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  • The EMBO Journal (1998) 17, 1973 - 1985
  • doi:10.1093/emboj/17.7.1973

Btk/Tec kinases regulate sustained increases in intracellular Ca2+ following B-cell receptor activation

Anne-Catherine Fluckiger1,7, Zuomei Li1,7, Roberta M. Kato2, Matthew I. Wahl1, Hans D. Ochs3, Richard Longnecker4, Jean-Pierre Kinet5, Owen N. Witte1,6, Andrew M. Scharenberg5 and David J. Rawlings2

  1. Department of Microbiology and Molecular Genetics University of California at Los Angeles, Los Angeles, CA 90095-1662, USA
  2. Department of Pediatrics, University of California at Los Angeles, Los Angeles, CA 90095-1752, USA
  3. Division of Infectious Diseases, Immunology and Rheumatology, University of Washington, Seattle, WA 98195-6320, USA
  4. Department of Microbiology and Immunology, Northwestern University, Chicago, IL 60611, USA
  5. Laboratory of Allergy and Immunology, Beth Israel Hospital and Harvard Medical School, 99 Brookline Avenue, Boston, MA 02215, USA
  6. Howard Hughes Medical Institute, University of California at Los Angeles, Los Angeles, CA 90095-1662, USA
  7. A.-C.Fluckiger and Z.Li contributed equally to this work

Correspondence to:

David J. Rawlings, E-mail: drawling@pediatrics.medsch.ucla.edu

Received 24 November 1997; Accepted 9 February 1998; Revised 20 January 1998

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.

  • Keywords:

    • calcium stores,
    • FcgammaRIIb1,
    • phospholipase Cgamma,
    • Syk,
    • thapsigargin