We show here that a zinc finger transcriptional repressor, Slug, which is aberrantly upregulated by the E2A-HLF oncoprotein in pro-B cell acute leukemia, functions as an antiapoptotic factor in normal hematopoietic progenitor cells. Slug(-/-) mice were much more radiosensitive than wild-type mice, dying earlier and showing accentuated decreases in peripheral blood cell counts, as well as abundant microhemorrhages and widely disseminated bacterial microabscesses throughout the body. Slug expression was detected in diverse subsets of hematopoietic progenitors, but not in more differentiated B and T lymphoid cells, and there was a significant increase in apoptotic (TUNEL-positive) bone marrow progenitor cells in irradiated Slug(-/-) mice compared to wild-type controls. These results implicate Slug in a novel survival pathway that protects hematopoietic progenitors from apoptosis after DNA damage.

The growth suppressor promyelocytic leukemia protein (PML) is disrupted by the chromosomal translocation t(15;17) in acute promyelocytic leukemia (APL). PML plays a key role in multiple pathways of apoptosis and regulates cell cycle progression. The present study demonstrates that PML represses transcription by functionally and physically interacting with histone deacetylase (HDAC). Transcriptional repression mediated by PML can be inhibited by trichostatin A, a specific inhibitor of HDAC. PML coimmunoprecipitates a significant level of HDAC activity in several cell lines. PML is associated with HDAC in vivo and directly interacts with HDAC in vitro. The fusion protein PML-RAR␣ encoded by the t(15;17) breakpoint interacts with HDAC poorly. PML interacts with all three isoforms of HDAC through specific domains, and its expression deacetylates histone H3 in vivo. Together, the results of our study show that PML modulates histone deacetylation and that loss of this function in APL alters chromatin remodeling and gene expression. This event may contribute to the development of leukemia.The nonrandom chromosomal translocation t(15;17), a cytogenetic hallmark of acute promyelocytic leukemia (APL), fuses the retinoic acid receptor ␣ gene (RAR␣) and the promyelocytic leukemia gene (PML) (8,17,34). The fusion gene PML-RAR␣ encodes a fusion protein that has been shown to interfere with leukemia cell differentiation (25,26) and to cause leukemia in animal models (11,27,32,33). Disruption of PML's growth suppressor function in APL is also believed to play a role in leukemogenesis (51). PML is a nuclear-matrixassociated protein localized in the nucleus in a distinct nuclear speckled pattern designated the PML nuclear body (NB), which is disrupted in the leukemic blasts of APL (14,15,20,75). A significant number (Ͼ90%) of APL patients can be induced to complete clinical remission by high-dose all-transretinoic acid (ATRA) or arsenic trioxide (As 2 O 3 ) therapy (16,59,60,72,74). Retinoic acid (RA) treatment induces differentiation of the leukemic blasts, rapid degradation of the fusion protein PML-RAR␣, and restoration of a normal PML NB (20,75). Recent studies demonstrated that PML-RAR␣ recruits histone deacetylase (HDAC) by directly interacting with the N-CoR-Sin3 complex through the RAR␣ portion of the fusion protein, turning the fusion protein into a strong transcription repressor for RA-responsive genes. Treating APL cells with high-dose ATRA reverses the binding of PML-RAR␣ to the N-CoR-Sin3 corepressor complex and reactivates RA-responsive genes (24,32,45). PML belongs to a family of nuclear proteins consisting of the RING finger motif and two other Cys-His domains designated the B-box motif. The region following is the ␣-helical domain, which is responsible for dimerization (57). PML is the major component of this novel NB, and many proteins associated with PML have been identified. For example, the ubiquitin-like protein modifier SUMO-1 (PIC-1 or sentrin) (7,35,36,53,62), interferon-induced protein ISG20 (23), the im...

The discovery that Slug has a vital anti-apoptotic role in the normal response of hematopoietic progenitors to genotoxic stress compelled us to investigate the underlying cellular and molecular mechanism(s) of this effect. Here we show that, although the development of myeloid progenitors in Slug−/− mice is not impaired under steady-state conditions, their ability to repopulate the compartment after γ-irradiation is reduced. We demonstrate that the radiation-induced death of Slug−/− mice exclusively reflects bone marrow failure and show that Slug protects mice from γ-irradiation-induced death in a cell-autonomous manner. We also establish that Slug confers radioprotection by inhibiting the mitochondria-dependent apoptotic pathway activated by γ-irradiation in hematopoietic progenitors. We show that Slug acts as a transcriptional repressor by directly antagonizing p53-mediated upregulation of the BH3-only gene Puma, which was recently shown to encode a critical mediator of p53-induced apoptosis. Finally, we provide evidence for a novel feedback loop in the hematopoietic progenitor cells after DNA damage: Slug is itself induced by p53. Thus, the survival of hematopoietic progenitor cells after genotoxic stress relies on induction of Slug by p53 and Slug-mediated repression of Puma.

Background:Insulin/insulin-like growth factor-1 signalling may underlie the promoting effect of type 2 diabetes on cancer. This study examined the association of diabetes, including steroid-induced diabetes (SID), and the impact of anti-diabetic medication on clinical outcomes of multiple myeloma (MM).Methods:A retrospective review was conducted of 1240 MM patients. Overall survival (OS) and MM disease status prior to death were analysed.Results:Diabetic patients had a significantly shorter OS than non-diabetic patients (median: 65.4 vs 98.7 months). In multivariate analysis, SID was a significant predictor of decreased OS, along with age, comorbidity, MM stage, and cytogenetic abnormalities. Analyzing only the diabetic MM patients, Cox regression showed that metformin predicted an increased OS, whereas use of insulin/analogues predicted a decreased OS. Competing risk analysis showed that DM was associated with increased cumulative incidence of death with progressive MM. Among the diabetics, multivariate regression showed that insulin/analogues were associated with increased, but metformin with decreased death with progressive MM. Potential immortal time bias was evaluated by landmark analyses.Conclusions:DM, SID in particular, is associated with poor clinical outcomes in MM. Insulin/analogues are associated with poor outcomes, whereas metformin is associated with improved outcomes. No conclusion about causal relationships can be made at this time. Managing hyperglycaemia with non-insulin regimens should be investigated in randomised trials.

Bone marrow injury is a major adverse side effect of radiation and chemotherapy.

Foxm1, a mammalian Forkhead Box M1 protein, is known as a typical proliferation-associated transcription factor. Here, we find that Foxm1 was essential for maintenance of hematopoietic stem cell (HSC) quiescence and self-renewal capacity in vivo in mice. Reducing expression of FOXM1 also decreased quiescence in human CD34+ HSCs and progenitor cells and its down-regulation was associated with a subset of myelodysplastic syndrome (MDS). Mechanistically, Foxm1 directly bound to the promoter region of Nurr1, inducing transcription while forced expression of Nurr1 reversed the loss of quiescence observed in Foxm1-deficient cells in vivo. Thus, our studies reveal a previously unrecognized role of Foxm1 as a critical regulator of HSC quiescence and self-renewal, mediated at least in part, by control of Nurr1 expression.

Fusion transcripts are used as biomarkers in companion diagnoses. Although more than 15,000 fusion RNAs have been identified from diverse cancer types, few common features have been reported. Here, we compared 16,410 fusion transcripts detected in cancer (from a published cohort of 9,966 tumor samples of 33 cancer types) with genome-wide RNA–DNA interactions mapped in two normal, noncancerous cell types [using iMARGI, an enhanced version of the mapping of RNA–genome interactions (MARGI) assay]. Among the top 10 most significant RNA–DNA interactions in normal cells, 5 colocalized with the gene pairs that formed fusion RNAs in cancer. Furthermore, throughout the genome, the frequency of a gene pair to exhibit RNA–DNA interactions is positively correlated with the probability of this gene pair to present documented fusion transcripts in cancer. To test whether RNA–DNA interactions in normal cells are predictive of fusion RNAs, we analyzed these in a validation cohort of 96 lung cancer samples using RNA sequencing (RNA-seq). Thirty-seven of 42 fusion transcripts in the validation cohort were found to exhibit RNA–DNA interactions in normal cells. Finally, by combining RNA-seq, single-molecule RNA FISH, and DNA FISH, we detected a cancer sample with EML4-ALK fusion RNA without forming the EML4-ALK fusion gene. Collectively, these data suggest an RNA-poise model, where spatial proximity of RNA and DNA could poise for the creation of fusion transcripts.

Chromatin-associated RNA (caRNA) has been proposed as a type of epigenomic modifier. Here, we test whether environmental stress can induce cellular dysfunction through modulating RNA-chromatin interactions. We induce endothelial cell (EC) dysfunction with high glucose and TNFα (H + T), that mimic the common stress in diabetes mellitus. We characterize the H + T-induced changes in gene expression by single cell (sc)RNA-seq, DNA interactions by Hi-C, and RNA-chromatin interactions by iMARGI. H + T induce inter-chromosomal RNA-chromatin interactions, particularly among the super enhancers. To test the causal relationship between H + T-induced RNA-chromatin interactions and the expression of EC dysfunction-related genes, we suppress the LINC00607 RNA. This suppression attenuates the expression of SERPINE1, a critical pro-inflammatory and pro-fibrotic gene. Furthermore, the changes of the co-expression gene network between diabetic and healthy donor-derived ECs corroborate the H + T-induced RNA-chromatin interactions. Taken together, caRNA-mediated dysregulation of gene expression modulates EC dysfunction, a crucial mechanism underlying numerous diseases.