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

Abstract

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 PKCα, βI, βII, and ε whereas lower doses of CD40 stimulation activates PKCδ, ζ, and λ. Infection of macrophages with the protozoan parasite Leishmania major impairs PKCα, βI, βII, and ε isoforms but enhances PKCδ, ζ, and λ isoforms, suggesting a reciprocity among these PKC isoforms. Indeed, PKCα, βI, βII, and ε isoforms mediate CD40-induced p38MAPK phosphorylation, IL-12 expression, and Leishmania killing; PKCδ and ζ/λ mediate ERK1/2 phosphorylation, IL-10 production, and parasite growth. Treatment of the susceptible BALB/c mice with the lentivirally expressed PKCδ- or ζ-specific short hairpin RNA significantly reduces the infection and reinstates host-protective IFN-γ–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 curative effect of fucoidan on visceral leishmaniasis is mediated by activation of MAP kinases through specific protein kinase C isoforms

“…Moreover, functional inhibition of PKC-a and -b markedly abrogated fucoidan-induced p38 phosphorylation and, to a lesser extent, that of ERK1/2, along with the induction of IL-12 and TNF-a, which suggests that the fucoidan-mediated leishmanicidal effect may be dependent upon differential regulation of PKC isoforms, in agreement with similar observations. 36 Recent evidence suggests a crucial role for the NF-kB family of transcription factors in expressing pro-inflammatory genes and NO, which are pivotal for controlling Leishmania infection. 8 Some studies suggest that the AP-1 transcription factor may also be involved in NO production.…”

Counteractive functions are encrypted in the residues of CD154

“…Unlike the manifestation of counteractive functions by two counteracting receptors on the same cell, we first described that a single receptor like CD40 can exhibit duality in its functions (5)(6)(7)(25)(26)(27). We showed that depending upon the dose of the ligand (6,7) or differential ligand binding to CD40 on macrophages (8), the receptor builds two constitutionally different signalosome complexes eliciting counteractive effector functions such as promoting Leishmania infection through ERK1/2-mediated IL-10 production or host-protection through p38MAPK-mediated IL-12 production (5-8).…”

Macrophage Kinases in Leishmaniasis

“…It was shown recently that a weaker CD40 stimulation activates PKCd and PKCf, whereas a stronger CD40 stimulation activates PKCa, PKCb, and PKCe. In L. major-infected macrophages, CD40-induced PKCd and PKCf activation would be enhanced, whereas CD40-induced PKCa and PKCb activation would be impaired [39]. Studies with these inhibitors and siRNAs specific for these PKC isoforms have shown that PKCd and PKCf are associated with CD40-induced ERK-1/2 phosphorylation and IL-10 production, whereas the PKCa, PKCb and PKCe isoforms are associated with CD40-induced p38MAPK phosphorylation and IL-12 production.…”

“…Indeed, the treatment of L. major-infected susceptible BALB/c mice with the anti-CD40 agonistic antibody and lentivirus particles delivering syk shRNA or PKCd and PKCf shRNA or MKP-1 shRNA or SHP-1 shRNA significantly reduced L. major infection pathology and restored the host-protective immune response [37,39,40].…”