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Galectin‐12 is a tissue‐specific galectin that has been largely defined by its role in the regulation of adipocyte differentiation and lipogenesis. This study aimed to evaluate the role of galectin‐12 in the differentiation and polarization of neutrophils within a model of acute myeloid leukemia HL‐60 cells. All‐trans retinoic acid and dimethyl sulfoxide were used to induce differentiation of HL‐60 cells which led to the generation of two phenotypes of neutrophil‐like cells with opposite changes in galectin‐12 gene (LGALS12) expression and different functional responses to N‐formyl‐ l‐methionyl‐ l‐leucyl‐ l‐phenylalanine. These phenotypes showed significant differences of differentially expressed genes on a global scale based on bioinformatics analysis of available Gene Expression Omnibus (GEO) data sets. We also demonstrated that HL‐60 cells could secrete and accumulate galectin‐12 in cell culture medium under normal growth conditions. This secretion was found to be entirely inhibited upon neutrophilic differentiation and was accompanied by an increase in intracellular lipid droplet content and significant enrichment of 22 lipid gene ontology terms related to lipid metabolism in differentiated cells. These findings suggest that galectin‐12 could serve as a marker of neutrophilic plasticity or polarization into different phenotypes and that galectin‐12 secretion may be influenced by lipid droplet biogenesis. [ABSTRACT FROM AUTHOR]

Mammalian cells repress expression of repetitive genomic sequences by forming heterochromatin. However, the consequences of ectopic repeat expression remain unclear. Here we demonstrate that inhibitors of EZH2, the catalytic subunit of the Polycomb repressive complex 2 (PRC2), stimulate repeat misexpression and cell death in resting splenic B cells. B cells are uniquely sensitive to these agents because they exhibit high levels of histone H3 lysine 27 trimethylation (H3K27me3) and correspondingly low DNA methylation at repeat elements. We generated a pattern recognition receptor loss‐of‐function mouse model, called RIC, with mutations in Rigi (encoding for RIG‐I), Ifih1 (MDA5), and Cgas. In both wildtype and RIC mutant B cells, EZH2 inhibition caused loss of H3K27me3 at repetitive elements and upregulated their expression. However, NF‐κB‐dependent expression of inflammatory chemokines and subsequent cell death was suppressed by the RIC mutations. We further show that inhibition of EZH2 in cancer cells requires the same pattern recognition receptors to activate an interferon response. Together, the results reveal chemokine expression induced by EZH2 inhibitors in B cells as a novel inflammatory response to genomic repeat expression. Given the overlap of genes induced by EZH2 inhibitors and Epstein–Barr virus infection, this response can be described as a form of viral mimicry. Synopsis: Expression of repetitive genomic elements can activate inflammatory signaling via binding of pattern recognition receptors. Here, inhibition of PRC2 subunit EZH2 is shown to cause repeat element expression and activation of different cytokine or chemokine pathways in normal and transformed cells. EZH2 inhibition induces sterile inflammation and cell death selectively in resting splenic B cells.Cytosolic pattern recognition receptors are required to activate inflammation induced by EZH2 inhibition.Resting B cells respond to EZH2 inhibition by inducing NF‐kB pathway‐dependent chemokine expression, while cancer cells activate an interferon expression program. [ABSTRACT FROM AUTHOR]

Spi-C is an Ets family transcription factor closely related to PU.1 and Spi-B. Expression of Spi-C is developmentally regulated in the B-cell lineage, but its function remains unknown. To determine the function of Spi-C in B-cell development, we generated mice expressing a B-cell-specific Spi-C transgene under the control of the IgH intronic enhancer. Spi-C transgenic mice had 50% fewer B cells than wild-type littermates. Flow cytometric analyses showed that splenic transitional B cells and bone marrow pre-B or immature B cells from transgenic mice were dramatically reduced compared with those of wild type. Both nonspecific and Ag-specific serum IgM levels were significantly increased in transgenic mice, while serum IgG levels were significantly decreased compared with wild type. Spi-C transgenic B cells proliferated poorly after stimulation by anti-IgM or anti-CD40 in vitro, although they responded normally to LPS stimulation. Using real-time RT-PCR, we found that several BCR signaling-related mediators were downregulated at pre-B-cell and mature B-cell stages in transgenic mice, while an inhibitor of BCR signaling was upregulated. Taken together, these data indicate that ectopic expression of Spi-C can impair B-cell development and function by affecting genes associated with BCR signaling. [ABSTRACT FROM AUTHOR]

PU.1 is a unique regulatory protein required for the generation of both the innate and the adaptive immune system. It functions exclusively in a cell-intrinsic manner to control the development of granulocytes, macrophages, and B and T lymphocytes. We demonstrate that mutation of the PU.1 gene causes a severe reduction in myeloid (granulocyte/macrophage) progenitors. PU.1 ­/­ myeloid progenitors can proliferate in vitro in response to the multilineage cytokines interleukin-3 (IL-3), IL-6 and stem cell factor but are unresponsive to the myeloid-specific cytokines granulocyte­macrophage colony-stimulating factor (GM-CSF), G-CSF and M-CSF. The failure of PU.1 ­/­ progenitors to respond to G-CSF is bypassed by transient signaling with IL-3. In the presence of IL-3 and G-CSF, PU.1 ­/­ progenitors can differentiate into granulocytic precursors containing myeloperoxidase-positive granules. Thus PU.1 is not essential for specification of granulocytic precursors, but is required for their further differentiation. The failure of PU.1 ­/­ progenitors to respond to M-CSF is due to lack of c-fms gene transcription. Transduction of c-fms into PU.1 ­/­ myeloid progenitors bypasses the block to M-CSF-dependent proliferation but does not induce detectable macrophage differentiation. Therefore, PU.1 appears to be essential for specification of monocytic precursors. Importantly, retroviral transduction of PU.1 into mutant progenitors restores responsiveness to myeloid-specific cytokines and development of mature granulocytes and macrophages. Thus PU.1 controls myelopoiesis by regulating both proliferation and differentiation pathways. [ABSTRACT FROM AUTHOR]

Spi-C is an Ets family transcription factor closely related to PU.1 and Spi-B. Expression of Spi-C is developmentally regulated in the B cell lineage, but its function remains unknown. To determine potential functions for Spi-C in B cell development, we generated mice expressing a Spi-C transgene under control of the IgH intronic enhancer. Eμ-Spi-C transgenic mice had 50% fewer B cells than wild type littermates. Flow cytometric analysis showed a dramatic reduction of pre-B and immature B cells in the bone marrow, and transitional B cells in the spleen of transgenic mice. Serum IgM levels in transgenic mice were significantly increased, while serum IgG levels were significantly decreased compared to wild type. Moreover, antigen-specific IgM responses were also significantly increased in transgenic mice, while antigen-specific IgG responses were decreased. Spi-C transgenic B cells proliferated poorly and died in response to stimulation by anti-IgM or anti-CD40 antibody in vitro. Analysis of gene expression in Spi-C transgenic B cells revealed a pattern of changes that account for reduced B cell receptor (BCR) signaling. Taken together, these data suggest that ectopic expression of Spi-C impairs B cell development by altering expression of genes required for appropriate BCR signal transduction. [ABSTRACT FROM AUTHOR]