ATF4-Dependent Oxidative Induction of the DNA Repair Enzyme Ape1 Counteracts Arsenite Cytotoxicity and Suppresses Arsenite-Mediated Mutagenesis

Abstract

Arsenite is a human carcinogen causing skin, bladder, and lung tumors, but the cellular mechanisms underlying these effects remain unclear. We investigated expression of the essential base excision DNA repair enzyme apurinic endonuclease 1 (Ape1) in response to sodium arsenite. In mouse 10T 1 ⁄2 fibroblasts, Ape1 induction in response to arsenite occurred about equally at the mRNA, protein, and enzyme activity levels. Analysis of the APE1 promoter region revealed an AP-1/CREB binding site essential for arsenite-induced transcriptional activation in both mouse and human cells. Electrophoretic mobility shift assays indicated that an ATF4/c-Jun heterodimer was the responsible transcription factor. RNA interference targeting c-Jun or ATF4 eliminated arsenite-induced APE1 transcription. Suppression of Ape1 or ATF4 sensitized both mouse fibroblasts (10T 1 ⁄2) and human lymphoblastoid cells (TK6) to arsenite cytotoxicity. Expression of Ape1 from a transgene did not efficiently restore arsenite resistance in ATF4-depleted cells but did offset initial accumulation of abasic DNA damage following arsenite treatment. Mutagenesis by arsenite (at the TK and HPRT loci in TK6 cells) was observed only for ATF4-depleted cells, which was strongly offset by Ape1 expression from a transgene. Therefore, the ATF4-mediated up-regulation of Ape1 and other genes plays a key role against arsenite-mediated toxicity and mutagenesis.Epidemiological studies from Bangladesh, India (West Bengal), Taiwan, and South America indicate that arsenic ingestion, typically via contaminated drinking water, is associated with increased incidence of diverse human diseases, such as atherosclerosis, diabetes, and cancers of the skin, bladder, and lung (55). The arsenic found in drinking water is overwhelmingly one of the inorganic arsenic forms, mostly pentavalent arsenate and trivalent arsenite (55).Arsenite treatment has recently been introduced as therapy for acute promyelocytic leukemia (61). The pathological and therapeutic mechanisms of arsenic are actively debated, and DNA may be an important target for arsenic-related damage. For example, comet assays demonstrate that exposure to as little as 1 nM of sodium arsenite could rapidly (within 30 min) induce DNA base damage in human HeLa, neutrophilic NB4, and HL-60 cells (59, 69). For comparison, the reported mean blood arsenic concentration in people consuming highly contaminated water was 560 nM (49), while the mean plasma arsenite concentration for cancer treatment was 1,000 to 6,000 nM (60). However, many cell-based assays have failed to detect a significant increase in point mutations due to arsenite (55). One conclusion from these observations is that a strong cellular antimutagenesis mechanism counteracts the mutational potential of arsenite-induced DNA damage.Oxidized and other small base lesions are excised by DNA glycosylases, which channel damage into the base excision DNA repair (BER) pathway. In mammalian cells, glycosylase products are processed by the abasic (apurinic/apyrimidinic [AP]) end...

miR-214 protects erythroid cells against oxidative stress by targeting ATF4 and EZH2

“…4C). Consistent with previous observations [59], cell death was nearly doubled in ATF4 knockdown cells upon As treatment (Po 0.05), verifying the indispensable role of ATF4 against oxidative stress. Second, As-induced ATF4 protein expression was substantially inhibited in MEL cells with Nrf2 knockdown, compared to the scrambled control (Fig.…”

ATF4 is directly recruited by TLR4 signaling and positively regulates TLR4-trigged cytokine production in human monocytes

“…The lentivirus infection system that we used in the experiment is only sustained for 1 h, and a scramble control was included, which have been used in many other studies. 35,36 ATF4 acts as a transcription activator and inhibitor. 35,[37][38][39][40] The results of our cytokine array assay revealed that ATF4 positively regulated the secretion of RANTES, sICAM-1, IL-6, IL-8 and IFN-c, all of which are proinflammatory cytokines.…”

“…52,53 In the present study, we investigated c-Jun as the possible downstream mediator of ATF4 in the TLR4-trigged signaling pathway, which was prompted by previous reports showing that heterodimerization of ATF4 and c-Jun might occur. 36,54 The study by An et al 26 has indicated that there is an AP-1 response element within the IL-6 promoter. The RANTES/CCL5 promoter displays binding activity with AP-1, C/EBP and NF-kB, 55 while the IL-8 promoter contains NF-kB, AP-1, OCT-1 and C/EBP-binding sites.…”

Apurinic/apyrimidinic endonuclease APE1 is required for PACAP-induced neuroprotection against global cerebral ischemia

“…APE1 promoter contains an AP-1/ cAMP responsive element (CRE)-binding site that is implicated in transcriptional regulation of the APE1 gene (18). Thus, PACAP may act via CREB to stimulate transactivation of the APE1 promoter.…”

“…S5F). The APE1 promoter contains a canonical CRE binding site (18), and we explored whether the CRE site of the APE1 promoter mediates transactivation of APE1 by CREB and ATF2 in response to PACAP. Mutation of the CRE site in the APE1 promoter of the luciferase reporter construct greatly reduced the increase in luciferase activity induced by PACAP (Fig.…”