Cytoplasmic Protein Tyrosine Phosphatase Research Articles

Abstract 1183: A first-in-class and SHP1 allosteric inhibitor, SB8091, shows a good efficacy and safety profile in preclinical models

Abstract Introduction: Src homology 2 domain-containing phosphatase 1 (SHP1) is a cytoplasmic protein tyrosine phosphatase (PTP) that is primarily expressed in hematopoietic cells and is commonly recognized as a negative regulator of multiple signaling pathways1. Previously, we showed that inhibition of the phosphatase activity of SHP1 by a novel SHP1 allosteric inhibitor, SB6299, results in the activation of innate and adaptive immune cells and enhanced anti-tumor immune responses2. Here, we report SB8091, an advanced SHP1 allosteric inhibitor with a promising initial safety profile and improved pharmacokinetic properties. Methods: SHP1 inhibitors were developed through a structure-based drug design approach, and optimized for cellular activity on target, in vitro ADME, and in vivo pharmacokinetic properties. Pharmacokinetic (PK) and preliminary toxicity studies were performed with mice. The lead series was assessed in in-vitro studies with mouse or human primary immune cells. In-vivo efficacy and pharmacodynamic data were generated using mouse syngeneic tumor models. Results: Structurally, SB8091 seemed to stabilize the autoinhibitory form of SHP1 as an allosteric inhibitor, in a nanomolar range and which can explain the outstanding selectivity compared to other PTP enzymes, including SHP2. In several human primary immune cell types, SB8091 significantly increased cytokine responses and demonstrated significantly enhanced activity in NK cells and macrophages against various cancer target cells. As a single agent, this compound exhibited inhibitory effects on tumor growth when administered orally, and the efficacy was further enhanced when co-administered with anti-PD1 antibodies in various syngeneic tumor models. Notably, this effect was associated with a pharmacodynamic response marked by increased levels of phosphorylated substrates regulated by SHP1. SB8091 exhibited favorable pharmacokinetic properties for oral administration, and SafetyScreen data showed a very low potential for off-target activity and drug-drug interactions. Additionally, during a 2-week repeat pilot toxicity study in mice, SB8091 demonstrated excellent tolerability even at high doses, indicating a high therapeutic index (TI > 100). Conclusion: Our advanced compound, SB8091, is a potent, highly selective, and orally bioavailable allosteric inhibitor of SHP1. It has demonstrated excellent efficacy as a monotherapy or in combination with immune checkpoint blockers, with favorable drug properties and safety profiles. Research to advance to the clinical stage is being conducted.

PTPN11/Corkscrew activates local presynaptic MAPK signaling to regulate Synapsin, synaptic vesicle pools, and neurotransmission strength, with a dual requirement in neurons and glia.

Cytoplasmic protein tyrosine phosphatase (PTP) non-receptor type 11 (PTPN11) and Drosophila homolog Corkscrew (Csw) regulate the mitogen-activated protein kinase (MAPK) pathway via a conserved autoinhibitory mechanism. Disease causing loss-of-function (LoF) and gain-of-function (GoF) mutations both disrupt this autoinhibition to potentiate MAPK signaling. At the Drosophila neuromuscular junction (NMJ) glutamatergic synapse, LoF/GoF mutations elevate transmission strength and reduce activity-dependent synaptic depression. In both sexes of LoF/GoF mutations, the synaptic vesicles (SV) colocalized Synapsin phosphoprotein tether is highly elevated at rest, but quickly reduced with stimulation, suggesting a larger SV reserve pool with greatly heightened activity-dependent recruitment. Transmission electron microscopy of mutants reveals an elevated number of SVs clustered at the presynaptic active zones, suggesting that the increased vesicle availability is causative for the elevated neurotransmission. Direct neuron-targeted extracellular signal-regulated kinase (ERK) GoF phenocopies both increased local presynaptic MAPK/ERK signaling and synaptic transmission strength in mutants, confirming the presynaptic regulatory mechanism. Synapsin loss blocks this elevation in both presynaptic PTPN11 and ERK mutants. However, csw null mutants cannot be rescued by wildtype Csw in neurons: neurotransmission is only rescued by expressing Csw in both neurons and glia simultaneously. Nevertheless, targeted LoF/GoF mutations in either neurons or glia alone recapitulates the elevated neurotransmission. Thus, PTPN11/Csw mutations in either cell type is sufficient to upregulate presynaptic function, but a dual requirement in neurons and glia is necessary for neurotransmission. Taken together, we conclude PTPN11/Csw acts in both neurons and glia, with LoF and GoF similarly upregulating MAPK/ERK signaling to enhance presynaptic Synapsin-mediated SV trafficking.Significance statement Noonan syndrome (NS) is, by far, the most common RASopathy; a group of clinically-classified genetic syndromes caused by MAPK pathway alterations: it affects 1 in every 1000-2000 people. Patients present with cognitive deficits caused by PTPN11 mutations; with gain-of-function the most common basis for NS, and loss-of-function resulting in NS with multiple lentigines (NSML). We find NS/NSML patient-derived LoF/GoF PTPN11 mutations, as well as Drosophila homolog corkscrew LoF/GoF mutations, all increase presynaptic MAPK signaling, Synapsin turnover, and synaptic vesicle availability at presynaptic release sites. Surprisingly, we find PTPN11/corkscrew to be required in both glia and neurons to control neurotransmission strength. These findings suggest disease interventions manipulating presynaptic vesicle trafficking mechanisms, as well as therapeutic strategies targeting both glia and neurons.

Discovery of a potent and selective allosteric inhibitor targeting the SHP2 tunnel site for RTK-driven cancer treatment

Src homology 2 domain-containing phosphatase 2 (SHP2) is a cytoplasmic protein tyrosine phosphatase (PTP) that regulates signal transduction of receptor tyrosine kinases (RTKs). Abnormal SHP2 activity is associated with tumorigenesis and metastasis. Because SHP2 contains multiple allosteric sites, identifying inhibitors at specific allosteric binding sites remains challenging. Here, we used structure-based virtual screening to directly search for the SHP2 “tunnel site” allosteric inhibitor. A novel hit (70) was identified as the SHP2 allosteric inhibitor with an IC50 of 10.2 μM against full-length SHP2. Derivatization of hit compound 70 using molecular modeling-guided structure-based modification allowed the discovery of an effective and selective SHP2 inhibitor, compound 129, with 122-fold improved potency compared to the hit. Further studies revealed that 129 effectively inhibited signaling in multiple RTK-driven cancers and RTK inhibitor-resistant cancer cells. Remarkably, 129 was orally bioavailable (F = 55%) and significantly inhibited tumor growth in haematological malignancy. Taken together, compound 129 developed in this study may serve as a promising lead or candidate for cancers bearing RTK oncogenic drivers and SHP2-related diseases.

Progress in the correlation between PTPN12 gene expression and human tumors.

Background:The global morbidity of cancer is rising rapidly. Despite advances in molecular biology, immunology, and cytotoxic and immune-anticancer therapies, cancer remains a major cause of death worldwide. Protein tyrosine phosphatase non-receptor type 12 (PTPN12) is a new member of the cytoplasmic protein tyrosine phosphatase family, isolated from a cDNA library of adult colon tissue. Thus far, no studies have reviewed the correlation between PTPN12 gene expression and human tumors.Methods:This article summarizes the latest domestic and international research developments on how the expression of PTPN12 relates to human tumors. The extensive search in Web of Science and PubMed with the keywords including PTPN12, tumor, renal cell carcinoma, proto-oncogenes, tumor suppressor genes was undertaken.Results:More and more studies have shown that a tumor is essentially a genetic disease, arising from a broken antagonistic function between proto-oncogenes and tumor suppressor genes. When their antagonistic effect is out of balance, it may cause uncontrolled growth of cells and lead to the occurrence of tumors. PTPN12 is a tumor suppressor gene, so inhibiting its activity will lead directly or indirectly to the occurrence of tumors.Conclusion:The etiology, prevention, and treatment of tumors have become the focus of research around the world. PTPN12 is a tumor suppressor gene. In the future, PTPN12 might serve as a novel molecular marker to benefit patients, and even the development of tumor suppressor gene activation agents can form a practical research direction.

PTPN9 induces cell apoptosis by mitigating the activation of Stat3 and acts as a tumor suppressor in colorectal cancer.

BackgroundAccumulating evidence has shown that protein tyrosine phosphatases (PTPs) are involved in regulating the transduction of many signaling pathways and play important roles in modulating the progression of some cancers, but the functions of PTPs in cancers have not been well elucidated until now. Here, we aimed to identify the roles of protein tyrosine phosphatase nonreceptor type 9 (PTPN9), a cytoplasmic PTP, in the development of colorectal cancer and elucidate the regulatory mechanism involved.Materials and methodsCell viability assessment, colony formation assay, caspase-3 and caspase-9 activity assay, real-time PCR, and Western blot analysis were applied.ResultsOur results showed that PTPN9 expression was frequently downregulated in colorectal cancer tissues compared with adjacent normal tissues. Overexpression of PTPN9 mitigated cell growth and colony formation and induced cell apoptosis in colorectal cancer. Conversely, PTPN9 knockdown promoted cell growth and survival. Moreover, PTPN9 negatively regulated the activation of Stat3 and depressed its nuclear translocation in colorectal cancer. The effects of PTPN9 knockdown on cell apoptosis were attenuated by inhibition of the Stat3 pathway.ConclusionThese results indicate that PTPN9 inhibits cell growth and survival by repressing the activation of Stat3 in colorectal cancer, which suggests an important underlying mechanism of regulating cell growth and provides a novel candidate therapeutic target for colorectal cancer.

PTPN12/PTP-PEST Regulates Phosphorylation-Dependent Ubiquitination and Stability of Focal Adhesion Substrates in Invasive Glioblastoma Cells.

Glioblastoma (GBM) is an invasive brain cancer with tumor cells that disperse from the primary mass, escaping surgical resection and invariably giving rise to lethal recurrent lesions. Here we report that PTP-PEST, a cytoplasmic protein tyrosine phosphatase, controls GBM cell invasion by physically bridging the focal adhesion protein Crk-associated substrate (Cas) to valosin-containing protein (Vcp), an ATP-dependent protein segregase that selectively extracts ubiquitinated proteins from multiprotein complexes and targets them for degradation via the ubiquitin proteasome system. Both Cas and Vcp are substrates for PTP-PEST, with the phosphorylation status of tyrosine 805 (Y805) in Vcp impacting affinity for Cas in focal adhesions and controlling ubiquitination levels and protein stability. Perturbing PTP-PEST-mediated phosphorylation of Cas and Vcp led to alterations in GBM cell-invasive growth in vitro and in preclinical mouse models. Collectively, these data reveal a novel regulatory mechanism involving PTP-PEST, Vcp, and Cas that dynamically balances phosphorylation-dependent ubiquitination of key focal proteins involved in GBM cell invasion.Significance: PTP-PEST balances GBM cell growth and invasion by interacting with the ATP-dependent ubiquitin segregase Vcp/p97 and regulating phosphorylation and stability of the focal adhesion protein p130Cas.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/78/14/3809/F1.large.jpg Cancer Res; 78(14); 3809-22. ©2018 AACR.

Dual Allosteric Inhibition of SHP2 Phosphatase.

SHP2 is a cytoplasmic protein tyrosine phosphatase encoded by the PTPN11 gene and is involved in cell proliferation, differentiation, and survival. Recently, we reported an allosteric mechanism of inhibition that stabilizes the auto-inhibited conformation of SHP2. SHP099 (1) was identified and characterized as a moderately potent, orally bioavailable, allosteric small molecule inhibitor, which binds to a tunnel-like pocket formed by the confluence of three domains of SHP2. In this report, we describe further screening strategies that enabled the identification of a second, distinct small molecule allosteric site. SHP244 (2) was identified as a weak inhibitor of SHP2 with modest thermal stabilization of the enzyme. X-ray crystallography revealed that 2 binds and stabilizes the inactive, closed conformation of SHP2, at a distinct, previously unexplored binding site-a cleft formed at the interface of the N-terminal SH2 and PTP domains. Derivatization of 2 using structure-based design resulted in an increase in SHP2 thermal stabilization, biochemical inhibition, and subsequent MAPK pathway modulation. Downregulation of DUSP6 mRNA, a downstream MAPK pathway marker, was observed in KYSE-520 cancer cells. Remarkably, simultaneous occupation of both allosteric sites by 1 and 2 was possible, as characterized by cooperative biochemical inhibition experiments and X-ray crystallography. Combining an allosteric site 1 inhibitor with an allosteric site 2 inhibitor led to enhanced pharmacological pathway inhibition in cells. This work illustrates a rare example of dual allosteric targeted protein inhibition, demonstrates screening methodology and tactics to identify allosteric inhibitors, and enables further interrogation of SHP2 in cancer and related pathologies.

Allosteric Inhibitors of SHP2 with Therapeutic Potential for Cancer Treatment.

SHP2, a cytoplasmic protein-tyrosine phosphatase encoded by the PTPN11 gene, is involved in multiple cell signaling processes including Ras/MAPK and Hippo/YAP pathways. SHP2 has been shown to contribute to the progression of a number of cancer types including leukemia, gastric, and breast cancers. It also regulates T-cell activation by interacting with inhibitory immune checkpoint receptors such as the programmed cell death 1 (PD-1) and B- and T-lymphocyte attenuator (BTLA). Thus, SHP2 inhibitors have drawn great attention by both inhibiting tumor cell proliferation and activating T cell immune responses toward cancer cells. In this study, we report the identification of an allosteric SHP2 inhibitor 1-(4-(6-bromonaphthalen-2-yl)thiazol-2-yl)-4-methylpiperidin-4-amine (23) that locks SHP2 in a closed conformation by binding to the interface of the N-terminal SH2, C-terminal SH2, and phosphatase domains. Compound 23 suppresses MAPK signaling pathway and YAP transcriptional activity and shows antitumor activity in vivo. The results indicate that allosteric inhibition of SHP2 could be a feasible approach for cancer therapy.

Identification of an allosteric benzothiazolopyrimidone inhibitor of the oncogenic protein tyrosine phosphatase SHP2

The PTPN11 oncogene encodes the cytoplasmic protein tyrosine phosphatase SHP2, which, through its role in multiple signaling pathways, promotes the progression of hematological malignancies and other cancers. Here, we employ high-throughput screening to discover a lead chemical scaffold, the benzothiazolopyrimidones, that allosterically inhibits this oncogenic phosphatase by simultaneously engaging the C-SH2 and PTP domains. We improved our lead to generate an analogue that better suppresses SHP2 activity in vitro. Suppression of Erk phopsphorylation by the lead compound is also consistent with SHP2 inhibition in AML cells. Our findings provide an alternative starting point for therapeutic intervention and will catalyze investigations into the relationship between SHP2 conformational regulation, activity, and disease progression.

SHP2 Regulates the Osteogenic Fate of Growth Plate Hypertrophic Chondrocytes

Transdifferentiation of hypertrophic chondrocytes into bone-forming osteoblasts has been reported, yet the underlying molecular mechanism remains incompletely understood. SHP2 is an ubiquitously expressed cytoplasmic protein tyrosine phosphatase. SHP2 loss-of-function mutations in chondroid cells are linked to metachondromatosis in humans and mice, suggesting a crucial role for SHP2 in the skeleton. However, the specific role of SHP2 in skeletal cells has not been elucidated. To approach this question, we ablated SHP2 in collagen 2α1(Col2α1)-Cre- and collagen 10α1(Col10α1)-Cre-expressing cells, predominantly proliferating and hypertrophic chondrocytes, using “Cre-loxP”-mediated gene excision. Mice lacking SHP2 in Col2α1-Cre-expressing cells die at mid-gestation. Postnatal SHP2 ablation in the same cell population caused dwarfism, chondrodysplasia and exostoses. In contrast, mice in which SHP2 was ablated in the Col10α1-Cre-expressing cells appeared normal but were osteopenic. Further mechanistic studies revealed that SHP2 exerted its influence partly by regulating the abundance of SOX9 in chondrocytes. Elevated and sustained SOX9 in SHP2-deficient hypertrophic chondrocytes impaired their differentiation to osteoblasts and impaired endochondral ossification. Our study uncovered an important role of SHP2 in bone development and cartilage homeostasis by influencing the osteogenic differentiation of hypertrophic chondrocytes and provided insight into the pathogenesis and potential treatment of skeletal diseases, such as osteopenia and osteoporosis.

SHP2 regulates proliferation and tumorigenicity of glioma stem cells.

SHP2 is a cytoplasmic protein tyrosine phosphatase (PTPase) involved in multiple signaling pathways and was the first identified proto-oncogene PTPase. Previous work in glioblastoma (GBM) has demonstrated the role of SHP2 PTPase activity in modulating the oncogenic phenotype of adherent GBM cell lines. Mutations in PTPN11, the gene encoding SHP2, have been identified with increasing frequency in GBM. Given the importance of SHP2 in developing neural stem cells, and the importance of glioma stem cells (GSCs) in GBM oncogenesis, we explored the functional role of SHP2 in GSCs. Using paired differentiated and stem cell primary cultures, we investigated the association of SHP2 expression with the tumor stem cell compartment. Proliferation and soft agar assays were used to demonstrate the functional contribution of SHP2 to cell growth and transformation. SHP2 expression correlated with SOX2 expression in GSC lines and was decreased in differentiated cells. Forced differentiation of GSCs by removal of growth factors, as confirmed by loss of SOX2 expression, also resulted in decreased SHP2 expression. Lentiviral-mediated knockdown of SHP2 inhibited proliferation. Finally, growth in soft-agar was similarly inhibited by loss of SHP2 expression. Our results show that SHP2 function is required for cell growth and transformation of the GSC compartment in GBM.

Structural Elucidation of the Binding of the Vav‐SH2 Domain to the EphA2 Cytoplasmic Region

The Vav guanine nucleotide exchange factors (GEFs) facilitate the GDP/GTP exchange of the Rac/Rho family of small GTPases to modulate cytoskeletal organization, cell morphology and mobility. In endothelial cells, Vav interacts with the EphA2 receptor tyrosine kinase (RTK) with its C‐terminal SH2 domain and plays a crucial role in EphA2‐mediated angiogenesis in cancers. Two closely‐spaced tyrosines in the juxtamembrane segment (JM) of the EphA2 cytoplasmic region, Y588 and Y594, were the postulated Vav‐SH2 recognition sites. Quantitative mass spectrometry data suggests that both JM tyrosines are phosphorylated with high stoichiometry in mammalian cells. However, they exhibit different rates of dephosphorylation by human cytoplasmic protein tyrosine phosphatases (HCPTPs). To characterize the role of each JM phosphotyrosine in Vav‐SH2 binding, isothermal titration calorimetry (ITC) and 15N‐HSQC titration experiments were performed using bacterially expressed Vav1‐SH2 and synthetic JM peptides with different tyrosine phosphorylation patterns. The ITC data indicates Vav1‐SH2 binds preferentially to the doubly phosphorylated and the Y594‐phosphorylated version of JM peptide (JMpYpY and JMYpY), with a KD 10‐fold smaller than the Y588‐phosphorylated version (JMpYY). The 15N‐HSQC spectra suggests all three versions of synthetic JM phosphopeptides bind Vav‐SH2 in similar fashions. The chemical shift perturbation (CSP) analysis of the titration spectra reveals both the primary and secondary phosphotyrosine binding pockets of Vav1‐SH2 are involved in JM phosphopeptide recognition, suggesting each phosphotyrosine has its designated binding pocket. Subsequent 3D NOESY‐HSQC experiments and crystallization trials are undergoing in order to resolve the peptide configuration in the complex of the Vav‐SH2 domain and the JM phosphopeptides.Support or Funding InformationPurdue University Center for Cancer Research

The PTPN14 Tumor Suppressor Is a Degradation Target of Human Papillomavirus E7.

Activation of signaling pathways ensuring cell growth is essential for the proliferative competence of human papillomavirus (HPV)-infected cells. Tyrosine kinases and phosphatases are key regulators of cellular growth control pathways. A recently identified potential cellular target of HPV E7 is the cytoplasmic protein tyrosine phosphatase PTPN14, which is a potential tumor suppressor and is linked to the control of the Hippo and Wnt/beta-catenin signaling pathways. In this study, we show that the E7 proteins of both high-risk and low-risk mucosal HPV types can interact with PTPN14. This interaction is independent of retinoblastoma protein (pRb) and involves residues in the carboxy-terminal region of E7. We also show that high-risk E7 induces proteasome-mediated degradation of PTPN14 in cells derived from cervical tumors. This degradation appears to be independent of cullin-1 or cullin-2 but most likely involves the UBR4/p600 ubiquitin ligase. The degree to which E7 downregulates PTPN14 would suggest that this interaction is important for the viral life cycle and potentially also for the development of malignancy. In support of this we find that overexpression of PTPN14 decreases the ability of HPV-16 E7 to cooperate with activated EJ-ras in primary cell transformation assays.IMPORTANCE This study links HPV E7 to the deregulation of protein tyrosine phosphatase signaling pathways. PTPN14 is classified as a potential tumor suppressor protein, and here we show that it is very susceptible to HPV E7-induced proteasome-mediated degradation. Intriguingly, this appears to use a mechanism that is different from that employed by E7 to target pRb. Therefore, this study has important implications for our understanding of the molecular basis for E7 function and also sheds important light on the potential role of PTPN14 as a tumor suppressor.

Structural and Functional Consequences of Three Cancer-Associated Mutations of the Oncogenic Phosphatase SHP2.

The proto-oncogene PTPN11 encodes a cytoplasmic protein tyrosine phosphatase, SHP2, which is required for normal development and sustained activation of the Ras-MAPK signaling pathway. Germline mutations in SHP2 cause developmental disorders, and somatic mutations have been identified in childhood and adult cancers and drive leukemia in mice. Despite our knowledge of the PTPN11 variations associated with pathology, the structural and functional consequences of many disease-associated mutants remain poorly understood. Here, we combine X-ray crystallography, small-angle X-ray scattering, and biochemistry to elucidate structural and mechanistic features of three cancer-associated SHP2 variants harboring single point mutations within the N-SH2:PTP interdomain autoinhibitory interface. Our findings directly compare the impact of each mutation on autoinhibition of the phosphatase and advance the development of structure-guided and mutation-specific SHP2 therapies.

Loss of PTPN12 Stimulates Progression of ErbB2-Dependent Breast Cancer by Enhancing Cell Survival, Migration, and Epithelial-to-Mesenchymal Transition.

PTPN12 is a cytoplasmic protein tyrosine phosphatase (PTP) reported to be a tumor suppressor in breast cancer, through its capacity to dephosphorylate oncogenic receptor protein tyrosine kinases (PTKs), such as ErbB2. However, the precise molecular and cellular impact of PTPN12 deficiency in breast cancer progression remains to be fully clarified. Here, we addressed this issue by examining the effect of PTPN12 deficiency on breast cancer progression in vivo, in a mouse model of ErbB2-dependent breast cancer using a conditional PTPN12-deficient mouse. Our studies showed that lack of PTPN12 in breast epithelial cells accelerated breast cancer development and lung metastases in vivo. PTPN12-deficient breast cancer cells displayed enhanced tyrosine phosphorylation of the adaptor Cas, the adaptor paxillin, and the kinase Pyk2. They exhibited no detectable increase in ErbB2 tyrosine phosphorylation. PTPN12-deficient cells were more resistant to anoikis and had augmented migratory and invasive properties. Enhanced migration was corrected by inhibiting Pyk2. PTPN12-deficient breast cancer cells also acquired partial features of epithelial-to-mesenchymal transition (EMT), a feature of more aggressive forms of breast cancer. Hence, loss of PTPN12 promoted tumor progression in a mouse model of breast cancer, supporting the notion that PTPN12 is a tumor suppressor in human breast cancer. This function was related to the ability of PTPN12 to suppress cell survival, migration, invasiveness, and EMT and to inhibit tyrosine phosphorylation of Cas, Pyk2, and paxillin. These findings enhance our understanding of the role and mechanism of action of PTPN12 in the control of breast cancer progression.

SHP-2 Mediates Cryptosporidium parvum Infectivity in Human Intestinal Epithelial Cells.

The parasite, Cryptosporidium parvum, induces human gastroenteritis through infection of host epithelial cells in the small intestine. During the initial stage of infection, C. parvum is reported to engage host mechanisms at the host cell-parasite interface to form a parasitophorous vacuole. We determined that upon infection, the larger molecular weight proteins in human small intestinal epithelial host cells (FHs 74 Int) appeared to globally undergo tyrosine dephosphorylation. In parallel, expression of the cytoplasmic protein tyrosine phosphatase Src homology-2 domain-containing phosphatase 2 (SHP-2) increased in a time-dependent manner. SHP-2 co-localized with the C. parvum sporozoite and this interaction increased the rate of C. parvum infectivity through SH2-mediated SHP-2 activity. Furthermore, we show that one potential target that SHP-2 acts upon is the focal adhesion protein, paxillin, which undergoes moderate dephosphorylation following infection, with inhibition of SHP-2 rescuing paxillin phosphorylation. Importantly, treatment with an inhibitor to SHP-2 and with an inhibitor to paxillin and Src family kinases, effectively decreased the multiplicity of C. parvum infection in a dose-dependent manner. Thus, our study reveals an important role for SHP-2 in the pathogenesis of C. parvum. Furthermore, while host proteins can be recruited to participate in the development of the electron dense band at the host cell-parasite interface, our study implies for the first time that SHP-2 appears to be recruited by the C. parvum sporozoite to regulate infectivity. Taken together, these findings suggest that SHP-2 and its down-stream target paxillin could serve as targets for intervention.

SHP2 regulates osteoclastogenesis by promoting preosteoclast fusion.

Genes that regulate osteoclast (OC) development and function in both physiologic and disease conditions remain incompletely understood. Shp2 (the Src homology-2 domain containing protein tyrosine phosphatase 2), a ubiquitously expressed cytoplasmic protein tyrosine phosphatase, is implicated in regulating M-CSF and receptor activator of nuclear factor-κB ligand (RANKL)-evoked signaling; its role in osteoclastogenesis and bone homeostasis, however, remains unknown. Using a tissue-specific gene knockout approach, we inactivated Shp2 expression in murine OCs. Shp2 mutant mice are phenotypically osteopetrotic, featuring a marked increase of bone volume (BV)/total volume (TV) (+42.8%), trabeculae number (Tb.N) (+84.1%), structure model index (+119%), and a decrease of trabecular thickness (Tb.Th) (-34.1%) and trabecular spacing (Tb.Sp) (-41.0%). Biochemical analyses demonstrate that Shp2 is required for RANKL-induced formation of giant multinucleated OCs by up-regulating the expression of nuclear factor of activated T cells, cytoplasmic 1 (Nfatc1), a master transcription factor that is indispensable for terminal OC differentiation. Shp2 deletion, however, has minimal effect on M-CSF-dependent survival and proliferation of OC precursors. Instead, its deficiency aborts the fusion of OC precursors and formation of multinucleated OCs and decreases bone matrix resorption. Moreover, pharmacological intervention of Shp2 is sufficient to prevent preosteoclast fusion in vitro. These findings uncover a novel mechanism through which Shp2 regulates osteoclastogenesis by promoting preosteoclast fusion. Shp2 or its signaling partners could potentially serve as pharmacological targets to regulate the population of OCs locally and/or systematically, and thus treat OC-related diseases, such as periprosthetic osteolysis and osteoporosis.

Role of the Protein Tyrosine Phosphatase Shp2 in Homeostasis of the Intestinal Epithelium

Protein tyrosine phosphorylation is thought to be important for regulation of the proliferation, differentiation, and rapid turnover of intestinal epithelial cells (IECs). The role of protein tyrosine phosphatases in such homeostatic regulation of IECs has remained largely unknown, however. Src homology 2–containing protein tyrosine phosphatase (Shp2) is a ubiquitously expressed cytoplasmic protein tyrosine phosphatase that functions as a positive regulator of the Ras–mitogen-activated protein kinase (MAPK) signaling pathway operative downstream of the receptors for various growth factors and cytokines, and it is thereby thought to contribute to the regulation of cell proliferation and differentiation. We now show that mice lacking Shp2 specifically in IECs (Shp2 CKO mice) develop severe colitis and die as early as 3 to 4 weeks after birth. The number of goblet cells in both the small intestine and colon of Shp2 CKO mice was markedly reduced compared with that for control mice. Furthermore, Shp2 CKO mice showed marked impairment of both IEC migration along the crypt-villus axis in the small intestine and the development of intestinal organoids from isolated crypts. The colitis as well as the reduction in the number of goblet cells apparent in Shp2 CKO mice were normalized by expression of an activated form of K-Ras in IECs. Our results thus suggest that Shp2 regulates IEC homeostasis through activation of Ras and thereby protects against the development of colitis.

Macrophage Fusion Is Controlled by the Cytoplasmic Protein Tyrosine Phosphatase PTP-PEST/PTPN12

Macrophages can undergo cell-cell fusion, leading to the formation of multinucleated giant cells and osteoclasts. This process is believed to promote the proteolytic activity of macrophages toward pathogens, foreign bodies, and extracellular matrices. Here, we examined the role of PTP-PEST (PTPN12), a cytoplasmic protein tyrosine phosphatase, in macrophage fusion. Using a macrophage-targeted PTP-PEST-deficient mouse, we determined that PTP-PEST was not needed for macrophage differentiation or cytokine production. However, it was necessary for interleukin-4-induced macrophage fusion into multinucleated giant cells in vitro. It was also needed for macrophage fusion following implantation of a foreign body in vivo. Moreover, in the RAW264.7 macrophage cell line, PTP-PEST was required for receptor activator of nuclear factor kappa-B ligand (RANKL)-triggered macrophage fusion into osteoclasts. PTP-PEST had no impact on expression of fusion mediators such as β-integrins, E-cadherin, and CD47, which enable macrophages to become fusion competent. However, it was needed for polarization of macrophages, migration induced by the chemokine CC chemokine ligand 2 (CCL2), and integrin-induced spreading, three key events in the fusion process. PTP-PEST deficiency resulted in specific hyperphosphorylation of the protein tyrosine kinase Pyk2 and the adaptor paxillin. Moreover, a fusion defect was induced upon treatment of normal macrophages with a Pyk2 inhibitor. Together, these data argue that macrophage fusion is critically dependent on PTP-PEST. This function is seemingly due to the ability of PTP-PEST to control phosphorylation of Pyk2 and paxillin, thereby regulating cell polarization, migration, and spreading.

A critical role for SHP2 in STAT5 activation and growth factor–mediated proliferation, survival, and differentiation of human CD34+ cells

AbstractSHP2, a cytoplasmic protein-tyrosine phosphatase encoded by the PTPN11 gene, plays a critical role in developmental hematopoiesis in the mouse, and gain-of-function mutations of SHP2 are associated with hematopoietic malignancies. However, the role of SHP2 in adult hematopoiesis has not been addressed in previous studies. In addition, the role of SHP2 in human hematopoiesis has not been described. These questions are of considerable importance given the interest in development of SHP2 inhibitors for cancer treatment. We used shRNA-mediated inhibition of SHP2 expression to investigate the function of SHP2 in growth factor (GF) signaling in normal human CD34+ cells. SHP2 knockdown resulted in markedly reduced proliferation and survival of cells cultured with GF, and reduced colony-forming cell growth. Cells expressing gain-of-function SHP2 mutations demonstrated increased dependency on SHP2 expression for survival compared with cells expressing wild-type SHP2. SHP2 knockdown was associated with significantly reduced myeloid and erythroid differentiation with retention of CD34+ progenitors with enhanced proliferative capacity. Inhibition of SHP2 expression initially enhanced and later inhibited STAT5 phosphorylation and reduced expression of the antiapoptotic genes MCL1 and BCLXL. These results indicate an important role for SHP2 in STAT5 activation and GF-mediated proliferation, survival, and differentiation of human progenitor cells.