Differential STIM1 expression in T and B cell subsets suggests a role in determining antigen receptor signal amplitude

Ca2+ acts ubiquitously as a second messenger in transmembrane signal transduction. In lymphocytes, calcium mobilization is triggered by antigen and chemokine receptors, among others, and controls cell functions ranging from proliferation to migration. The primary mechanism of extracellular Ca2+ entry in lymphocytes is the CRAC influx. STIM1 is a crucial component of the CRAC influx mechanism in lymphocytes, acting as a sensor of low Ca2+ concentration in the ER and an activator of the Ca2+ selective channel ORAI1 in the plasma membrane. While STIM1 function has been studied extensively, little is known regarding whether it is differentially expressed and thereby affects the magnitude of calcium mobilization responses. We report here that STIM1 expression differs in murine T and B lymphocytes, and in respective subsets. For example, mature T cells express ∼4 times more STIM1 than mature B cells. Furthermore, we show that through the physiologic range of expression, STIM1 levels determine the magnitude of Ca2+ influx responses that follow BCR-induced intracellular store depletion. Considered in view of previous reports that differences in amplitude of lymphocyte Ca2+ mobilization determine alternate biological responses, these findings suggest that differential STIM1 expression may be important determinant of biological responses.

► STIM1 expression differs in B and T lymphocytes and their subsets. ► Through its physiological range of expression, STIM1 levels determine the magnitude of antigen receptor mediated Ca influx. ► STIM1 expression levels determine alternate biological responses.