RESUMO
Nasal-type natural killer/T-cell lymphoma (NKTCL) is an aggressive disease characterized by frequent deletions on 6q, and constitutive activation of signal transducer and activator of transcription 3 (STAT3). Phosphorylation at Tyr705 activates STAT3, inducing dimerization, nuclear translocation, and DNA binding. In this study, we investigated whether receptor-type tyrosine-protein phosphatase κ (PTPRK), the only protein tyrosine phosphatase at 6q that contains a STAT3-specifying motif, negatively regulates STAT3 activation in NKTCL. PTPRK was highly expressed in normal NK cells but was underexpressed in 4 of 5 (80%) NKTCL cell lines and 15 of 27 (55.6%) primary tumors. Significantly, PTPRK protein expression was inversely correlated with nuclear phospho-STAT3(Tyr705) expression in NKTCL cell lines (P = .025) and tumors (P = .040). PTPRK restoration decreased nuclear phospho-STAT3(Tyr705) levels, whereas knockdown of PTPRK increased such levels in NKTCL cells. Phosphatase substrate-trapping mutant assays demonstrated the binding of PTPRK to STAT3, and phosphatase assays showed that PTPRK directly dephosphorylated phospho-STAT3(Tyr705). Restoration of PTPRK inhibited tumor cell growth and reduced the migration and invasion ability of NKTCL cells. Monoallelic deletion and promoter hypermethylation caused underexpression of PTPRK messenger RNA in NKTCL, and methylation of the PTPRK promoter significantly correlated with inferior overall survival (P = .049) in NKTCL patients treated with the steroid-dexamethasone, methotrexate, ifosfamide, l-asparaginase, and etoposide regimen. Altogether, our findings show that PTPRK underexpression leads to STAT3 activation and contributes to NKTCL pathogenesis.
Assuntos
Linfoma Extranodal de Células T-NK/metabolismo , Neoplasias Nasais/metabolismo , Proteínas Tirosina Fosfatases Classe 2 Semelhantes a Receptores/metabolismo , Fator de Transcrição STAT3/metabolismo , Proteínas Supressoras de Tumor/metabolismo , Apoptose , Caspases/metabolismo , Linhagem Celular Tumoral , Núcleo Celular/metabolismo , Proliferação de Células , Metilação de DNA , Análise Mutacional de DNA , Regulação para Baixo , Feminino , Deleção de Genes , Técnicas de Silenciamento de Genes , Humanos , Linfoma Extranodal de Células T-NK/genética , Linfoma Extranodal de Células T-NK/patologia , Masculino , Pessoa de Meia-Idade , Invasividade Neoplásica , Neoplasias Nasais/genética , Neoplasias Nasais/patologia , Fosforilação , Prognóstico , Regiões Promotoras Genéticas , Ligação Proteica , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , RNA Neoplásico/genética , RNA Neoplásico/metabolismo , Proteínas Tirosina Fosfatases Classe 2 Semelhantes a Receptores/deficiência , Proteínas Tirosina Fosfatases Classe 2 Semelhantes a Receptores/genética , Fator de Transcrição STAT3/química , Proteínas Supressoras de Tumor/deficiência , Proteínas Supressoras de Tumor/genéticaRESUMO
Using inverse polymerase chain reaction, we identified CD44, located on chromosome 11p13, as a novel translocation partner of IGH in 9 of 114 cases of gastric, nongastric extranodal, follicular, and nodal diffuse large B-cell lymphoma (DLBCL). Notably, these translocations involving IGHSmu were detected in follicular lymphomas and exclusively in germinal center B cell-ike (GCB)-DLBCLs. CD44 is not expressed in reactive GC B cells. The IGHSmu/CD44 translocations substitute Smu for the CD44 promoter and remove exon 1 of CD44, resulting in the overexpression of Imu-CD44 hybrid mRNA transcripts activated from derivative 11 that encode a new CD44 variant lacking the leader peptide and with a unique C-terminus (CD44DeltaEx1). When overexpressed in vitro in the CD44(-) GCB-DLBCL cell line BJAB, CD44DeltaEx1-green fluorescent protein localized to the cytoplasm and nucleus, whereas CD44s-green fluorescent protein (standard form) localized to the plasma membrane. The ectopic expression of CD44DeltaEx1 in BJAB cells enhanced their proliferation rate and clonogenic ability, indicating a possible pathogenic role of the translocation.