Human apul'inic/apyrimidinic endonuclease l/redox effector factor-1 (APEl/Ref·l) is a perfect paradigm of the functional complexity of a biological macromolecule. First, it plays a crucial role, by both redox-dependent and -independent mechanisms, as a transcriptional coactivator for different trnnscription factors, either ubiquitous (i.e., AP-1, Egr-1, NF-KB, p53, HIF) or tissue-specific (i.e., PEBP-2, Pax-Sand -8, TTF-1), in controlling different cellular processes such as apoptosis, proliferation, and differentiation. Second, it acts, as an apurinidapyrimidinic endonuclease, during the second step of the DNA base excision repair pathway, which is responsible for the repair of cellular alkylation and oxidative DNA damages. Thil'd, it controls the intracellular reactive oxygen species production by negatively regulating the activity of the Ras-related GTPase Rael. Despite these known functions of APEl/Ref-1, information is still scanty about the molecular mechanisms responsible for the coordinated control of its several activities. Some evidence suggests that the expression and subcellular localization of APEl/Ref-1 are finely tuned. APEl/Ref-1 is a ubiquitous protein, but its expression pattern differs according to the different cell types. APEl/Ref-1 subcellular localization is mainly nuclear, but cytop1asmic staining has also been reported, the latter being associated with mitochondria and/or presence within the endoplasmic reticulum. It is not by chance that both expression and sub cellular localization a1·e altered in several metabolic and proliferative disorde1·s, such as in tumors and aging. Moreover, a fundamental role played by different posttranslational modifications in modulating APEl/Ref·l functional activity is becoming eYident. In the present review, we tded to put togethe1· a growing body of information concerning APEl/Ref-l's different functions, shedding new light on present and future directions to understand fully this unique molecule. Antioxid. Redox Signal. 7,[367][368][369][370][371][372][373][374][375][376][377][378][379][380][381][382][383][384]

Studies of bacterial ion channels have provided significant insights into the structure-function relationships of mechanosensitive and voltage-gated ion channels. However, to date, very few bacterial channels that respond to small molecules have been identified, cloned, and characterized. Here, we use bioinformatics to identify a novel family of bacterial cyclic nucleotide-gated (bCNG) ion channels containing a channel domain related by sequence homology to the mechanosensitive channel of small conductance (MscS). In this initial report, we clone selected members of this channel family, use electrophysiological measurements to verify their ability to directly gate in response to cyclic nucleotides, and use osmotic downshock to demonstrate their lack of mechanosensitivity. In addition to providing insight into bacterial physiology, these channels will provide researchers with a useful model system to investigate the role of ligand-gated ion channels (LGICs) in the signaling processes of higher organisms. The identification of these channels provides a foundation for structural and functional studies of LGICs that would be difficult to perform on mammalian channels. Moreover, the discovery of bCNG channels implies that bacteria have cyclic nucleotide-gated and cyclic nucleotide-modulated ion channels, which are analogous to the ion channels involved in eukaryotic secondary messenger signaling pathways.

Bacterial cyclic nucleotide gated (bCNG) channels are generally a nonmechanosensitive subset of the mechanosensitive channel of small conductance (MscS) superfamily. bCNG channels are composed of an MscS channel domain, a linking domain, and a cyclic nucleotide binding domain. Among bCNG channels, the channel domain of Ss-bCNGa, a bCNG channel from Synechocystis sp. PCC 6803, is most identical to Escherichia coli (Ec) MscS. This channel also exhibits limited mechanosensation in response to osmotic downshock assays, making it the only known full-length bCNG channel to respond to hypoosmotic stress. Here, we compare and contrast the ability of Ss-bCNGa to gate in response to mechanical tension with Se-bCNG, a nonmechanosensitive bCNG channel, and Ec-MscS, a prototypical mechanosensitive channel. Compared with Ec-MscS, Ss-bCNGa only exhibits limited mechanosensation, which is most likely a result of the inability of Ss-bCNGa to form the strong lipid contacts needed for significant function. Unlike Ec-MscS, Ss-bCNGa displays a mechanical response that increases with protein expression level, which may result from channel clustering driven by interchannel cation-π interactions.

In an effort to improve the efficacy of cancer chemotherapy by intervening into the cellular responses to chemotherapeutic change, we have used adenoviral overexpression of N-methylpurine DNA glycosylase (MPG or ANPG/AAG) in breast cancer cells to study its ability to imbalance base excision repair (BER) and sensitize cancer cells to alkylating agents. Our results show that MPG-overexpressing cells are significantly more sensitive to the alkylating agents methyl methanesulfonate, N-methyl-N′-nitro-N-nitrosoguanidine, methylnitrosourea, dimethyl sulfate, and the clinical chemotherapeutic temozolomide. Sensitivity is further increased through coadministration of the BER inhibitor methoxyamine, which covalently binds abasic or apurinic/apyrimidinic (AP) sites and makes them refractory to subsequent repair. Methoxyamine reduction of cell survival is significantly greater in cells overexpressing MPG than in control cells, suggesting a heightened production of AP sites that, if made persistent, results in increased cellular toxicity. We further explored the mechanism of MPG-induced sensitivity and found that sensitivity was associated with a significant increase in the number of AP sites and/or single-strand breaks in overexpressing cells, confirming a MPG-driven accumulation of toxic BER intermediates. These data establish transient MPG overexpression as a potential therapeutic approach for increasing cellular sensitivity to alkylating agent chemotherapy.

Toremifene (TOR) is a selective estrogen receptor modulator (SERM) used in adjuvant therapy for breast cancer, and more recently is in clinical trials for prostate cancer prevention in patients with high grade PIN. The chemical structure of TOR differs from tamoxifen (TAM) only by the presence of a chlorine atom in the ethyl side chain. That difference results in distinct breakdown products of the two drugs, which may provide for a more favorable toxicity spectrum with TOR compared to TAM. TOR has a similar mechanism of action to that of TAM, in that its 4-hydroxy metabolites bind specifically to estrogen receptors and, as an estrogen receptor-TOR complex, to chromatin. Interestingly, studies have indicated that a subset of patients who fail on TAM therapy benefit from high-dose TOR therapy, indicating that pharmacogenomics could be an important determinant of response to treatment with TOR. Several studies have indicated that functional genetic variants in the TAM metabolic pathway influence response to therapy, but to date, pharmacogenomic studies of patients treated with TOR are lacking. In order to perform candidate gene association studies, it is necessary to identify the enzymes involved in TOR metabolism. While the Phase I metabolism of TOR has been well-characterized, Phase II metabolism of the active 4-OH-TOR is not well-defined. In this study, we examined individual variability in sulfation of TOR, and found 20-fold variation in human liver cytosols from 100 subjects. Examination of recombinant sulfotransferases revealed that SULT1A1, SULT1E1, and to a lesser extent, SULT2A1 catalyzed the sulfation of TOR. SULT1A1 is the most highly expressed hepatic sulfotransferase, and there was a significant association between SULT1A1*1/*2 genotype and TOR sulfation in human liver cytosols (p=0.001). Since target tissue metabolism is also a critical determinant of clinical efficacy, we also examined the presence of sulfotransferase isoforms in normal prostate (n= 8), BPH tissue (n= 12), and prostate cancer (n=4). Quantitative RT-PCR analysis showed the presence of SULT1A1 and SULT2B1b in BPH and Prostate cancer tissues. These results indicate that variability in sulfation, in terms of both first-pass metabolism and target tissue metabolism, contributes to response to TOR for prostate cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2619.