Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:Q00604 (X-linked)
 16,883 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The CBA/N mouse carries the X-linked immunodeficiency xid, resulting in defective B cell development. B cells from these animals cannot mount antibody responses to type 2 T-independent antigens, and do not synthesize DNA when stimulated with anti-immunoglobulin (Ig) antibodies which are mitogenic for normal B cells. The primary antibody responses of CBA/N mice to T-dependent antigens have also been reported to be abnormal. Here we describe the results of experiments which demonstrate that the B cells from these animals respond abnormally to ligation of CD40, a B cell surface molecule now known to play a key role during T cell-B cell interactions, via its interaction with the counterligand (CD40L) expressed by activated T cells. Hence, xid B cells fail to proliferate when cultured with preactivated T helper type 2 (Th2)T cells (known to express CD40L), with a soluble CD40L-CD8 fusion protein, or in response to monoclonal antibodies to CD40, even in the presence of IL-4 and/or anti-Ig reagents. However, xid B cells do receive abortive activation signals following ligation of CD40, as manifested by up-regulation of class II major histocompatibility complex and CD23 antigens. Since the xid defect has now been identified as a point mutation in the protein tyrosine kinase Btk, our results point to an important role for this kinase in the downstream signaling cascade elicited in response to ligation of either surface Ig or CD40.
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PMID:B cells from CBA/N mice do not proliferate following ligation of CD40. 751 60

Tyrosine phosphorylation of several cellular proteins is one of the earliest signaling events induced by cross-linking of the high-affinity receptor for immunoglobulin E (Fc epsilon RI) on mast cells or basophils. Tyrosine kinases activated during this process include the Src family kinases, Lyn, c-Yes, and c-Src, and members of another subfamily, Syk and PTK72 (identical or highly related to Syk). Recently, some of us described two novel tyrosine kinases, Emb and Emt, whose expression was limited to subsets of hematopoietic cells, including mast cells. Emb turned out to be identical to Btk, a gene product defective in human X-linked agammaglobulinemia and in X-linked immunodeficient (xid) mice. Here we report that Fc epsilon RI cross-linking induced rapid phosphorylation on tyrosine, serine, and threonine residues and activation of Btk in mouse bone marrow-derived mast cells. A small fraction of Btk translocated from the cytosol to the membrane compartment following receptor cross-linking. Tyrosine phosphorylation of Btk was not induced by either a Ca2+ ionophore (A23187), phorbol 12-myristate 13-acetate, or a combination of the two reagents. Co-immunoprecipitation between Btk and receptor subunit beta or gamma was not detected. The data collectively suggest that Btk is not associated with Fc epsilon but that its activation takes place prior to protein kinase C activation and plays a novel role in the Fc epsilon RI signaling pathway.
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PMID:Tyrosine phosphorylation and activation of Bruton tyrosine kinase upon Fc epsilon RI cross-linking. 751 58

Bruton tyrosine kinase (EC 2.7.1.112) [Btk, encoded by Btk in mice and BTK in humans (formerly known as atk, BPK, or emb)], which is variously mutated in chromosome X-linked agammaglobulinemia patients and X-linked immunodeficient (xid) mice, has the pleckstrin homology (PH) domain at its amino terminus. The PH domain of Btk expressed as a bacterial fusion protein directly interacts with protein kinase C in mast cell lysates. Evidence was obtained that Btk is physically associated with protein kinase C in intact murine mast cells as well. Both Ca(2+)-dependent (alpha, beta I, and beta II) and Ca(2+)-independent protein kinase C isoforms (epsilon and zeta) in mast cells interact with the PH domain of Btk in vitro, and protein kinase C beta I is associated with Btk in vivo. Btk served as a substrate of protein kinase C, and its enzymatic activity was down-regulated by protein kinase C-mediated phosphorylation. Furthermore, depletion or inhibition of protein kinase C with pharmacological agents resulted in an enhancement of the tyrosine phosphorylation of Btk induced by mast cell activation.
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PMID:The pleckstrin homology domain of Bruton tyrosine kinase interacts with protein kinase C. 752 30

The gene encoding Bruton tyrosine kinase (Btk) is known to be mutated in human X chromosome-linked agammaglobulinemia and in the Xid mouse. This kinase was examined in B lymphocytes before and after antigen receptor ligation and also in pre-B cells. Btk was found to be catalytically activated and tyrosine phosphorylated in response to anti-IgM stimulation in B cells. This kinase is also constitutively phosphorylated on tyrosine residues in pre-B cells. These findings point to a functional role for Btk in pre-antigen and antigen receptor signaling during B-cell development and provide a biochemical explanation for the X-linked genetic syndromes already linked to this kinase.
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PMID:Bruton tyrosine kinase is tyrosine phosphorylated and activated in pre-B lymphocytes and receptor-ligated B cells. 752 98

Mutations in the gene encoding the protein tyrosine kinase Btk are associated with the human B cell immunodeficiency X-linked agammaglobulinemia (XLA). In the mouse, a point mutation in the Btk pleckstrin homology domain segregates with a milder X-linked immunodeficiency (xid). To assess the importance of Btk function in murine lymphopoiesis, we generated multiple embryonic stem cell clones bearing a targeted disruption of the btk gene and examined their potential to produce lymphocytes in both C57BL/6 and RAG2-/- host chimeric animals. These mice provide a complementary set of in vivo competition assays that formally establish the genetic basis for the xid phenotype. Although the null mutation yields a phenotype quite similar to that of xid, it also compromises expansion of B cell precursors. Our results suggest that the murine and human consequences of Btk deficiency differ only quantitatively, and represent the same disease process.
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PMID:Impaired expansion of mouse B cell progenitors lacking Btk. 755 95

The protein-tyrosine kinase gene Itk is expressed preferentially in T lymphoid cells of the mouse and is induced by IL-2. A related gene, Btk, is expressed in the murine B lymphoid and myeloid lineages. Because mutations in Btk and the corresponding human gene are associated with X-linked immunodeficiency syndromes, it was of interest to map Itk and its human counterpart. By Southern blot analysis of DNA from the progeny of two multilocus crosses, murine Itk was mapped to Chromosome 11. By fluorescence in situ hybridization, human ITK was mapped to 5q32-q33. Murine Itk and its human homologue lie within regions of conserved synteny that include several growth factor and growth factor receptor genes. This region in humans is frequently deleted in the myelodysplastic syndrome, suggesting possible involvement of ITK in this disorder.
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PMID:Mapping of the gene for the tyrosine kinase Itk to a region of conserved synteny between mouse chromosome 11 and human chromosome 5q. 782 87

A gene for a novel, putative cytoplasmic tyrosine kinase, TXK has been isolated from a human peripheral blood cDNA library. The complete nucleotide sequence of the cDNA indicates that it is related most closely to EMT, a tyrosine kinase of T cells and to the B-cell tyrosine kinase Btk, which is mutated in X-linked agammaglobulinemia (XLA) in humans and X-linked immunodeficiency disease (XID) in mouse. TXK, like BTK, is a member of the Tec sub-family of Src-type (non-receptor) tyrosine kinases. Like similar Tec sub-family members, and unlike the other Src kinases, TXK lacks both the N-terminal myristylation signal and the C-terminal regulatory tyrosine. TXK expression is detected primarily in T cells and some myeloid cell lines but not in a number of other cell types. TXK shares 60% amino acid homology with EMT and 57% with BTK over the SH3, SH2 (Src-homology) and catalytic domains but unlike BTK, EMT and tec, it lacks Gap 1 homology and steroid hormone receptor homology in the N-terminal region. Genomic clones containing TXK have been isolated and hybridize to chromosome position 4p12.
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PMID:TXK, a novel human tyrosine kinase expressed in T cells shares sequence identity with Tec family kinases and maps to 4p12. 795 Dec 33

The X-ray crystal structure of the pleckstrin homology (PH) domain from human dynamin has been refined to 2.2 A resolution. A seven-stranded beta sandwich of two orthogonal antiparallel beta sheets is closed at one corner by a C-terminal alpha helix. Opposite this helix are the three loops that vary most among PH domains. The basic fold is very similar to that of two other PH domains recently determined by nuclear magnetic resonance, confirming that PH domain with known structure is electrostatically polarized, with the three variable loops forming a positively charged surface. This surface includes the position of the X-linked immunodeficiency mutation in the Btk PH domain and may serve as a ligand-binding surface.
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PMID:Crystal structure at 2.2 A resolution of the pleckstrin homology domain from human dynamin. 795 89

A regional physical and transcription map involving yeast artificial chromosomes (YACs), cosmids, and cDNAs has been constructed for Xq21.3-q22 around the gene BTK (formerly atk or BPK) defective in X-linked agammaglobulinemia (XLA). With a positional cloning strategy employing direct cDNA selection, novel cDNAs were found to cluster in the region of approximately 100 kb flanking the XLA and alpha-galactosidase A loci. While these widely expressed transcripts are in the area known to contain CpG islands, a less evolutionarily conserved gene, located more than 130 kb distal of DXS178, maps to cosmid clones that could not be digested with rare-cutting restriction enzymes. The presence of transcribed sequences flanking the BTK allowed us to investigate their involvement in complex XLA phenotypes. Southern blot analysis using cDNA clones isolated from this region permitted us to exclude a contiguous deletion syndrome as an underlying defect in three patients with XLA and associated growth hormone deficiency. A single XLA patient with torsion dystonia and cosegregating X-linked deafness has been found with a deletion in the 3' part of BTK extending centromerically into the flanking expressed sequence DXS1274E. This suggests a possible involvement of the DXS1274E in this phenotype. The GenBank accession numbers for novel cDNA sequences are as follows: DXS1269E (L20773), DXS1271E (UO1923), DXS1273E (UO1925), and DXS1274E (UO1922).
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PMID:Isolation of cosmid and cDNA clones in the region surrounding the BTK gene at Xq21.3-q22. 795 28

Btk is a cytoplasmic protein tyrosine kinase (PTK) that has been directly implicated in the pathogenesis of X-linked agammaglobulinaemia (XLA) in humans and X-linked immunodeficiency (Xid) in mice. We have isolated phage and cosmid clones that allowed us to deduce the genomic structure of mouse and human Btk loci. The mouse and human genes are contained within genomic regions that span approximately 43.5 kb and 37.5 kb, respectively. Both loci contain 18 coding exons ranging between 55 and 560 bp in size with introns ranging in size from 164 bp to approximately 9 kb. The 5'-untranslated regions are encoded by single exons located approximately 9 kb upstream of the first coding exon. Exon 18 encodes for the last 23 carboxyl-terminal amino acids and the entire 3'-untranslated region. The location of intron/exon boundaries in the catalytic domains of the mouse and human Btk loci differs from that found in other described sub-families of intracellular PTKs, namely that of Src, Fes/Fer, Csk, and Abl/Arg. This observation is consistent with the classification of Btk together with the recently characterized kinases, Tec and Itk, into a separate sub-family of cytoplasmic PTKs. Putative transcription initiation sites in the mouse and human Btk loci have been determined by using the rapid amplification of cDNA ends assay. Similar to many other PTK specific genes, the putative Btk promoters lack obvious TATAA and CAAAT motifs. Putative initiator elements and potential binding sites for Ets (PEA-3), zeste, and PuF transcription factors are located within the 300 bp which are located upstream of the major transcription start site in both species. These sequences can mediate promoter activity when placed upstream of a promotorless chloramphenicol acetyl transferase reporter gene in an orientation-dependent manner. The present analysis will significantly facilitate the mutational analyses of patients with XLA and the further characterization of the function and regulation of the Btk molecule.
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PMID:Genomic organization of mouse and human Bruton's agammaglobulinemia tyrosine kinase (Btk) loci. 798 60


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