Protein Tyrosine Phosphatase Receptor T Research Articles

Targeting Neoantigens in Cancer: Possibilities and Opportunities in Breast Cancer.

As one of the most prevalent forms of cancer worldwide, breast cancer has garnered significant attention within the clinical research setting. While traditional treatment employs a multidisciplinary approach including a variety of therapies such as chemotherapy, hormone therapy, and even surgery, researchers have since directed their attention to the budding role of neoantigens. Neoantigens are defined as tumor-specific antigens that result from a multitude of genetic alterations, the most prevalent of which is the single nucleotide variant. As a result of their foreign nature, neoantigens elicit immune responses upon presentation by Major Histocompatibility Complexes I and II followed by recognition by T cell receptors. Previously, researchers have been able to utilize these immunogenic properties and manufacture neoantigen-specific T-cells and neoantigen vaccines. Within the context of breast cancer, biomarkers such as tumor protein 53 (TP53), Survivin, Partner and Localizer of BRCA2 (PALB2), and protein tyrosine phosphatase receptor T (PTPRT) display exceeding potential to serve as neoantigens. However, despite their seemingly limitless potential, neoantigens must overcome various obstacles if they are to be fairly distributed to patients. For instance, a prolonged period between the identification of a neoantigen and the dispersal of treatment poses a serious risk within the context of breast cancer. Regardless of these current obstacles, it appears highly promising that future research into neoantigens will make an everlasting impact on the health outcomes within the realm of breast cancer. The purpose of this literature review is to comprehensively discuss the etiology of various forms of breast cancer and current treatment modalities followed by the significance of neoantigens in cancer therapeutics and their application to breast cancer. Further, we have discussed the limitations, future directions, and the role of transcriptomics in neoantigen identification and personalized medicine. The concepts discussed in the original and review articles were included in this review article.

Association of MUC16 mutation with survival of immune checkpoint inhibitor in patients with cancer

Abstract Background Mutation in the gene encoding Protein Tyrosine Phosphatase Receptor T (PTPRT) has been shown to influence survival outcomes in cancers. However, the association of PTPRT mutation with clinical outcomes of immune checkpoint inhibitor (ICI) remains unclear. Here we performed comprehensive analysis of PTPRT mutation frequency and clinically validated PTPRT mutation as a predictive biomarker of ICI in patients with cancer. Methods This study analyzed cancer genomic data from the cBioPortal database. All patients treated with ICI were included. Nonsynonymous mutations of PTPRT were considered. Kaplan-Meier survival analysis and logistic regression models were applied. Primary outcomes were overall survival (OS) and progression-free survival (PFS). Results Among 2129 patients with non–small cell lung cancer (NSCLC) (n = 510), melanoma (n = 596), and other tumor types (n = 1,023), the tumor mutation burden of patients with PTPRT mutation was significantly higher than in those without the mutations in NSCLC, melanoma, and pancancer (Wilcoxon rank sum test, all P Conclusion We demonstrated that PTPRT mutation can predict survival benefit from cancer ICI therapy. PTPRT mutation might be an important component of the immunogenetic landscape and should be integrated into predictive biomarker panels for ICI therapy and be validated in future prospective clinical trials. Legal entity responsible for the study Herui Yao. Funding This study was supported by grants from the National Natural Science Foundation of China (81372819, 81572596, U1601223), the Natural Science Foundation of Guangdong Province (2017A030313828), the Guangzhou Science and Technology Program (201704020131), the Sun Yat-Sen University Clinical Research 5010 Program (2018007). Disclosure All authors have declared no conflicts of interest.

PTPRT epigenetic silencing defines lung cancer with STAT3 activation and can direct STAT3 targeted therapies

ABSTRACT Signal Transducers and Activators of Transcription-3 (STAT3), a potent oncogenic transcription factor, is constitutively activated in lung cancer, but mutations in pathway genes are infrequent. Protein Tyrosine Phosphatase Receptor-T (PTPRT) is an endogenous inhibitor of STAT3 and PTPRT loss-of-function represents one potential mechanism of STAT3 hyperactivation as observed in other malignancies. We determined the role of PTPRT promoter methylation and sensitivity to STAT3 pathway inhibitors in non-small cell lung cancer (NSCLC). TCGA and Pittsburgh lung cancer cohort methylation data revealed hypermethylation of PTPRT associated with diminished mRNA expression in a subset of NSCLC patients. We report frequent hypermethylation of the PTPRT promoter which correlates with transcriptional silencing of PTPRT and increased STAT3 phosphorylation (Y705) as determined by methylation-specific PCR (MSP) and real time quantitative reverse transcription (RT)-PCR in NSCLC cell lines. Silencing of PTPRT using siRNA in H520 lung cancer cell line resulted in increased pSTAT3Tyr705 and upregulation of STAT3 target genes such as Cyclin D1 and Bcl-XL expression. We show this association of PRPRT methylation with upregulation of the STAT3 target genes Cyclin D1 and Bcl-XL in patient derived lung tumour samples. We further demonstrate that PTPRT promoter methylation associated with different levels of pSTAT3Ty705 in lung cancer cell lines had selective sensitivity to STAT3 pathway small molecule inhibitors (SID 864,669 and SID 4,248,543). Our data strongly suggest that silencing of PTPRT by promoter hypermethylation is an important mechanism of STAT3 hyperactivation and targeting STAT3 may be an effective approach for the development of new lung cancer therapeutics.

Hemopoietic Cell Kinase amplification with Protein Tyrosine Phosphatase Receptor T depletion leads to polycythemia, aberrant marrow erythoid maturation, and splenomegaly

Deletion of long arm of chromosome 20 [del(20q)] is the second most frequent recurrent chromosomal abnormality in hematological malignancies. It is detected in 10% of myeloproliferative neoplasms, 4–5% of myelodysplastic syndromes, and 1–2% of acute myeloid leukaemia. Recurrent, non-random occurrence of del(20q) indicates that it is a pathogenic driver in myeloid malignancies. Genetic mapping of patient samples has identified two regions of interest on 20q – the “Common Deleted Region” (CDR) and “Common Retained Region” (CRR), which was often amplified. We proposed that the CDR contained tumor suppressor gene(s) (TSG) and the CRR harbored oncogene(s); loss of a TSG together with over-expression of an oncogene favored development of myeloid malignancies. Protein Tyrosine Phosphatase Receptor T (PTPRT) and Hemopoietic cell kinase (HCK) were identified to be the likely candidate TSG and oncogene respectively. Retroviral transduction of HCK into PTPRT-null murine LKS+ stem and progenitor cells resulted in hyperproliferation in colony forming assays and hyperphosphorylation of intracellular STAT3. Furthermore, over half of the murine recipients of these transduced cells developed erythroid hyperplasia, polycythemia and splenomegaly at 12 months, although no leukemic phenotype was observed. The findings suggested that HCK amplification coupled with PTPRT loss in del(20q) leads to development of a myeloproliferative phenotype.

Abstract 2379: PTPRT pseudo-phosphatase domain is a denitrase that contributes to its tumor suppressor function

Abstract Department of Genetics & Genome Sciences and Case Comprehensive Cancer Center, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio 44106, USA. In addition to phosphorylation, tyrosine residues in proteins can have nitration at the 3-carbon position on the phenol ring (Y-NO2). Protein tyrosine nitration occurs under both physiological and pathologic conditions. However, enzymes that add or remove this protein modification remain to be identified. Protein tyrosine phosphatase receptor T (PTPRT) is one of the twelve receptor protein tyrosine phosphatases (RPTPs) that have two catalytic PTP domains in their intracellular parts. While the membrane proximal PTP domains (D1) are protein tyrosine phosphatases, it has been thought that the C-terminal PTP domains (D2) are pseudo-phosphatase that lack enzymatic activity. Here we report that the pseudo-phosphatase domain (D2) of PTPRT is a denitrase that removes nitro-groups from tyrosine residues in paxillin. PTPRT normally functions as a tumor suppressor and is frequently mutated in a variety of human cancers including colorectal cancer. Interestingly, a fifth of tumor-derived mutations of PTPRT are located in the D2 pseudo-PTP domain. We demonstrate that some of the tumor-derived mutations located in the pseudo-phosphatase domain impair the denitrase activity. Moreover, PTPRT mutant mice that inactivate the denitrase activity are susceptible to carcinogen-induced colon tumor formation. Our study uncovers a novel enzyme that functions as a tumor suppressor. Citation Format: Yiqing Zhao, Zhenghe Wang. PTPRT pseudo-phosphatase domain is a denitrase that contributes to its tumor suppressor function [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 2379.

Abstract 3365: Epigenetic inactivation of PTPRT and sensitivity to STAT3 inhibition in lung cancer

Abstract Signal Transducers and Activators of Transcription-3 (STAT3), a potent oncogenic transcription factor is persistently activated in several malignancies including lung cancer. Protein Tyrosine Phosphatase Receptor-T (PTPRT) is an endogenous inhibitor of STAT3 transcriptional activity, and is methylated in many types of human cancer. Loss-of-function of PTPRT by promoter methylation contributes to STAT3 mediated growth and survival and represent one of the plausible mechanism of STAT3 hyperactivation. We report identification of hypermethylation in CpG islands of the PTPRT promoter which correlates with its transcriptional silencing as well as expression of pSTAT3 protein and STAT3 target genes in both lung cancer cell lines and primary human tumors. Analyses of the TCGA (The Cancer Genome Atlas) data revealed that PTPRT promoter is frequently hypermethylated in a subset of lung squamous cell carcinoma and approximately 25% of adenocarcinoma tumors in association with downregulation of PTPRT mRNA expression. This observation was verified in vitro using lung cancer cell lines. Out of the 7 lung cancer cell lines examined, one lung cancer cell line showed lack of methylation (only unmethylated sequences) of the PTPRT promoter region and revealed mRNA expression (H520). All 6 cell lines which showed PTPRT promoter methylation had nearly absent PTPRT mRNA and had high levels of pSTAT3Tyr705, while H520 had little or no pSTAT3Tyr705 protein expression. Silencing of PTPRT using siRNA in H520, where PTPRT was not endogenously silenced by promoter hypermethylation, resulted in the upregulation of the STAT3 target genes such as cyclin D1 and Bcl-XL mRNA and protein expression as well as increased pSTAT3Tyr705 level. Analyses of the methylation status in the PTPRT promoter region in primary lung tumor samples revealed methylation in one of the 3 tumor samples. This correlated with increased STAT3 target genes (cyclin D1 and Bcl-XL) mRNA expression. In lung cancer cell lines, PTPRT promoter methylation is associated with sensitivity to STAT3 inhibition. Our data suggests that silencing of PTPRT by promoter hypermethylation is a frequent mechanism of STAT3 hyperactivation, and targeting STAT3 may be an effective molecular targeted approach in the treatment of this subset of lung cancer. Citation Format: Malabika Sen, Audrey Kindsfather, James G. Herman. Epigenetic inactivation of PTPRT and sensitivity to STAT3 inhibition in lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3365. doi:10.1158/1538-7445.AM2017-3365

Regulation of paxillin-p130-PI3K-AKT signaling axis by Src and PTPRT impacts colon tumorigenesis.

Protein tyrosine phosphatase receptor T (PTPRT) is frequently mutated in a variety of human cancers including colorectal cancer. Here we report that PTPRT knockout increases the size of mouse colon tumors in the Apcmin+/− genetic background, suggesting that inactivation of PTPRT promotes tumor progression. We previously demonstrated that PTPRT dephosphorylates paxillin at tyrosine-Y88 residue. Consistently, phosphorylation of Y88 paxillin (pY88) is up-regulated in colon tumors derived from Apcmin+/− Ptprt−/− mice. An important downstream effector of pY88 paxillin is the oncogene Akt. Here, we show that pY88 paxillin impacts the Akt pathway by regulating the interaction between p130cas and the p85 regulatory subunit of PI3-Kinase. Additionally, while pY88 paxillin is a substrate of the tumor suppressor phosphatase PTPRT, the corresponding kinase has not been previously identified. In this study, we demonstrate that the oncogenic kinase Src directly phosphorylates paxillin at Y88. Moreover, colorectal cancer cells that express high levels of pY88 paxillin are sensitive to dasatinib treatment, suggesting that pY88 paxillin may serve as a predictive biomarker for Src family kinase inhibitors.

Identification and Analysis of Oncogenic Pathways in Deletion 20q Acute Myeloid Leukaemia

Deletion of the long arm of chromosome 20 [del(20q)] is a common recurrent chromosomal abnormality in acute myeloid leukaemia (AML) and myeloproliferative neoplasms (MPN). The abnormal chromosome 20 has a “Common Deleted Region” (CDR) that contains Protein Tyrosine Phosphatase Receptor T (PTPRT), a tyrosine phosphatase that is mutated in many human cancers. We have previously reported (MacKinnon et al, Genes, Chromosomes and Cancer 2010) that del(20q) also harbours an amplified “Common Retained Region,” (CRR) which contains multiple copies of Haemopoietic Cell Kinase (HCK). HCK is an oncogenic Src tyrosine kinase and its aberrant activation has been shown to contribute to the pathogenesis of some haematological malignancies.Our hypothesis is that the amplification of HCK in the CRR cooperated with the loss of PTPRT in the CDR. Indeed, our results strongly suggested that HCK amplification with PTPRT loss led to a myeloproliferative phenotype seen in MPN.Our model proposed that MPN occurred either through the consequence of direct interaction between HCK and PTPRT, or through aberrant activation of Signal Transducer and Activator of Transcription 3 (STAT3). Constitutively activated STAT3 has been shown to be oncogenic in several haematological malignancies. STAT3 is a direct target of both HCK and PTPRT. It is phosphorylated (hence activated) by HCK, and dephosphorylated (hence inactivated) by PTPRT. This provides a downstream leukaemogenic pathway for our model.The ultimate aim of our experiments is to prove this hypothesis using mouse models. Murine haemopoietic stem cells (HSC) were isolated from the bone marrows of wild type C57BL/6 (WT) and PTPRT-null mice by Fluorescence Activated Cell Sorting for Lineage negative, C-kit and Sca-1 positive (LKS+) cells. Retroviral constructs of HCK were generated by cloning it into the retroviral vector pMSCViresEGFP(MIG), with GFP as reporter. Murine HSC were transduced with either retroviral HCK or MIG vector control. Hence wild type (WT) and PTPRT-null murine HSC transduced with either MIG or HCK were used in our experiments (WTMIG, WTHCK, PTPRTMIG, PTPRTHCK).We have previously presented that PTPRTHCK showed a significant increase in methylcelluose colony numbers and colony sizes compared to PTPRTMIG, while there was no difference between WTMIG and WTHCK. In addition, an intracellular anti-phosphoSTAT3 antibody assay demonstrated that in both WTHCK and PTPRTHCK, significant STAT3 hyperphosphorylation, and hence overactivation, occurred. This response was more exaggerated in the PTPRTHCK. Finally, direct interaction between HCK and PTPRT was shown with an interaction assay using recombinant proteins. We now present the in vivo data in the murine recipients.In Vivo ReconstitutionLKS+ HSC transduced with either MIG or HCK were transplanted into lethally irradiated SJL/PTPRCa murine recipients to assess AML or MPN formation in a reconstitution study over 12 months. The recipients from the four cohorts (WTMIG, WTHCK, PTPRTMIG and PTPRTHCK) were regularly analysed by full blood counts, peripheral blood GFP%, and blood films. At 12 months, they were culled and the organs harvested and analysed by flow cytometry, cytospin, and paraffin-embedded histology (H + E and immunohistochemistry). Recipents of PTPRTHCK HSC had a significantly higher proportion of nucleated erythroid populations in the bone marrow by flow and larger splenic size by weight. They also showed a higher haemoglobin (Hb) at 12 months, although this did not reach statistical significance. [Display omitted] [Display omitted] [Display omitted] ConclusionThe data reveal a likely new oncogenic-signalling cascade: that HCK amplification and loss of PTPRT in del(20q) may cooperate to cause MPN directly, or by aberrant activity of hyperphosphorylated STAT3. DisclosuresNo relevant conflicts of interest to declare.

PTPRT Regulates High-Fat Diet-Induced Obesity and Insulin Resistance

Obesity is a risk factor for many human diseases. However, the underlying molecular causes of obesity are not well understood. Here, we report that protein tyrosine phosphatase receptor T (PTPRT) knockout mice are resistant to high-fat diet-induced obesity. Those mice avoid many deleterious side effects of high-fat diet-induced obesity, displaying improved peripheral insulin sensitivity, lower blood glucose and insulin levels. Compared to wild type littermates, PTPRT knockout mice show reduced food intake. Consistently, STAT3 phosphorylation is up-regulated in the hypothalamus of PTPRT knockout mice. These studies implicate PTPRT-modulated STAT3 signaling in the regulation of high-fat diet-induced obesity.

PTPRT regulates the interaction of Syntaxin-binding protein 1 with Syntaxin 1 through dephosphorylation of specific tyrosine residue

PTPRT (protein tyrosine phosphatase receptor T), a brain-specific tyrosine phosphatase, has been found to regulate synaptic formation and development of hippocampal neurons, but its regulation mechanism is not yet fully understood. Here, Syntaxin-binding protein 1, a key component of synaptic vesicle fusion machinery, was identified as a possible interaction partner and an endogenous substrate of PTPRT. PTPRT interacted with Syntaxin-binding protein 1 in rat synaptosome, and co-localized with Syntaxin-binding protein 1 in cultured hippocampal neurons. PTPRT dephosphorylated tyrosine 145 located around the linker between domain 1 and 2 of Syntaxin-binding protein 1. Syntaxin-binding protein 1 directly binds to Syntaxin 1, a t-SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) protein, and plays a role as catalysts of SNARE complex formation. Syntaxin-binding protein 1 mutant mimicking non-phosphorylation (Y145F) enhanced the interaction with Syntaxin 1 compared to wild type, and therefore, dephosphorylation of Syntaxin-binding protein 1 appeared to be important for SNARE-complex formation. In conclusion, PTPRT could regulate the interaction of Syntaxin-binding protein 1 with Syntaxin 1, and as a result, the synaptic vesicle fusion appeared to be controlled through dephosphorylation of Syntaxin-binding protein 1.

Identification and Analysis of Oncogenic Pathways in Deletion 20q Acute Myeloid Leukaemia

Abstract 1324Deletion of the long arm of chromosome 20 [del(20q)] is a common recurrent chromosomal abnormality in acute myeloid leukaemia (AML). It is a key step in AML development and a better understanding of the associated molecular events is important. The abnormal chromosome 20 in del(20q) AML has been shown to have lost a “Common Deleted Region” (CDR) that contains Protein Tyrosine Phosphatase Receptor T (PTPRT), a tyrosine phosphatase that is mutated in many human cancers such as AML. We have previously reported (MacKinnon et al, Genes, Chromosomes and Cancer 2010) that del(20q) also harbours an amplified “Common Retained Region,” (CRR) which contains Haemopoietic Cell Kinase (HCK). HCK is anoncogenic Src tyrosine kinase and its aberrant activation has been shown to contribute to the pathogenesis of some haematological malignancies.We hypothesize that the amplification of HCK in the CRR cooperates with the loss of PTPRT in the CDR to cause AML. Our model proposes that AML occurs either through direct interaction between HCK and PTPRT, or through aberrant activation of Signal Transducer and Activator of Transcription 3 (STAT3), a cytoplasmic second messenger that is important in cellular signalling. Constitutively activated STAT3 has been shown to be oncogenic in several malignancies, including AML. STAT3 is a direct target of both HCK and PTPRT. It is phosphorylated (hence activated) by HCK, and dephosphorylated (hence inactivated) by PTPRT. This provides a downstream leukaemogenic pathway for our model. The ultimate aim of our experiments is to prove this hypothesis using mouse models. Murine haemopoietic stem cells (HSC) were isolated from the bone marrows of wild type C57BL/6 (WT) and PTPRT-null mice by Fluorescence Activated Cell Sorting for Lineage negative, C-kit and Sca-1 positive (LKS+) cells. Retroviral constructs of HCK were generated by cloning it into the retroviral vector pMSCViresEGFP(MIG), with GFP as reporter. Murine HSC were transduced with either retroviral HCK or MIG vector control and Phoenix cell system was used for retroviral packaging. Experiments using isolated LKS+ HSC were performed to examine for features of AML.Examination of bone marrow cells from del(20q) AML patients by quantitative PCR revealed an increase in HCK mRNA expression and a reduction in PTPRT expression. Wild type (WT) and PTPRT-null murine HSC transduced with either MIG or HCK were cultured in methylcellulose media. Colony forming units (CFU) were enumerated on day7 and day12. We found that both WT and PTPRT-null HSC transduced with HCK showed a significant increase in colony numbers compared to MIG transduced HSC. Furthermore, the fold increment in colony number was higher in the PTPRT-null genotype as shown in figure 1. [Display omitted] Moreover, an intracellular anti-phosphoSTAT3 assay was performed to assess STAT3 phosphorylation levels in the transduced HSC. It demonstrated that in both WT and PTPRT-null HSC that have been transduced with HCK, STAT3 hyperphosphorylation, and hence overactivation, occured. This response was again more exaggerated in the PTPRT-null HSC, as seen in figure 2. [Display omitted] We are currently transplanting transduced LKS+ HSC (either MIG or HCK) into lethally irradiated murine recipients to assess AML formation in a reconstitution study. The recipient mice will be assessed for evidence of engraftment and subsequent AML.The preliminary data reveals a likely new oncogenic-signalling cascade: that HCK amplification and loss of PTPRT in del(20q) AML may cooperate to cause AML directly, or by aberrant activity of hyperphosphorylated STAT3. Disclosures:No relevant conflicts of interest to declare.

Somatic PTPRT and ANGPT2 Mutations in Large Granulocyte Leukemia

AbstractAbstract 1302 Introduction:T-cell large granular lymphocyte (T-LGL) leukemia is a rare, clonal disease characterized by the expansion of mature CD3+CD8+ cytotoxic T-cells. It is often associated with autoimmune disorders and immune-mediated cytopenias. Our recent findings suggest that up to 40% of T-LGL patients harbor mutations in the STAT3 gene (Koskela et al, NEJM, 2012). In the remaining T-LGL patients, the pathogenetic mutations are not known. Methods:To identify additional somatic mutations, we chose two STAT3 mutation negative T-LGL leukemia patients for exome sequencing. CD8+ T-cells were used as test cells and matched CD4+ T-cells as control. The exome was captured with the Nimblegen SeqCap EZ Exome Library v2.0 and the sequencing was performed with the Illumina HiSeq2000 sequencing platform. Candidate somatic mutations were identified with a bioinformatics pipeline consisting of BWA for sequence alignment, Samtools for alignment filtering and Varscan for somatic mutation calling. Results:Index patient 1 was diagnosed with T-LGL leukemia at the age of 70 and a TCR repertoire assay revealed one minor T- cell clone in the leukemic sample (Vβ7.1: 28 %). Exome sequencing revealed 10 nonsynonymous nucleotide variants with p-values lower than 0.01, of which the tumor suppressor gene Protein tyrosine phosphatase (PTP) receptor T (PTPRT) had a variant frequency of 14%. PTPRT has previously been found to reverse Tyr705 phosphorylation on STAT3, a modification associated with STAT3 deactivation. In this novel mutation, a highly conserved hydrophobic valine residue is converted into methionine (V995M). The mutation occurs in the cytoplasmic part of the protein, within the tyrosine-protein phosphatase 1 domain. The PTPRT V995M mutation may thereby affect STAT3 activity by reducing dephosphorylation of Tyr705, thus increasing the expression of STAT3 target genes.Index patient 2 was a 40 year-old male with untreated T-LGL leukemia. A TCR repertoire assay showed one predominant T-cell clone in the leukemic T-cells (Vβ13.2: 70%). Exome sequencing revealed 8 nonsynonymous nucleotide variants with p-values lower than 0.01. The missense mutation K436E in Angiopoietin-2 (ANGPT2), presenting with the lowest somatic p-value (1,06−09) and highest variant frequency (34%), was the most relevant candidate involved in the pathogenesis of leukemia. The mutation occurs on the surface of ANGPT2 within the well-conserved fibrinogen C-terminal domain. This domain binds the receptor TIE2 and the change in the polarity induced by K436E mutation is likely to affect the binding of TIE2 by ANGPT2. Overexpression of ANGPT2 has previously been shown to confer an adverse prognostic factor in other forms of leukemia. While these mutations appear biologically relevant and exciting, we have not yet seen them in other LGL patients screened so far (n=80). Conclusions:Somatic mutations in the PTPRT and ANGPT2 genes may represent rare genetic causes for T-LGL leukemia. Screening for these mutations in a larger cohort of patients is warranted. The mutation in the PTPRT gene is particularly exciting as it may directly impact the STAT3 pathway, which is a common pathogenetic event in T-LGL leukemia. Inactivating mutations of the PTPRT gene may have the same functional consequence as activating mutations of STAT3 in LGL patients. Disclosures:Koskela:Novartis: Honoraria; BMS: Honoraria; Janssen-Cilag: Honoraria. Kallioniemi:TEKES-FiDiPro: Research Funding. Porkka:Bristol-Myers Squibb: Honoraria, Research Funding; Novartis: Honoraria, Research Funding. Maciejewski:NIH: Research Funding; Aplastic Anemia&MDS International Foundation: Research Funding. Mustjoki:Bristol-Myers Squibb: Honoraria, Research Funding; Novartis: Honoraria.

Regulation of dendritic arborization by BCR Rac1 GTPase-activating protein, a new substrate of protein tyrosine phosphatase receptor T

Dendritic arborization is important for neuronal development as well as the formation of neural circuits. Rac1 is a member of the Rho GTPase family that serve as regulators of neuronal development. Breakpoint cluster region protein (BCR) is a Rac1 GTPase-activating protein that is abundantly expressed in the central nervous system. Here, we show that BCR plays a key role in neuronal development. Dendritic arborization and actin polymerization were attenuated by overexpression of BCR in hippocampal neurons. Knockdown of BCR using specific shRNAs increased the dendritic arborization as well as actin polymerization. The number of dendrites in null mutant BCR(-/-) mice was considerably increased compared with that in wild-type mice. We found that the function of the BCR GTPase-activating domain could be modulated by protein tyrosine phosphatase receptor T (PTPRT), which is expressed principally in the brain. We demonstrate that tyrosine 177 of BCR was the main target of PTPRT and the BCR mutant mimicking dephosphorylation of tyrosine 177 alleviated the attenuation of dendritic arborization. Additionally the attenuated dendritic arborization found upon BCR overexpression was relieved upon co-expression of PTPRT. When PTPRT was knocked down by a specific shRNA, the dendritic arborization was significantly reduced. The activity of the BCR GTPase-activating domain was modulated by means of conversions between the intra- and inter-molecular interactions, which are finely regulated through the dephosphorylation of a specific tyrosine residue by PTPRT. We thus show conclusively that BCR is a novel substrate of PTPRT and that BCR is involved in the regulation of neuronal development via control of the BCR GTPase-activating domain function by PTPRT.

Tumour suppressor function of protein tyrosine phosphatase receptor-T

It has long been thought that PTPs (protein tyrosine phosphatases) normally function as tumour suppressors. Recent high-throughput mutational analysis identified loss-of-function mutations in six PTPs in human colon cancers, providing critical cancer genetics evidence that PTPs can act as tumour suppressor genes. PTPRT (protein tyrosine phosphatase receptor-T), a member of the family of typeIIB receptor-like PTPs, is the most frequently mutated PTP among them. Consistent with the notion that PTPRT is a tumour suppressor, PTPRT knockout mice are hypersensitive to AOM (azoxymethane)-induced colon cancer. The present review focuses on the physiological and pathological functions of PTPRT as well as the cellular pathways regulated by this phosphatase.

Identification of STAT3 as a substrate of receptor protein tyrosine phosphatase T

Protein tyrosine phosphatase (PTP) receptor T (PTPRT) is the most frequently mutated PTP in human cancers. However, the cell signaling pathways regulated by PTPRT have not yet been elucidated. Here, we report identification of signal transducer and activator of transcription 3 (STAT3) as a substrate of PTPRT. Phosphorylation of a tyrosine at amino acid Y705 is essential for the function of STAT3, and PTPRT specifically dephosphorylated STAT3 at this position. Accordingly, overexpression of normal PTPRT in colorectal cancer cells reduced the expression of STAT3 target genes. These studies illuminate a mechanism regulating the STAT3 pathway and suggest that this signaling pathway plays an important role in colorectal tumorigenesis.