Project description:Previous study revealed that the protective effect of TIGAR in cell survival is mediated through the increase in PPP (pentose phosphate pathway) flux. However, it remains unexplored if TIGAR plays an important role in DNA damage and repair. This study investigated the role of TIGAR in DNA damage response (DDR) induced by genotoxic drugs and hypoxia in tumor cells. Results showed that TIGAR was increased and relocated to the nucleus after epirubicin or hypoxia treatment in cancer cells. Knockdown of TIGAR exacerbated DNA damage and the effects were partly reversed by the supplementation of PPP products NADPH, ribose, or the ROS scavenger NAC. Further studies with pharmacological and genetic approaches revealed that TIGAR regulated the phosphorylation of ATM, a key protein in DDR, through Cdk5. The Cdk5-AMT signal pathway involved in regulation of DDR by TIGAR defines a new role of TIGAR in cancer cell survival and it suggests that TIGAR may be a therapeutic target for cancers.
Project description:DNA damage as a result of environmental stress is recognized by sensor proteins that trigger repair mechanisms, or, if repair is unsuccessful, initiate apoptosis. Defects in DNA damage-induced apoptosis promote genomic instability and tumourigenesis. The protein ataxia-telangiectasia mutated (ATM) is activated by DNA double-strand breaks and regulates apoptosis via p53. Here we show that FOXO3 interacts with the ATM-Chk2-p53 complex, augments phosphorylation of the complex and induces the formation of nuclear foci in cells on DNA damage. FOXO3 is essential for DNA damage-induced apoptosis and conversely FOXO3 requires ATM, Chk2 and phosphorylated p53 isoforms to trigger apoptosis as a result of DNA damage. Under these conditions FOXO3 may also have a role in regulating chromatin retention of phosphorylated p53. These results suggest an essential link between FOXO3 and the ATM-Chk2-p53-mediated apoptotic programme following DNA damage.
Project description:RAD6 participates in DNA double-strand breaks (DSBs) repair by ubiquitinating histone H2B in mitotic cells. In terminally differentiated cells, however, the mechanisms of DNA damage repair are less well known. In this study, we investigate whether RAD6B is involved in DSBs repair in neurons and effects of RAD6B deficiency on neuronal survival. We compared neurons of RAD6B-deficient mice with those of littermate wild type (WT) mice and induced DNA damage by X-ray irradiation. We provide evidence that RAD6B is essential for neural DDR and RAD6B deficiency results in increased genomic instability and neurodegeneration. Moreover, higher levels of p53 and p21 are present in the brains of RAD6B-deficient mice, which may be responsible for neuronal senescence, and degeneration. In addition, behavioral experiments show that RAD6B-deficient mice exhibit marked learning and memory deficits. In conclusion, these findings suggest that RAD6B is critical for neural integrity and that the absence of RAD6B accelerates neurodegeneration in mice.
Project description:Cellular response to genotoxic stress is a very complex process, and it usually starts with the "sensing" or "detection" of the DNA damage, followed by a series of events that include signal transduction and activation of transcription factors. The activated transcription factors induce expressions of many genes which are involved in cellular functions such as DNA repair, cell cycle arrest, and cell death. There have been extensive studies from multiple disciplines exploring the mechanisms of cellular genotoxic responses, which have resulted in the identification of many cellular components involved in this process, including the mitogen-activated protein kinases (MAPKs) cascade. Although the initial activation of protein kinase cascade is not fully understood, human protein kinases ATM (ataxia-telangiectasia, mutated) and ATR (ATM and Rad3-related) are emerging as potential sensors of DNA damage. Current progresses in ATM/ATR research and related signaling pathways are discussed in this review, in an effort to facilitate a better understanding of genotoxic stress response.
Project description:Human papillomaviruses (HPV) are the causative agents of cervical cancers. The infectious HPV life cycle is closely linked to the differentiation state of the host epithelia, with viral genome amplification, late gene expression and virion production restricted to suprabasal cells. The E6 and E7 proteins provide an environment conducive to DNA synthesis upon differentiation, but little is known concerning the mechanisms that regulate productive viral genome amplification. Using keratinocytes that stably maintain HPV-31 episomes, and chemical inhibitors, we demonstrate that viral proteins activate the ATM DNA damage response in differentiating cells, as indicated by phosphorylation of CHK2, BRCA1 and NBS1. This activation is necessary for viral genome amplification, as well as for formation of viral replication foci. In contrast, inhibition of ATM kinase activity in undifferentiated keratinocytes had no effect on the stable maintenance of viral genomes. Previous studies have shown that HPVs induce low levels of caspase 3/7 activation upon differentiation and that this is important for cleavage of the E1 replication protein and genome amplification. Our studies demonstrate that caspase cleavage is induced upon differentiation of HPV positive cells through the action of the DNA damage protein kinase CHK2, which may be activated as a result of E7 binding to the ATM kinase. These findings identify a major regulatory mechanism responsible for productive HPV replication in differentiating cells. Our results have potential implications for the development of anti-viral therapies to treat HPV infections.
Project description:Cyclin D1 binding protein 1 (CCNDBP1) is considered a tumor suppressor, and when expressed in tumor cells, CCNDBP1 can contribute to the viability of cancer cells by rescuing these cells from chemotherapy-induced DNA damage. Therefore, this study focused on investigating the function of CCNDBP1, which is directly related to the survival of cancer cells by escaping DNA damage and chemoresistance. Hepatocellular carcinoma (HCC) cells and tissues obtained from Ccndbp1 knockout mice were used for the in vitro and in vivo examination of the molecular mechanisms of CCNDBP1 associated with the recovery of cells from DNA damage. Subsequently, gene and protein expression changes associated with the upregulation, downregulation, and irradiation of CCNDBP1 were assessed. The overexpression of CCNDBP1 in HCC cells stimulated cell growth and showed resistance to X-ray-induced DNA damage. Gene expression analysis of CCNDBP1-overexpressed cells and Ccndbp1 knockout mice revealed that Ccndbp1 activated the Atm-Chk2 pathway through the inhibition of Ezh2 expression, accounting for resistance to DNA damage. Our study demonstrated that by inhibiting EZH2, CCNDBP1 contributed to the activation of the ATM-CHK2 pathway to alleviate DNA damage, leading to chemoresistance.
Project description:Protein phosphatase 1 (PP1), a major protein phosphatase important for a variety of cellular responses, is activated in response to ionizing irradiation (IR)-induced DNA damage. Here, we report that IR induces the rapid dissociation of PP1 from its regulatory subunit inhibitor-2 (I-2) and that the process requires ataxia-telangiectasia mutated (ATM), a protein kinase central to DNA damage responses. In response to IR, ATM phosphorylates I-2 on serine 43, leading to the dissociation of the PP1-I-2 complex and the activation of PP1. Furthermore, ATM-mediated I-2 phosphorylation results in the inhibition of the Aurora-B kinase, the down-regulation of histone H3 serine 10 phosphorylation, and the activation of the G(2)/M checkpoint. Collectively, the results of these studies demonstrate a novel pathway that links ATM, PP1, and I-2 in the cellular response to DNA damage.
Project description:Plants are constantly exposed to microbial pathogens in the environment. One branch of innate plant immunity is mediated by cell-membrane-localized receptors, but less is known about associations between DNA damage and plant immune responses. Here, we show that rice (Oryza sativa) mesophyll cells are prone to DNA double-stranded breaks (DSBs) in response to ZJ173, a strain of Xanthomonas oryzae pv. oryzae (Xoo). The DSB signal transducer ataxia telangiectasia mutated (ATM), but not the ATM and Rad3-related branch, confers resistance against Xoo. Mechanistically, the MRE11-ATM module phosphorylates suppressor of gamma response 1 (SOG1), which activates several phenylpropanoid pathway genes and prompts downstream phytoalexin biosynthesis during Xoo infection. Intriguingly, overexpression of the topoisomerase gene TOP6A3 causes a switch from the classic non-homologous end joining (NHEJ) pathway to the alternative NHEJ and homologous recombination pathways at Xoo-induced DSBs. The enhanced ATM signaling of the alternative NHEJ pathway strengthens the SOG1-regulated phenylpropanoid pathway and thereby boosts Xoo-induced phytoalexin biosynthesis in TOP6A3-OE1 overexpression lines. Overall, the MRE11-ATM-SOG1 pathway serves as a prime example of plant-pathogen interactions that occur via host non-specific recognition. The function of TOP6-facilitated ATM signaling in the defense response makes it a promising target for breeding of rice germplasm that exhibits resistance to bacterial blight disease without a growth penalty.
Project description:Expression of microRNAs (miRNAs) involves transcription of miRNA genes and maturation of the primary transcripts. Recent studies have shown that posttranscriptional processing of primary and precursor miRNAs is induced after DNA damage through regulatory RNA-binding proteins in the Drosha and Dicer complexes, such as DDX5 and KSRP. However, little is known about the regulation of nuclear export of pre-miRNAs in the DNA-damage response, a critical step in miRNA maturation. Here, we show that nuclear export of pre-miRNAs is accelerated after DNA damage in an ATM-dependent manner. The ATM-activated AKT kinase phosphorylates Nup153, a key component of the nucleopore, leading to enhanced interaction between Nup153 and Exportin-5 (XPO5) and increased nuclear export of pre-miRNAs. These findings define an important role of DNA-damage signaling in miRNA transport and maturation.
Project description:Intercellular communication is essential for multicellular tissue vitality and homeostasis. We show that healthy cells message protective signals through direct cell-cell connections to adjacent DNA-damaged cells in a microtubule-dependent manner. In DNA-damaged cells, mitochondria restoration is facilitated by fusion with undamaged mitochondria from healthy cells and their DNA damage repair is optimized in presence of healthy cells. Both, mitochondria transfer and intercellular signaling for an enhanced DNA damage response are critically regulated by the activity of the DNA repair protein ataxia telangiectasia mutated (ATM). These healthy-to-damaged prosurvival processes sustain normal tissue integrity and may be exploitable for overcoming resistance to therapy in diseases such as cancer.