Identification of phosphorylation sites for Bruton's tyrosine kinase within the transcriptional regulator BAP/TFII-I

J Biol Chem. 2001 Jul 27;276(30):27806-15. doi: 10.1074/jbc.M103692200. Epub 2001 May 23.


Bruton's tyrosine kinase (Btk), a member of the Tec family of cytosolic kinases, is essential for B cell development and function. BAP/TFII-I, a protein implicated in transcriptional regulation, is associated with Btk in B cells and is transiently phosphorylated on tyrosine following B cell receptor engagement. BAP/TFII-I is a substrate for Btk in vitro and is hyperphosphorylated on tyrosine upon coexpression with Btk in mammalian cells. In an effort to understand the physiologic consequences of BAP/TFII-I tyrosine phosphorylation following B cell receptor stimulation, site-directed mutagenesis and phosphopeptide mapping were used to locate the predominant sites of BAP/TFII-I phosphorylation by Btk in vitro. These residues, Tyr248, Tyr357, and Tyr462, were also found to be the major sites for Btk-dependent phosphorylation of BAP/TFII-I in vivo. Residues Tyr357 and Tyr462 are contained within the loop regions of adjacent helix-loop-helix-like repeats within BAP/TFII-I. Mutation of either Tyr248, Tyr357, or Tyr462 to phenylalanine reduced transcription from a c-fos promoter relative to wild-type BAP/TFII-I in transfected COS-7 cells, consistent with the interpretation that phosphorylation at these sites contributes to transcriptional activation. Phosphorylation of BAP/TFII-I by Btk may link engagement of receptors such as surface immunoglobulin to modulation of gene expression.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Agammaglobulinaemia Tyrosine Kinase
  • Amino Acid Sequence
  • Animals
  • B-Lymphocytes / metabolism
  • Binding Sites
  • COS Cells
  • Cell Line
  • DNA-Binding Proteins / chemistry*
  • DNA-Binding Proteins / metabolism*
  • Dose-Response Relationship, Drug
  • Epitopes / chemistry
  • Escherichia coli / metabolism
  • Genes, Reporter
  • Humans
  • Mice
  • Molecular Sequence Data
  • Mutation
  • Phenylalanine / chemistry
  • Phosphorylation
  • Plasmids / metabolism
  • Point Mutation
  • Precipitin Tests
  • Protein Structure, Tertiary
  • Protein-Tyrosine Kinases / chemistry*
  • Protein-Tyrosine Kinases / metabolism*
  • Proto-Oncogene Proteins c-fos / metabolism
  • Recombinant Proteins / metabolism
  • Transcription Factors / chemistry*
  • Transcription Factors / metabolism*
  • Transcription, Genetic
  • Transcriptional Activation
  • Transfection
  • Trypsin / metabolism
  • Tyrosine / chemistry


  • DNA-Binding Proteins
  • Epitopes
  • Proto-Oncogene Proteins c-fos
  • Recombinant Proteins
  • Transcription Factors
  • Tyrosine
  • Phenylalanine
  • Protein-Tyrosine Kinases
  • Agammaglobulinaemia Tyrosine Kinase
  • BTK protein, human
  • Btk protein, mouse
  • Trypsin