Regulation of Btk by Src family tyrosine kinases.
Loss of function of Bruton's tyrosine kinase (Btk) results in X-linked immunodeficiencies characterized by a broad spectrum of signaling defects, including those dependent on Src family kinase-linked cell surface receptors. A gain-of-function mutant, Btk*, induces the growth of fibroblasts in soft agar and relieves the interleukin-5 dependence of a pre-B-cell line. To genetically define Btk signaling pathways, we used a strategy to either activate or inactivate Src family kinases in fibroblasts that express Btk*. The transformation potential of Btk* was dramatically increased by coexpression with a partly activated c-Src mutant (E-378 --> G). This synergy was further potentiated by deletion of the Btk Src homology 3 domain. Downregulation of Src family kinases by the C-terminal Src kinase (Csk) suppressed Btk* activation and biological potency. In contrast, kinase-inactive Csk (K-222 --> R), which functioned as a dominant negative molecule, synergized with Btk* in biological transformation. Activation of Btk* correlated with increased phosphotyrosine on transphosphorylation and autophosphorylation sites. These findings suggest that the Src and Btk kinase families form specific signaling units in tissues in which both are expressed.
Afar
D E
DE
Department of Microbiology, Howard Hughes Medical Institute, University of California--Los Angeles, 90095-1662, USA.
Park
H
H
Howell
B W
BW
Rawlings
D J
DJ
Cooper
J
J
Witte
O N
ON
D000077329:Agammaglobulinaemia Tyrosine Kinase; D000818:Animals; D015153:Blotting, Western; D000081247:CSK Tyrosine-Protein Kinase; D002460:Cell Line; D006801:Humans; D010449:Peptide Mapping; D010748:Phosphopeptides / Q000737:chemistry / Q000302:isolation & purification; D010766:Phosphorylation; D017354:Point Mutation; D011505:Protein-Tyrosine Kinases / Q000302:isolation & purification / Q000378:metabolism*; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000378:metabolism*; D051381:Rats; D011994:Recombinant Proteins / Q000302:isolation & purification / Q000378:metabolism; D014162:Transfection; D019061:src-Family Kinases
D010748:Phosphopeptides; D011994:Recombinant Proteins; D011505:Protein-Tyrosine Kinases; D000077329:Agammaglobulinaemia Tyrosine Kinase; C000625949:BTK protein, human; D000081247:CSK Tyrosine-Protein Kinase; D016392:Proto-Oncogene Proteins pp60(c-src); D019061:src-Family Kinases; C000631346:CSK protein, human