title: Constitutive STAT6 activation in primary mediastinal large B-cell lymphoma.
abstract: Primary mediastinal large B-cell lymphoma (PMBL), currently recognized as a diffuse large B-cell lymphoma (DLBCL) subtype, shows increased expression of interleukin 4 (IL-4)/IL-13 signaling effectors and targets, suggesting constitutive activation of these pathways. We therefore investigated the functional state of the signal transducer and activator of transcription 6 (STAT6), mediating IL-4/IL-13 transcriptional effects. Constitutive STAT6 phosphorylation and DNA-binding activity were detected in PMBL cell lines but not DLBCL cell lines. Moreover, immunohistochemical analysis revealed nuclear phosphorylated STAT6 (P-STAT6) in 8 of 11 PMBL, compared with 1 of 10 DLBCL primary tumors (P =.01). IL-4 and IL-13 transcripts were absent in PMBL cell lines and expressed at low levels in tumors, indicating that, contrary to classical Hodgkin lymphoma (cHL), STAT6 activation is not due to an autocrine IL-4/IL-13 secretion. We demonstrated an amplification of the JAK2 gene in 2 of 6 PMBL cases, and showed higher JAK2 mRNA levels in PMBL compared with DLBCL (P =.005). The Janus kinase 2 (JAK2) was constitutively phosphorylated in the PMBL MedB1 cell line. MedB1 treatment with JAK2 inhibitor AG490 partially decreased STAT6 phosphorylation, suggesting that JAK2 is partially involved in STAT6 activation in these cells. Our findings highlight phosphorylated STAT6 as a characteristic distinguishing PMBL from DLBCL, but a common feature to PMBL and cHL, supporting the hypothesis of common pathogenic events in these 2 lymphomas.
authors.affiliation: U617, INSERM, Université Paris XII/Département de Pathologie, Hôpital Henri Mondor, AP-HP, 51 avenue du Maréchal de Lattre de Tassigny, 94010 Créteil, France.
authors.forename: Chrystelle
authors.initials: C
authors.lastname: Guiter
authors.forename: Isabelle
authors.initials: I
authors.lastname: Dusanter-Fourt
authors.forename: Christiane
authors.initials: C
authors.lastname: Copie-Bergman
authors.forename: Marie-Laure
authors.initials: ML
authors.lastname: Boulland
authors.forename: Sabine
authors.initials: S
authors.lastname: Le Gouvello
authors.forename: Philippe
authors.initials: P
authors.lastname: Gaulard
authors.forename: Karen
authors.initials: K
authors.lastname: Leroy
authors.forename: Flavia
authors.initials: F
authors.lastname: Castellano
mesh_terms: D045744:Cell Line, Tumor; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D018793:Interleukin-13 / Q000235:genetics; D015847:Interleukin-4 / Q000235:genetics; D053614:Janus Kinase 2; D016393:Lymphoma, B-Cell / Q000378:metabolism* / Q000503:physiopathology; D016403:Lymphoma, Large B-Cell, Diffuse / Q000378:metabolism* / Q000503:physiopathology; D008479:Mediastinal Neoplasms / Q000378:metabolism* / Q000503:physiopathology; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D050800:STAT6 Transcription Factor; D015534:Trans-Activators / Q000378:metabolism*
chemical_list: D018793:Interleukin-13; D011518:Proto-Oncogene Proteins; D050800:STAT6 Transcription Factor; C494101:STAT6 protein, human; D015534:Trans-Activators; D015847:Interleukin-4; D011505:Protein-Tyrosine Kinases; C507924:JAK2 protein, human; D053614:Janus Kinase 2