Btk/Tec kinases regulate sustained increases in intracellular Ca2+ following B-cell receptor activation.
Bruton's tyrosine kinase (Btk) is essential for B-lineage development and represents an emerging family of non-receptor tyrosine kinases implicated in signal transduction events initiated by a range of cell surface receptors. Increased dosage of Btk in normal B cells resulted in a striking enhancement of extracellular calcium influx following B-cell antigen receptor (BCR) cross-linking. Ectopic expression of Btk, or related Btk/Tec family kinases, restored deficient extracellular Ca2+ influx in a series of novel Btk-deficient human B-cell lines. Btk and phospholipase Cgamma (PLCgamma) co-expression resulted in tyrosine phosphorylation of PLCgamma and required the same Btk domains as those for Btk-dependent calcium influx. Receptor-dependent Btk activation led to enhanced peak inositol trisphosphate (IP3) generation and depletion of thapsigargin (Tg)-sensitive intracellular calcium stores. These results suggest that Btk maintains increased intracellular calcium levels by controlling a Tg-sensitive, IP3-gated calcium store(s) that regulates store-operated calcium entry. Overexpression of dominant-negative Syk dramatically reduced the initial phase calcium response, demonstrating that Btk/Tec and Syk family kinases may exert distinct effects on calcium signaling. Finally, co-cross-linking of the BCR and the inhibitory receptor, FcgammaRIIb1, completely abrogated Btk-dependent IP3 production and calcium store depletion. Together, these data demonstrate that Btk functions at a critical crossroads in the events controlling calcium signaling by regulating peak IP3 levels and calcium store depletion.
Fluckiger
A C
AC
Department of Microbiology and Molecular Genetics, University of California at Los Angeles, Los Angeles, CA 90095-1662, USA.
Li
Z
Z
Kato
R M
RM
Wahl
M I
MI
Ochs
H D
HD
Longnecker
R
R
Kinet
J P
JP
Witte
O N
ON
Scharenberg
A M
AM
Rawlings
D J
DJ
D000077329:Agammaglobulinaemia Tyrosine Kinase; D000361:Agammaglobulinemia; D001402:B-Lymphocytes; D002118:Calcium / Q000378:metabolism*; D002461:Cell Line, Transformed; D003432:Cross-Linking Reagents; D019281:Dimerization; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004792:Enzyme Precursors / Q000235:genetics / Q000502:physiology; D006801:Humans; D007140:Immunoglobulin Fab Fragments; D007295:Inositol Phosphates / Q000096:biosynthesis; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes / Q000235:genetics / Q000502:physiology; D051966:Phospholipase C gamma; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D011947:Receptors, Antigen, B-Cell / Q000378:metabolism*; D017452:Receptors, IgG / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology*; D000072377:Syk Kinase; D019284:Thapsigargin / Q000494:pharmacology; D010738:Type C Phospholipases / Q000235:genetics / Q000502:physiology; D014763:Viral Matrix Proteins / Q000502:physiology
D003432:Cross-Linking Reagents; C037662:EBV-associated membrane antigen, Epstein-Barr virus; D004791:Enzyme Inhibitors; D004792:Enzyme Precursors; D007140:Immunoglobulin Fab Fragments; D007295:Inositol Phosphates; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes; D011947:Receptors, Antigen, B-Cell; D017452:Receptors, IgG; D014763:Viral Matrix Proteins; D019284:Thapsigargin; C089848:Tec protein-tyrosine kinase; D011505:Protein-Tyrosine Kinases; D000077329:Agammaglobulinaemia Tyrosine Kinase; C000625949:BTK protein, human; C000606896:SYK protein, human; D000072377:Syk Kinase; C080813:emt protein-tyrosine kinase; D010738:Type C Phospholipases; D051966:Phospholipase C gamma; D002118:Calcium