Intracellular calcium dependence of gene expression in single T lymphocytes.

In T lymphocytes, intracellular Ca2+ concentration (Ca2+i) rises within seconds of T-cell antigen-receptor stimulation and initiates the synthesis and secretion of interleukin 2, a cytokine essential for T-cell proliferation and the immune response. Using video-imaging techniques, we tracked Ca2+i signals in individual T cells and measured subsequent expression of a beta-galactosidase reporter gene (lacZ) controlled by the NF-AT element of the interleukin 2 enhancer. Ca2+i spikes elicited by monoclonal antibody binding to the CD3 epsilon subunit of the T-cell receptor were positively correlated with gene expression, but varied widely between individual cells and were therefore difficult to relate quantitatively to lacZ expression. The Ca2+i dependence of NF-AT-regulated gene expression was determined by elevating Ca2+i with either thapsigargin or ionomycin and then "clamping" Ca2+i to various, stable levels by altering either extracellular Ca2+ or extracellular K+. Raising Ca2+i from resting levels of 70 nM to between 200 nM and 1.6 microM increased the fraction of cells expressing lacZ, with Kd approximately 1 microM. Activation of protein kinase C enhanced the Ca2+i sensitivity of gene expression (Kd = 210 nM), whereas stimulation of protein kinase A inhibited Ca2+i-dependent gene expression. The experiments described here provide single-cell measurements linking a second messenger to gene expression in individual cells.