On the basis mainly of pharmacological experiments, the p38α MAP kinase isoform has been established as an important regulator of immune and inflammatory responses. However, the role of the related p38γ and p38δ kinases has remained unclear. Here, we show that deletion of p38γ and p38δ impaired the innate immune response to lipopolysaccharide (LPS), a Toll-like receptor 4 (TLR4) ligand, by blocking the extracellular signal-regulated kinase 1/2 (ERK1/2) activation in macrophages and dendritic cells. p38γ and p38δ were necessary to maintain steady-state levels of tumor progression locus 2 (TPL2), the MKK kinase that mediates ERK1/2 activation after TLR4 stimulation. TNFα, IL-1β, and IL-10 production were reduced in LPS-stimulated macrophages from p38γ/δ-null mice, whereas IL-12 and IFNβ production increased, in accordance with the known effects of TPL2/ERK1/2 signaling on the induction of these cytokines. Furthermore, p38γ/δ-deficient mice were less sensitive than controls to LPS-induced septic shock, showing lower TNFα and IL-1β levels after challenge. Together, our results establish p38γ and p38δ as key components in innate immune responses.

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Abstractp38 MAPK signaling has been implicated in the regulation of processes leading to cancer development and progression. Chronic inflammation is a known risk factor for tumorigenesis, yet the precise mechanism of this association remains largely unknown. The related p38aMAPK (MAPK14) proteins p38g (MAPK12) and p38d (MAPK13) were recently shown to modulate the immune response, although their role in tumorigenesis remains controversial and their function in inflammation-associated cancer has not been studied. We analyzed the role of p38g and p38d in colon cancer associated to colitis using the azoxymethane/dextran sodium sulphate (AOM/DSS) colitis-associated colon cancer model in wild-type (WT), p38g-, p38d-, and p38g/ d-deficient (p38g/d À/À ) mice. We found that p38g/d deficiency significantly decreased tumor formation, in parallel with a decrease in proinflammatory cytokine and chemokine production. Analysis of leukocyte populations in p38g/d À/À mouse colon showed less macrophage and neutrophil recruitment than in WT mice. Together, our results establish that p38g and p38d are central to colitis-associated colon cancer formation through regulation of hematopoietic cell response to injury, and validate p38g and p38d as potential targets for cancer therapy. Cancer Res; 74(21); 6150-60. Ó2014 AACR.

The protein kinases p38γ and p38δ belong to the p38 mitogen-activated protein kinase (MAPK) family. p38MAPK signaling controls many cellular processes and is one of the most conserved mechanisms in eukaryotes for the cellular response to environmental stress and inflammation. Although p38γ and p38δ are widely expressed, it is likely that they perform specific functions in different tissues. Their involvement in human pathologies such as inflammation-related diseases or cancer is starting to be uncovered. In this article we give a general overview and highlight recent advances made in defining the functions of p38γ and p38δ, focusing in innate immunity and inflammation. We consider the potential of the pharmacological targeting of MAPK pathways to treat autoimmune and inflammatory diseases and cancer.

Candida albicans is a frequent aetiologic agent of sepsis associated with high mortality in immunocompromised patients. Developing new antifungal therapies is a medical need due to the low efficiency and resistance to current antifungal drugs. Here, we show that p38γ and p38δ regulate the innate immune response to C. albicans. We describe a new TAK1‐TPL2‐MKK1‐ERK1/2 pathway in macrophages, which is activated by Dectin‐1 engagement and positively regulated by p38γ/p38δ. In mice, p38γ/p38δ deficiency protects against C. albicans infection by increasing ROS and iNOS production and thus the antifungal capacity of neutrophils and macrophages, and by decreasing the hyper‐inflammation that leads to severe host damage. Leucocyte recruitment to infected kidneys and production of inflammatory mediators are decreased in p38γ/δ‐null mice, reducing septic shock. p38γ/p38δ in myeloid cells are critical for this effect. Moreover, pharmacological inhibition of p38γ/p38δ in mice reduces fungal burden, revealing that these p38MAPKs may be therapeutic targets for treating C. albicans infection in humans.

Objective. The role of most p38 MAPK isoforms in inflammatory arthritis is not known. This study was undertaken to evaluate p38␥ and p38␦ deficiency in the collagen-induced arthritis (CIA) model.Methods. Wild-type, p38␥ ؊/؊ , p38␦ ؊/؊ , and p38␥/␦ ؊/؊ mice were immunized with chicken type II collagen, and disease activity was evaluated by semiquantitative scoring and histologic assessment. Serum cytokine levels and in vitro T cell cytokine responses were quantified by flow cytometry and multiplex analysis, and serum anticollagen antibody levels by enzymelinked immunosorbent assay. Cytokine and p38 MAPK isoform expression in joints were determined by quantitative polymerase chain reaction.Results. Compound p38␥ and p38␦ deficiency markedly reduced arthritis severity compared with that in wild-type mice, whereas lack of either p38␥ or p38␦ had an intermediate effect. Joint damage was minimal in arthritic p38␥/␦ ؊/؊ mice compared with wild-type mice. The p38␥/␦ ؊/؊ mice had lower levels of pathogenic anticollagen antibodies and interleukin-1␤ (IL-1␤) and tumor necrosis factor ␣ than controls. In vitro T cell assays showed reduced proliferation, interferon-␥ (IFN␥) production, and IL-17 production by lymph node cells from p38␥/␦ ؊/؊ mice. IL-17 and IFN␥ messenger RNA expression in joints was significantly inhibited in p38␥/␦ ؊/؊ mice. Wild-type chimeric mice with p38␥/␦ ؊/؊ bone marrow did not show decreased CIA.Conclusion. Reduced disease severity in p38␥/␦ ؊/؊ mice was associated with lower cytokine production and anticollagen antibody responses than in controls, indicating that p38␥ and p38␦ are crucial regulators of inflammatory joint destruction in CIA. Our findings indicate that p38␥ and p38␦ are potential therapeutic targets in complex diseases, such as rheumatoid arthritis, that involve innate and adaptive immune responses.

The contribution of chronic skin inflammation to the development of squamous cell carcinoma (SCC) is poorly understood. While the mitogen-activated protein kinase p38α regulates inflammatory responses and tumour development, little is known about the role of p38γ and p38δ in these processes. Here we show that combined p38γ and p38δ (p38γ/δ) deletion blocked skin tumour development in a chemically induced carcinogenesis model. p38γ/δ deletion reduced TPA-induced epidermal hyperproliferation and inflammation; it inhibited expression of proinflammatory cytokines and chemokines in keratinocytes in vitro and in whole skin in vivo, resulting in decreased neutrophil recruitment to skin. Our data indicate that p38γ/δ in keratinocytes promote carcinogenesis by enabling formation of a proinflammatory microenvironment that fosters epidermal hyperproliferation and tumourigenesis. These findings provide genetic evidence that p38γ and p38δ have essential roles in skin tumour development, and suggest that targeting inflammation through p38γ/δ offers a therapeutic strategy for SCC treatment and prevention.

It is well known that the expansion of the mammary epithelium during the ovarian cycles in female mammals is supported by the transient increase in mammary epithelial stem cells (MaSCs). However, dissecting the molecular mechanisms that govern MaSC function and differentiation is poorly understood due to the lack of standardized methods for their identification and isolation. The development of robust single-cell mRNA sequencing () technologies and the computational methods to analyze them provides us with novel tools to approach the challenge of studying MaSCs in a completely unbiased way without. Here, we have performed the largest scRNA-seq analysis of individual mammary epithelial cells (~70,000 cells). Our study identified a distinct cell population presenting molecular features of MaSCs. Importantly, further purification and additional in-depth single-cell analysis of these cells revealed that they are not a fully homogenous entity. Instead, we identified three subpopulations representing early stages of lineage commitment. By tracking their molecular evolution through single-cell network analysis we found that one of these subpopulations represents bipotent MaSCs from which luminal and basal lineages diverge. Importantly, we also confirmed the presence of these cells in human mammary glands. Finally, through expression and network analysis studies, we have uncovered transcription factors that are activated early during lineage commitment. These data identified E2-2 (Tcf4) and ID3 as a potential molecular switch of mammary epithelial stem cell differentiation.