Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0004135 (ATM)
 13,001 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Arsenic compounds are potent human carcinogens. Accumulated evidence has shown that arsenite-induced cytogenetic alterations are associated with the carcinogenicity of arsenic. Because p53 plays a guarding role in maintaining genome integrity and accuracy of chromosome segregation, the mechanistic effects of arsenite on p53 activation were analyzed. In the present study, arsenite-induced DNA strand breaks were confirmed by alkaline single-cell gel electrophoresis (comet assay) in human fibroblast (HFW) cells. Accompanying the appearance of DNA strand breaks was a significant accumulation of p53 in arsenite-treated HFW cells, as demonstrated by immunoblotting and immunofluorescence techniques. p53 downstream proteins, such as p21 and the human homologue of murine double minute-2, were also significantly induced by arsenite treatment. Cell cycle retardation and G2-M arrest were observed in 5-bromo-2'-deoxyuridine pulse-labeled HFW cells by flow cytometry. Wortmannin, an inhibitor of phosphatidylinositol 3-kinases, inhibited arsenite- or X-ray irradiation-induced p53 accumulation but did not alter UV irradiation- or N-acetyl-Leu-Leu-norleucinal-induced p53 accumulation. p53 phosphorylation on serine 15 was also confirmed by immunoblotting technique in arsenite- and X-ray-treated HFW cells but was not observed in UV- or N-acetyl-Leu-Leu-norleucinal-treated HFW cells. These results suggest the involvement of a phosphatidylinositol 3-kinase-related protein kinase in arsenite-induced p53 accumulation. For confirmation, we demonstrated that arsenite treatment, similar to X-ray irradiation, did not induce p53 accumulation in GM3395 fibroblasts derived from a patient with ataxia telangiectasia. In contrast, UV irradiation did cause p53 accumulation in these cells. Together, these findings infer that arsenite-induced DNA strand breaks may lead to p53 phosphorylation and accumulation through an ataxia telangiectasia mutated-dependent pathway in HFW cells.
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PMID:Arsenite induces p53 accumulation through an ATM-dependent pathway in human fibroblasts. 1110 96

Phosphoinositide kinases and ATM-related genes play a central role in many physiological processes. Activation of phosphoinositide 3-kinase (PI 3-kinase) is essential for signal transduction by many growth factors and oncogenes and may contribute to tumor progression. In the nanomolar range, Wortmannin (WM), a fungal metabolite, is a potent inhibitor of type I PI 3-kinase; it covalently modifies its catalytic subunit. Because WM is soluble only in organic solvents and unstable in water, there are difficulties in its use in vivo. To generate a water-soluble WM derivative, we used a conjugate of N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer and 11-O-desacetylwortmannin (DAWM), which has a slightly lower inhibitory activity than WM. We covalently attached DAWM to HPMA copolymer containing oligopeptide (GFLG) side-chains. The final product had an estimated molecular mass of 20 kDa and contained 2 wt.% of DAWM. The HPMA copolymer (PHPMA)-DAWM conjugate inhibited type I PI 3-kinase activity in vitro and growth factor-stimulated activation of Akt in vivo; it possessed approximately 50% of the inhibitory activity of DMSO solubilized WM. The specificity and stability of the PHPMA-DAWM conjugate is currently under investigation. The new water-soluble form of WM may be useful in investigations of the role of PI 3-kinase in tumor progression and other cellular biological functions in vivo.
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PMID:Water-soluble HPMA copolymer-wortmannin conjugate retains phosphoinositide 3-kinase inhibitory activity in vitro and in vivo. 1148 7

Ionizing radiation (IR) is known to activate multiple cell cycle checkpoints that are thought to enhance the ability of cells to respond to DNA damage. Protein phosphatase 2A (PP2A) has been implicated in IR-induced activation of checkpoints; therefore, Jurkat cells were exposed to an activating dose of IR or sham treatment as control, and nuclear extracts were analyzed for PP2A by Mono Q anion exchange chromatography and microcystin affinity chromatography. PP2A exists in eukaryotic cells both as a heterodimer consisting of a 65-kDa scaffolding subunit (A) plus a 36-kDa catalytic subunit (C) and as ABC heterotrimers, containing one of a variety of regulatory (B) subunits. Here we show that IR produces a transient and reversible reduction in the amount of nuclear AB55C heterotrimer without affecting the AB'C heterotrimer or AC heterodimer. In ataxia telangiectasia-mutated (ATM)-deficient cells the amount of nuclear PP2A heterotrimer relative to heterodimer was not reduced by radiation, but the radiation response was restored by transfection of these cells with plasmids encoding ATM. Wortmannin, an inhibitor of kinases such as phosphatidylinositol 3-kinase, also prevented the IR-induced reduction in nuclear PP2A heterotrimer. The changes in nuclear PP2A occurred without a noticeable difference in the carboxyl-terminal methylation of the C subunit, which is known to influence association with B subunits. We conclude a novel ATM-dependent mechanism is regulating association of B55 subunits with nuclear PP2A in response to IR.
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PMID:ATM-dependent dissociation of B55 regulatory subunit from nuclear PP2A in response to ionizing radiation. 1172 36

Although p53 responses after DNA damage have been investigated extensively, p53 responses after heat shock, which exerts cytotoxic action by mechanisms other than direct induction of DNA damage, are less well characterized. We investigated, therefore, the effect of hyperthermic exposures on the levels and DNA-binding activity of p53. Experiments were carried out with U2OS and ML-1 cells, known to express wild-type p53 protein. Although heating at 41 degrees C for up to 6 h had only a small effect on p53 levels or DNA binding activity, exposure to temperatures between 42.5 and 45.5 degrees C caused an immediate decrease in protein levels that was associated with a reduction in DNA binding activity. This observation is compatible with a high lability of p53 to heat shock, or heat sensitivity of the pathway regulating p53 levels in non-stressed cells. When cells were heated to 42.5 degrees C and returned to normal temperatures, a strong p53 response associated with an increase in protein levels and DNA binding activity was observed, suggesting the production of p53-inducing cellular damage. At higher temperatures, however, this response was compromised in an exposure-time-dependent manner. The increase in DNA binding activity was more heat sensitive than the increase in p53 levels and was inhibited at lower temperatures and shorter exposure times. Thus, the pathway of p53 activation is itself heat sensitive and compromised at high levels of exposure. Compared to p53 activation after exposure to ionizing radiation, heat-induced activation is rapid and short lived. When cells were exposed to combined heat and radiation, the response observed approximated that of cells exposed to heat alone. Wortmannin at 10 microM inhibited p53 activation for up to 2 h after heat shock suggesting the involvement of wortmannin-sensitive kinases, such as DNA-PK and ATM. Heat shock causes phosphorylation of p53 at Serine-15, but there is no correlation between phosphorylation at this site and activation of the protein. The results in aggregate indicate p53 activation in the absence of DNA damage by a heat-sensitive mechanism operating with faster kinetics than radiation-induced p53 activation. The former response may induce pathways preventing other stimuli from activating p53, as heat-induced activation of p53 is dominant over activation of p53 by DNA damage in combined-treatment experiments. These observations suggest means for abrogating p53 induction after DNA damage with the purpose of potentiating response and enhancing cell killing.
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PMID:Effects of hyperthermia on p53 protein expression and activity. 1185 52

Wortmannin is an inhibitor of PI3-kinase and acts on cultured cells at dosages below 1 microM. Wortmannin also inhibits the gene products of the PI3-kinase family such as ATM or DNA-PK at dosages above 10 microM in cultured cells. There are many reports on the enhancement of radiosensitivity by a high dose of wortmannin inhibiting the proteins of the PI3-kinase family. However, there have been no reports on the effect on radiosensitivity of low doses of wortmannin inhibiting PI3-kinase. We found that low doses of wortmannin reduced the radiosensitivity of human A172 glioblastoma cells. This effect was shown only in wild-type p53 cells, but was not shown in mutant p53 cells such as T98G or A172/248W carrying a dominant point-mutated p53 gene. This result indicates that the PI3-kinase, or another wortmannin-sensitive enzyme, may affect the signal transduction of p53. We examined the response of the p53 pathway by X-ray irradiation. A low dose of wortmannin did not affect the accumulation of p53 and the phosphorylation of p53 at ser-15, but reduced the induction of WAF1 and enhanced the induction of GADD45.
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PMID:Low dose of wortmannin reduces radiosensitivity of human glioblastoma cells through the p53 pathway. 1206 22

Radioadaptive response is a biological defense mechanism in which low-dose ionizing irradiation elicits cellular resistance to the genotoxic effects of subsequent irradiation. However, its molecular mechanism remains largely unknown. We previously demonstrated that the dose recognition and adaptive response could be mediated by a feedback signaling pathway involving protein kinase C (PKC), p38 mitogen activated protein kinase (p38MAPK) and phospholipase C (PLC). Further, to elucidate the downstream effector pathway, we studied the X-ray-induced adaptive response in cultured mouse and human cells with different genetic background relevant to the DNA damage response pathway, such as deficiencies in TP53, DNA-PKcs, ATM and FANCA genes. The results showed that p53 protein played a key role in the adaptive response while DNA-PKcs, ATM and FANCA were not responsible. Wortmannin, a specific inhibitor of phosphatidylinositol 3-kinase (PI3K), mimicked the priming irradiation in that the inhibitor alone rendered the cells resistant against the induction of chromosome aberrations and apoptosis by the subsequent X-ray irradiation. The adaptive response, whether it was afforded by low-dose X-rays or wortmannin, occurred in parallel with the reduction of apoptotic cell death by challenging doses. The inhibitor of p38MAPK which blocks the adaptive response did not suppress apoptosis. These observations indicate that the adaptive response and apoptotic cell death constitute a complementary defense system via life-or-death decisions. The p53 has a pivotal role in channeling the radiation-induced DNA double-strand breaks (DSBs) into an adaptive legitimate repair pathway, where the signals are integrated into p53 by a circuitous PKC-p38MAPK-PLC damage sensing pathway, and hence turning off the signals to an alternative pathway to illegitimate repair and apoptosis. A possible molecular mechanism of adaptive response to low-dose ionizing irradiation has been discussed in relation to the repair of DSBs and implicated to the current controversial observations on the expression of adaptive response.
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PMID:DNA damage response pathway in radioadaptive response. 1210 51

Following exposure to genotoxic stress, proliferating cells actively slow down DNA replication through an S phase checkpoint to provide time for repair. The ATM-dependent pathway plays an important role in the S phase checkpoint response following ionizing irradiation. We report that there is a stronger S phase checkpoint response in irradiated Ku80(-/-) cells as compared with their wild-type counterparts, which has no relationship to DNA-dependent protein kinase (DNA-PK) activity but correlates with a higher ATM activity and with more ATM bound to chromatin DNA in such cells. Wortmannin, a nonspecific inhibitor of ATM, not only reduces the higher activity of ATM kinase, but also abolishes the stronger S phase checkpoint response in Ku80(-/-) cells. Furthermore, a specific ATM antisense oligonucleotide abolishes the stronger S checkpoint response in Ku80(-/-) cells and renders these cells practically indistinguishable from Ku80(+/+) cells for this endpoint. These results in aggregate indicate that the stronger S checkpoint in irradiated Ku80(-/-) cells is due to the higher ATM kinase activity.
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PMID:Ku affects the ATM-dependent S phase checkpoint following ionizing radiation. 1221 78

Recent developments in the use of small inhibitory RNA molecules (siRNAs) to inhibit specific protein expression have highlighted the potential use of siRNA as a therapeutic agent. The double-strand break signaling/repair proteins ATM, ATR, and DNA-dependent protein kinase catalytic subunit (DNA-PK(cs)) are attractive targets to confer enhanced radio and chemosensitivity to tumor cells. We have designed and exogenously delivered plasmids encoding siRNAs targeting these critical kinases to human cancer cells to assess the feasibility of this concept as a clinically translatable experimental therapeutic. siRNA led to a approximately 90% reduction in target protein expression. siRNAs targeting ATM and DNA-PK(cs) gave rise to a dose-reduction factor of approximately 1.4 compared with untransfected and control vector-transfected cells at the clinically relevant radiation doses. This was greater than the radiosensitivity achieved using the phosphatidylinositol 3'-kinase inhibitor Wortmannin or DNA-PK(cs) competitive inhibitor LY294002. A similar increased sensitivity to the alkylating agent methyl methanesulfonate (MMS) was also observed for siRNA-mediated ATR silencing. Together, these data provide strong evidence for the potential use of siRNA as a novel radiation/chemotherapy-sensitizing agent.
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PMID:Enhanced radiation and chemotherapy-mediated cell killing of human cancer cells by small inhibitory RNA silencing of DNA repair factors. 1267 Sep 3

The p21(WAF1/Cip1) gene plays a central role in cell cycle regulation. Here we show that topoisomerase II inhibitors, genistein and etoposide, induce p21(WAF1/Cip1) expression mainly in a p53-dependent manner in human lung cancer cell line A549. However, although p53 accumulated, p21(WAF1/Cip1) expression did not depend on the level of Ser15 phosphorylation of p53. Caffeine, an ataxia telangiectasia-mutated (ATM), and ATM- and Rad3-related kinase (ATR) inhibitor, abrogated genistein-induced p21(WAF1/Cip1) and largely blocked etoposide-induced p21(WAF1/Cip1) expression. Wortmannin, an ATM- and DNA-dependent protein kinase inhibitor, partially inhibited p21(WAF1/Cip1) expression induced by genistein and etoposide, whereas UCN-01, a Chk1 inhibitor, partially blocked etoposide, but not genistein-induced p21(WAF1/Cip1) expression. These data suggest that both genistein and etoposide induce p21(WAF1/Cip1) expression in a p53-dependent manner. Genistein appears to stimulate p21(WAF1/Cip1) expression through p53 via ATM, whereas etoposide may activate both ATM and ATR pathways. Our results suggest different mechanisms participate in genistein and etoposide induced p21(WAF1/Cip1) expression.
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PMID:P21 response to DNA damage induced by genistein and etoposide in human lung cancer cells. 1276 22

The effect of wortmannin posttreatment was studied in cells derived from different species (hamster, mouse, chicken, and human) with normal and defective DNA-dependent protein kinase (DNA-PK) activity, cells with and without the ataxia telangiectasia (ATM) gene, and cells lacking other regulatory proteins involved in the DNA double-strand break (DSB) repair pathways. Clonogenic assays were used to obtain all results. Wortmannin radiosensitization was observed in Chinese hamster cells (V79-B310H , CHO-K1), mouse mammary carcinoma cells (SR-1), transformed human fibroblast (N2KYSV), chicken B lymphocyte wild-type cells (DT40), and chicken Rad54 knockout cells (Rad54-/-). However, mouse mammary carcinoma cells (SX9) with defects in the DNA-PK and chicken DNA-PK catalytic subunit (DNA-PKcs) knockout cells (DNA-PKcs-/-/-) failed to exhibit wortmannin radiosensitization. On the other hand, SCID mouse cells (SC3VA2) exposed to wortmannin exhibited significant increases in radiosensitivity, possibly because of some residual function of DNA-PKcs. Moreover, the transformed human cells derived from AT patients (AT2KYSV) and chicken ATM knockout cells (ATM-/-) showed pronounced wortmannin radiosensitization. These studies demonstrate confirm that the mechanism underlying wortmannin radiosensitization is the inhibition of DNA-PK, but not of ATM, thereby resulting in the inhibition of DSB repair via nonhomologous endjoining (NHEJ).
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PMID:DNA-PK: the major target for wortmannin-mediated radiosensitization by the inhibition of DSB repair via NHEJ pathway. 1367 45


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