Epigenetic modifications play an important role in human cancer. One such modification, histone methylation, contributes to human cancer through deregulation of cancer-relevant genes. The yeast Dot1 and its human counterpart, hDOT1L, methylate lysine 79 located within the globular domain of histone H3. Here we report that hDOT1L interacts with AF10, an MLL (mixed lineage leukemia) fusion partner involved in acute myeloid leukemia, through the OM-LZ region of AF10 required for MLL-AF10-mediated leukemogenesis. We demonstrate that direct fusion of hDOT1L to MLL results in leukemic transformation in an hDOT1L methyltransferase activity-dependent manner. Transformation by MLL-hDOT1L and MLL-AF10 results in upregulation of a number of leukemia-relevant genes, such as Hoxa9, concomitant with hypermethylation of H3-K79. Our studies thus establish that mistargeting of hDOT1L to Hoxa9 plays an important role in MLL-AF10-mediated leukemogenesis and suggests that the enzymatic activity of hDOT1L may provide a potential target for therapeutic intervention.

China experienced severe haze pollution in January 2013. Here we have a detailed characterization of the sources and evolution mechanisms of this haze pollution with a focus on four haze episodes that occurred during 10-14 January in Beijing. The main source of data analyzed is from submicron aerosol measurements by an Aerodyne Aerosol Chemical Speciation Monitor. The average PM1 mass concentration during the four haze episodes ranged from 144 to 300 μg m À3, which was more than 10 times higher than that observed during clean periods. All submicron aerosol species showed substantial increases during haze episodes with sulfate being the largest. Secondary inorganic species played enhanced roles in the haze formation as suggested by their elevated contributions during haze episodes. Positive matrix factorization analysis resolved six organic aerosol (OA) factors including three primary OA (POA) factors from traffic, cooking, and coal combustion emissions, respectively, and three secondary OA (SOA) factors. Overall, SOA contributed 41-59% of OA with the rest being POA. Coal combustion OA (CCOA) was the largest primary source, on average accounting for 20-32% of OA, and showed the most significant enhancement during haze episodes. A regional SOA (RSOA) was resolved for the first time which showed a pronounced peak only during the record-breaking haze episode (Ep3) on 12-13 January. The regional contributions estimated based on the steep evolution of air pollutants were found to play dominant roles for the formation of Ep3, on average accounting for 66% of PM1 during the peak of Ep3 with sulfate, CCOA, and RSOA being the largest fractions (>~75%). Our results suggest that stagnant meteorological conditions, coal combustion, secondary production, and regional transport are four main factors driving the formation and evolution of haze pollution in Beijing during wintertime.

Air pollution is a major environmental concern during all seasons in the megacity of Beijing, China. Here we present the results from a winter study that was conducted from 21 November 2011 to 20 January 2012 with an Aerodyne Aerosol Chemical Speciation Monitor (ACSM) and various collocated instruments. The non-refractory submicron aerosol (NR-PM₁) species vary dramatically with clean periods and pollution episodes alternating frequently. Compared to summer, wintertime submicron aerosols show much enhanced organics and chloride, which on average account for 52% and 5%, respectively, of the total NR-PM₁ mass. All NR-PM₁ species show quite different diurnal behaviors between summer and winter. For example, the wintertime nitrate presents a gradual increase during daytime and correlates well with secondary organic aerosol (OA), indicating a dominant role of photochemical production over gas–particle partitioning. Positive matrix factorization was performed on ACSM OA mass spectra, and identified three primary OA (POA) factors, i.e., hydrocarbon-like OA (HOA), cooking OA (COA), and coal combustion OA (CCOA), and one secondary factor, i.e., oxygenated OA (OOA). The POA dominates OA during wintertime, contributing 69%, with the other 31% being SOA. Further, all POA components show pronounced diurnal cycles with the highest concentrations occurring at nighttime. CCOA is the largest primary source during the heating season, on average accounting for 33% of OA and 17% of NR-PM₁. CCOA also plays a significant role in chemically resolved particulate matter (PM) pollution as its mass contribution increases linearly as a function of NR-PM₁ mass loadings. The SOA, however, presents a reverse trend, which might indicate the limited SOA formation during high PM pollution episodes in winter. The effects of meteorology on PM pollution and aerosol processing were also explored. In particular, the sulfate mass is largely enhanced during periods with high humidity because of fog processing of high concentration of precursor SO₂. In addition, the increased traffic-related HOA emission at low temperature is also highlighted

Chromosomal translocation is a common cause of leukaemia 1 and the most common chromosome translocations found in leukaemia patients involve the mixed lineage leukaemia (MLL) gene 2,3 . AF10 is one of more than 30 MLL fusion partners in leukaemia 4 . We have recently demonstrated that the H3K79 methyltransferase hDOT1L contributes to MLL-AF10-mediated leukaemogenesis through its interaction with AF10 (ref. 5). In addition to MLL, AF10 has also been reported to fuse to CALM (clathrin-assembly protein-like lymphoid-myeloid) in patients with T-cell acute lymphoblastic leukaemia (T-ALL) and acute myeloid leukaemia (AML) 6,7 . Here, we analysed the molecular mechanism of leukaemogenesis by CALM-AF10. We demonstrate that CALM-AF10 fusion is both necessary and sufficient for leukaemic transformation. Additionally, we provide evidence that hDOT1L has an important role in the transformation process. hDOT1L contributes to CALM-AF10-mediated leukaemic transformation by preventing nuclear export of CALM-AF10 and by upregulating the Hoxa5 gene through H3K79 methylation. Thus, our study establishes CALM-AF10 fusion as a cause of leukaemia and reveals that mistargeting of hDOT1L and upregulation of Hoxa5 through H3K79 methylation is the underlying mechanism behind leukaemia caused by CALM-AF10 fusion. © 2006 Nature Publishing GroupReprints and permissions information is available online at http://npg.nature.com/naturecellbiology/ 6 Correspondence should be addressed to Y.Z. (yi_zhang@med.unc.edu).Note: Supplementary Information is available on the Nature Cell Biology website. COMPETING FINANCIAL INTERESTSThe authors declare that they have no competing financial interests. HHS Public Access Author Manuscript Author ManuscriptAuthor Manuscript Author ManuscriptOur interest in CALM-AF10 fusion protein stems from our recent demonstration that hDOT1L, a histone H3K79 methyltransferase 8 , has an important role in MLL-AF10-mediated leukaemogenesis 5 . We demonstrated that mistargeting of hDOT1L to the Hoxa9 gene by MLL-AF10 results in H3K79 methylation and Hoxa9 upregulation, which contributes to leukaemic transformation 5 . We further demonstrated that the hDOT1L and MLL-AF10 interaction involves the octapeptide motif-leucine zipper (OM-LZ) region of AF10, this is also required for MLL-AF10-mediated leukaemic transformation 9 . The observation that the OM-LZ region is retained in the CALM-AF10 fusion protein raises the possibility that hDOT1L may also function in CALM-AF10-mediated leukaemia. To examine the potential role for hDOT1L in CALM-AF10-mediated leukaemia, we first attempted to establish a causal relationship between the CALM-AF10 fusion protein and leukaemia.Previous studies have established that the human monocytic leukemia cell line U937 expresses the CALM-AF10 fusion protein 10,11 . To determine whether CALM-AF10 is relevant for cell proliferation and transformation, CALM-AF10 was knocked down in U937 cells using a vector-based RNA interference (RNAi) approach 5 . Results shown in Fig. 1a indicate that we were...

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CD4 ؉ CD25 ؉ regulatory T cells (T regs ) have been shown to inhibit graft-versus-host disease (GVHD) in murine models, and this suppression was mediated by T regs expressing the lymphoid homing molecule L-selectin. Here, we demonstrate that T regs lacking expression of the chemokine receptor CCR5 were far less effective in preventing lethality from GVHD. Survival of irradiated recipient animals given transplants supplemented with CCR5 ؊/؊ T regs was significantly decreased, and GVHD scores were enhanced compared with animals receiving wild-type (WT) T regs . CCR5 ؊/؊ T regs were functional in suppressing T-cell proliferation in vitro and ex vivo. However, although the accumulation of T regs within lymphoid tissues during the first week after transplantation was not dependent on CCR5, the lack of function of CCR5 ؊/؊ T regs correlated with impaired accumulation of these cells in the liver, lung, spleen, and mesenteric lymph node, more than one week after transplantation. These data are the first to definitively demonstrate a requirement for CCR5 in T reg function, and indicate that in addition to their previously defined role in inhibiting effector T-cell expansion in lymphoid tissues during GVHD, later recruitment of T regs to both lymphoid tissues and GVHD target organs is important in their ability to prolong survival after allogeneic bone marrow transplantation. ( IntroductionAcute graft-versus-host disease (GVHD) is a severe and potentially fatal complication of allogeneic bone marrow transplantation (allo-BMT). Acute GVHD is caused by mature donor T cells that recognize alloantigens presented initially by host antigen presenting cells (APCs). 1,2 Our group has demonstrated that the accumulation of donor T cells during the peritransplantation period takes place primarily in lymphoid tissues, followed by recruitment to parenchymal tissues such as the gastrointestinal (GI) tract, liver, lung, and skin. 3 We and others have recently demonstrated that eliminating expression of the chemokine receptor CCR5 from donor T cells in an experimental GVHD model resulted in exacerbated GVHD and increased T-cell infiltration of the liver and lung in lethally irradiated recipient animals. 4,5 These data suggested that the primary role for CCR5 during GVHD in conditioned transplant recipients is not to direct effector-cell recruitment as originally hypothesized, but to down-modulate target organ inflammation.Chemokines are predominantly 8-kDa to 12-kDa chemotactic proteins, which bind a family of 7-transmembrane-spanning G protein-coupled receptors, and function primarily in leukocyte migration (reviewed in Moser et al 6 ). The chemokine receptor CCR5 is expressed on activated T helper-1/T cytotoxic-1 (T H 1/ T C 1) T cells, natural killer (NK) cells, macrophages, and dendritic cells. 7 The ligands for this receptor, CCL3, CCL4, and CCL5, are expressed at sites of inflammation during acute GVHD. 4,[8][9][10][11] CCR5 may play a role in directing effector cells to sites of inflammation. [12][13][14][15] Interestingly howeve...

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Total body irradiation (TBI) can induce lethal myelosuppression, due to the sensitivity of proliferating hematopoietic stem/progenitor cells (HSPCs) to ionizing radiation (IR). No effective therapy exists to mitigate the hematologic toxicities of TBI. Here, using selective and structurally distinct small molecule inhibitors of cyclin-dependent kinase 4 (CDK4) and CDK6, we have demonstrated that selective cellular quiescence increases radioresistance of human cell lines in vitro and mice in vivo. Cell lines dependent on CDK4/6 were resistant to IR and other DNA-damaging agents when treated with CDK4/6 inhibitors. In contrast, CDK4/6 inhibitors did not protect cell lines that proliferated independently of CDK4/6 activity. Treatment of wild-type mice with CDK4/6 inhibitors induced reversible pharmacological quiescence (PQ) of early HSPCs but not most other cycling cells in the bone marrow or other tissues. Selective PQ of HSPCs decreased the hematopoietic toxicity of TBI, even when the CDK4/6 inhibitor was administered several hours after TBI. Moreover, PQ at the time of administration of therapeutic IR to mice harboring autochthonous cancers reduced treatment toxicity without compromising the therapeutic tumor response. These results demonstrate an effective method to mitigate the hematopoietic toxicity of IR in mammals, which may be potentially useful after radiological disaster or as an adjuvant to anticancer therapy.