Prolonged Classical NF‐κB Activation Prevents Autophagy upon E. coli Stimulation In Vitro: A Potential Resolving Mechanism of Inflammation

Abstract

Activation of NF-κB is known to prevent apoptosis but may also act as proapoptotic factor in order to eliminate inflammatory cells. Here, we show that classical NF-κB activation in RAW 264.7 and bone marrow-derived macrophages upon short E. coli coculture is necessary to promote cell death at late time points. At 48 hours subsequent to short-term, E. coli challenge increased survival of NF-κB-suppressed macrophages was associated with pattern of autophagy whereas macrophages with normal NF-κB signalling die. Cell death of normal macrophages was indicated by preceding downregulation of autophagy associated genes atg5 and beclin1. Restimulation of macrophages with LPS at 48 hours after E. coli treatment results in augmented proinflammatory cytokine production in NF-κB-suppressed macrophages compared to control cells. We thus demonstrate that classical NF-κB activation inhibits autophagy and promotes delayed programmed cell death. This mechanism is likely to prevent the recovery of inflammatory cells and thus contributes to the resolution of inflammation.

Jun Proteins Are Starvation-Regulated Inhibitors of Autophagy

“…Thus, it is conceivable that inactivation of NF-κB results in downregulation of JunB transcription. Conversely, identification of the ability of JunB to inhibit autophagy may provide some theoretical explanation for the ability of NF-κB to inhibit starvationinduced and other types of autophagy (43,44). The posttranscriptional downregulation of JunB following starvation is at least partially dependent on the activity of mTOR as previously reported by others (35); hence, the significant decrease in mTOR activity following starvation is predicted to reduce JunB expression.…”

Overview of macroautophagy regulation in mammalian cells

“…However, in contrast to this stimulatory role of NF-κB in the regulation of autophagy, the inhibition of NF-κB favors TNFα-dependent and starvation-dependent autophagy [139,140]. Moreover, Schlottmann et al reported that activation of NF-κB prevents autophagy in macrophages by down-regulating the expression of Atg5 and Beclin 1 [141]. E2F1 E2F transcription factors are known to be involved in cellular proliferation, but also in DNA repair, differentiation and development [142].…”

The update on transcriptional regulation of autophagy in normal and pathologic cells: A novel therapeutic target

“…In contrast, in cells lacking NF-kappa B activation, TNF-alpha treatment upregulated the expression of the autophagy-promoting protein Beclin1 and subsequently induced the accumulation of autophagic vacuoles. Schlottmann et al [121] also described a new function of classical NF-kappa B signaling in pathogen-activated macrophages, which inhibited ''self-healing'' autophagy thereby contributing to the resolution of inflammation. Specifically, their observation of E. coli leading to downregulation of autophagy-related genes, such as Beclin1 and ATG5 in NF-kappa B-competent macrophages argued for a mechanism that acted via gene inactivation [121].…”

“…Schlottmann et al [121] also described a new function of classical NF-kappa B signaling in pathogen-activated macrophages, which inhibited ''self-healing'' autophagy thereby contributing to the resolution of inflammation. Specifically, their observation of E. coli leading to downregulation of autophagy-related genes, such as Beclin1 and ATG5 in NF-kappa B-competent macrophages argued for a mechanism that acted via gene inactivation [121]. In contrast, NF-kappa B inactivation by PDTC led to specific accumulation in autophagic vacuoles which proved autophagy in cells [121].…”