A role for protein kinase CβI in the regulation of Ca2+ entry in Jurkat T cells

Abstract

T cell activation leading to cytokine production and cellular proliferation involves a regulated increase and subsequent decrease in the intracellular concentration of Ca2+ ([Ca2+](i)). While much is understood about agonist-induced increases in [Ca2+](i), less is known about down- regulation of this pathway. Understanding the mechanism of this down- regulation is critical to the prevention of cell death that can be the consequence of a sustained elevation in [Ca2+](i). Protein kinase C (PKC), activated by the diacylglycerol produced as a consequence of T cell receptor engagement, has long been presumed to be involved in this down-regulation, although the precise mechanism is not wholly clear. In this report we demonstrate that activation of PKC by phorbol esters slightly decreases the rate of Ca2+ efflux from the cytosol of Jurkat T cells following stimulation through the T cell receptor or stimulation in a receptor- independent manner by thapsigargin. On the other hand, phorbol ester treatment dramatically reduces the rate of Ca2+ influx following stimulation. Phorbol ester treatment is without an effect on Ca2+ influx in a different T cell line, HSB. Down-regulation of PKCβI expression by 18-h phorbol ester treatment is associated with a loss of the response to acute phorhol ester treatment in Jurkat cells, suggesting that PKCβI may be the isozyme responsible for the effects on Ca2+ influx. Electroporation of an anti-PKCβI antibody, but not antibodies against PKCα or PKCγ, led to an increase in the rate of Ca2+ influx following stimulation. Taken together, these data suggest that PKCβI may be a component of the down-regulation of increases in [Ca2+](i) associated with Jurkat T cell activation.