MEK5/ERK5 signaling mediates IL-4-induced M2 macrophage differentiation through regulation of c-Myc expression.

Macrophages are highly plastic cells, responding to diverse environmental stimuli to acquire different functional phenotypes. Signaling through MAPKs has been reported to regulate the differentiation of macrophages, but the role of ERK5 in IL-4-mediated M2 macrophage differentiation is still unclear. Here, we showed that the ERK5 signaling pathway plays a critical role in IL-4-induced M2 macrophage differentiation. Pharmacologic inhibition of MEK5, an upstream activator of ERK5, markedly reduced the expression of classical M2 markers, such as Arg-1, Ym-1, and Fizz-1, as well as the production of M2-related chemokines and cytokines, CCL22, CCL17, and IGF-1 in IL-4-stimulated macrophages. Moreover, pharmacologic inhibition of ERK5 also decreased the expression of several M2 markers induced by IL-4. In accordance, myeloid cell-specific Erk5 depletion (Erk5∆mye ), using LysMcre /Erk5f/f mice, confirmed the involvement of ERK5 in IL-4-induced M2 polarization. Mechanistically, the inhibition of ERK5 did not affect STAT3 or STAT6 phosphorylation, suggesting that ERK5 signaling regulates M2 differentiation in a STAT3 and STAT6-independent manner. However, genetic deficiency or pharmacologic inhibition of the MEK5/ERK5 pathway reduced the expression of c-Myc in IL-4-activated macrophages, which is a critical transcription factor involved in M2 differentiation. Our study thus suggests that the MEK5/ERK5 signaling pathway is crucial in IL-4-induced M2 macrophage differentiation through the induction of c-Myc expression.

Paclitaxel Reduces Tumor Growth by Reprogramming Tumor-Associated Macrophages to an M1 Profile in a TLR4-Dependent Manner.

Paclitaxel is an antineoplastic agent widely used to treat several solid tumor types. The primary mechanism of action of paclitaxel is based on microtubule stabilization inducing cell-cycle arrest. Here, we use several tumor models to show that paclitaxel not only induces tumor cell-cycle arrest, but also promotes antitumor immunity. In vitro, paclitaxel reprogrammed M2-polarized macrophages to the M1-like phenotype in a TLR4-dependent manner, similarly to LPS. Paclitaxel also modulated the tumor-associated macrophage (TAM) profile in mouse models of breast and melanoma tumors; gene expression analysis showed that paclitaxel altered the M2-like signature of TAMs toward an M1-like profile. In mice selectively lacking TLR4 on myeloid cells, for example, macrophages (LysM-Cre+/-/TLR4fl/fl), the antitumor effect of paclitaxel was attenuated. Gene expression analysis of tumor samples from patients with ovarian cancer before and after treatment with paclitaxel detected an enrichment of genes linked to the M1 macrophage activation profile (IFNγ-stimulated macrophages). These findings indicate that paclitaxel skews TAMs toward an immunocompetent profile via TLR4, which might contribute to the antitumor effect of paclitaxel and provide a rationale for new combination regimens comprising paclitaxel and immunotherapies as an anticancer treatment.Significance: This study provides new evidence that the antitumor effect of paclitaxel occurs in part via reactivation of the immune response against cancer, guiding tumor-associated macrophages toward the M1-like antitumor phenotype.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/78/20/5891/F1.large.jpg Cancer Res; 78(20); 5891-900. ©2018 AACR See related commentary by Garassino et al., p. 5729.

NLRP3 Inflammasome Mediates Aldosterone-Induced Vascular Damage.

BACKGROUND: Inflammation is a key feature of aldosterone-induced vascular damage and dysfunction, but molecular mechanisms by which aldosterone triggers inflammation remain unclear. The NLRP3 inflammasome is a pivotal immune sensor that recognizes endogenous danger signals triggering sterile inflammation. METHODS: We analyzed vascular function and inflammatory profile of wild-type (WT), NLRP3 knockout (NLRP3-/-), caspase-1 knockout (Casp-1-/-), and interleukin-1 receptor knockout (IL-1R-/-) mice treated with vehicle or aldosterone (600 µg·kg-1·d-1 for 14 days through osmotic mini-pump) while receiving 1% saline to drink. RESULTS: Here, we show that NLRP3 inflammasome plays a central role in aldosterone-induced vascular dysfunction. Long-term infusion of aldosterone in mice resulted in elevation of plasma interleukin-1ß levels and vascular abnormalities. Mice lacking the IL-1R or the inflammasome components NLRP3 and caspase-1 were protected from aldosterone-induced vascular damage. In vitro, aldosterone stimulated NLRP3-dependent interleukin-1ß secretion by bone marrow-derived macrophages by activating nuclear factor-κB signaling and reactive oxygen species generation. Moreover, chimeric mice reconstituted with NLRP3-deficient hematopoietic cells showed that NLRP3 in immune cells mediates aldosterone-induced vascular damage. In addition, aldosterone increased the expression of NLRP3, active caspase-1, and mature interleukin-1ß in human peripheral blood mononuclear cells. Hypertensive patients with hyperaldosteronism or normal levels of aldosterone exhibited increased activity of NLRP3 inflammasome, suggesting that the effect of hyperaldosteronism on the inflammasome may be mediated through high blood pressure. CONCLUSIONS: Together, these data demonstrate that NLRP3 inflammasome, through activation of IL-1R, is critically involved in the deleterious vascular effects of aldosterone, placing NLRP3 as a potential target for therapeutic interventions in conditions with high aldosterone levels.