Analysis of senescence-like growth arrest induced by RUNX1 and its fusion derived oncoproteins

Cellular senescence is an end point of a signal transduction programme leading to irreversible cell cycle arresst accompanied by characteristic alterations to cell morphology, biochemical properties and gene expression profile. This phenotype can be triggered by a variety of stimuli including telomere shortening, DNA damage or activated oncogenes. Senescence is now recognised as a tumour suppressor mechanism mediated by p53 and pRB pathways which act to prevent the proliferatio of cells that are at risk of tumourigenic transformation. RUNX1 is a transcription factor essential for definitive hematopoiesis and is frequently targeted in human leukaemias by chromosomal rearrangements. RUNX1 has been also demonstrated to act as a dominant oncogene in mice and the ectopic expression of RUNX1 in murine embryonic fibroblasts has been shown to cause senescence. The central aim of this study was to investigate the mechanism of senescence induction by RUNX1 and its fusion derived leukaemogenic oncoproteins in primary fibroblasts. My work showed that RUNX1 induces a strong senescence-like response in murine and human primary fibroblasts that requires intact DNA binding, CBFB interaction and C-terminal transcriptional activation/repression domains. However, surprising differences were found between the major RUNX1 fusion oncoprotein derivatives. The N-terminal fusion protein TEL-RUNX1 fails to induce senescence despite retention of a virtually full-lenght RUNX1 moiety, while the senescence-inducing potential is exaggerated in the truncated C-terminal fusion protein RUNX1-ETO (AML1-ETO). The potential to drive senescence is retained by the deletion mutant RUNX1-ETO[]469 which lacks critical corepressor binding sites suggesting that the repression of target genes may be a primary mechanism implicated in RUNX1-ETO induced senescence. Interestingly, CBFB-MYH11 fusion oncoprotein that affects RUNX1 indirectly by targeting CBFB cn also induce senescence when ectopically expressed in human primary cells. The RUNX1 and RUNX1-ETO induced senescent phenotypes differ from archetypal H-Ras [superscript v12] as arrest occurs without a preliminary phase of proliferation and the arrested cells lack prominent foci of DNA strand breaks and chromatin condensation. Notably however, RUNX1 and RUNX1-ETO display differences in their potency and the extent of engagement of p53 and Rb effector pathways. RUNX1-ETO is highly dependent on p53 function and unlike RUNX1 drives senescence in cells lacking intact p16Ink4a. RUNX1-ETO appears to exert its unique effects through potent induction of reactive oxygen species and p38MAPK phosphorylation. These findings illustrate the heterogeneous manifestations of senescence-like growth arrest and elucidate the distinctive biology and oncogenic properies of RUNX1 and its fusion derivatives

Runx1 Loss Minimally Impacts Long-Term Hematopoietic Stem Cells

RUNX1 encodes a DNA binding subunit of the core-binding transcription factors and is frequently mutated in acute leukemia, therapy-related leukemia, myelodysplastic syndrome, and chronic myelomonocytic leukemia. Mutations in RUNX1 are thought to confer upon hematopoietic stem cells (HSCs) a pre-leukemic state, but the fundamental properties of Runx1 deficient pre-leukemic HSCs are not well defined. Here we show that Runx1 deficiency decreases both apoptosis and proliferation, but only minimally impacts the frequency of long term repopulating HSCs (LT-HSCs). It has been variously reported that Runx1 loss increases LT-HSC numbers, decreases LT-HSC numbers, or causes age-related HSC exhaustion. We attempt to resolve these discrepancies by showing that Runx1 deficiency alters the expression of several key HSC markers, and that the number of functional LT-HSCs varies depending on the criteria used to score them. Finally, we identify genes and pathways, including the cell cycle and p53 pathways that are dysregulated in Runx1 deficient HSCs

Stimulating p53 down-under: a report from the 1st Australian p53 Workshop

Burgeoning interest in the tumour suppressor p53 in the Australasian region provoked the birth of the first Australian p53 Workshop, held at the Peter MacCallum Cancer Centre in Melbourne, 19–21 November 2012 and attended by over 130 international and national delegates. The Workshop was organized by Ygal Haupt, Andreas Strasser, Sue Haupt, Antony Braithwaite and Paul Neilsen: 33 oral presentations and 23 posters communicated exciting new p53 findings.PM Neilsen, AW Braithwaite, C Gamell, S Haupt, A Janic, A Strasser, K Wolyniec and Y Haup

Lipid pattern in middle-aged inhabitants of the Lower Silesian region of Poland. The PURE Poland sub-study

Introduction. A decreased serum high density lipoprotein-cholesterol (HDL-C) is a strong predictor of cardiovascular risk. However, total HDL is a very dynamic, changeable fraction, and does not perform the function of atherosclerosis markers. In the presented study, the pattern of serum lipids, including HDL-C subclasses (HDL2- and HDL3-cholesterol), in a middleaged Polish Lower Silesia population was defined. Materials and method. A group of 746 males and 1,298 females, aged 35–70, were investigated. All subjects were participants in the PURE study. Mean serum lipid levels were determined for groups selected on the basis of gender, age, cigarette smoking, drinking alcohol and place of residence (urban/rural area). The data were analyzed using STATISTICA 6.0 PL. Results. In multiple linear regression models, age was the most important independent and consistent predictor of total cholesterol (TC) and LDL cholesterol (LDL-C). The prevalence of low HDL-C (threshold 40 mg/dL in males, 50 mg/dL in females) was 16.5% for males and 22.6% for females. This gender-conditioned difference in the prevalence of low HDL-C was greater in rural (20.0% vs. 30.9%, respectively, in males and females) in comparison to urban (14.4% vs. 17.1%) areas. The lipid pattern was significantly worse in rural than in urban females. Female rural inhabitants showed higher triglycerides (TG) and lower HDL cholesterol (total and contained in subclasses HDL2 and HDL3). Simultaneously, a higher BMI, higher percent of smokers and drinkers and lower age of smoking female rural inhabitants in comparison to urban females were estimated. In the total population, cigarette smoking or drinking alcohol were associated with significant increases in TC, LDL-C and TG, also with decreased HDL-C (smoking) or HDL2-C (drinking). Two-way analysis of variance showed the existence of interaction between these risk factors in their influence on HDL-C and HDL3-C. Conclusion. In the middle-aged population of the Lower Silesian region in Poland the place of residence (urban/rural area) had a significant impact on the lipid pattern. This pattern is more atherogenic in rural women than in urban women

Genomewide Linkage Scan for Bipolar-Disorder Susceptibility Loci among Ashkenazi Jewish Families

The relatively short history of linkage studies in bipolar disorders (BPs) has produced inconsistent findings. Implicated regions have been large, with reduced levels of significance and modest effect sizes. Both phenotypic and genetic heterogeneity may have contributed to the failure to define risk loci. BP is part of a spectrum of apparently familial affective disorders, which have been organized by severity. Heterogeneity may arise because of insufficient data to define the spectrum boundaries, and, in general, the less-severe disorders are more difficult to diagnose reliably. To address the inherent complexities in detecting BP susceptibility loci, we have used restricted diagnostic classifications and a genetically more homogeneous (Ashkenazi Jewish) family collection to perform a 9-cM autosomal genomewide linkage scan. Although they are genetically more homogeneous, there are no data to suggest that the rate of illness in the Ashkenazim differs from that in other populations. In a genome scan of 41 Ashkenazi pedigrees with a proband affected with bipolar I disorder (BPI) and at least one other member affected with BPI or bipolar II disorder (BPII), we identified four regions suggestive of linkage on chromosomes 1, 3, 11, and 18. Follow-up genotyping showed that the regions on chromosomes 1, 3, and 18 are also suggestive of linkage in a subset of pedigrees limited to relative pairs affected with BPI. Furthermore, our chromosome 18q22 signal (D18S541 and D18S477) overlaps with previous BP findings. This research is being conducted in parallel with our companion study of schizophrenia, in which, by use of an identical approach, we recently reported significant evidence for a schizophrenia susceptibility locus in the Ashkenazim on chromosome 10q22

Genomewide Linkage Scan for Schizophrenia Susceptibility Loci among Ashkenazi Jewish Families Shows Evidence of Linkage on Chromosome 10q22

Previous linkage studies in schizophrenia have been discouraging due to inconsistent findings and weak signals. Genetic heterogeneity has been cited as one of the primary culprits for such inconsistencies. We have performed a 10-cM autosomal genomewide linkage scan for schizophrenia susceptibility regions, using 29 multiplex families of Ashkenazi Jewish descent. Although there is no evidence that the rate of schizophrenia among the Ashkenazim differs from that in other populations, we have focused on this population in hopes of reducing genetic heterogeneity among families and increasing the detectable effects of any particular locus. We pursued both allele-sharing and parametric linkage analyses as implemented in Genehunter, version 2.0. Our strongest signal was achieved at chromosome 10q22.3 (D10S1686), with a nonparametric linkage score (NPL) of 3.35 (genomewide empirical P=.035) and a dominant heterogeneity LOD score (HLOD) of 3.14. Six other regions gave NPL scores >2.00 (on chromosomes 1p32.2, 4q34.3, 6p21.31, 7p15.2, 15q11.2, and 21q21.2). Upon follow-up with an additional 23 markers in the chromosome 10q region, our peak NPL score increased to 4.27 (D10S1774; empirical P=.00002), with a 95% confidence interval of 12.2 Mb for the location of the trait locus (D10S1677 to D10S1753). We find these results encouraging for the study of schizophrenia among Ashkenazi families and suggest further linkage and association studies in this chromosome 10q region