHP-1 by a 1000-fold increase in local concentration. The work highlights how molecular reach regulates the activity of membrane-recruited SHP-1 with insights applicable to other membrane-tethered reactions.

Overriding Adaptive Resistance to Sorafenib Through Combination Therapy With Src Homology 2 Domain-Containing Phosphatase 2 Blockade in Hepatocellular Carcinoma.

BACKGROUND AND AIMS: The survival benefit of sorafenib for patients with hepatocellular carcinoma (HCC) is unsatisfactory due to the development of adaptive resistance. Increasing evidence has demonstrated that drug resistance can be acquired by cancer cells by activating a number of signaling pathways through receptor tyrosine kinases (RTKs); nevertheless, the detailed mechanism for the activation of these alternative pathways is not fully understood. APPROACH AND RESULTS: Given the physiological role of Src homology 2 domain-containing phosphatase 2 (SHP2) as a downstream effector of many RTKs for activation of various signaling cascades, we first found that SHP2 was markedly up-regulated in our established sorafenib-resistant cell lines as well as patient-derived xenografts. Upon sorafenib treatment, adaptive resistance was acquired in HCC cells through activation of RTKs including AXL, epidermal growth factor receptor, EPH receptor A2, and insulin-like growth factor 1 receptor, leading to RAS/mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK), and AKT reactivation. We found that the SHP2 inhibitor SHP099 abrogated sorafenib resistance in HCC cell lines and organoid culture in vitro by blocking this negative feedback mechanism. Interestingly, this sensitization effect was also mediated by induction of cellular senescence. SHP099 in combination with sorafenib was highly efficacious in the treatment of xenografts and genetically engineered models of HCC. CONCLUSIONS: SHP2 blockade by SHP099 in combination with sorafenib attenuated the adaptive resistance to sorafenib by impeding RTK-induced reactivation of the MEK/ERK and AKT signaling pathways. SHP099 in combination with sorafenib may be a safe therapeutic strategy against HCC.

Siglec-G Deficiency Ameliorates Hyper-Inflammation and Immune Collapse in Sepsis via Regulating Src Activation.

Hyper-inflammation during acute phase and sequential hypo-inflammation during immunosuppressive phase in macrophages/monocytes lead to multiorgan failure syndrome and immune collapse of sepsis, in which toll-like receptor (TLR)-triggered inflammatory responses play a major role. Here, we reported that Siglecg deficiency attenuated TLR4-triggered pro-inflammatory cytokine production and increased anti-inflammatory cytokine [interleukin-10 [IL-10]] production in vivo and in vitro at both acute and immunosuppressive phases. Siglecg deficiency also protected mice from lipopolysaccharide (LPS)-induced sepsis with less inflammation in the lung and less tissue destruction in the spleen. Siglec-G inhibited proto-oncogene tyrosine-protein kinase Src (Src) activation via recruiting and activating tyrosine phosphatase Src homology region 2 domain-containing phosphatase-1 (SHP1) through immunoreceptor tyrosine-based inhibitory motif (ITIM) domain. Src could inhibit TLR4-induced inflammatory cytokines and promote anti-inflammatory cytokine IL-10. Mechanical investigation showed that Src could interact with and phosphorylate STAT3. Src could also promote HIF1α degradation through activating GSK3ß. Our study reveals that Siglec-G orchestrates TLR-induced inflammation, which outlines that blocking Siglec-G or activating Src may be a promising strategy for both acute and chronic inflammatory diseases.

Valproic acid increases NO production via the SH-PTP1-CDK5-eNOS-Ser(116) signaling cascade in endothelial cells and mice.

Valproic acid (VPA) with its inhibitory activity of histone deacetylase has been used in the treatment of epilepsy and bipolar disorder associated with cerebrovascular dysfunction. Because nitric oxide (NO) produced by endothelial NO synthase (eNOS) plays a role in the maintenance of vascular function, NO is likely to mediate VPA׳s drug effect, but its effect on NO production remains controversial. We investigated whether and how VPA regulates NO production in bovine aortic endothelial cells (BAECs) and mice. VPA increased NO production in BAECs, which was accompanied by a decrease in phosphorylation of eNOS at serine 116 (eNOS-Ser(116)) and cyclin-dependent kinase 5 at tyrosine 15 (CDK5-Tyr(15)). Ectopic expression of p25, a CDK5 activator, restored the VPA-inhibited eNOS-Ser(116) phosphorylation. In silico analysis revealed that the CDK5-Tyr(15) residue might be a substrate for SH2 domain-containing protein tyrosine phosphatase 1 (SH-PTP1), and CDK5 actually interacted with SH-PTP1. VPA increased SH-PTP1 expression and its activity. Stibogluconate, a specific SH-PTP1 inhibitor, reversed the VPA-inhibited phosphorylation of CDK5-Tyr(15) and eNOS-Ser(116). Knockdown of SH-PTP1 using small interfering RNA also reversed all the observed effects of VPA. Finally, both serum NO level and acetylcholine-induced aortic relaxation increased in VPA-medicated male mice. These increases were accompanied by increased SH-PTP1 expression and decreased phosphorylation of CDK5-Tyr(15) and eNOS-Ser(116) in mouse aortas. In conclusion, VPA increases NO production by inhibiting the CDK5-Tyr(15)-eNOS-Ser(116) phosphorylation axis; this process is mediated by SH-PTP1. VPA may be useful in the treatment of NO-related cerebrocardiovascular diseases.

Synthetic peptides containing ITIM-like sequences of IREM-1 (CD300F) differentially regulate MyD88 and TRIF-mediated TLR signalling through activation of SHP and/or PI3K.

The immune receptor expressed on myeloid cells 1 (IREM-1/CD300F) has been shown to inhibit various inflammatory processes in myeloid cells, such as macrophages and mast cells. IREM-1 exerts its inhibitory effect through its intracellular immunoreceptor tyrosine-based inhibition motifs (ITIMs). In order to generate immunomodulatory molecules that can regulate the inflammatory activation of macrophages, decapeptides representing each of the five ITIM-like sequences in the cytoplasmic tail of IREM-1 were synthesized in conjugation with human immunodeficiency virus-transactivator of transcription (HIV-TAT(48-57)), which was added to promote internalization of the peptides. Interestingly, all these TAT-ITIM fusion peptides inhibited Toll-like receptor (TLR)-mediated production of proinflammatory molecules, including matrix metalloproteinase (MMP)-9, tumour necrosis factor (TNF)-α, monocyte chemotactic protein-1 (MCP-1) and interleukin (IL)-8. When various TLR ligands were used to stimulate the human macrophage-like cell line human acute monocytic leukaemia cell line (THP)-1, the TAT-ITIM peptides blocked both myeloid differentiation factor 88 (MyD88) and Toll-interleukin 1 receptor (TIR)-domain-containing adapter-inducing interferon-ß (TRIF)-mediated TLR signalling pathways. Utilization of specific inhibitors and detection of the active form of signalling adaptors by Western blot analysis further demonstrated that the inhibitory effects of these TAT-ITIM peptides require activation of Src homology 2 (SH2)-containing tyrosine phosphatase (SHP) and/or phosphoinositide 3-kinase (PI3K). These data indicate that these synthetic peptides may be used to regulate immune responses that involve TLR-mediated inflammatory activation of macrophages.

Syk protein tyrosine kinase involves PECAM-1 signaling through tandem immunotyrosine inhibitory motifs in human THP-1 macrophages.

Although recent evidence supports a functional relationship between platelet endothelial cell adhesion molecule (PECAM-1) and Syk tyrosine kinase, little is known about the interaction of Syk with PECAM-1. We report that down-regulation of Syk inhibits the spreading of human THP-1 macrophage cells. Moreover, our data indicate that Syk binds PECAM-1 through its immune tyrosine-based inhibitory motif (ITIM), and dual phosphorylation of the ITIM domain of PECAM-1 leads to activation of Syk. Our results indicate that the distance between the phosphotyrosines could be up to 22 amino acids in length, depending on the conformational flexibility, and that the dual ITIM tyrosine motifs of PECAM-1 facilitate immunoreceptor tyrosine-based activation motif-like signaling. The preferential binding of PECAM-1 to Src homology region 2 domain-containing phosphatase-2 or Syk may depend on their relative affinities, and could provide a mechanism by which signal transduction from PECAM-1 is internally regulated by both positive and negative signaling enzymes.

Docking protein Gab1 is an essential component of postnatal angiogenesis after ischemia via HGF/c-met signaling.

RATIONALE: Grb2-associated binder (Gab) docking proteins, consisting of Gab1, Gab2, and Gab3, have crucial roles in growth factor-dependent signaling. Various proangiogenic growth factors regulate angiogenesis and endothelial function. However, the roles of Gab proteins in angiogenesis remain elusive. OBJECTIVE: To elucidate the role of Gab proteins in postnatal angiogenesis. METHODS AND RESULTS: Endothelium-specific Gab1 knockout (Gab1ECKO) mice were viable and showed no obvious defects in vascular development. Therefore, we analyzed a hindlimb ischemia (HLI) model of control, Gab1ECKO, or conventional Gab2 knockout (Gab2KO) mice. Intriguingly, impaired blood flow recovery and necrosis in the operated limb was observed in all of Gab1ECKO, but not in control or Gab2KO mice. Among several proangiogenic growth factors, hepatocyte growth factor (HGF) induced the most prominent tyrosine phosphorylation of Gab1 and subsequent complex formation of Gab1 with SHP2 (Src homology-2-containing protein tyrosine phosphatase 2) and phosphatidylinositol 3-kinase subunit p85 in human endothelial cells (ECs). Gab1-SHP2 complex was required for HGF-induced migration and proliferation of ECs via extracellular signal-regulated kinase (ERK)1/2 pathway and for HGF-induced stabilization of ECs via ERK5. In contrast, Gab1-p85 complex regulated activation of AKT and contributed partially to migration of ECs after HGF stimulation. Microarray analysis demonstrated that HGF upregulated angiogenesis-related genes such as KLF2 (Krüppel-like factor 2) and Egr1 (early growth response 1) via Gab1-SHP2 complex in human ECs. In Gab1ECKO mice, gene transfer of vascular endothelial growth factor, but not HGF, improved blood flow recovery and ameliorated limb necrosis after HLI. CONCLUSION: Gab1 is essential for postnatal angiogenesis after ischemia via HGF/c-Met signaling.

Redox regulation of SH2-domain-containing protein tyrosine phosphatases by two backdoor cysteines.

Protein tyrosine phosphatases (PTPs) are known to be regulated by phosphorylation, localization, and protein-protein interactions. More recently, redox-dependent inactivation has emerged as a critical factor in attenuating PTP activity in response to cellular stimuli. The tandem Src homology 2 domain-containing PTPs (SHPs) belong to the family of nonreceptor PTPs whose activity can be modulated by reversible oxidation in vivo. Herein we have investigated in vitro the kinetic and mechanistic details of reversible oxidation of SHP-1 and SHP-2. We have confirmed the susceptibility of the active site cysteines of SHPs to oxidative inactivation, with rate constants for oxidation similar to other PTPs (2-10 M(-1) s(-1)). Both SHP-1 and SHP-2 can be reduced and reactivated with the reductants DTT and gluthathione, whereas only the catalytic domain of SHP-2 is subject to reactivation by thioredoxin. Stabilization of the reversible oxidation state of the SHPs proceeds via a novel mechanism unlike for other PTPs wherein oxidation yields either a disulfide between the catalytic cysteine and a nearby "backdoor" cysteine or a sulfenylamide bond with the amide backbone nitrogen of the adjacent amino acid. Instead, in the reversibly oxidized and inactivated SHPs, the catalytic cysteine is rereduced while two conserved backdoor cysteines form an intramolecular disulfide. Formation of this backdoor-backdoor disulfide is dependent on the presence of the active site cysteine and can proceed via either active site cysteine-backdoor cysteine intermediate. Removal of both backdoor cysteines leads to irreversible oxidative inactivation, demonstrating that these two cysteines are necessary and sufficient for ensuring reversible oxidation of the SHPs. Our results extend the mechanisms by which redox regulation of PTPs is used to modulate intracellular signaling pathways.

Tyrosine phosphatase SHP-2 is a regulator of p27(Kip1) tyrosine phosphorylation.

Tyrosine phosphorylation of the cell cycle regulator p27(Kip1) plays a crucial role in its binding to cyclin dependent kinases and its subcellular localization. While Src and Bcr-Abl were shown to be responsible for tyrosine phosphorylation, no data are available on the dephosphorylation of p27(Kip1) and the phosphatase involved. Considering the associated dephosphorylation as a pivotal event in the regulation of cell cycle proteins, we focused on the tyrosine phosphatase SHP-2, which is regulated in promyelocytic leukemia cells on G-CSF stimulation. SHP-2 was thus found in association with p27(Kip1) and the G-CSF receptor, and we observed a nuclear translocation of SHP-2 on G-CSF stimulation. Using a catalytically inactive form of SHP-2 and siRNA directed against SHP-2, we could demonstrate the involvement of SHP-2 in tyrosine dephosphorylation of p27(Kip1). Moreover, SHP-2 was strongly activated on G-CSF stimulation and specifically dephosphorylated p27(Kip1) in vitro. Most importantly, we could illustrate that SHP-2 modulates p27(Kip1) stability and contributes to p27(Kip1)-mediated cell cycle progression. Taken together, our results demonstrate that SHP-2 is a key regulator of p27(Kip1) tyrosine phosphorylation.

Phosphorylation and localization of protein-zero related (PZR) in cultured endothelial cells.

Protein-zero related (PZR) is an immunoglobulin V (IgV)-type immunoreceptor with two immunoreceptor tyrosine-based inhibitory motifs (ITIMs). PZR interacts with Src homology 2 domain-containing tyrosine phosphatase (SHP-2) via its tyrosine-phosphorylated ITIMs, for which c-Src is a putative kinase. Towards elucidating PZR function in endothelial cells (ECs), the authors cloned PZR from bovine aortic endothelial cells (BAECs) and characterized it. Mature bovine PZR had 94.8% and 92.7% sequence identity with canine and human proteins, respectively, and the two ITIM sequences were conserved among higher vertebrates. PZR was expressed in many cell types and was localized to cell contacts and intracellular granules in BAECs and mesothelioma (REN) cells. Coimmunoprecipitation revealed that PZR, Grb-2-associated binder-1 (Gab1), and platelet endothelial cell adhesion molecule-1 (PECAM-1) were three major SHP-2-binding proteins in BAECs. H(2)O(2) enhanced PZR tyrosine phosphorylation and PZR/SHP-2 interaction in ECs in a dose-and time-dependent manner. To see if tyrosine kinases other than Src are also capable of phosphorylating PZR, the authors cotransfected HEK293 cells with PZR and one of several tyrosine kinases and found that c-Src, c-Fyn, c-Lyn, Csk, and c-Abl, but not c-Fes, phosphorylated PZR and increased PZR/SHP-2 interaction. These results suggest that PZR is a cell adhesion protein that may be involved in SHP-2-dependent signaling at interendothelial cell contacts.

[Expression of tyrosine phosphatase containing C-src homology SH-2 in benign prostate hyperplasia].

OBJECTIVE: To explore the expression of tyrosine phosphatase containing C-src homology SH-2 (SHP-1 and SHP-2) in benign prostate hyperplasia. METHODS: With En Vision two-step method, the expression of SHP-1 and SHP-2 was detected in 10 cases of normal prostate tissue, 30 cases of BPH, 20 cases of PIN, 20 cases of high differential Pca and 20 cases of low differential Pca. RESULT: The expression of SHP-2 in normal group was mainly distributed in the cytoplasm of secretive cells and basal cells, and a little part in the nucleu. In BPH it was distributed equally in the plasm and nucleu. In PIN, high differential Pca and low differential Pca, SHP-2 expressed mainly in nucleu. The average dyeing index of SHP-2 in each group is 0.4, 1.7, 2.1, 2.2 and 2.6. SHP-1 positive expression in normal prostate, BPH, PIN and high differential Pca showed differentiating layer staining in the cytoplasm of secretive cells and basal cells, while not in low differential Pca. The average dyeing index of SHP-1 in each group is 1.8, 1.8, 1.5, 1.2 and 0.4. CONCLUSION: There are transformation in signal transduction relation with SHP-1 and SHP-2 in the progress of prostate cell proliferation, differentiation and malignant. The abnormal activation and distribution of SHP-2 might induce prostate reconstruction and hyperplasia, even carcinoma.

Oxidation sensitivity of the catalytic cysteine of the protein-tyrosine phosphatases SHP-1 and SHP-2.

Reversible oxidation of the catalytic cysteine of protein-tyrosine phosphatases (PTPs) has emerged as a putative mechanism of activity regulation by physiological cell stimulation with growth factors, and by cell treatments with adverse agents such as UV irradiation. We compared SHP-1 and SHP-2, two structurally related cytoplasmic protein-tyrosine phosphatases with different cellular functions and cell-specific expression patterns, for their intrinsic susceptibility to oxidation by H(2)O(2). The extent of oxidation was monitored by detecting the modification of the PTP catalytic cysteine by three different methods, including a modified in-gel PTP assay, alkylation with a biotinylated iodoacetic acid derivative, and an antibody against oxidized PTPs. Dose-response curves for oxidation of the catalytic domains of SHP-1 and SHP-2 were similar. SHP-1 and -2 require relatively high H(2)O(2) concentrations for oxidation (half-maximal oxidation at 0.1-0.5 mM). For SHP-1, the SH2 domains had a significant protective function with respect to oxidation. In EOL-1 cells, SHP oxidation by exogenous H(2)O(2) in general and SHP-2 oxidation in particular was strongly diminished compared to HEK293 cells, at least partially related to a generally lower oxidant sensitivity of the EOL-1 cells. The data suggest that the differential cell functions of SHP-1 and SHP-2 are not related to differences in oxidation sensitivity. The modulating effects of SH2 domains for oxidation of these PTPs are in support of an enhanced oxidation susceptibility of activated SHPs.

The tyrosine phosphatase Shp2 interacts with NPM-ALK and regulates anaplastic lymphoma cell growth and migration.

Anaplastic large cell lymphomas (ALCL) are mainly characterized by the reciprocal translocation t(2;5)(p23;q35) that involves the anaplastic lymphoma kinase (ALK) gene and generates the fusion protein NPM-ALK with intrinsic tyrosine kinase activity. NPM-ALK triggers several signaling cascades, leading to increased cell growth, resistance to apoptosis, and changes in morphology and migration of transformed cells. To search for new NPM-ALK interacting molecules, we developed a mass spectrometry-based proteomic approach in HEK293 cells expressing an inducible NPM-ALK and identified the tyrosine phosphatase Shp2 as a candidate substrate. We found that NPM-ALK was able to bind Shp2 in coprecipitation experiments and to induce its phosphorylation in the tyrosine residues Y542 and Y580 both in HEK293 cells and ALCL cell lines. In primary lymphomas, antibodies against the phosphorylated tyrosine Y542 of Shp2 mainly stained ALK-positive cells. In ALCL cell lines, Shp2-constitutive phosphorylation was dependent on NPM-ALK, as it significantly decreased after short hairpin RNA (shRNA)-mediated NPM-ALK knock down. In addition, only the constitutively active NPM-ALK, but not the kinase dead NPM-ALK(K210R), formed a complex with Shp2, Gab2, and growth factor receptor binding protein 2 (Grb2), where Grb2 bound to the phosphorylated Shp2 through its SH2 domain. Shp2 knock down by specific shRNA decreased the phosphorylation of extracellular signal-regulated kinase 1/2 and of the tyrosine residue Y416 in the activation loop of Src, resulting in impaired ALCL cell proliferation and growth disadvantage. Finally, migration of ALCL cells was reduced by Shp2 shRNA. These findings show a direct involvement of Shp2 in NPM-ALK lymphomagenesis, highlighting its critical role in lymphoma cell proliferation and migration.

The role of Shp2 (PTPN11) in cancer.

Tyrosyl phosphorylation, which is controlled by protein-tyrosine kinases (PTKs) and protein-tyrosine phosphatases (PTPs), regulates numerous cellular processes. Altered expression and/or mutations in PTKs are linked to many forms of cancer, yet until recently little was known about the roles of PTPs in normal cells or in cancer. Earlier work established that a member of the PTP superfamily, PTEN, is an important tumor suppressor gene. We now know that at least one other PTP, the SH2 domain-containing phosphatase Shp2, is a bona fide oncogene that is mutated in several types of leukemia and hyperactivated by other mechanisms in some solid tumors. Understanding how Shp2 and other PTPs contribute to oncogenesis should provide new insights into pathogenesis and might suggest new targets for anti-neoplastic drugs.

Novel mitochondrial DNA mutations implicated in Noonan syndrome.

We report a case of Noonan syndrome with compound mutations in a sarcomeric contractile protein gene and several novel mutations in mitochondrial genes. Our case forms the first report, which emphasizes the importance of mtDNA mutations in Noonan syndrome and extends the scope for mitochondrial related syndromes.

The role of Helicobacter pylori CagA in gastric carcinogenesis.

Gastric carcinoma is the second most common cause of cancer-related deaths in the world, accounting for more than 400,000 deaths each year. Infection with cagA-positive Helicobacter pylori plays a pivotal role in the development of gastric adenocarcinoma. The cagA gene product CagA is directly delivered into gastric epithelial cells via the type IV secretion system. Following membrane localization and subsequent tyrosine phosphorylation by Src family kinases, CagA interacts with a variety of host cell proteins that are involved in the regulation of cell growth and motility in both phosphorylation-dependent and -independent manners. Of special interest is the interaction of CagA with the SH2 domain-containing tyrosine phosphatase SHP-2, gain-of-function mutations of which have recently been found in human malignancies. CagA binds to and activates SHP-2 in a tyrosine phosphorylation-dependent manner, thereby provoking abnormal activation of Erk MAP kinase while inducing elevated cell motility. Perturbation of SHP-2 and other signaling molecules by H pylori CagA may predispose cells to accumulate multiple genetic and epigenetic changes that promote multistep gastric carcinogenesis. Intriguingly, the structural polymorphism of CagA accounts for the differences in pathophysiological activity of individual CagA proteins, raising the possibility of subclassification of H pylori strains into benign and malignant strains.

ROS fusion tyrosine kinase activates a SH2 domain-containing phosphatase-2/phosphatidylinositol 3-kinase/mammalian target of rapamycin signaling axis to form glioblastoma in mice.

Glioblastoma multiforme is the most common and lethal form of primary brain cancer. Diagnosis of this advanced glioma has a poor prognosis due to the ineffectiveness of current therapies. Aberrant expression of receptor tyrosine kinases (RTK) in glioblastoma multiformes is suggestive of their role in initiation and maintenance of these tumors of the central nervous system. In fact, ectopic expression of the orphan RTK ROS is a frequent event in human brain cancers, yet the pathologic significance of this expression remains undetermined. Here, we show that a glioblastoma-associated, ligand-independent rearrangement product of ROS (FIG-ROS) cooperates with loss of the tumor suppressor gene locus Ink4a;Arf to produce glioblastomas in the mouse. We show that this FIG-ROS-mediated tumor formation in vivo parallels the activation of the tyrosine phosphatase SH2 domain-containing phosphatase-2 (SHP-2) and a phosphatidylinositol 3-kinase/Akt/mammalian target of rapamycin signaling axis in tumors and tumor-derived cell lines. We have established a fully penetrant preclinical model for adult onset of glioblastoma multiforme in keeping with major genetic events observed in the human disease. These findings provide novel and important insights into the role of ROS and SHP-2 function in solid tumor biology and set the stage for preclinical testing of targeted therapeutic approaches.