Identification of phosphorylation sites for Bruton's tyrosine kinase within the transcriptional regulator BAP/TFII-I.
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.
Mesh Terms:
Amino Acid Sequence, Animals, B-Lymphocytes, Binding Sites, COS Cells, Cell Line, DNA-Binding Proteins, Dose-Response Relationship, Drug, Epitopes, Escherichia coli, Genes, Reporter, Humans, Mice, Molecular Sequence Data, Mutation, Phenylalanine, Phosphorylation, Plasmids, Point Mutation, Precipitin Tests, Protein Structure, Tertiary, Protein-Tyrosine Kinases, Proto-Oncogene Proteins c-fos, Recombinant Proteins, Transcription Factors, Transcription, Genetic, Transcriptional Activation, Transfection, Trypsin, Tyrosine
Amino Acid Sequence, Animals, B-Lymphocytes, Binding Sites, COS Cells, Cell Line, DNA-Binding Proteins, Dose-Response Relationship, Drug, Epitopes, Escherichia coli, Genes, Reporter, Humans, Mice, Molecular Sequence Data, Mutation, Phenylalanine, Phosphorylation, Plasmids, Point Mutation, Precipitin Tests, Protein Structure, Tertiary, Protein-Tyrosine Kinases, Proto-Oncogene Proteins c-fos, Recombinant Proteins, Transcription Factors, Transcription, Genetic, Transcriptional Activation, Transfection, Trypsin, Tyrosine
J. Biol. Chem.
Date: Jul. 27, 2001
PubMed ID: 11373296
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