Elp3-mediated codon-dependent translation promotes mTORC2 activation and regulates macrophage polarization.

Macrophage polarization is a process whereby macrophages acquire distinct effector states (M1 or M2) to carry out multiple and sometimes opposite functions. We show here that translational reprogramming occurs during macrophage polarization and that this relies on the Elongator complex subunit Elp3, an enzyme that modifies the wobble uridine base U34 in cytosolic tRNAs. Elp3 expression is downregulated by classical M1-activating signals in myeloid cells, where it limits the production of pro-inflammatory cytokines via FoxO1 phosphorylation, and attenuates experimental colitis in mice. In contrast, alternative M2-activating signals upregulate Elp3 expression through a PI3K- and STAT6-dependent signaling pathway. The metabolic reprogramming linked to M2 macrophage polarization relies on Elp3 and the translation of multiple candidates, including the mitochondrial ribosome large subunit proteins Mrpl3, Mrpl13, and Mrpl47. By promoting translation of its activator Ric8b in a codon-dependent manner, Elp3 also regulates mTORC2 activation. Elp3 expression in myeloid cells further promotes Wnt-driven tumor initiation in the intestine by maintaining a pool of tumor-associated macrophages exhibiting M2 features. Collectively, our data establish a functional link between tRNA modifications, mTORC2 activation, and macrophage polarization.

NF-κB Signaling in Ex-Vivo Mouse Intestinal Organoids.

We describe here a protocol to assess NF-κB activation in ex-vivo organoids generated from mouse intestinal crypts. These structures are maintained in culture as crypt-villus forming organoids. These ex-vivo organoids maintain both self-renewal and multilineage differentiation overtime. We also describe the generation of ex-vivo organoids from Apc-mutated mouse intestinal crypts. Both wild-type and Apc-mutated organoids respond very well to NF-κB-activating signals such as TNFα but not to LPS. The kinetic of NF-κB activation in response to these signals in ex-vivo intestinal organoids is very similar to what we see in 2D cell lines. This protocol provides investigators a powerful tool to assess NF-κB activation in both healthy and transformed intestinal epitheliums maintained in culture as 3D structures.

Dusp3 deletion in mice promotes experimental lung tumour metastasis in a macrophage dependent manner.

Vaccinia-H1 Related (VHR) dual-specificity phosphatase, or DUSP3, plays an important role in cell cycle regulation and its expression is altered in several human cancers. In mouse model, DUSP3 deletion prevents neo-angiogenesis and b-FGF-induced microvessel outgrowth. Considering the importance of angiogenesis in metastasis formation, our study aimed to investigate the role of DUSP3 in tumour cell dissemination. Using a Lewis Lung carcinoma (LLC) experimental metastasis model, we observed that DUSP3-/- mice developed larger lung metastases than littermate controls. DUSP3-/- bone marrow transfer to lethally irradiated DUSP3+/+ mice was sufficient to transfer the phenotype to DUSP3+/+ mice, indicating that hematopoietic cells compartment was involved in the increased tumour cell dissemination to lung tissues. Interestingly, we found a higher percentage of tumour-promoting Ly6Cint macrophages in DUSP3-/- LLC-bearing lung homogenates that was at least partially due to a better recruitment of these cells. This was confirmed by 1) the presence of higher number of the Ly6Bhi macrophages in DUSP3-/- lung homogenates and by 2) the better migration of DUSP3-/- bone marrow sorted monocytes, peritoneal macrophages and bone marrow derived macrophages (BMDMs), compared to DUSP3+/+ monocytes, macrophages and BMDMs, in response to LLC-conditioned medium. Our study demonstrates that DUSP3 phosphatase plays a key role in metastatic growth through a mechanism involving the recruitment of macrophages towards LLC-bearing lungs.

Dual-Specificity Phosphatase 3 Deletion Protects Female, but Not Male, Mice from Endotoxemia-Induced and Polymicrobial-Induced Septic Shock.

Dual-specificity phosphatase 3 (DUSP3) is a small phosphatase with poorly known physiological functions and for which only a few substrates are known. Using knockout mice, we recently reported that DUSP3 deficiency confers resistance to endotoxin- and polymicrobial-induced septic shock. We showed that this protection was macrophage dependent. In this study, we further investigated the role of DUSP3 in sepsis tolerance and showed that the resistance is sex dependent. Using adoptive-transfer experiments and ovariectomized mice, we highlighted the role of female sex hormones in the phenotype. Indeed, in ovariectomized females and in male mice, the dominance of M2-like macrophages observed in DUSP3-/- female mice was reduced, suggesting a role for this cell subset in sepsis tolerance. At the molecular level, DUSP3 deletion was associated with estrogen-dependent decreased phosphorylation of ERK1/2 and Akt in peritoneal macrophages stimulated ex vivo by LPS. Our results demonstrate that estrogens may modulate M2-like responses during endotoxemia in a DUSP3-dependent manner.