Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P16104 (H2AX)
 3,930 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Human tyrosyl-DNA phosphodiesterase (TDP1) hydrolyzes the phosphodiester bond at a DNA 3' end linked to a tyrosyl moiety. This type of linkage is found at stalled topoisomerase I (Top1)-DNA covalent complexes, and TDP1 has been implicated in the repair of such complexes. Here we show that Top1-associated DNA double-stranded breaks (DSBs) induce the phosphorylation of TDP1 at S81. This phosphorylation is mediated by the protein kinases: ataxia-telangiectasia-mutated (ATM) and DNA-dependent protein kinase (DNA-PK). Phosphorylated TDP1 forms nuclear foci that co-localize with those of phosphorylated histone H2AX (gammaH2AX). Both Top1-induced replication- and transcription-mediated DNA damages induce TDP1 phosphorylation. Furthermore, we show that S81 phosphorylation stabilizes TDP1, induces the formation of XRCC1 (X-ray cross-complementing group 1)-TDP1 complexes and enhances the mobilization of TDP1 to DNA damage sites. Finally, we provide evidence that TDP1-S81 phosphorylation promotes cell survival and DNA repair in response to CPT-induced DSBs. Together; our findings provide a new mechanism for TDP1 post-translational regulation by ATM and DNA-PK.
EMBO J 2009 Dec 02
PMID:Optimal function of the DNA repair enzyme TDP1 requires its phosphorylation by ATM and/or DNA-PK. 1985 Dec 85

Sirt1 appear to be NAD(+)-dependent deacetylase that deacetylates histones and several non-histone proteins. In this study, we identified Sirt1 as a physical interaction partner of Tip60, which is a mammalian MYST-type histone acetyl-transferase that specifically acetylates histones H2A and H4. Although Tip60 also acetylates DNA damage-specific histone H2A variant H2AX in response to DNA damage, which is a process required for appropriate DNA damage response, overexpression of Sirt1 represses Tip60-mediated acetylation of H2AX. Furthermore, Sirt1 depletion by RNAi causes excessive acetylation of H2AX, and enhances accumulation of gamma-ray irradiation-induced MDC1, BRCA1, and Rad51 foci in nuclei. These findings suggest that Sirt1 functions as negative regulator of Tip60-mediated acetylation of H2AX. Moreover, Sirt1 deacetylates an acetylated Tip60 in response to DNA damage and stimulates proteasome-dependent Tip60 degradation in vivo, suggesting that Sirt1 negatively regulates the protein level of Tip60 in vivo. Sirt1 may thus repress excessive activation of the DNA damage response and Rad51-homologous recombination repair by suppressing the function of Tip60.
Biochem Biophys Res Commun 2009 Dec 25
PMID:Sirt1 physically interacts with Tip60 and negatively regulates Tip60-mediated acetylation of H2AX. 1989 90

Cyclin A is a major regulator in vertebrate cell cycle, associated with cyclin-dependent kinase (Cdk), and involved in S-phase progression and entry into mitosis. It has been known that cyclin A overexpression not only causes premature S-phase entry but also induces prolongation of S phase. Here we show that ectopic expression of cyclin A leads to extensive gamma-H2AX focus formation, which is indicative of DNA double-strand breaks. Likewise, cyclin E, but not cyclin B1 and cyclin D1, also induced the gamma-H2AX focus formation, suggesting that these DNA lesions may be induced via aberrant DNA replication process. Moreover, the gamma-H2AX focus formation was suppressed by co-expressing p21(Cip1/Waf1) or dominant-negative Cdk2 mutant, suggesting that aberrant cyclin A-Cdk2 activation induces the chromosomal double-strand breaks.
Cell Cycle 2009 Dec
PMID:Cyclin A overexpression induces chromosomal double-strand breaks in mammalian cells. 2040 25

Cells that sustain double-strand breaks (DSB) can develop genomic instability, which contributes to carcinogenesis, and agents that cause DSBs are considered potential carcinogens. We looked for evidence of acid-induced DNA damage, including DSBs, in benign Barrett's epithelial (BAR-T) cell lines in vitro and in patients with Barrett's esophagus in vivo. In BAR-T cells, we also explored the mechanisms underlying acid-induced DNA damage. We exposed BAR-T cells to acid in the presence of a fluorescent probe for reactive oxygen species (ROS) and in the presence or absence of disodium 4,4'-diisothiocyanatostilbene-2,2'-disulfonate (which prevents intracellular acidification) and N-acety-l-cysteine (a scavenger of ROS). DSBs were detected by Western blotting and immunofluorescence for histone H2AX phosphorylation and by CometAssay. During endoscopy in patients with Barrett's esophagus, we took biopsy specimens from the metaplastic mucosa before and after esophageal perfusion with 0.1 N HCl for 3 min and sought DSBs by Western blotting for histone H2AX phosphorylation. In BAR-T cells, acid exposure resulted in ROS production and caused a time-dependent increase in levels of phospho-H2AX that continued for at least 48 h. Pretreatment with disodium 4,4'-diisothiocyanatostilbene-2,2'-disulfonate or N-acety-l-cysteine prevented the acid-induced increase in phospho-H2AX levels. DSBs also were detected in biopsy specimens of Barrett's metaplasia following esophageal acid perfusion in all of 6 patients with Barrett's esophagus. Acid exposure causes DSBs in Barrett's epithelial cells through ROS produced as a consequence of intracellular acidification. These findings suggest that acid can be considered a carcinogen in Barrett's esophagus.
Cancer Res 2009 Dec 01
PMID:In benign Barrett's epithelial cells, acid exposure generates reactive oxygen species that cause DNA double-strand breaks. 1992 Jan 91

Testicular germ cell tumors (TGCT) are the most common solid tumors of 15- to 35-year-old men. TGCT patients are frequently cured with cytotoxic cisplatin-based therapy. However, TGCT patients refractory to cisplatin-based chemotherapy have a poor prognosis, as do those having a late relapse. Pluripotent embryonal carcinomas (EC) are the malignant counterparts to embryonic stem cells and are considered the stem cells of TGCTs. Here, we show that human EC cells are highly sensitive to 5-aza-deoxycytidine (5-aza-CdR) compared with somatic solid tumor cells. Decreased proliferation and survival with low nanomolar concentrations of 5-aza-CdR is associated with ATM activation, H2AX phosphorylation, increased expression of p21, and the induction of genes known to be methylated in TGCTs (MGMT, RASSF1A, and HOXA9). Notably, 5-aza-CdR hypersensitivity is associated with markedly abundant expression of the pluripotency-associated DNA methyltransferase 3B (DNMT3B) compared with somatic tumor cells. Knockdown of DNMT3B in EC cells results in substantial resistance to 5-aza-CdR, strongly indicating that 5-aza-CdR sensitivity is mechanistically linked to high levels of DNMT3B. Intriguingly, cisplatin-resistant EC cells retain an exquisite sensitivity to low-dose 5-aza-CdR treatment, and pretreatment of 5-aza-CdR resensitizes these cells to cisplatin-mediated toxicity. This resensitization is also partially dependent on high DNMT3B levels. These novel findings indicate that high expression of DNMT3B, a likely byproduct of their pluripotency and germ cell origin, sensitizes TGCT-derived EC cells to low-dose 5-aza-CdR treatment.
Cancer Res 2009 Dec 15
PMID:High DNA methyltransferase 3B expression mediates 5-aza-deoxycytidine hypersensitivity in testicular germ cell tumors. 1995 90

Lamellarin D, a potent cytotoxic marine alkaloid, exerts its antitumor action through two complementary pathways: a nuclear route via topoisomerase I inhibition and a mitochondrial targeting. The present study was designed to investigate the contribution of these two pathways for apoptosis in cancer cells. Lamellarin D promoted nuclear apoptosis in leukemia cells without prominent cell cycle arrest. Signals transmitted by lamellarin D initiated apoptosis via the intrinsic apoptotic pathway. The drug induced conformational activation of Bax and decreased the expression levels of antiapoptotic proteins Bcl-2 and cIAP2 in association with activation of caspase-9 and caspase-3. Upon lamellarin D exposure, Fas and Fas-L expression was not modified in leukemia cells. Moreover, leukemia cells deficient in caspase-8 or Fas-associated protein with death domain underwent apoptosis through the typical mitochondrial apoptotic cascade, indicating that cell death induced by lamellarin D was independent of the extrinsic apoptotic pathway. Lamellarin D also exerted a topoisomerase I-mediated DNA damage response resulting in H2AX phosphorylation, and the upregulation of the DNA repair protein Rad51 and of p53, as well as the phosphorylation of p53 at serine 15. However, lamellarin D killed efficiently mutated p53 or p53 null cancer cells, and sensitivity to lamellarin D was abrogated neither by cycloheximide nor in enucleated cells. Lamellarin D-induced cytochrome c release occurs independently of nuclear factors in a cell-free system. These results suggest that lamellarin D exerts its cytotoxic effects primarily by inducing mitochondrial apoptosis independently of nuclear signaling. Thus, lamellarin D constitutes a new proapoptotic agent that may bypass certain forms of apoptosis resistance that occur in tumor cells.
Mol Cancer Ther 2009 Dec
PMID:Essential role of mitochondria in apoptosis of cancer cells induced by the marine alkaloid Lamellarin D. 1995 18

The gene mutated in Bloom's syndrome, BLM, is important in the repair of damaged replication forks, and it has both pro- and anti-recombinogenic roles in homologous recombination (HR). At damaged forks, BLM interacts with RAD51 recombinase, the essential enzyme in HR that catalyzes homology-dependent strand invasion. We have previously shown that defects in BLM modification by the small ubiquitin-related modifier (SUMO) cause increased gamma-H2AX foci. Because the increased gamma-H2AX could result from defective repair of spontaneous DNA damage, we hypothesized that SUMO modification regulates BLM's function in HR repair at damaged forks. To test this hypothesis, we treated cells that stably expressed a normal BLM (BLM+) or a SUMO-mutant BLM (SM-BLM) with hydroxyurea (HU) and examined the effects of stalled replication forks on RAD51 and its DNA repair functions. HU treatment generated excess gamma-H2AX in SM-BLM compared to BLM+ cells, consistent with a defect in replication-fork repair. SM-BLM cells accumulated increased numbers of DNA breaks and were hypersensitive to DNA damage. Importantly, HU treatment failed to induce sister-chromatid exchanges in SM-BLM cells compared to BLM+ cells, indicating a specific defect in HR repair and suggesting that RAD51 function could be compromised. Consistent with this hypothesis, RAD51 localization to HU-induced repair foci was impaired in SM-BLM cells. These data suggested that RAD51 might interact noncovalently with SUMO. We found that in vitro RAD51 interacts noncovalently with SUMO and that it interacts more efficiently with SUMO-modified BLM compared to unmodified BLM. These data suggest that SUMOylation controls the switch between BLM's pro- and anti-recombinogenic roles in HR. In the absence of BLM SUMOylation, BLM perturbs RAD51 localization at damaged replication forks and inhibits fork repair by HR. Conversely, BLM SUMOylation relieves its inhibitory effects on HR, and it promotes RAD51 function.
PLoS Biol 2009 Dec
PMID:SUMO modification regulates BLM and RAD51 interaction at damaged replication forks. 1995 65

Agents stabilizing G-quadruplexes have the potential to destroy the functional structure of telomere and could therefore act as antitumor agents. We previously reported that SYUIQ-5 could stabilize G-quadruplex, induce senescence, and inhibit c-myc gene promoter activity. In this study, we showed that SYUIQ-5 inhibited proliferation of CNE2 and HeLa cancer cells, triggered a rapid and potent telomere DNA damage response characterized by the formation of telomeric foci gamma-H2AX, and obviously induced autophagy with the features of increased LC3-II and a punctuated pattern of YFP-LC3 fluorescence. These phenomena may primarily depend on the delocalization of TRF2 from telomere, which was further degraded by proteasomes. Furthermore, overexpression of TRF2 inhibited SYUIQ-5-induced gamma-H2AX expression. Also, ATM was activated following SYUIQ-5 treatment. The pretreatment with ATM inhibitor ku55933 and ATM siRNA effectively reduced the production of gamma-H2AX and LC3-II. ATM knockdown partially antagonized the anticancer effects of SYUIQ-5. Moreover, inhibition of autophagy by short hairpin RNA against the autophagy-related gene ATG5 attenuated the cytotoxicity of SYUIQ-5. These results indicated that SYUIQ-5 triggered potent telomere damage through TRF2 delocalization from telomeres, and eventually induced autophagic cell death in cancer cells. Our findings exhibit a novel mechanism that is responsible for the antitumor effects of SYUIQ-5.
Mol Cancer Ther 2009 Dec
PMID:G-quadruplex ligand SYUIQ-5 induces autophagy by telomere damage and TRF2 delocalization in cancer cells. 1999 77

SNF2L, a chromatin remodeling gene expressed in diverse tissues, cancers, and derived cell lines, contributes to the chromatin remodeling complex that facilitates transcription. Because of this wide expression, it has not been exploited as a cancer therapeutic target. However, based on our present studies, we find that cancer cells, although expressing SNF2L at similar levels as their normal counterparts, are sensitive to its knockdown. This is not observed when its imitation SWI ortholog, SNF2H, is inhibited. SNF2L siRNA inhibition using two different siRNAs separately reduced SNF2L transcript levels and protein in both normal and cancer lines, but only the cancer lines showed significant growth inhibition, DNA damage, a DNA damage response, and phosphorylation of checkpoint proteins and marked apoptosis. DNA damage and the damage response preceded apoptosis rather than being consequences of it. The damage response consisted of increased phosphorylation of multiple substrates including ATR, BRCA1, CHK1, CHK2, and H2AX. Both the total and phosphorylated levels of p53 increased. The downstream targets of p53, p21, GADD45A, and 14-3-3sigma, were also upregulated. The alterations in checkpoint proteins included increased phosphorylated cdc2 but not Rb, which resulted in a modest G(2)-M arrest. Although apoptosis may be mediated by Apaf-1/caspase 9, other caspases could be involved. Other members of the chromatin remodeling or SWI/SNF gene families exhibited overall reduced levels of expression in the cancer lines compared with the normal lines. This raised the hypothesis that cancers are sensitive to SNF2L knockdown because, unlike their normal counterparts, they lack sufficient compensation from other family members.
Mol Cancer Res 2009 Dec
PMID:Inhibition of expression of the chromatin remodeling gene, SNF2L, selectively leads to DNA damage, growth inhibition, and cancer cell death. 1999 4

DNA double-strand breaks (DSBs) are highly cytotoxic lesions that are generated by ionizing radiation and various DNA-damaging chemicals. Following DSB formation, cells activate the DNA-damage response (DDR) protein kinases ATM, ATR and DNA-PK (also known as PRKDC). These then trigger histone H2AX (also known as H2AFX) phosphorylation and the accumulation of proteins such as MDC1, 53BP1 (also known as TP53BP1), BRCA1, CtIP (also known as RBBP8), RNF8 and RNF168/RIDDLIN into ionizing radiation-induced foci (IRIF) that amplify DSB signalling and promote DSB repair. Attachment of small ubiquitin-related modifier (SUMO) to target proteins controls diverse cellular functions. Here, we show that SUMO1, SUMO2 and SUMO3 accumulate at DSB sites in mammalian cells, with SUMO1 and SUMO2/3 accrual requiring the E3 ligase enzymes PIAS4 and PIAS1. We also establish that PIAS1 and PIAS4 are recruited to damage sites via mechanisms requiring their SAP domains, and are needed for the productive association of 53BP1, BRCA1 and RNF168 with such regions. Furthermore, we show that PIAS1 and PIAS4 promote DSB repair and confer ionizing radiation resistance. Finally, we establish that PIAS1 and PIAS4 are required for effective ubiquitin-adduct formation mediated by RNF8, RNF168 and BRCA1 at sites of DNA damage. These findings thus identify PIAS1 and PIAS4 as components of the DDR and reveal how protein recruitment to DSB sites is controlled by coordinated SUMOylation and ubiquitylation.
Nature 2009 Dec 17
PMID:Mammalian SUMO E3-ligases PIAS1 and PIAS4 promote responses to DNA double-strand breaks. 2001 86


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