Mnt Loss Triggers Myc Transcription Targets, Proliferation, Apoptosis, and Transformation

Myc oncoproteins are overexpressed in most cancers and are sufficient to accelerate cell proliferation and provoke transformation. However, in normal cells Myc also triggers apoptosis. All of the effects of Myc require its function as a transcription factor that dimerizes with Max. This complex induces genes containing CACGTG E-boxes, such as Ornithine decarboxylase (Odc), which harbors two of these elements. Here we report that in quiescent cells the Odc E-boxes are occupied by Max and Mnt, a putative Myc antagonist, and that this complex is displaced by Myc-Max complexes in proliferating cells. Knockdown of Mnt expression by stable retroviral RNA interference triggers many targets typical of the “Myc” response and provokes accelerated proliferation and apoptosis. Strikingly, these effects of Mnt knockdown are even manifest in cells lacking c-myc. Moreover, Mnt knockdown is sufficient to transform primary fibroblasts in conjunction with Ras. Therefore, Mnt behaves as a tumor suppressor. These findings support a model where Mnt represses Myc target genes and Myc functions as an oncogene by relieving Mnt-mediated repression

Identification of sensitive serum microRNA biomarkers for radiation biodosimetry.

Exposure to ionizing radiation through environmental, occupational or a nuclear reactor accident such as the recent Fukushima Daiichi incident often results in major consequences to human health. The injury caused by radiation can manifest as acute radiation syndromes within weeks in organs with proliferating cells such as hematopoietic and gastrointestinal systems. Cancers, fibrosis and degenerative diseases are also reported in organs with differentiated cells, months or years later. Studies conducted on atom bomb survivors, nuclear reactor workers and animal models have shown a direct correlation of these effects with the absorbed dose. Physical dosimeters and the available radio-responsive biologics in body fluids, whose responses are rather indirect, have limitations to accurately evaluate the extent of post exposure damage. We have used an amplification-free, hybridization based quantitative assay utilizing the nCounter multiplex platform developed by nanoString Technologies to compare the levels of over 600 miRNAs in serum from mice irradiated at a range of 1 to 12 Gy at 24 and 48 hr time points. Development of a novel normalization strategy using multiple spike-in oligonucleotides allowed accurate measurement of radiation dose and time dependent changes in serum miRNAs. The response of several evolutionarily conserved miRNAs abundant in serum, were found to be robust and sensitive in the dose range relevant for medical triage and in patients who receive total body radiation as preparative regimen for bone marrow transplantation. Notably, miRNA-150, abundant in lymphocytes, exhibited a dose and time dependent decrease in serum, which we propose as a sensitive marker indicative of lymphocyte depletion and bone marrow damage. Our study has identified several markers useful for evaluation of an individual's response by minimally invasive methods, relevant to triage in case of a radiation accident and evaluation of toxicity and response during and after therapeutic radiation

c-Myc is essential for vasculogenesis and angiogenesis during development and tumor progression

c-Myc promotes cell growth and transformation by ill-defined mechanisms. c-myc(−/−) mice die by embryonic day 10.5 (E10.5) with defects in growth and in cardiac and neural development. Here we report that the lethality of c-myc(−/−) embryos is also associated with profound defects in vasculogenesis and primitive erythropoiesis. Furthermore, c-myc(−/−) embryonic stem (ES) and yolk sac cells are compromised in their differentiative and growth potential. These defects are intrinsic to c-Myc, and are in part associated with a requirement for c-Myc for the expression of vascular endothelial growth factor (VEGF), as VEGF can partially rescue these defects. However, c-Myc is also required for the proper expression of other angiogenic factors in ES and yolk sac cells, including angiopoietin-2, and the angiogenic inhibitors thrombospondin-1 and angiopoietin-1. Finally, c-myc(−/−) ES cells are dramatically impaired in their ability to form tumors in immune-compromised mice, and the small tumors that sometimes develop are poorly vascularized. Therefore, c-Myc function is also necessary for the angiogenic switch that is indispensable for the progression and metastasis of tumors. These findings support the model wherein c-Myc promotes cell growth and transformation, as well as vascular and hematopoietic development, by functioning as a master regulator of angiogenic factors

Identification of differentially expressed serum miRNAs with varying doses of radiation at 24 hrs.

<p>A: Heat map generated from the actual counts for 88 miRNAs detected in serum. B: Heat map showing variations in a panel of 18 radio-responsive miRNAs, identified by ANOVA with a cutoff p-value of 0.05. C: Dendrogram with a panel of markers identified with coefficient of variance across samples with a cutoff value of 0.4. D: Overlapping set of miRNAs from ANOVA and CV. Red marks high and green marks low expression.</p

Dose and time dependent depletion of miRNA-150 in animals exposed to 1, 2, 4, 6 and 8 Gy with reference to controls analyzed at 24 hrs (A) and 48 hrs (B).

<p>Statistical analysis was performed using an unpaired two-tailed students t-test (*) = <i>p<0.05</i>; (**) = <i>p<0.005;</i> (***) = <i>p<0.0005</i>. C: Kinetics of depletion of miRNA-150 as a function of dose and time relative to respective controls.</p