Long-term cultures under hypoxic conditions have been demonstrated to maintain the phenotype of mesenchymal stromal/stem cells (MSCs) and to prevent the emergence of senescence. According to several studies, hypoxia has frequently been reported to drive genomic instability in cancer cells and in MSCs by hindering the DNA damage response and DNA repair. Thus, we evaluated the occurrence of DNA damage and repair events during the ex vivo expansion of clinical-grade adipose-derived stromal cells (ADSCs) and bone marrow (BM)-derived MSCs cultured with platelet lysate under 21% (normoxia) or 1% (hypoxia) O 2 conditions. Hypoxia did not impair cell survival after DNA damage, regardless of MSC origin. However, ADSCs, unlike BMMSCs, displayed altered cH2AX signaling and increased ubiquitylated cH2AX levels under hypoxic conditions, indicating an impaired resolution of DNA damage-induced foci. Moreover, hypoxia specifically promoted BM-MSC DNA integrity, with increased Ku80, TP53BP1, BRCA1, and RAD51 expression levels and more efficient nonhomologous end joining and homologous recombination repair. We further observed that hypoxia favored mtDNA stability and maintenance of differentiation potential after genotoxic stress. We conclude that long-term cultures under 1% O 2 were more suitable for BM-MSCs as suggested by improved genomic stability compared with ADSCs. STEM CELLS 2015;33:3608-3620
SIGNIFICANCE STATEMENTHuman mesenchymal stem cells (MSCs) feature differentiation capacities, immunomodulatory properties and therefore represent a great potential for medicine. In vitro culture allows their amplification for suitable clinical uses. Hypoxia seems relevant for the prevention of senescence and loss of MSC features. However, hypoxia is shown to promote cancer or DNA damage response (DDR) and repair failures. We demonstrate that long-term culture of MSCs with platelet lysate in hypoxia does not necessarily inhibit DDR and DNA repair. Here, bone marrowMSCs conserved or rather improved their DDR and DNA repair (NHEJ, HR), mtDNA stability in hypoxia compared to adipose-derived stem cells. Moreover, the ubiquitylation status of gH2AX between BM-MSCs and ADSCs might be responsible for changes in their DNA repair activities. Appropriate oxygen tension seems crucial to preserve the MSCs genomic stability according to their origins.
ING3 (Inhibitor of Growth 3) is a candidate tumor suppressor gene whose expression is lost in tumors such as hepatocellular carcinoma, head and neck squamous cell carcinoma and melanoma. In the present study, we show that ING3-depleted human cells and yeast cells deleted for its ortholog YNG2 are sensitive to DNA damage suggesting a conserved role in response to such stress. In human cells, ING3 is recruited to DNA double strand breaks and is required for ATM activation. Remarkably, in response to doxorubicin, ATM activation is dependent on ING3 but not on TIP60, whose recruitment to DNA breaks also depends on ING3.These events lead to ATM-mediated phosphorylation of NBS1 and the subsequent recruitment of RNF8, RNF168, 53BP1 and BRCA1, which are major mediators of the DNA damage response. Accordingly, upon genotoxic stress, DNA repair by Non Homologous End Joining (NHEJ) or Homologous Recombination (HR) were impaired in absence of ING3. Finally, immunoglobulin Class Switch Recombination (CSR), a physiological mechanism requiring NHEJ repair, was impaired in the absence of ING3. Since deregulation of DNA double strand break repair is associated with genomic instability, we propose a novel function of ING3 as a caretaker tumor suppressor involved in the DNA damage signaling and repair.Finally, we found that ING3 deficiency in B-cells results in decreased Class Switch Recombination (CSR).
Review on ING3, with data on DNA/RNA, on the protein encoded and where the gene is implicated.
IdentityOther names: Eaf4, ING2, MEAF4, p47ING3 HGNC (Hugo): ING3 Location: 7q31.31
DNA/RNA
DescriptionIn 1996, Karl Riabowol's group identified a new Tumor Suppressor Gene (TSG) by using subtractive hybridization between cDNAs from normal mammary epithelial cells and mammary epithelial cells from tumor. This experiment was followed by an in vivo screen for tumourigenesis. Using this method, the authors identified a new candidate TSG that they named ING1 for INhibitor of Growth 1 (Garkavtsev et al., 1996). Few years later, ING2, ING3, ING4 and ING5 were identified by homology search. ING3 was identified through bioinformatic analyses in order to find human EST clone showing a high homology with the p33ING1b and p33ING2 cDNAs (Nagashima et al., 2003).
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