Rac-mediated stimulation of phospholipase C-{gamma}2 amplifies B cell receptor-induced calcium signaling [Immunology]

April 22nd, 2015 by Walliser, C., Tron, K., Clauss, K., Gutman, O., Kobitski, A. Y., Retlich, M., Schade, A., Rocker, C., Henis, Y. I., Nienhaus, G. U., Gierschik, P.

The Rho GTPase Rac is crucially involved in controlling multiple B cell functions, including those regulated by the B-cell-receptor (BCR) through increased cytosolic Ca2+. The underlying molecular mechanisms and their relevance to the functions of intact B cells have thus far remained unknown. We have previously shown that the activity of phospholipase C-γ2 (PLCγ2), a key constituent of the BCR signalosome, is stimulated by activated Rac through direct protein-protein-interaction. Here, we use a Rac-resistant mutant of PLCγ2 to functionally reconstitute cultured PLCγ2-deficient DT40 B cells and to examine the effects of the Rac.PLCγ2 interaction on BCR-mediated changes of intracellular Ca2+ and regulation of Ca2+- and NFAT-regulated gene transcription at the level of single, intact B cells. The results show that the functional Rac.PLCγ2 interaction causes marked increases in (i) the sensitivity of B cells to BCR ligation, (ii) the BCR-mediated Ca2+ release from intracellular stores, (iii) the Ca2+ entry from the extracellular compartment, and (iv) the nuclear translocation of the Ca2+-regulated transcription factor NFAT. Hence, Rac-mediated stimulation of PLCγ2 activity serves to amplify B cell receptor-induced Ca2+ signaling.