Blocking the function of tyrosine phosphatase SHP-2 by targeting its Src homology 2 domains

PZR suppresses innate immune response to RNA viral infection by inhibiting MAVS activation in interferon signaling mediated by RIG-I and MDA5

RNA viral infections seriously endanger human health. Src homology 2 (SH2) domain-containing protein tyrosine phosphatase 2 (SHP2) suppresses innate immunity against influenza A virus, and pharmacological inhibition of SHP2 provokes hepatic innate immunity. SHP2 binds and catalyzes tyrosyl dephosphorylation of protein zero-related (PZR), but the regulatory effect of PZR on innate immune response to viral infection is unclear. In this study, the transcription and protein level of PZR in host cells were found to be decreased with RNA viral infection, and high level of PZR was uncovered to inhibit interferon (IFN) signaling mediated by RIG-I and MDA5. Through localizing in mitochondria, PZR targeted and interacted with MAVS (also known as IPS-1/VISA/Cardif), suppressing the aggregation and activation of MAVS. Specifically, Y263 residue in ITIM is critical for PZR to exert immunosuppression under RNA viral infection. Moreover, the recruited SHP2 by PZR that modified with tyrosine phosphorylation under RNA viral infection might inhibit phosphorylation activation of MAVS. In conclusion, PZR and SHP2 suppress innate immune response to RNA viral infection through inhibiting MAVS activation. This study reveals the regulatory mechanism of PZR-SHP2-MAVS signal axis on IFN signaling mediated by RIG-I and MDA5, which may provide new sight for developing antiviral drugs.

Overcoming Immune Checkpoint Therapy Resistance with SHP2 Inhibition in Cancer and Immune Cells: A Review of the Literature and Novel Combinatorial Approaches

SHP2 (Src Homology 2 Domain-Containing Phosphatase 2) is a protein tyrosine phosphatase widely expressed in various cell types. SHP2 plays a crucial role in different cellular processes, such as cell proliferation, differentiation, and survival. Aberrant activation of SHP2 has been implicated in multiple human cancers and is considered a promising therapeutic target for treating these malignancies. The PTPN11 gene and functions encode SHP2 as a critical signal transduction regulator that interacts with key signaling molecules in both the RAS/ERK and PD-1/PD-L1 pathways; SHP2 is also implicated in T-cell signaling. SHP2 may be inhibited by molecules that cause allosteric (bind to sites other than the active site and attenuate activation) or orthosteric (bind to the active site and stop activation) inhibition or via potent SHP2 degraders. These inhibitors have anti-proliferative effects in cancer cells and suppress tumor growth in preclinical models. In addition, several SHP2 inhibitors are currently in clinical trials for cancer treatment. This review aims to provide an overview of the current research on SHP2 inhibitors, including their mechanism of action, structure-activity relationships, and clinical development, focusing on immune modulation effects and novel therapeutic strategies in the immune-oncology field.

PZR promotes tumorigenicity of lung cancer cells by regulating cell migration and invasion via modulating oxidative stress and cell adhesion

PZR is a transmembrane glycoprotein encoded by the MPZL1 gene. It serves as a specific binding protein and substrate of tyrosine phosphatase SHP-2 whose mutations cause developmental diseases and cancers. Bioinformatic analyses of cancer gene databases revealed that PZR is overexpressed in lung cancer and correlated with unfavorable prognosis. To investigate the role of PZR in lung cancer, we employed the CRISPR technique to knockout its expression and recombinant lentiviruses to overexpress it in lung adenocarcinoma SPC-A1 cells. While knockout of PZR reduced colony formation, migration, and invasion, overexpression of PZR had the opposite effects. Furthermore, when implanted in immunodeficient mice, PZR-knockout SPC-A1 cells showed suppressed tumor-forming ability. Finally, the underlying molecular mechanism for these functions of PZR is its positive role in activating tyrosine kinases FAK and c-Src and in maintaining the intracellular level of reactive oxygen species (ROS). In conclusion, our data indicated that PZR plays an important role in lung cancer development, and it may serve as a therapeutic target for anti-cancer development and as a biomarker for cancer prognosis.

Low-dose Dasatinib Ameliorates Hypertrophic Cardiomyopathy in Noonan Syndrome with Multiple Lentigines

Purpose

Noonan syndrome with multiple lentigines (NSML) is an autosomal dominant disorder presenting with hypertrophic cardiomyopathy (HCM). Up to 85% of NSML cases are caused by mutations in the PTPN11 gene that encodes for the Src homology 2 (SH2) domain-containing protein tyrosine phosphatase 2 (SHP2). We previously showed that low-dose dasatinib protects from the development of cardiac fibrosis in a mouse model of NSML harboring a Ptpn11^Y279C mutation. This study is performed to determine the pharmacokinetic (PK) and pharmacodynamic (PD) properties of a low-dose of dasatinib in NSML mice and to determine its effectiveness in ameliorating the development of HCM.

Methods

Dasatinib was administered intraperitoneally into NSML mice with doses ranging from 0.05 to 0.5 mg/kg. PK parameters of dasatinib in NSML mice were determined. PD parameters were obtained for biochemical analyses from heart tissue. Dasatinib-treated NSML mice (0.1 mg/kg) were subjected to echocardiography and assessment of markers of HCM by qRT-PCR. Transcriptome analysis was performed from the heart tissue of low-dose dasatinib-treated mice.

Results

Low-dose dasatinib exhibited PK properties that were linear across doses in NSML mice. Dasatinib treatment of between 0.05 and 0.5 mg/kg in NSML mice yielded an exposure-dependent inhibition of c-Src and PZR tyrosyl phosphorylation and inhibited AKT phosphorylation. We found that doses as low as 0.1 mg/kg of dasatinib prevented HCM in NSML mice. Transcriptome analysis identified differentially expressed HCM-associated genes in the heart of NSML mice that were reverted to wild type levels by low-dose dasatinib administration.

Conclusion

These data demonstrate that low-dose dasatinib exhibits desirable therapeutic PK properties that is sufficient for effective target engagement to ameliorate HCM progression in NSML mice. These data demonstrate that low-dose dasatinib treatment may be an effective therapy against HCM in NSML patients.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10557-021-07169-z.

Emerging chemical scaffolds with potential SHP2 phosphatase inhibitory capabilities - A comprehensive review

The drug discovery panorama is cluttered with promising therapeutic targets that have been deserted because of inadequate authentication and screening failures. Molecular targets formerly tagged as "undruggable" are nowadays being more cautiously cross-examined, and whilst they stay intriguing, numerous targets are emerging more accessible. Protein tyrosine phosphatases (PTPs) excellently exemplifies a class of molecular targets that have transpired as druggable, with several small molecules and antibodies recently turned available for further development. In this respect, SHP2, a PTP, has emerged as one of the potential targets in the current pharmacological research, particularly for cancer, due to its critical role in various signalling pathways. Recently, few molecules with excellent potency have entered clinical trials, but none could reach the clinic. Consequently, search for novel, non-toxic, and specific SHP2 inhibitors are on purview. In this review, general aspects of SHP2 including its structure and mechanistic role in carcinogenesis have been presented. It also sheds light on the development of novel molecular architectures belonging to diverse chemical classes that have been proposed as SHP2-specific inhibitors along with their structure-activity relationships (SARs), stemming from chemical, mechanism-based and computer-aided studies reported since January 2015 to July 2020 (excluding patents), focusing on their potency and selectivity. The encyclopedic facts and discussions presented herein will hopefully facilitate researchers to design new ligands with better efficacy and selectivity against SHP2.

Tyrosyl phosphorylation of PZR promotes hypertrophic cardiomyopathy in PTPN11-associated Noonan syndrome with multiple lentigines

Noonan syndrome with multiple lentigines (NSML) is a rare autosomal dominant disorder that presents with cardio-cutaneous-craniofacial defects. Hypertrophic cardiomyopathy (HCM) represents the major life-threatening presentation in NSML. Mutations in the PTPN11 gene that encodes for the protein tyrosine phosphatase (PTP), SHP2, represents the predominant cause of HCM in NSML. NSML-associated PTPN11 mutations render SHP2 catalytically inactive with an "open" conformation. NSML-associated PTPN11 mutations cause hypertyrosyl phosphorylation of the transmembrane glycoprotein, protein zero-related (PZR), resulting in increased SHP2 binding. Here we show that NSML mice harboring a tyrosyl phosphorylation-defective mutant of PZR (NSML/PZRY242F) that is defective for SHP2 binding fail to develop HCM. Enhanced AKT/S6 kinase signaling in heart lysates of NSML mice was reversed in NSML/PZRY242F mice, demonstrating that PZR/SHP2 interactions promote aberrant AKT/S6 kinase activity in NSML. Enhanced PZR tyrosyl phosphorylation in the hearts of NSML mice was found to drive myocardial fibrosis by engaging an Src/NF-κB pathway, resulting in increased activation of IL-6. Increased expression of IL-6 in the hearts of NSML mice was reversed in NSML/PZRY242F mice, and PZRY242F mutant fibroblasts were defective for IL-6 secretion and STAT3-mediated fibrogenesis. These results demonstrate that NSML-associated PTPN11 mutations that induce PZR hypertyrosyl phosphorylation trigger pathophysiological signaling that promotes HCM and cardiac fibrosis.

MPZL1 is highly expressed in advanced gallbladder carcinoma and promotes the aggressive behavior of human gallbladder carcinoma GBC‑SD cells

Myelin protein 0‑like 1 (MPZL1) has been reported to have a role in hepatocellular carcinoma. However, to the best of our knowledge, there have been no studies on the function and molecular mechanism of MPZL1 gene in gallbladder carcinoma. The present study confirmed that MPZL1 was upregulated in four gallbladder carcinoma tissues according to the mRNA microarray analysis. The results of the immunohistochemical analysis of tissues from 82 patients with gallbladder carcinoma demonstrated that patients with advanced tumor stages (both T and N stage) had higher positive expression of MPZL1. Moreover, a total of 20 cases of gallbladder carcinoma and matched paired paracarcinoma tissues along with 20 samples of healthy gallbladder tissue from patients with cholecystitis were analyzed using reverse transcription‑quantitative PCR and western blotting. The results demonstrated that the expression of MPZL1 in gallbladder carcinoma tissues was significantly higher than that of paired paracarcinoma tissues and randomly matched normal gallbladder epithelial tissues. According to the Tumor‑Node‑Metastasis classification, the expression level of MPZL1 protein in stage IV gallbladder carcinoma was significantly higher than that in stage III gallbladder carcinoma. The enhanced expression of MPZL1 gene appeared to improve the migration ability of GBC‑SD cells. Conversely, GBC‑SD cells that transfected with MPZL1 siRNA exhibited decreased migration ability. The results of proliferation experiments showed that the knockdown of MPZL1 siRNA caused impairments in GBC‑SD cell proliferation. On the contrary, the overexpression of MPZL1 increased the proliferation ability of GBC‑SD cells. The results of flow cytometry analyses indicated that the upregulation of MPZL1 had an anti‑apoptotic effect on GBC‑SD cells. In conclusion, the present study showed that the expression and protein levels of MPZL1 were significantly higher in gallbladder carcinoma tissues, especially in patients diagnosed with advanced tumor stages. Overexpression of MPZL1 may have promoted the invasion, metastasis, proliferation and survival of GBC‑SD cells.

PZR promotes metastasis of colorectal cancer through increasing FAK and Src phosphorylation

Metastasis is the main cause of death in patients with colorectal cancer (CRC), but the molecular mechanism is not yet fully understood. Previous studies have shown that P zero-related protein (PZR), a member of the immunoglobulin family, can promote fibronectin-dependent migration of mouse embryonic fibroblasts as well as invasion and metastasis of hepatic carcinoma cells. However, the role of PZR in CRC remains unclear. In this study, we determined the ectopic expression of PZR in CRC tissues, and results showed that PZR expression was increased not only in tumors with higher pathological stage, but also in tumors with distant metastasis. Through PZR-knockdown and overexpression in CRC cell lines, we found that the expression of PZR had significant effect on the invasion and migration of CRC cells as well as the phosphorylation of pro-metastasis proteins including focal adhesion kinase (FAK) and Src. Taken together, this study indicates that PZR may promote the invasion and migration of CRC cells through increasing the phosphorylation of FAK and Src, which provides a new theoretical basis and a possible marker for the diagnosis or prognosis of CRC metastasis.

Structural and biochemical studies of the extracellular domain of Myelin protein zero-like protein 1

Myelin protein zero-like protein 1 (MPZL1) is a member of the immunoglobulin superfamily, and is also a receptor of concanavalin A (ConA). MPZL1 is upregulated in hepatocellular carcinoma (HCC) and accelerates migration of HCC cells. However, function of MPZL1 as a receptor of ConA and its role in HCC development are largely unknown. To elucidate the functional basis, we have determined the crystal structure of the extracellular domain of MPZL1 at 2.7 Å resolution. Overall, it folds like a typical immunoglobulin variable-like domain that is much like MPZ. Unexpectedly, we found Asn50 is a unique glycosylation site and the glycosylation mediates its interaction with ConA. Furthermore, we also found that MPZL1 exists as a homodimer in the crystal, in which hydrogen bonds between Ser86 and Val145 play an important role. Our results demonstrate that glycosylation of Asn50 is essential for its function as a receptor of ConA. We propose that dimerization of MPZL1 participates in control of its signal transmission in cell adhesion.

Sequential combination of docetaxel with a SHP-1 agonist enhanced suppression of p-STAT3 signaling and apoptosis in triple negative breast cancer cells

Triple negative breast cancer (TNBC) is an aggressive cancer for which prognosis remains poor. Combination therapy is a promising strategy for enhancing treatment efficacy. Blockade of STAT3 signaling may enhance the response of cancer cells to conventional chemotherapeutic agents. Here we used a SHP-1 agonist SC-43 to dephosphorylate STAT3 thereby suppressing oncogenic STAT3 signaling and tested it in combination with docetaxel in TNBC cells. We first analyzed messenger RNA (mRNA) expression of SHP-1 gene (PTPN6) in a public TNBC dataset (TCGA) and found that higher SHP-1 mRNA expression is associated with better overall survival in TNBC patients. Sequential combination of docetaxel and SC-43 in vitro showed enhanced anti-proliferation and apoptosis associated with decreased p-STAT3 and decreased STAT3-downstream effector cyclin D1 in the TNBC cell lines MDA-MB-231, MDA-MB-468, and HCC-1937. Ectopic expression of STAT3 reduced the increased cytotoxicity induced by the combination therapy. In addition, this sequential combination showed enhanced SHP-1 activity compared to SC-43 alone. Furthermore, the combination treatment-induced apoptosis was attenuated by small interfering RNA (siRNA) against SHP-1 or by ectopic expression of SHP-1 mutants that caused SC-43 to lose its SHP-1 agonist capability. Moreover, combination of docetaxel and SC-43 showed enhanced tumor growth inhibition compared to single-agent therapy in mice bearing MDA-MB-231 tumor xenografts. Our results suggest that the novel SHP-1 agonist SC-43 enhanced docetaxel-induced cytotoxicity by SHP-1 dependent STAT3 inhibition in human triple negative breast cancer cells. TNBC patients with high SHP-1 expressions show better survival. Docetaxel combined with SC-43 enhances cell apoptosis and reduces p-STAT3. SHP-1 inhibition reduces the enhanced effect of docetaxel-SC-43 combination. Docetaxel-SC-43 combination suppresses xenograft tumor growth and reduces p-STAT3.

KEY MESSAGES

TNBC patients with high SHP-1 expressions show better survival. Docetaxel combined with SC-43 enhances cell apoptosis and reduces p-STAT3. SHP-1 inhibition reduces the enhanced effect of docetaxel-SC-43 combination. Docetaxel-SC-43 combination suppresses xenograft tumor growth and reduces p-STAT3.

A sorafenib derivative and novel SHP-1 agonist, SC-59, acts synergistically with radiotherapy in hepatocellular carcinoma cells through inhibition of STAT3

Radiotherapy shows limited benefit as treatment for hepatocellular carcinoma (HCC). In this study, we aimed to overcome the radioresistance of HCC by using a novel sorafenib derivative, SC-59 that targets SHP-1-related signaling. HCC cell lines (SK-Hep1, Hep3B, and Huh7) were treated with sorafenib, SC-59, radiation, sorafenib plus radiation, or SC-59 plus radiation, and then apoptosis, colony formation, signal transduction and the phosphatase activity were analyzed. The synergistic effect of radiotherapy and SC-59 was analyzed using a combination index (CI) approach. In vivo efficacy was determined in a Huh7-bearing subcutaneous model. Mice were treated with radiation (5 Gy, one fraction per day) for 4 days, SC-59 (10mg/kg/day) for 24 days, or a combination. Tumor samples were further analyzed for p-STAT3 and SHP-1 activity. SC-59 displayed a better synergistic effect when used in combination with radiotherapy than sorafenib in HCC cell lines. SC-59 downregulated p-STAT3 and its downstream targets and increased SHP-1 phosphatase activity. Both ectopic STAT3 and inhibition of SHP-1 abolished SC-59-induced radiosensitization. Moreover, SC-59 significantly synergized radiotherapy in a Huh7 xenograft model by targeting SHP-1/STAT3 signaling. The novel sorafenib derivative, SC-59, acting as a SHP-1 agonist, displays a better synergistic effect when used in combination with radiotherapy than sorafenib for the treatment of HCC. Further clinical investigation is warranted.

Amplification of MPZL1/PZR promotes tumor cell migration through Src-mediated phosphorylation of cortactin in hepatocellular carcinoma

We have previously identified 1 241 regions of somatic copy number alterations (CNAs) in hepatocellular carcinoma (HCC). In the present study, we found that a novel recurrent focal amplicon, 1q24.1-24.2, targets the MPZL1 gene in HCC. Notably, there is a positive correlation between the expression levels of MPZL1 and intrahepatic metastasis of the HCC specimens. MPZL1 can significantly enhance the migratory and metastatic potential of the HCC cells. Moreover, we found that one of the mechanisms by which MPZL1 promotes HCC cell migration is by inducing the phosphorylation and activation of the pro-metastatic protein, cortactin. Additionally, we found that Src kinase mediates the phosphorylation and activation of cortactin induced by MPZL1 overexpression. Taken together, these findings suggest that MPZL1 is a novel pro-metastatic gene targeted by a recurrent region of copy number amplification at 1q24.1-24.2 in HCC.

SC-60, a dimer-based sorafenib derivative, shows a better anti-hepatocellular carcinoma effect than sorafenib in a preclinical hepatocellular carcinoma model

Sorafenib is the first approved targeted therapeutic reagent for hepatocellular carcinoma. Here, we report that SC-60, a dimer-based sorafenib derivative, overcomes the resistance of sorafenib and shows a better anti-hepatocellular carcinoma effect in vitro and in vivo. SC-60 substantially increased SH2 domain-containing phosphatase 1 (SHP-1) phosphatase activity in hepatocellular carcinoma cells and purified SHP-1 proteins, suggesting that SC-60 affects SHP-1 directly. Molecular docking and truncated mutants of SHP-1 further confirmed that SC-60 interferes with the inhibitory N-SH2 domain to relieve the closed catalytic protein tyrosine phosphatase domain of SHP-1. Deletion of N-SH2 domain (dN1) or point mutation (D61A) of SHP-1 abolished the effect of SC-60 on SHP-1, p-STAT3, and apoptosis. Importantly, SC-60 exhibited significant survival benefits compared with sorafenib in a hepatocellular carcinoma orthotopic model via targeting the SHP-1/STAT3-related signaling pathway. In summary, dimer derivative of sorafenib, SC-60, is a SHP-1 agonist and may be a potent reagent for hepatocellular carcinoma-targeted therapy.

Targeting protein tyrosine phosphatase SHP2 for the treatment of PTPN11-associated malignancies

Activating mutations in PTPN11 (encoding SHP2), a protein tyrosine phosphatase (PTP) that plays an overall positive role in growth factor and cytokine signaling, are directly associated with the pathogenesis of Noonan syndrome and childhood leukemias. Identification of SHP2-selective inhibitors could lead to the development of new drugs that ultimately serve as treatments for PTPN11-associated diseases. As the catalytic core of SHP2 shares extremely high homology to those of SHP1 and other PTPs that play negative roles in cell signaling, to identify selective inhibitors of SHP2 using computer-aided drug design, we targeted a protein surface pocket that is adjacent to the catalytic site, is predicted to be important for binding to phosphopeptide substrates, and has structural features unique to SHP2. From computationally selected candidate compounds, #220-324 effectively inhibited SHP2 activity with an IC50 of 14 μmol/L. Fluorescence titration experiments confirmed its direct binding to SHP2. This active compound was further verified for its ability to inhibit SHP2-mediated cell signaling and cellular function with minimal off-target effects. Furthermore, mouse myeloid progenitors with the activating mutation (E76K) in PTPN11 and patient leukemic cells with the same mutation were more sensitive to this inhibitor than wild-type cells. This study provides evidence that SHP2 is a "druggable" target for the treatment of PTPN11-associated diseases. As the small-molecule SHP2 inhibitor identified has a simple chemical structure, it represents an ideal lead compound for the development of novel anti-SHP2 drugs. Mol Cancer Ther; 12(9); 1738-48. ©2013 AACR.

Non-lineage/stage-restricted effects of a gain-of-function mutation in tyrosine phosphatase Ptpn11 (Shp2) on malignant transformation of hematopoietic cells

A common Shp2 mutation leads to myeloproliferative disease and malignant acute leukemia in stem cells and committed progenitors, associated with Shp2 maintaining chromosomal stability

Activating mutations in protein tyrosine phosphatase 11 (Ptpn11) have been identified in childhood acute leukemias, in addition to juvenile myelomonocytic leukemia (JMML), which is a myeloproliferative disorder (MPD). It is not clear whether activating mutations of this phosphatase play a causal role in the pathogenesis of acute leukemias. If so, the cell origin of leukemia-initiating stem cells (LSCs) remains to be determined. Ptpn11^E76K mutation is the most common and most active Ptpn11 mutation found in JMML and acute leukemias. However, the pathogenic effects of this mutation have not been well characterized. We have created Ptpn11^E76K conditional knock-in mice. Global Ptpn11^E76K/+ mutation results in early embryonic lethality. Induced knock-in of this mutation in pan hematopoietic cells leads to MPD as a result of aberrant activation of hematopoietic stem cells (HSCs) and myeloid progenitors. These animals subsequently progress to acute leukemias. Intriguingly, in addition to acute myeloid leukemia (AML), T cell acute lymphoblastic leukemia/lymphoma (T-ALL) and B-ALL are evolved. Moreover, tissue-specific knock-in of Ptpn11^E76K/+ mutation in lineage-committed myeloid, T lymphoid, and B lymphoid progenitors also results in AML, T-ALL, and B-ALL, respectively. Further analyses have revealed that Shp2 (encoded by Ptpn11) is distributed to centrosomes and that Ptpn11^E76K/+ mutation promotes LSC development, partly by causing centrosome amplification and genomic instability. Thus, Ptpn11^E76K mutation has non–lineage-specific effects on malignant transformation of hematopoietic cells and initiates acute leukemias at various stages of hematopoiesis.

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.

The murine ortholog of the SHP-2 binding molecule, PZR accelerates cell migration on fibronectin and is expressed in early embryo formation

The human P zero-related protein (hPZR) has a unique function in regulating cell migration. This activity is dependent on both its cytoplasmic immunoreceptor tyrosine inhibitory motif (ITIM) and its interaction with the tyrosine protein phosphatase, src homology phosphatase-2 (SHP-2). Here, using in silico and cDNA cloning approaches, we identify the murine ITIM-containing hPZR ortholog, mPZR, together with its ITIM-less isoform, mPZRb. We demonstrate that, like hPZR, these type 1 integral murine transmembrane isoforms are derived by differential splicing from a single gene transcription unit on mouse chromosome 1, and differ only in the sequence of their cytoplasmic domains. Importantly, mPZR mimicks hPZR functionally by accelerating SHP-2-mediated cell migration on fibronectin. Interestingly, we further demonstrate that although neither mPZR nor mPZRb is expressed in murine pluripotent embryonic stem cells, they first appear at approximately day 3 of blastocyst formation in vivo and of embryoid body formation in vitro. These studies thus provide the basis for defining the function of the mPZR isoforms in vivo, particularly with respect to their roles in regulating SHP-2-dependent cell migration during development.

Antagonism or synergism. Role of tyrosine phosphatases SHP-1 and SHP-2 in growth factor signaling

SHP-1 and SHP-2 are two Src homology 2 domain-containing tyrosine phosphatases with major pathological implications in cell growth regulating signaling. They share significant overall sequence identity, but their biological functions are often opposite. SHP-1 is generally considered as a negative signal transducer and SHP-2 as a positive one. However, the precise role of each enzyme in shared signaling pathways is not well defined. In this study, we investigated the interaction of these two enzymes in a single cell system by knocking down their expressions with small interfering RNAs and analyzing the effects on epidermal growth factor signaling. Interestingly, knockdown of either SHP-1 or SHP-2 caused significant reduction in the activation of ERK1/2 but not Akt. Furthermore, SHP-1, SHP-2, and Gab1 formed a signaling complex, and SHP-1 and SHP-2 interact with each other. The interaction of SHP-1 with Gab1 is mediated by SHP-2 because it was abrogated by knockdown of SHP-2, and SHP-2, but not SHP-1, binds directly to tyrosine-phosphorylated Gab1. Together, the data revealed that both SHP-1 and SHP-2 have a positive role in epidermal growth factor-induced ERK1/2 activation and that they act cooperatively rather than antagonistically. The interaction of SHP-1 and SHP-2 may be responsible for previously unexpected novel regulatory mechanism of cell signaling by tyrosine phosphatases.

FLT3/ITD mutation signaling includes suppression of SHP-1

Mutations in the FLT3 gene are the most common genetic alteration found in AML patients. FLT3 internal tandem duplication (ITD) mutations result in constitutive activation of FLT3 tyrosine kinase activity. The consequences of this activation are an increase in total phosphotyrosine content, persistent downstream signaling, and ultimately transformation of hematopoietic cells to factor-independent growth. The Src homology (SH)2 domain-containing protein-tyrosine phosphatase (SHP)-1 is involved in the down-regulation of a broad range of growth factor and cytokine-driven signaling cascades. Loss-of-function or deficiency of SHP-1 activity results in a hyperproliferative response of myelomonocytic cell populations to growth factor stimulation. In this study, we examined the possible role of SHP-1 in regulating FLT3 signaling. We found that transformation of TF-1 cells with FLT3/ITD mutations suppressed the activity of SHP-1 by approximately 3-fold. Suppression was caused by decreased SHP-1 protein expression, as analyzed at both the protein and RNA levels. In contrast, protein levels of SHP-2, a phosphatase that plays a stimulatory role in signaling through a variety of receptors, did not change significantly in FLT3 mutant cells. Suppressed SHP-1 protein levels in TF-1/ITD cells were partially overcome after cells were exposed to CEP-701, a selective FLT3 inhibitor. SHP-1 protein levels also increased in naturally occurring FLT3/ITD expressing AML cell lines and in primary FLT3/ITD AML samples after CEP-701 treatment. Furthermore, a small but reproducible growth/survival advantage was observed in both TF-1 and TF-1/ITD cells when SHP-1 expression was knocked down by RNAi. Taken together, these data provide the first evidence that suppression of SHP-1 by FLT3/ITD signaling may be another mechanism contributing to the transformation by FLT3/ITD mutations.