Calcium and protein kinase C as mediators of T cell activation

Jaime Freddy Modiano, University of Pennsylvania


Among the earliest biochemical changes in activated T cells are an increase in the concentration of ionized free calcium (Ca$\sp{++}$), and the activation of protein kinase(s) C (PKC). These appear to be critical second messengers in the events preceding cell division. This study analyzed the roles of extracellular Ca$\sp{++}$ and PKC in interleukin 2 (IL2) production and IL2 receptor expression by human T cells, since these are the factors that ultimately mediate lymphocyte proliferation. Phytohemagglutinin (PHA), a phorbol ester (TPA), or a calcium ionophore (ionomycin) stimulated normal peripheral blood lymphocytes (PBL) to produce IL2, express IL2 receptors, and proliferate. PHA + TPA also stimulated either of two human T cell lines to produce IL2. IL2 production was abrogated in PBL stimulated by PHA or by ionomycin, or either cell line stimulated with PHA + TPA, when extracellular Ca$\sp{++}$ was reduced from 300 $\mu$M to 1 $\mu$M. This effect was due to the inhibition of IL2 gene expression and did not occur in PBL stimulated with TPA. The expression of the IL2 gene was restored when the extracellular Ca$\sp{++}$ was reconstituted. Inhibiting protein kinase C (PKC) activity also abrogated IL2 production by mitogen-stimulated human T lymphocytes. This was due to a 50% decrease in IL2 gene expression, and to a marked inhibition of IL2 secretion. Chelating extracellular Ca$\sp{++}$ or inhibiting PKC also affected IL2 receptor expression. IL2 receptor $\alpha$ mRNA, and surface IL2 receptors were reduced 40%-60% in PHA-stimulated PBL when the extracellular Ca$\sp{++}$ was 1 $\mu$M. Inhibiting PKC had little effect on gene expression or on the membrane-bound form of the receptor, but it decreased soluble receptors in the supernatants by 50-80%. Finally, MgCl$\sb2$, but not choline chloride, could partially replace Ca$\sp{++}$ to allow IL2 production and IL2 receptor expression by PBL stimulated with PHA, but not ionomycin. Taken together, these data indicate that an out-in chemical concentration gradient of Ca$\sp{++} >$10 (i.e., (Ca$\sb0\sp{++}$) $\gg$1 $\mu$M) is required for IL2 production by mitogen-stimulated human T cells. Also, in addition to the previously defined role of PKC in gene expression, it can also importantly regulate extracellular secretion of proteins critical for T cell proliferation.

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Recommended Citation

Modiano, Jaime Freddy, "Calcium and protein kinase C as mediators of T cell activation" (1991). Dissertations available from ProQuest. AAI9125722.