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Although all murine MDSCs are defined as Gr1+CD11b+, their true immunophenotype remains elusive. In this study, we found murine Gr1+CD11b+ cells can be divided into two subsets: Gr1+CD11b+B220- and Gr1+CD11b+B220+, especially in the spleen tissues. Unlike the dominant B220- subset, the B220+ sub-population was not induced by tumor in vivo. Moreover, Gr1+CD11b+B220+ cells from tumor-bearing mice spleens were unable to induce arginase 1 and inducible nitric oxide synthase expression, inhibit T cell proliferation, or promote tumor growth in primary tumor site. Nevertheless, these cells suppressed tumor metastasis in vivo and reduced cancer cell motility in vitro, while Gr1+CD11b+B220- cells from tumor-bearing mice spleens promoted tumor metastasis and enhanced cancer cell motility. Furthermore, both the polymorphonuclear (PMN-MDSCs) and monocytic MDSCs (Mo-MDSCs) could be further divided into B220- and B220+ subsets; interestingly, tumor only induced the expansion of B220- PMN-MDSCs and B220- Mo-MDSCs, but not the B220+ counterparts. Compared with B220- PMN-MDSCs and B220- Mo-MDSCs, the Ly6G+Ly6C-CD11b+B220+ and Ly6G-Ly6C+CD11b+B220+ cells from tumor-bearing mice spleens exhibited a more mature phenotype without immunosuppressive activity. Additionally, IL-6 deficiency attenuated the tumor-induced accumulation of MDSCs, B220- MDSCs and B220- PMN-MDSCs but increased the percentages of Gr1+CD11b+B220+, Ly6G+Ly6C-CD11b+B220+, and Ly6G-Ly6C+CD11b+B220+ cells, indicating the opposing roles of the IL-6 signaling pathway in the expansion of B220- MDSCs and their B220+ counterparts. Taken together, our findings indicate that the B220+ subset is a distinct subset of Gr1+CD11b+ cells functionally different from the B220- subpopulation during tumorigenesis and induction of MDSCs to B220+ cells may be helpful for cancer therapy. [ABSTRACT FROM AUTHOR]

Mixed-lineage leukemia 1 (MLL1), which exerts its H3K4 methyltransferase activity by interacting with WDR5, ASH2L, and RBBP5, plays a pivotal role in regulating hematopoietic stem cell homeostasis. Disrupting the integrity of MLL1-complex has been reported to be associated with acute leukemia. However, the exact role of MLL1-complex in myeloid cells is unknown. In this study, microarray analysis revealed that the core components of the Mll1-complex, Wdr5, Ash2l, and Mll1, were concurrently downregulated by tumor-secreted factors as well as GM-CSF + IL-6 during the accumulation and activation of murine myeloidderived suppressor cells (MDSCs). These changes were further validated by quantitative RT-PCR and Western blotting both in vitro and in vivo. The expression levels of WDR5 and ASH2L were also significantly decreased in bone marrow MDSCs of lung cancer patients compared with that of healthy controls. Functionally, ectopic expression of Wdr5, Ash2l, and Mll1 (C terminus) reversed the accumulation and function of GM-CSF + IL-6-induced as well as tumor-cocultured polymorphonuclear MDSCs (PMN-MDSCs) by promoting them to differentiate into mature neutrophil-like cells. Mechanistically, GM-CSF + IL-6-activated Stat3 and Cebpb synergistically induced the expression of miR-21a, miR-21b, and miR-181b, and thus inhibited the expression of Wdr5, Ash2l, and Mll1 by targeting to their 39 untranslated regions, respectively. Furthermore, knockdown of these microRNAs also suppressed the expansion and function of GM-CSF + IL-6-induced PMN-MDSCs. Taken together, our findings indicate that the Stat3/Cebpb-miR-21a/b/181b-Mll1-complex axis may play a critical role in PMN-MDSC expansion, activation, and differentiation, and this axis may provide an effectively immunological therapeutic approach for patients with cancer or other immunological diseases. [ABSTRACT FROM AUTHOR]

Hippo signalling plays key role in tissue growth and homeostasis, and its dysregulation is implicated in various human diseases. Expanded (Ex) is an important upstream activator of Hippo signalling; however, how Ex activates Hippo signalling is still poorly understood. Here, we demonstrate that Ex forms a homodimer via C-terminal interaction, and that the ExC2 region (912-1164 aa) is sufficient and essential for Ex dimerization. Functional analysis shows that ExC2 is required for Ex to promote the phosphorylation and inactivation of Yki in Drosophila cells. Further in vivo analysis shows that ExC2 is important for Ex to control Drosophila tissue growth. Our study, thus, uncovers a novel mechanism whereby Ex homodimerization mediates its full activation to promote Hippo signalling in growth control. [ABSTRACT FROM AUTHOR]