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OP0199 Amplification of IL-21 Signaling Pathway Through Bruton’s Tyrosine Kinase (BTK) in Human B Cells
  1. S.-P. Wang1,
  2. S. Iwata2,
  3. K. Yamaoka2,
  4. H. Niiro3,
  5. S. Nakayamada2,
  6. S. J. Tabrizi3,
  7. S. Kubo2,
  8. M. Kondo2,
  9. K. Akashi3,
  10. Y. Tanaka2
  1. 1The First Department of Internal Medicine, University of Occupational and Environmental Health, Japan
  2. 2The First Department of Internal Medicine, University of Occupational and Environmental Health, Kitakyushu
  3. 3Department of Medicine and Biosystemic Science, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan

Abstract

Background B cells play a pivotal role in pathological processes of autoimmune diseases. Btk, which mediates BCR signaling, is considered as a suitable target for the treatment of autoimmune diseases. However, the underlying mechanisms of B cell activation mediated by Btk remain elusive.

Objectives The aim of this study is to investigate the mechanism underlying human B cell activation and to assess the role of Btk in this process.

Methods Purified B cells from healthy donors were stimulated with BCR, sCD40L/BAFF, and sIL-21 with/without a Btk inhibitor. B cell line, BJAB was utilized to assess the molecular mechanism.

Results The expression of AICDA, encoding a RNA-editing deaminase and involved in class-switch recombination of Ig, was slightly induced by IL-21 stimulation alone in human primary B cells. Likewise, under BCR and/or CD40/BAFF stimulation, very little AICDA expression was induced. However, combinatorial stimulation with BCR, CD40/BAFF and IL-21 induced robust expression of AICDA, BCL6 and XBP1 and IgG production. A Btk inhibitor (ONO-A) significantly abrogated the expression to the extent of IL-21 alone in a dose-dependent manner. To assess the mechanism by which Btk regulates the genes induced by IL-21 in human B cells, we set up the Btk knock-down (KD) cell line by using BJAB. The transient exposure of IL-21 induced both p-STAT1 and p-STAT3 in BJAB. However, in Btk KD BJAB, p-STAT1 was not induced in the nucleus, while it was induced in the cytoplasm. Furthermore, IL-21-induced expression of T-bet significantly decreased in Btk-KD cells, compared to mock transferred BJAB, indicating that phosphorylation of STAT-1 by IL-21 affected its target gene T-bet, resulting in robust activation of B cells through Btk.

Conclusions Our results suggest that Btk activation induced by BCR and CD40/BAFF amplify IL-21 signaling to induce robust expression of differentiation- and class-switch DNA recombination (CSR)-related genes and IgG production in human B cells. Btk-mediated signal directly regulate p-STAT1 translocation from the cytoplasm to the nucleus, thereby allowing efficient propagation of IL-21-signal critical for human B cell differentiation and CSR. These results underscore the potential role of Btk in B cell-mediated pathological processes in autoimmune diseases.

Disclosure of Interest S.-P. Wang: None Declared, S. Iwata: None Declared, K. Yamaoka: None Declared, H. Niiro: None Declared, S. Nakayamada: None Declared, S. Tabrizi: None Declared, S. Kubo: None Declared, M. Kondo: None Declared, K. Akashi: None Declared, Y. Tanaka Grant/research support from: Bristol-Myers Squibb, MSD K.K., Chugai Pharma Co., Ltd., Mitsubishi-Tanabe Pharma Co., Ltd., Astellas Pharma Inc., Abbott Japan Co., Ltd., Eisai Co., Ltd. and Janssen Pharmaceutical K.K., Speakers bureau: Mitsubishi-Tanabe Pharma Co., Ltd., Abbott Japan Co., Ltd., Eisai Co., Ltd., Chugai Pharma Co., Ltd., Janssen Pharma K.K., Santen Pharma Co., Ltd., Pfizer Japan Inc., Astellas Pharma Inc., Daiichi-Sankyo Co., Ltd., GlaxoSmithKline K.K., Astra-Zeneca, Otsuka Pharma Co., Ltd., Actelion Pharma Japan Ltd., Eli Lilly Japan K.K., Nippon Kayaku Co., Ltd., UCB Japan Co., Ltd., Quintiles Transnational Japan Co. Ltd., Ono Pharma Co., Ltd.,

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