Bruton's tyrosine kinase inhibition induces rewiring of proximal and distal B‐cell receptor signaling in mice

• Published in: European journal of immunology 2021-09, Vol.51 (9), p.2251-2265
• Main Authors: Rip, Jasper, Bruijn, Marjolein J. W., Neys, Stefan F. H., Singh, Simar Pal, Willar, Jonas, Hulst, Jennifer A. C., Hendriks, Rudi W., Corneth, Odilia B. J.
• Format: Article
• Language: English
• Subjects: 1-Phosphatidylinositol 3-kinase; Acalabrutinib; AKT protein; B cell; Basic; BCR signaling; Bruton's tyrosine kinase; Cell differentiation; Extracellular signal-regulated kinase; Kinases; Leukemia; Lymphocytes B; Molecular immunology and signaling; Phosphoflow cytometry; Phosphorylation; Signal transduction; Syk protein; Transgenic mice; Tyrosine kinase inhibitors
• ISSN: 0014-2980; 1521-4141
• DOI: 10.1002/eji.202048968

Bruton′s tyrosine kinase (Btk) is a crucial signaling molecule in BCR signaling and a key regulator of B‐ cell differentiation and function. Btk inhibition has shown impressive clinical efficacy in various B‐cell malignancies. However, it remains unknown whether inhibition additionally induces changes in BCR signaling due to feedback mechanisms, a phenomenon referred to as BCR rewiring. In this report, we studied the impact of Btk activity on major components of the BCR signaling pathway in mice. As expected, NF‐κB and Akt/S6 signaling was decreased in Btk‐deficient B cells. Unexpectedly, phosphorylation of several proximal signaling molecules, including CD79a, Syk, and PI3K, as well as the key Btk‐effector PLCγ2 and the more downstream kinase Erk, were significantly increased. This pattern of BCR rewiring was essentially opposite in B cells from transgenic mice overexpressing Btk. Importantly, prolonged Btk inhibitor treatment of WT mice or mice engrafted with leukemic B cells also resulted in increased phosho‐CD79a and phospho‐PLCγ2 in B cells. Our findings show that Btk enzymatic function determines phosphorylation of proximal and distal BCR signaling molecules in B cells. We conclude that Btk inhibitor treatment results in rewiring of BCR signaling, which may affect both malignant and healthy B cells. BCR signaling is altered in the absence of Bruton's tyrosine kinase (Btk) activity. Using phosphoflow cytometry, we observed that Btk‐deficiency or treatment with the Btk inhibitor acalabrutinib reduced major downstream signaling events following BCR engagement, as expected. However, proximal BCR signaling and Erk phosphorylation was remarkably increased.