PKCα and PKCϵ differentially regulateLegionella pneumophila-induced GM-CSF

Abstract

Legionella pneumophila is an important causative agent of severe pneumonia in humans. The human alveolar epithelium is an effective barrier for inhaled microorganisms and actively participates in the initiation of innate host defense. Although secretion of granulocytemacrophage colony-stimulating factor (GM-CSF) is essential for the elimination of invading Legionella spp., mechanisms of Legionella pneumophila-induced release of this cytokine are widely unknown.In this study, we have demonstrated a toll-like receptor (TLR)2-and TLR5-dependent release of GM-CSF in L. pneumophila-infected human alveolar epithelial cells. GM-CSF secretion was not dependent on the bacteria type II or type IV secretion system. Furthermore, an increase in protein kinase C (PKC) activity, particularly PKCa and PKCe, was noted. Blocking of PKCa and PKCe activity or expression, but not of PKCb, PKCd, PKCg, PKCh, and PKCf, significantly reduced the synthesis of GM-CSF in infected cells. While PKCa was critical for the initiation of a nuclear factorkB-mediated GM-CSF expression, PKCe regulated GM-CSF production via activator protein 1.Thus, differential regulation of GM-CSF, production by PKC isoforms, contributes to the host response in Legionnaires' disease.

Alveolar epithelial cells orchestrate DC function in murine viral pneumonia

“…We and others have previously demonstrated that AECs are a substantial source of GM-CSF in the inflamed distal lung (39,40), and GM-CSF was shown to be induced in a TLR-dependent way in alveolar epithelium following bacterial challenge in vitro (41). Nonetheless, leukocytes of lymphoid and myeloid lineages, especially resident macrophages, were also found to be sources of GM-CSF in inflamed tissues (42).…”

Differential Regulation of Gene Expression by Protein Kinase C Isozymes as Determined by Genome-wide Expression Analysis

“…Early studies identified TPA/PMA-responsive elements in gene promoters, and it was subsequently established that phorbol esters modulate gene expression through multiple pathways, including ERK, JNK/AP1, NF-B, and JAK/ STAT cascades (16 -21). Despite a few reports of genes differentially regulated by PKC isozymes, such as GM-CSF, NOX4, and IL-8 (22)(23)(24), there is essentially no information regarding the ability of individual members of the PKC family to regulate gene expression in a global manner. * This work was supported, in whole or in part, by National Institutes of Health Grant CA89202 (to M. G. K.).…”

Induction of human β-defensin-2 in pulmonary epithelial cells byLegionella pneumophila: involvement of TLR2 and TLR5, p38 MAPK, JNK, NF-κB, and AP-1

“…The role of the type IVB secretion system of Legionella appears to differ in the liberation of various proinflammatory mediators and/or antimicrobial agents. It was shown by our group and others that, e.g., Legionella-induced IL-8, granulocyte/macrophage colony-stimulating factor, and prostaglandin E2 in A549 cells were independent of the dot/ icm gene locus, whereas IFN-␤, TNF␣, and IL-6 expression was impaired in infections with type IVB secretion systemdeficient mutants (4,23,24,29,34).…”