Amplification of IL-21 signalling pathway through Bruton’s tyrosine kinase in human B cell activation

• Published in: Rheumatology (Oxford, England) Vol. 54; no. 8; pp. 1488 - 1497
• Main Authors: Wang, Sheau-Pey, Iwata, Shigeru, Nakayamada, Shingo, Niiro, Hiroaki, Jabbarzadeh-Tabrizi, Siamak, Kondo, Masahiro, Kubo, Satoshi, Yoshikawa, Maiko, Tanaka, Yoshiya
• Format: Journal Article
• Language: English
• Published: England 01.08.2015
• Subjects: Aged; Arthritis, Rheumatoid - metabolism; Arthritis, Rheumatoid - pathology; Arthritis, Rheumatoid - physiopathology; B-Cell Activating Factor - physiology; B-Lymphocytes - drug effects; B-Lymphocytes - pathology; B-Lymphocytes - physiology; Case-Control Studies; CD40 Antigens - pharmacology; CD40 Antigens - physiology; Cell Differentiation - drug effects; Cell Line; Cells, Cultured; Female; Gene Knockdown Techniques; Humans; In Vitro Techniques; Interleukins - pharmacology; Interleukins - physiology; Male; Middle Aged; Phosphorylation; Protein-Tyrosine Kinases - genetics; Protein-Tyrosine Kinases - physiology; Proto-Oncogene Proteins c-bcr - pharmacology; Proto-Oncogene Proteins c-bcr - physiology; Rheumatoid Factor - metabolism; Signal Transduction - physiology; STAT1 Transcription Factor - metabolism; autoimmune diseases; STAT1; class-switch DNA recombination; B cells; BCR signalling; rheumatoid arthritis; IL-21
• ISSN: 1462-0324; 1462-0332; 1462-0332
• DOI: 10.1093/rheumatology/keu532

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. 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. 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. 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.