Subfamily Of Protein Tyrosine Phosphatases Research Articles

Role of Protein Tyrosine Phosphatase Receptor Type E (PTPRE) in Chemoresistant Retinoblastoma.

Protein tyrosine phosphatase receptor type E (PTPRE) is a member of the "classical" protein tyrosine phosphatase subfamily and regulates a variety of cellular processes in a tissue-specific manner by antagonizing the function of protein tyrosine kinases. PTPRE plays a tumorigenic role in different human cancer cells, but its role in retinoblastoma (RB), the most common malignant eye cancer in children, remains to be elucidated. Etoposide-resistant RB cell lines and RB patients display significant higher PTPRE expression levels compared to chemosensitive counterparts and the healthy human retina, respectively. PTPRE promotor methylation analyses revealed that PTPRE expression in RB is not regulated via this mechanism. Lentiviral PTPRE knockdown (KD) induced a significant decrease in growth kinetics, cell viability, and anchorage-independent growth of etoposide-resistant Y79 and WERI RB cells. Caspase-dependent apoptosis rates were significantly increased and a re-sensitization for etoposide could be observed after PTPRE depletion. In vivo chicken chorioallantoic membrane (CAM) assays revealed decreased tumor formation capacity as well as reduced tumor size and weight following PTPRE KD. Expression levels of miR631 were significantly downregulated in etoposide-resistant RB cells and patients. Transient miR631 overexpression resulted in significantly decreased PTPRE levels and concomitantly decreased proliferation and increased apoptosis levels in etoposide-resistant RB cells. These impacts mirror PTPRE KD effects, indicating a regulation of PTPRE via this miR. Additionally, PTPRE KD led to altered phosphorylation of protein kinase SGK3 and-dependent on the cell line-AKT and ERK1/2, suggesting potential PTPRE downstream signaling pathways. In summary, these results indicate an oncogenic role of PTPRE in chemoresistant retinoblastoma.

Abstract 777: Dual-Specificity Phosphatase 6 Deficiency Protects Against Intimal Hyperplasia After Arterial Injury

Dysregulation of MAPK activation cascades has been implicated in various diseases. Dual-specificity phosphatases (DUSPs) are a subfamily of protein tyrosine phosphatases that dephosphorylate MAPKs and modulate critical signaling pathways. Studies have shown that DUSP6 plays an important role in the heart and diet-induced obesity. However, the role of DUSP6 in vascular disease is largely unclear. Our goal is to investigate whether DUSP6 has a role in occlusive vascular disease. To this end, we used a neointima formation model by denuding endothelium of mouse femoral arteries with a guide wire. We showed that DUSP6 was expressed at very low levels in the normal uninjured mouse arteries; however, DUSP6 expression was increased in the arterial wall of injured blood vessels, suggesting a potential role of DUSP6 in vascular disease. Compared with wild-type mice, DUSP6 deficiency reduced neointima formation 4 weeks after arterial injury in mice. BrdU incorporation assays revealed that lack of DUSP6 resulted in decreased smooth muscle cell (SMC) proliferation in the neointima and media 2 weeks after injury, indicating DUSP6 may promote SMC proliferation in response to injury. Indeed, overexpressing DUSP6 in primary SMCs increased cellular proliferation, similar to that exerted by inflammatory cytokine IL-1β while knocking down DUSP6 expression with siRNA abrogated IL-1β-induced SMC proliferation. Pathway analysis showed that IL-1β-induced ERK1/2 activation preceded DUSP6 induction in SMCs. Intriguingly, ERK1/2 inhibitor U0126 abolished IL-1β-mediated ERK1/2 activation, DUSP6 induction, and SMC proliferation. Taken together, our results indicate that DUSP6 induction promotes vascular remodeling under pathological conditions. DUSP6 might be a therapeutic target for preventing/treating occlusive vascular disease.

Abstract 4544: PTP4A3 expression associated with increased invasion in esophageal adenocarcinoma

Abstract Esophageal adenocarcinoma (EAC) is the most rapidly growing solid malignancy with an overall 5-year survival rate of only 19%. The majority of EACs are diagnosed with advanced locoregional disease requiring neoadjuvant chemoradiation followed by esophagectomy. Understanding the molecular mechanisms associated with locoregional invasion are crucial for improving the treatment outcome. Protein tyrosine phosphatase (PTP) type IVA member 3 (PTP4A3/PRL-3) is part of the PTP subfamily, which are phosphatases with dual-specificity. PTP4A3 has been shown to be overexpressed in a number of cancer types and often correlates with cell proliferation, migration, invasion, tumor growth, and metastasis. Here, we examine PTP4A3’s potential role in the invasive properties of EAC. Methods: We analyzed PTP4A3 mRNA levels of 122 chemo-naïve EAC samples using Human Gene 2.1 ST Arrays and compared these to available histological features. We also used RNA-seq analysis to examine the expression of PTP4A3 in 68 samples that consisted of Barrett’s Esophagus, low-grade dysplasia, high-grade dysplasia, and EAC. PTP4A3 knockdown was achieved by using small interfering RNA and a rhodamine derivative (BR-1) inhibitor and was confirmed by both RT-PCR and Western blot. WST and clonogenic assays were performed to assess cell proliferation in cell lines derived from EAC tumors. Cell invasion and migration were measured by matrigel invasion and cell migration assays. Results: PTP4A3 was significantly overexpressed in EAC samples compared to a cohort of normal esophageal samples (p<0.001). In addition, the expression of PTP4A3 increased with progression from Barrett’s to EAC. PTP4A3 was overexpressed in 15 EACs relative to 26 Barrett’s samples on U133A Array, which was confirmed in the 68-sample RNAseq progression cohort (p<0.01). Analysis of 122 EAC samples indicated that overexpression of PTP4A3 was significantly associated with decreased survival (p<0.05) and correlated with poor differentiation, high immune cell infiltration, and a high desmoplastic response (p<0.05). Inhibition of PTP4A3 in EAC cell lines led to a decrease in cell invasion and migration (p<0.01). However, there was no significant change in cell proliferation following knockdown. Conclusion: PTP4A3 is frequently overexpressed in EAC and is associated with decreased survival. Inhibition of PTP4A3 decreased matrigel invasion and cancer cell migration, suggesting that PTP4A3 may play a role in the invasion and metastases of EAC cells and could serve as a biomarker of more aggressive disease. Note: This abstract was not presented at the meeting. Citation Format: Zhuwen Wang. PTP4A3 expression associated with increased invasion in esophageal adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4544.

Abstract 2364: The phosphatase PRL-3 is a pro-survival oncogene in acute lymphoblastic leukemia

Abstract PRL-3, phosphatase of regenerating liver 3, is one member of a subfamily of protein tyrosine phosphatases that belongs to the dual-specificity phosphatases (DSPs). Accumulating evidence shows that PRL-3 is a biomarker of tumor progression and metastasis and high PRL-3 expression is associated with reduced overall and disease-free survival in a variety of solid tumors, suggesting it's importance in tumor recurrence. However, the role for PRL-3 in leukemia relapse has not yet been described. We have found that PRL-3 contributes to Acute Lymphoblastic Leukemia (ALL) malignancy by acting as a pro-survival gene, both in vitro and in vivo. Expression of PRL-3 in a MYC-induced zebrafish T-cell ALL model showed that PRL-3 expressing ALL had shorter latency and higher penetrance, compared with the fish injected with rag2:Myc; rag2:GFP alone. Growth after transplantation at low cell number was also significantly faster in the PRL3 expressing T-ALL, suggesting that PRL-3 plays an important role in ALL development and progression. We found PRL-3 to be highly expressed in a majority of human ALL compared to normal peripheral blood mononuclear cells (PBMNC), which suggests clinical relevance. Analysis of gene expression microarray data of 119 patient samples reveals that PRL-3 was highly expressed in 58% of the patients. In addition, PRL-3 had the highest expression in the most aggressive and treatment resistant subgroups of T-ALL, the TAL/LMO and Immature subtypes. PRL-3 is also expressed by human T-ALL cell lines using quantitative RT- PCR and immunoblotting. PRL-3 knockdown leads to significant apoptosis in T-ALL cells. The treatment of T-ALL cells using small molecule drugs including 2-cyano-2-ene-ester compound (Analog 3) and thieno [3,2-b] pyridine 1-oxide (thienopyridone) , also resulted in significant growth inhibition of T-ALL cells in part through >4-fold increase in apoptosis, measured by annexin V staining. In summary, our study provides evidence for a role of PRL-3 in T- ALL malignancy, and suggests that PRL3 may be a useful drug target in the treatment of this disease. Our future studies are focused on identifying the mechanisms by which PRL3 promotes T-ALL progression and survival. Citation Format: Min Wei, Kristin O'Leary, Jinpeng Liu, Chi Wang, Jessica Blackburn. The phosphatase PRL-3 is a pro-survival oncogene in acute lymphoblastic leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2364.

Structural and biochemical analysis of atypically low dephosphorylating activity of human dual-specificity phosphatase 28.

Dual-specificity phosphatases (DUSPs) constitute a subfamily of protein tyrosine phosphatases, and are intimately involved in the regulation of diverse parameters of cellular signaling and essential biological processes. DUSP28 is one of the DUSP subfamily members that is known to be implicated in the progression of hepatocellular and pancreatic cancers, and its biological functions and enzymatic characteristics are mostly unknown. Herein, we present the crystal structure of human DUSP28 determined to 2.1 Å resolution. DUSP28 adopts a typical DUSP fold, which is composed of a central β-sheet covered by α-helices on both sides and contains a well-ordered activation loop, as do other enzymatically active DUSP proteins. The catalytic pocket of DUSP28, however, appears hardly accessible to a substrate because of the presence of nonconserved bulky residues in the protein tyrosine phosphatase signature motif. Accordingly, DUSP28 showed an atypically low phosphatase activity in the biochemical assay, which was remarkably improved by mutations of two nonconserved residues in the activation loop. Overall, this work reports the structural and biochemical basis for understanding a putative oncological therapeutic target, DUSP28, and also provides a unique mechanism for the regulation of enzymatic activity in the DUSP subfamily proteins.

SmLMWPTP, a teleost low molecular weight protein tyrosine phosphatase, inhibits the immune response of peripheral blood leukocytes in a manner that depends on the conserved P-loop

Protein tyrosine phosphatases (PTPs) are a family of enzymes that play a key role in cellular signal transduction. Low molecular weight PTPs (LMWPTPs) are a subfamily of PTPs that are characterized by the presence of a conserved phosphate-binding loop (P-loop) with the signature sequence of (V/I)CXGNXCRS. To date, very little study on teleost LMWPTPs has been documented, and, as a result, the function of LMWPTPs in fish is essentially unknown. In this study, we identified a LMWPTP from turbot (Scophthalmus maximus) and examined its biological activity and functionality. The turbot LMWPTP (SmLMWPTP) is composed of 158 residues and possesses a typical P-loop sequence in the form of 12VCLGNICRS20. Purified recombinant SmLMWPTP (rSmLMWPTP) exhibited apparent phosphatase activity, which was optimal at pH 5 and 50°C. The activity of SmLMWPTP was abolished when C13 and, in particular, R19 of the P-loop were mutated. SmLMWPTP expression was detected in a wide range of tissues and upregulated by bacterial and viral infection. Subcellular localization analysis showed that SmLMWPTP was secreted by peripheral blood leukocytes (PBL) into the extracellular milieu. When PBL were treated with rSmLMWPTP, the cells exhibited significant reductions in (i) proliferative and respiratory burst activity, (ii) expression levels of multiple immune relevant genes, and (iii) phagocytic activity. In contrast, the mutant SmLMWPTP bearing R19 mutation had no effect on PBL activity. Taken together, these results indicate that SmLMWPTP is a secreted PTP that exerts a negative regulatory effect on the innate immune response of PBL in a manner that depends on the structural integrity of the P-loop.

Structure-guided studies of the SHP-1/JAK1 interaction provide new insights into phosphatase catalytic domain substrate recognition.

SHP-1 (PTPN6) is a member of the SHP sub-family of protein tyrosine phosphatases and plays a critical role in the regulation of the JAK/STAT signaling pathway. Previous studies suggested that SHP-1 contains a PTP1B-like second phosphotyrosine pocket that allows for binding of tandem phosphotyrosine residues, such as those found in the activation loop of JAK kinases. To discover the structural nature of the interaction between SHP-1 and the JAK family member, JAK1, we determined the 1.8Å co-crystal structure of the SHP-1 catalytic domain and a JAK1-derived substrate peptide. This structure reveals electron density for only one bound phosphotyrosine residue. To investigate the role of the predicted second site pocket we determined the structures of SHP-1 in complex with phosphate and sulfate to 1.37Å and 1.7Å, respectively, and performed anomalous scattering experiments for a selenate-soaked crystal. These crystallographic data suggest that SHP-1 does not contain a PTP1B-like second site pocket. This conclusion is further supported by analysis of the relative dephosphorylation and binding affinities of mono- and tandem-phosphorylated peptide substrates. The crystal structures instead indicate that SHP-1 contains an extended C-terminal helix α2' incompatible with the predicted second phosphotyrosine binding site. This study suggests that SHP-1 defines a new category of PTP1B-like protein tyrosine phosphatases with a hindered second phosphotyrosine pocket.

Myristoylation of the dual‐specificity phosphatase c‐JUN N‐terminal kinase (JNK) stimulatory phosphatase 1 is necessary for its activation of JNK signaling and apoptosis

Activation of the c-JUN N-terminal kinase (JNK) pathway is implicated in a number of important physiological processes, from embryonic morphogenesis to cell survival and apoptosis. JNK stimulatory phosphatase 1 (JSP1) is a member of the dual-specificity phosphatase subfamily of protein tyrosine phosphatases. In contrast to other dual-specificity phosphatases that catalyze the inactivation of mitogen-activated protein kinases, expression of JSP1 activates JNK-mediated signaling. JSP1 and its relative DUSP15 are unique among members of the protein tyrosine phosphatase family in that they contain a potential myristoylation site at the N-terminus (MGNGMXK). In this study, we investigated whether JSP1 was myristoylated and examined the functional consequences of myristoylation. Using mass spectrometry, we showed that wild-type JSP1, but not a JSP1 mutant in which Gly2 was mutated to Ala (JSP1-G2A), was myristoylated in cells. Although JSP1 maintained intrinsic phosphatase activity in the absence of myristoylation, the subcellular localization of the enzyme was altered. Compared with the wild type, the ability of nonmyristoylated JSP1 to induce JNK activation and phosphorylation of the transcription factor c-JUN was attenuated. Upon expression of wild-type JSP1, a subpopulation of cells, with the highest levels of the phosphatase, was induced to float off the dish and undergo apoptosis. In contrast, cells expressing similar levels of JSP1-G2A remained attached, further highlighting that the myristoylation mutant was functionally compromised.

Enzyme Activity of Phosphatase of Regenerating Liver Is Controlled by the Redox Environment and Its C-Terminal Residues

Phosphatase of regenerating liver-1 (PRL-1) belongs to a unique subfamily of protein tyrosine phosphatases (PTPases) associated with oncogenic and metastatic phenotypes. While considerable evidence supports a role for PRL-1 in promoting proliferation, the biological regulators and effectors of PRL-1 activity remain unknown. PRL-1 activity is inhibited by disulfide bond formation at the active site in vitro, suggesting PRL-1 may be susceptible to redox regulation in vivo. Because PRL-1 has been observed to localize to several different subcellular locations and cellular redox conditions vary with tissue type, age, stage of cell cycle, and subcellular location, we determined the reduction potential of the active site disulfide bond that controls phosphatase activity to improve our understanding of the function of PRL-1 in various cellular environments. We used high-resolution solution NMR spectroscopy to measure the potential and found it to be -364.3 +/- 1.5 mV. Because normal cellular environments range from -170 to -320 mV, we concluded that nascent PRL-1 would be primarily oxidized inside cells. Our studies show that a significant conformational change accompanies activation, suggesting a post-translational modification may alter the reduction potential, conferring activity. We further demonstrate that alteration of the C-terminus renders the protein reduced and active in vitro, implying the C-terminus is an important regulator of PRL-1 function. These data provide a basis for understanding how subcellular localization regulates the activity of PRL-1 and, with further investigation, may help reveal how PRL-1 promotes unique outcomes in different cellular systems, including proliferation in both normal and diseased states.

Protein tyrosine phosphatases: dual‐specificity phosphatases in health and disease

Dual-specificity phosphatases (DSPs) constitute a subfamily of protein tyrosine phosphatases (PTPs) that dephosphorylates phospho-Tyr, phospho-Ser and nonproteinaceous substrates. DSPs are involved in the regulation of both developmental and postnatal essential processes, such as early embryogenesis, placental development and immune responses. Several DSP genes are implicated in familial and sporadic human diseases, including tumor-related, neurological and muscle disorders, and cardiovascular and inflammatory diseases. This association ranges from disease-causative mutations to disease-risk-prone single-nucleotide polymorphisms, promoter methylation or gene duplication (most often in cancer). Deconvolution of the role of DSPs in disease is challenging. The enzymes' activities are regulated at many levels and they form part of extensive, intricate networks with other signaling components. Here, we review current knowledge of the role of cysteine-based PTP-domain DSPs in health and disease, and their suitability as putative therapeutic targets for drugs is discussed.

PRL3 Promotes Cell Invasion and Proliferation by Down-regulation of Csk Leading to Src Activation

Phosphatase of regenerating liver 3 (PRL3) is overexpressed in a variety of tumors, and high levels of PRL3 expression are associated with tumorigenesis and metastasis. Consistent with an oncogenic role for PRL3, we show that ectopic PRL3 expression promotes cell proliferation and invasion. However, little is known about the molecular basis for PRL3 function. Obtaining this knowledge is vital for understanding PRL3-mediated disease processes and for the development of novel anticancer therapies targeted to PRL3. Here we report that up-regulation of PRL3 activates the Src kinase, which initiates a number of signal pathways culminating in the phosphorylation of ERK1/2, STAT3, and p130(Cas). The activation of these pathways likely contributes to the increased cell growth and motility of PRL3 cells. We provide evidence that PRL3 induces Src activation through down-regulation of Csk, a negative regulator of Src. Importantly, Src activation and Csk down-regulation are also observed in colon cancer cells expressing a higher level of PRL3. Thus, we have revealed a biochemical mechanism for the PRL3-mediated cell invasion and proliferation in which elevated PRL3 expression causes a reduction in Csk level, leading to Src activation.

Protein tyrosine phosphatase 1B is located with glucagon vesicles, and its concentration is inversely correlated with the rate of glucagon secretion of INR1G9 cells.

High concentrations of protein tyrosine phosphatase (PTP) were found with secretory vesicles of glucagon-producing INR1G9 cells by electron microscopic immunocytochemistry, using a polyclonal antiserum specific for the PTP1B/T-cell (TC)PTP subfamily of PTP. Since TCPTP protein and mRNA were below the detection limit in the cells but significant amounts of PTP1B and mRNA were recognised by a specific monoclonal antibody and a mRNA probe we conclude, that the PTP associated with the vesicles is PTP1B. Only reverse transcriptase (RT)-PCR with primers specific for PTP1B yielded a product of the expected nucleotide sequence. Thus, we conclude that the PTP associated with the vesicles is PTP1B. The presence of vanadate for 48 h attenuated PTP1B expression and caused reduction of steady-state levels of the phosphatase. These conditions also led to a continuing increase in the steady-state rate of glucagon release by the cells. This rate and tyrosine phosphatase levels showed an inverse relationship, suggesting a suppressive role of PTP1B on the regulated secretion of glucagon by INR1G9 cells.

Crystal Structure of a Phosphoinositide Phosphatase, MTMR2: Insights into Myotubular Myopathy and Charcot-Marie-Tooth Syndrome

Myotubularin-related proteins are a large subfamily of protein tyrosine phosphatases (PTPs) that dephosphorylate D3-phosphorylated inositol lipids. Mutations in members of the myotubularin family cause the human neuromuscular disorders myotubular myopathy and type 4B Charcot-Marie-Tooth syndrome. The crystal structure of a representative member of this family, MTMR2, reveals a phosphatase domain that is structurally unique among PTPs. A series of mutants are described that exhibit altered enzymatic activity and provide insight into the specificity of myotubularin phosphatases toward phosphoinositide substrates. The structure also reveals that the GRAM domain, found in myotubularin family phosphatases and predicted to occur in ∼180 proteins, is part of a larger motif with a pleckstrin homology (PH) domain fold. Finally, the MTMR2 structure will serve as a model for other members of the myotubularin family and provide a framework for understanding the mechanism whereby mutations in these proteins lead to disease.

Identification of dual specificity phosphatases induced by olfactory bulbectomy in rat olfactory neuroepithelium

Dual specificity protein tyrosine phosphatases (dsPTPs) are a subfamily of protein tyrosine phosphatases implicated in the regulation of extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase/stress-activated protein kinase (JNK/SAPK), and p38 mitogen-activated protein kinases (MAPKs) which are target enzymes activated by a wide range of cell-surface stimuli. Like these kinases, a class of dsPTP has been implicated in cell differentiation, regeneration, and apoptosis. In order to isolate dsPTPs which might play an important role in neuronal regeneration and apoptosis in olfactory neuroepithelium, we subcloned DNA fragments amplified by reverse transcription-polymerase chain reaction (RT-PCR), using degenerate oligonucleotide primers based on the conserved amino acid regions within the catalytic domain of dsPTPs, from rat olfactory epithelial RNA 1 and 4 h after an olfactory bulbectomy. The PCR products were subcloned into the pCRII vector, and 23 clones were chosen for further characterization. The sequence of these 23 individual clones revealed that two clones were identical to the rat dsPTP, MKP-3, and the other 21 clones were identical to the rat dsPTP, MKP-1. By Northern analysis, the MKP-1 transcript was induced and peaked 4 h following a bulbectomy. Similar results were obtained with the MKP-3 transcript. These results suggest that MKP-1 and MKP-3 may be involved in the early steps of apoptosis in vivo in rat olfactory neuroepithelium.

A Novel Cytoplasmic Dual Specificity Protein Tyrosine Phosphatase Implicated in Muscle and Neuronal Differentiation

Dual specificity protein tyrosine phosphatases (dsPTPs) are a subfamily of protein tyrosine phosphatases implicated in the regulation of mitogen-activated protein kinase (MAPK). In addition to hydrolyzing phosphotyrosine, dsPTPs can hydrolyze phosphoserine/threonine-containing substrates and have been shown to dephosphorylate activated MAPK. We have identified a novel dsPTP, rVH6, from rat hippocampus. rVH6 contains the conserved dsPTP active site sequence, VXVHCX2GX2RSX5AY(L/I)M, and exhibits phosphatase activity against activated MAPK. In PC12 cells, rVH6 mRNA is induced during nerve growth factor-mediated differentiation but not during insulin or epidermal growth factor mitogenic stimulation. In MM14 muscle cells, rVH6 mRNA is highly expressed in proliferating cells and declines rapidly during differentiation. rVH6 expression correlates with the inability of fibroblast growth factor to stimulate MAPK activity in proliferating but not in differentiating MM14 cells. rVH6 protein localizes to the cytoplasm and is the first dsPTP to be localized outside the nucleus. This novel subcellular localization may expose rVH6 to potential substrates that differ from nuclear dsPTPs substrates.

Identification of two alternatively spliced transcripts of STEP: a subfamily of brain-enriched protein tyrosine phosphatases.

A brain-enriched protein tyrosine phosphatase termed STEP46 (striatal enriched phosphatase) was previously isolated and characterized. Immunological studies with a STEP monoclonal antibody recognized several STEP-immunoreactive proteins, and suggested that additional STEP-related polypeptides existed. This study reports the isolation of two alternatively spliced transcripts of the STEP gene. One of these, STEP20 (with a predicted molecular mass of 20 kDa) was further characterized and found to lack the conserved tyrosine phosphatase domain. Northern analysis detected a 2.8 kb STEP20 message in mouse brain. The second alternatively spliced transcript, STEP61, has a 5'-extended open reading frame that encodes a protein with a predicted molecular mass of 61 kDa and contains a single tyrosine phosphatase domain. The exon-intron organization responsible for the novel STEP20 and STEP61 sequences was determined in the mouse STEP genomic DNA. We propose that the original STEP46, along with STEP20 and STEP61, are members of a brain-enriched subfamily of protein tyrosine phosphatases, and that STEP isoforms may have distinct functions within the central nervous system.

Isolation and characterization of a human dual specificity protein-tyrosine phosphatase gene.

Vaccinia phosphatase VH-1 and its mammalian counterparts, including protein-tyrosine phosphatases (PTPase) CL100 and VHR, constitute a novel subfamily of protein-tyrosine phosphatases that exhibits dual substrate specificity for phosphotyrosine- and phosphoserine/threonine-containing substrates. The expression of human VH-1-like PTPase CL100 is rapidly inducible by mitogen stimulation and oxidative stress, suggesting that this gene is transcriptionally regulated. In order to study the mechanism underlying this transcriptional regulation, we isolated the first human gene of this subfamily, the CL100 gene, and characterized its promoter. The gene consists of four exons intervened by three short introns 400-500 base pairs in length. Analysis of the protein sequence encoded by each exon revealed that there is a second region of similarity between CL100 protein and cdc25 in addition to the PTPase catalytic domain. Promoter analysis of the CL100 gene indicates that an 800-base pair region flanking the transcriptional initiation site is sufficient to confer a transcriptional response to serum and 12-O-tetradecanoylphorbol-13-acetate stimulation. The CL100 gene is expressed in numerous tissues, including nonmitotic cells in the brain. Within the brain, CL100 mRNA is localized in discrete neuronal populations, suggesting that this PTPase is likely to play a key role in neurotransmission as well as in mitotic signaling. Finally, although extracellular signal-regulated kinase has recently been shown to act as substrate for CL100 in vitro, we find no clear correspondence between the distribution of extracellular signal-regulated kinase and CL100 mRNA in the brain. The potential significance of a second cdc25 homology domain of CL100 is discussed.