ARL11 regulates lipopolysaccharide-stimulated macrophage activation by promoting mitogen-activated protein kinase (MAPK) signaling

Abstract

ADP-ribosylation factor-like GTPase 11 (ARL11) is a cancer-predisposing gene that has remained functionally uncharacterized to date. In this study, we report that ARL11 is endogenously expressed in mouse and human macrophages and regulates their activation in response to lipopolysaccharide (LPS) stimulation. Accordingly, depletion of ARL11 impaired both LPS-stimulated pro-inflammatory cytokine production by macrophages and their ability to control intracellular replication of Salmonella. LPS-stimulated activation of extracellular signal–regulated kinase (ERK) and p38 mitogen-activated protein kinase (MAPK) was substantially compromised in Arl11-silenced macrophages. In contrast, increased expression of ARL11 led to constitutive ERK1/2 phosphorylation, resulting in macrophage exhaustion. Finally, we found that ARL11 forms a complex with phospho-ERK in macrophages within minutes of LPS stimulation. Taken together, our findings establish ARL11 as a novel regulator of ERK signaling in macrophages, required for macrophage activation and immune function.

Inhibition of EZH2 methyltransferase decreases immunoediting of mesothelioma cells by autologous macrophages through a PD-1–dependent mechanism

“…Because the inhibitor is washed out before macrophage inoculation, this experimental setting thus investigates RAW264.7 cytotoxicity rather than direct antitumor activity of EPZ. Pretreatment with LPS abolished the capacity of RAW264.7 cells to efficiently control AB1/AB12 tumor growth ( Figure 4, F-I) perhaps after LPS-induced inflammation or, as indicated by Supplemental Videos 1 and 4, after macrophage apoptosis or induction of endotoxin tolerance (18,(38)(39)(40)(41)(42). In fact, the macrophage response to LPS depended on the dose and the duration of stimulation.…”

Method for Studying the Effect of Gene Silencing on Bacterial Infection-induced ERK1/2 Signaling in Bone-marrow Derived Macrophages

“…Upon encounter of gram-negative bacteria by macrophages, LPS present on either the surface of a bacterium or shed by bacteria in the blood flow is captured by LBP (LPS-binding protein) and presented as a ligand to TLR4, a type I transmembrane protein present on the plasma membrane of macrophage that mediate the recognition of PAMPS such as LPS (Shimazu et al, 1999). The engagement of LPS with TLR4 (along with other co-stimulatory molecules) leads to recruitment of several adaptor proteins at the cytoplasmic tail of TLR4 followed by a cascade of intracellular events leading to activation of the nuclear factor-κB (NF-κB) and mitogen-activated protein kinase (MAPK) signaling cascades downstream to TLR4 including ERK1/2 (Buscher et al, 1995; Schaeffer and Weber, 1999; Gay et al, 2014; Platko et al, 2018; Arya et al, 2018). These signaling pathways directly or indirectly phosphorylate and activate various transcription factors that lead to the expression of genes involved in production and release of pro-inflammatory cytokines, reactive oxygen species, nitrosative burst and promotes macrophage activation (Satoh and Akira, 2016).…”

MAPping the kinase landscape of macrophage activation

“…To test whether ARL11 expression is altered by TLR4-mediated pathogen detection, Arya et al (5) treated mouse macrophages with LPS and observed a concomitant increase in ARL11 protein expression after 30 min; this foundational observation supported the involvement of ARL11 in the signaling cascades of macrophage activation. To confirm the importance of this gene in macrophage activation, the authors used siRNA and short hairpin RNA to knock down ARL11 in a second mouse macrophage cell line.…”

“…alence of ARL11 expression in tissues known to play a role in the immune system, Arya et al (5) hypothesized that further examination of immune cells may uncover a novel role for ARL11. Indeed, the authors observed that ARL11 mRNA levels were expressed in several immune cell types, predominantly in macrophages, monocytes, and neutrophils.…”

“…Arya et al (5) next investigated whether ARL11 impacted any of the canonical MAPK signaling cascades, including the ERK1/2, p38 kinase, or c-Jun N-terminal kinase (JNK1/2) pathways. The authors observed that knockdown of ARL11 in two macrophage cell lines led to a significant reduction in LPSstimulated phosphorylation and activation of ERK1/2 and p38 kinases, but not JNK1/2.…”