Amplification of IL-21 signalling pathway through Bruton's tyrosine kinase in human B cell activation.
OBJECTIVE
B cells play an important role in the pathogenesis of autoimmune diseases. The role of Bruton's tyrosine kinase (Btk) in cytokine-induced human B cell differentiation and class-switch recombination remains incompletely defined. This study analysed the effect of Btk on human activated B cells.


METHODS
Purified B cells from healthy subjects were stimulated with B cell receptor (BCR) and other stimuli with or without a Btk inhibitor and gene expression was measured. The B cell line BJAB was used to assess Btk-associated signalling cascades. Phosphorylated Btk (p-Btk) in peripheral blood B cells obtained from 10 healthy subjects and 41 patients with RA was measured by flow cytometry and compared with patient backgrounds.


RESULTS
IL-21 signalling, in concert with BCR, CD40 and BAFF signals, led to robust expression of differentiation- and class-switch DNA recombination-related genes and IgG production in human B cells, all of which were significantly suppressed by the Btk inhibitor. Although phosphorylation of STAT1 and STAT3 was induced by co-stimulation with IL-21, BCR and CD40, STAT1 phosphorylation in the nucleus, but not in the cytoplasm, was exclusively impaired by Btk blockade. High levels of p-Btk were noted in B cells of RA patients compared with controls and they correlated significantly with titres of RF among RF-positive patients.


CONCLUSIONS
The findings elucidate a model in which Btk not only plays a fundamental role in the regulation of BCR signalling, but may also mediate crosstalk with cytokine signalling pathways through regulation of IL-21-induced phosphorylation of STAT1 in the nuclei of human B cells. Btk appears to have pathological relevance in RA.
First Department of Internal Medicine, University of Occupational and Environmental Health, Kitakyushu and.
Sheau-Pey
SP
Wang
First Department of Internal Medicine, University of Occupational and Environmental Health, Kitakyushu and.
Shigeru
S
Iwata
First Department of Internal Medicine, University of Occupational and Environmental Health, Kitakyushu and.
Shingo
S
Nakayamada
Graduate School of Medical Sciences, Department of Medicine and Biosystemic Science, Kyushu University, Fukuoka, Japan.
Hiroaki
H
Niiro
Graduate School of Medical Sciences, Department of Medicine and Biosystemic Science, Kyushu University, Fukuoka, Japan.
Siamak
S
Jabbarzadeh-Tabrizi
First Department of Internal Medicine, University of Occupational and Environmental Health, Kitakyushu and.
Masahiro
M
Kondo
First Department of Internal Medicine, University of Occupational and Environmental Health, Kitakyushu and.
Satoshi
S
Kubo
First Department of Internal Medicine, University of Occupational and Environmental Health, Kitakyushu and.
Maiko
M
Yoshikawa
First Department of Internal Medicine, University of Occupational and Environmental Health, Kitakyushu and tanaka@med.uoeh-u.ac.jp.
Yoshiya
Y
Tanaka
D000077329:Agammaglobulinaemia Tyrosine Kinase; D000368:Aged; D001172:Arthritis, Rheumatoid / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D053264:B-Cell Activating Factor / Q000502:physiology*; D001402:B-Lymphocytes / Q000187:drug effects / Q000473:pathology / Q000502:physiology*; D019013:CD40 Antigens / Q000494:pharmacology / Q000502:physiology*; D016022:Case-Control Studies; D002454:Cell Differentiation / Q000187:drug effects; D002460:Cell Line; D002478:Cells, Cultured; D005260:Female; D055785:Gene Knockdown Techniques; D006801:Humans; D066298:In Vitro Techniques; D007378:Interleukins / Q000494:pharmacology / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000502:physiology*; D051562:Proto-Oncogene Proteins c-bcr / Q000494:pharmacology / Q000502:physiology*; D012217:Rheumatoid Factor / Q000378:metabolism; D050794:STAT1 Transcription Factor / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D000098546:Interleukin-21
D053264:B-Cell Activating Factor; D019013:CD40 Antigens; D007378:Interleukins; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; C505719:TNFSF13B protein, human; D012217:Rheumatoid Factor; D011505:Protein-Tyrosine Kinases; D000077329:Agammaglobulinaemia Tyrosine Kinase; C000625949:BTK protein, human; C496613:BCR protein, human; D051562:Proto-Oncogene Proteins c-bcr; D000098546:Interleukin-21
B cells; BCR signalling; IL-21; STAT1; autoimmune diseases; class-switch DNA recombination; rheumatoid arthritis