Mutations in the gene encoding Bruton’s tyrosine kinase (known to cause

Mutations in the gene encoding Bruton’s tyrosine kinase (known to cause the xid phenotype prevents BCR-induced activation of NF-B. in number to 50% relative to wild type. The xid B cells that remain secrete reduced levels of serum IgM and IgG3, fail to respond to T cellCindependent type II antigensand are unable to proliferate in response to BCR stimulation (for review see BML-275 distributor reference 19). Recent studies indicate that this xid phenotype may arise from defects in cell cycle progression and BCR-directed induction of Bcl-XL, an antiapoptotic protein 4 5 20 21. However, the mechanisms by which BTK regulates these processes remain unclear. Like BTK, transcription factor nuclear factor (NF)-B is usually activated in response to BCR stimulation and has been implicated in ALK7 the regulation of Bcl-XL 22. Studies with NF-BCdeficient B cells have identified defects in BCR-induced survival and proliferation 23 24 25. Members of the NF-B/Rel family of proteins include p50/NF-B1, p52/NF-B2, RelA, c-Rel, and RelB, which have the capacity to form BML-275 distributor either homo- or heterodimers 26. In quiescent cells, NF-B dimers made up of the theory transactivating subunits RelA and c-Rel are found in the cytoplasmic compartment associated with members of the IB family of inhibitors, such as IB 26 27. Upon cellular activation, IB is usually subject to site-specific phosphorylation, which targets the inhibitor for degradation by the ubiquitinCproteasome pathway. Recent studies indicate that IB is usually phosphorylated by a multicomponent IB kinase (IKK) made up of two catalytic subunits (IKK and IKK) BML-275 distributor and one BML-275 distributor regulatory subunit (IKK; reference 27). The kinase activity of IKK is usually stimulated by a large set of NF-BCinducing brokers including the proinflammatory cytokines TNF- and IL-1. Although it is usually clear that BCR stimulation leads to the activation of NF-B 28, a role for either BTK or IKK in this B cell signal transduction pathway has not been elucidated. In this study, we investigated the significance of BTK in the BCR/NF-B signaling axis using a BTK-deficient B cell line and primary B lymphocytes isolated from BCR, B cell antigen receptor; BTK, Bruton’s tyrosine kinase; DTT, dithiothreitol; EMSAs, electrophoretic mobility shift assays; IKK, IB kinase; NF-B, nuclear factor B; PKC, protein kinase C; xid, X-linked immunodeficiency; XLA, X-linked agammaglobulinemia..