Cellular Cholesterol Involvement in Src, PKC, and p38/JNK Transduction Pathways by Porins

Abstract

Biological membranes are described as a mosaic of different domains where interactions between membrane components induce the formation of subdomains with different characteristics and functions. Lipids play an important role in the formation of lipid-enriched microdomains where they dynamically associate to form platforms important for membrane protein sorting and construction of signaling complexes. Cholesterol confined in lipid domains is a crucial component required by microorganisms, directly or indirectly, to enter or exit the intracellular compartment. Cellular activation mediated by superficial bacterial component may be modified by local cholesterol depletion. Therefore, new perspectives for unconventional therapeutic intervention in Gram-negative infections may be envisaged. We tested this hypothesis by using methyl-beta-cyclodextrin (mbetaCD) as a cholesterol-complexing agent to alter the U937 plasma membrane cholesterol content. Our results demonstrate that cholesterol depletion of U937 cells inhibited Salmonella enterica serovar Typhimurium porins-mediated phosphorylation of Src kinase family, protein kinase C (PKC), JNK, and p38, while cholesterol repletion restored the phosphorylation. Lipopolysaccharide (LPS) extracted from the same bacterial strain has been used as a control. Our data demonstrate that the lack of activation of signal transduction pathway observed following cholesterol depletion differently modulates the release of interleukin-6 (IL-6) or tumor necrosis factor-alpha (TNF-alpha), suggesting that Src, associated to lipid domains, may represent an important pathway in Gram-negative-induced cellular signal.

Cholesterol Oxidase Binds TLR2 and Modulates Functional Responses of Human Macrophages

“…Therefore, it is likely that the macrophage membrane is the main target for the binding and action of ChoD. It has also been documented by others [21] that intact cholesterol in the monocyte membrane is required for activation of intracellular signaling proteins (e.g., p38 MAPK) in these cells. We found that macrophages treated with ChoD release significant amounts of the anti-inflammatory cytokine IL-10, which inhibits the synthesis of proinflammatory cytokines such as interferon- γ , tumor necrosis factor- α , IL-2, and IL-1.…”

Modulation of Plasma Membrane Composition and Microdomain Organization Impairs Heat Shock Protein Expression in B16-F10 Mouse Melanoma Cells

“…For example, both JNK [33] and p38 MAP kinases [34] were previously suggested to take part in membrane-associated HSP25 induction. Of note, cholesterol depletion inhibited JNK and p38 MAP kinase-associated signaling in different model systems [35,36]. Thus, it is tempting to speculate that MβCD-or nystatin-induced PM modifications impair different signaling cascades towards HSF1 resulting in an altered PTM profile.…”