Reciprocal Regulation of Protein Kinase C Isoforms Results in Differential Cellular Responsiveness

Immunological homeostasis is often maintained by counteractive functions of two different cell types or two different receptors signaling through different intermediates in the same cell. One of these signaling intermediates is protein kinase C (PKC). Ten differentially regulated PKC isoforms are integral to receptor-triggered responses in different cells. So far, eight PKC isoforms are reported to be expressed in macrophages. Whether a single receptor differentially uses PKC isoforms to regulate counteractive effector functions has never been addressed. As CD40 is the only receptor characterized to trigger counteractive functions, we examined the relative role of PKC isoforms in the CD40-induced macrophage functions. We report that in BALB/c mouse macrophages, higher doses of CD40 stimulation induce optimum phosphorylation and translocation of PKC alpha, beta I, beta II, and epsilon whereas lower doses of CD40 stimulation activates PKC delta, zeta, and lambda. Infection of macrophages with the protozoan parasite Leishmania major impairs PKC alpha, beta I, beta II, and epsilon isoforms but enhances PKC delta, zeta, and lambda isoforms, suggesting a reciprocity among these PKC isoforms. Indeed, PKC alpha, beta I, beta II, and epsilon isoforms mediate CD40-induced p38MAPK phosphorylation, IL-12 expression, and Leishmania killing; PKC delta and zeta/lambda mediate ERK1/2 phosphorylation, IL-10 production, and parasite growth. Treatment of the susceptible BALB/c mice with the lentivirally expressed PKC delta- or zeta-specific short hairpin RNA significantly reduces the infection and reinstates host-protective IFN-gamma-dominated T cell response, defining the differential roles for PKC isoforms in immune homeostasis and novel PKC-targeted immunotherapeutic and parasite-derived immune evasion strategies. The Journal of Immunology, 2012, 188: 2328-2337.