title: Bruton's tyrosine kinase is involved in p65-mediated transactivation and phosphorylation of p65 on serine 536 during NFkappaB activation by lipopolysaccharide.
abstract: Bruton's tyrosine kinase (Btk) has recently been shown to participate in the induction of nuclear factor kappaB (NFkappaB)-dependent gene expression by the lipopolysaccharide (LPS) receptor Toll-like receptor-4 (TLR4). In this study we have examined the mechanism whereby Btk participates in this response. Treatment of the murine monocytic cell line Raw264.7 with LFM-A13, a specific Btk inhibitor, blocked LPS-induced NFkappaB-dependent reporter gene expression but not IkappaB alpha degradation. Transient transfection of HEK293 cells with Btk had no effect on NFkappaB-dependent reporter gene expression but strongly promoted transactivation of a reporter gene by a p65-Gal4 fusion protein. IkappaB alpha degradation activated by LPS was intact in macrophages from X-linked immunodeficiency (Xid) mice, which contain inactive Btk. Transfection of cells with a dominant negative form of Btk (BtkK430R) inhibited LPS-driven p65 mediated transactivation. Additionally LFM-A13 impaired phosphorylation of serine 536 on p65 induced by LPS in HEK293-TLR4 cells, and in Xid macrophages this response was impaired. This study therefore reveals a novel function for Btk. It is required for the signaling pathway activated by TLR4, which culminates in phosphorylation of p65 on serine 536 promoting transactivation by NFkappaB.
authors.affiliation: Department of Biochemistry and Biotechnology Institute, Trinity College, Dublin 2, Ireland.
authors.forename: Sarah L
authors.initials: SL
authors.lastname: Doyle
authors.forename: Caroline A
authors.initials: CA
authors.lastname: Jefferies
authors.forename: Luke A
authors.initials: LA
authors.lastname: O'Neill
mesh_terms: D000077329:Agammaglobulinaemia Tyrosine Kinase; D002460:Cell Line; D017930:Genes, Reporter; D006801:Humans; D008070:Lipopolysaccharides / Q000494:pharmacology*; D016328:NF-kappa B / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000502:physiology*; D012694:Serine / Q000378:metabolism*; D051996:Transcription Factor RelA; D015533:Transcriptional Activation / Q000502:physiology*
chemical_list: D008070:Lipopolysaccharides; D016328:NF-kappa B; D051996:Transcription Factor RelA; D012694:Serine; D011505:Protein-Tyrosine Kinases; D000077329:Agammaglobulinaemia Tyrosine Kinase; C000625949:BTK protein, human; C000625951:Btk protein, mouse