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Published online before print November 21, 2008
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© by The Society for Leukocyte Biology
Journal of Leukocyte Biology, doi:10.1189/jlb.0308193

Received for publication March 21, 2008.
Revised September 24, 2008.
Accepted for publication October 7, 2008.

Article

Role of initial protein phosphorylation events and localized release-activated calcium influx in B cell antigen receptor signaling

Taras Lyubchenko *{dagger}@, J. Paul Nielsen *, Sara M. Miller *, Ganna A. Liubchenko *, and V. Michael Holers *{dagger}

Departments of *Medicine and {dagger}Immunology, University of Colorado at Denver and Health Sciences Center, Aurora, Colorado, USA

@ To whom correspondence should be addressed. E-mail: taras.lyubchenko{at}uchsc.edu.


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Abstract

An increase in intracellular calcium concentration is one of the major initial steps in B cell activation following antigen receptor (BCR) ligation. We show herein that in C57BL/6 murine B lymphocytes and in model cell lines, BCR-mediated calcium ion (Ca2+) influx occurs via highly selective Ca2+ release-activated channels, and Ca2+ regulatory molecule stromal interaction molecule 1 plays an important role in this pathway. We also demonstrate the temporal relation between Ca2+-dependent signaling events and formation of the immune synapse. Our data indicate that cytoplasmic Ca2+ levels in areas adjacent to the immune synapse differ from those in the rest of the cytoplasm. Finally, a comparison of phosphorylation patterns of BCR-triggered signaling proteins in the presence or absence of Ca2+ revealed the unanticipated finding that initial BCR-triggered, Ca2+-dependent tyrosine phosphorylation events involve predominantly Ca2+ released from intracellular stores and that influx-derived Ca2+ is not essential. This suggests a different role for this phase of Ca2+ influx.

Key Words: signal transduction • Ca2+ • cytoplasm