Browsing by Subject "Ape1"

Now showing 1 - 4 of 4
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    Inhibition of Ape1's DNA Repair Activity as a Target in Cancer: Identification of Novel Small Molecules that have Translational Potential for Molecularly Targeted Cancer Therapy
    (2009-12) Bapat, Aditi Ajit; Kelley, Mark Richard, 1957-; Georgiadis, Millie M.; Turchi, John J.; Smith, Martin L.
    The DNA Base Excision Repair (BER) pathway repairs DNA damaged by endogenous and exogenous agents including chemotherapeutic agents. Removal of the damaged base by a DNA glycosylase creates an apurinic / apyrimidinic (AP) site. AP endonuclease1 (Ape1), a critical component in this pathway, hydrolyzes the phosphodiester backbone 5’ to the AP site to facilitate repair. Additionally, Ape1 also functions as a redox factor, known as Ref-1, to reduce and activate key transcription factors such as AP-1 (Fos/Jun), p53, HIF-1α and others. Elevated Ape1 levels in cancers are indicators of poor prognosis and chemotherapeutic resistance, and removal of Ape1 via methodology such as siRNA sensitizes cancer cell lines to chemotherapeutic agents. However, since Ape1 is a multifunctional protein, removing it from cells not only inhibits its DNA repair activity but also impairs its other functions. Our hypothesis is that a small molecule inhibitor of the DNA repair activity of Ape1 will help elucidate the importance (role) of its repair function in cancer progression as wells as tumor drug response and will also give us a pharmacological tool to enhance cancer cells’ sensitivity to chemotherapy. In order to discover an inhibitor of Ape1’s DNA repair function, a fluorescence-based high-throughput screening (HTS) assay was used to screen a library of drug-like compounds. Four distinct compounds (AR01, 02, 03 and 06) that inhibited Ape1’s DNA repair activity were identified. All four compounds inhibited the DNA repair activity of purified Ape1 protein and also inhibited Ape1’s activity in cellular extracts. Based on these and other in vitro studies, AR03 was utilized in cell culture-based assays to test our hypothesis that inhibition of the DNA repair activity of Ape1 would sensitize cancer cells to chemotherapeutic agents. The SF767 glioblastoma cell line was used in our assays as the chemotherapeutic agents used to treat gliobastomas induce lesions repaired by the BER pathway. AR03 is cytotoxic to SF767 glioblastoma cancer cells as a single agent and enhances the cytotoxicity of alkylating agents, which is consistent with Ape1’s inability to process the AP sites generated. I have identified a compound, which inhibits Ape1’s DNA repair activity and may have the potential in improving chemotherapeutic efficacy of selected chemotherapeutic agents as well as to help us understand better the role of Ape1’s repair function as opposed to its other functions in the cell.
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    Mass Spectrometric Approaches to Probing the Redox Function of Ape1
    (2012-07-03) Delaplane, Sarah Ann; Georgiadis, Millie M.; Bosron, William F.; Witzmann, F. A. (Frank A.)
    Human apurinic/apyrimidinic endonuclease 1 (hApe1) is a multi-functional protein having two major functions: apurinic/apyrimidinic endonuclease activity for DNA damage repair and redox activity for gene regulation. Many studies have shown the action of Ape1 in the base excision repair pathway leading to cell survival. It has also been reported that Ape1 reduces a number of important transcription factors that are involved in cancer promotion and progression. Though the repair activity is well understood, the redox mechanism is not yet clear. What is known about Ape1 is its structure and that it contains seven cysteines (C65, C93, C99, C138, C208, C296, and C310), none of which are disulfide bonded. Two of these cysteines, C99 and C138, are solvent-accessible, and C65, C93, and C99 are located in the redox domain. It is believed that one or more cysteines are involved in the redox function and is hypothesized that hApe1 reduces the down-stream transcription factors by a disulfide exchange mechanism. E3330, (2E)-3-[5-(2,3-dimethoxy-6-methyl-1,4-benzoquninoyl)]2-nonyl-2-propenoic acid, is a specific inhibitor for the redox function of hApe1. The interaction mechanism is not known. Using N-Ethylmaleimide (NEM) chemical footprinting, combined with Hydrogen/Deuterium Exchange (HDX) data, we propose that a locally unfolded form coexists with the folded form in an equilibrium that is driven by irreversible NEM labeling, and that E3330 interacts with and stabilizes this locally unfolded form. This locally unfolded form is thereby proposed to be the redox-active form. We further support this claim with LC-MS/MS analysis showing an increase of disulfide bonds induced by E3330 among the cysteines in the redox domain, which would be too far apart from each other in the folded form to form a disulfide bond. We also studied three analogs of E3330. The need for an E3330 analog is to develop a more efficient and effective compound that would allow for sub-micromolar levels of activity (E3330 requires a micromolar amount). Study of the analogs will also allow us to gain perspective of the mechanism or mechanisms of E3330’s activity in Ape1’s redox function.
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    RelA Is an Essential Target for Enhancing Cellular Responses to the DNA Repair/Ref-1 Redox Signaling Protein and Restoring Perturbated Cellular Redox Homeostasis in Mouse PDAC Cells
    (Frontiers Media, 2022-03-24) Mijit, Mahmut; Wireman, Randall; Armstrong, Lee; Gampala, Silpa; Hassan, Zonera; Schneeweis, Christian; Schneider, Guenter; Zhang, Chi; Fishel, Melissa L.; Kelley, Mark R.; Pediatrics, School of Medicine
    Pancreatic ductal adenocarcinoma (PDAC) is one of the deadliest cancers with a poor response to current treatment regimens. The multifunctional DNA repair-redox signaling protein Ref-1 has a redox signaling function that activates several transcriptional factors (TFs) including NF-κB (RelA), STAT3, AP-1. These have been implicated in signaling in PDAC and associated with cancer progression and therapy resistance. Numerous studies have shown a role for RelA in PDAC inflammatory responses and therapy resistance, little is known as to how these inflammatory responses are modulated through Ref-1 redox signaling pathways during pancreatic pathogenesis. RelA and STAT3 are two major targets of Ref-1 and are important in PDAC pathogenesis. To decipher the mechanistic role of RelA in response to Ref-1 inhibition, we used PDAC cells (KC3590) from a genetically engineered Kras G12D-driven mouse model that also is functionally deficient for RelA (Parent/Vector) or KC3590 cells with fully functional RelA added back (clone 13; C13). We demonstrated that RelA deficient cells are more resistant to Ref-1 redox inhibitors APX3330, APX2009, and APX2014, and their sensitivity is restored in the RelA proficient cells. Knockdown of STAT3 did not change cellular sensitivity to Ref-1 redox inhibitors in either cell type. Gene expression analysis demonstrated that Ref-1 inhibitors significantly decreased IL-8, FOSB, and c-Jun when functional RelA is present. We also demonstrated that PRDX1, a known Ref-1 redox modulator, contributes to Ref-1 inhibitor cellular response. Knockdown of PRDX1 when functional RelA is present resulted in dramatically increased PDAC killing in response to Ref-1 inhibitors. The enhanced cell killing was not due to increased intracellular ROS production. Although Ref-1 inhibition decreased the NADP/NADPH ratio in the cells, the addition of PRDX1 knockdown did not further this redox imbalance. This data suggests that the mechanism of cell killing following Ref-1 inhibition is at least partially mediated through RelA and not STAT3. Further imbalancing of the redox signaling through disruption of the PRDX1-Ref-1 interaction may have therapeutic implications. Our data further support a pivotal role of RelA in mediating Ref-1 redox signaling in PDAC cells with the Kras G12D genotype and provide novel therapeutic strategies to combat PDAC drug resistance.
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    Structure-function analysis of CXXC finger protein 1
    (2009-04) Tate, Courtney Marie; Skalnik, David Gordon; Bigsby, Robert M.; Dynlacht, Joseph R.; Wek, Ronald C.
    This dissertation describes structure-function studies of CXXC finger protein 1 (Cfp1), encoded by the CXXC1 gene, in order to determine the functional significance of Cfp1 protein domains and properties. Cfp1 is an important regulator of chromatin structure and is essential for mammalian development. Murine embryonic stem (ES) cells lacking Cfp1 (CXXC1-/-) are viable but demonstrate a variety of defects, including hypersensitivity to DNA damaging agents, reduced plating efficiency and growth, decreased global and gene-specific cytosine methylation, failure to achieve in vitro differentiation, aberrant histone methylation, and subnuclear mis-localization of Setd1A, the catalytic component of a histone H3K4 methyltransferase complex, and tri-methylated histone H3K4 (H3K4me3) with regions of heterochromatin. Expression of wild-type Cfp1 in CXXC1-/- ES cells rescues the observed defects, thereby providing a convenient method to assess structure-function relationships of Cfp1. Cfp1 cDNA expression constructs were stably transfected into CXXC1-/- ES cells to evaluate the ability of various Cfp1 fragments and mutations to rescue the CXXC1-/- ES cell phenotype. These experiments revealed that expression of either the amino half of Cfp1 (amino acids 1-367) or the carboxyl half of Cfp1 (amino acids 361-656) is sufficient to rescue the hypersensitivity to DNA damaging agents, plating efficiency, cytosine and histone methylation, and differentiation defects. These results reveal that Cfp1 contains redundant functional domains for appropriate regulation of cytosine methylation, histone methylation, and in vitro differentiation. Additional studies revealed that a point mutation (C169A) that abolishes DNA-binding activity of Cfp1 ablates the rescue activity of the 1-367 fragment, and a point mutation (C375A) that abolishes the interaction of Cfp1 with the Setd1A and Setd1B histone H3K4 methyltransferase complexes ablates the rescue activity of the 361-656 Cfp1 fragment. In addition, introduction of both point mutations (C169A and C375A) ablates the rescue activity of the full-length Cfp1 protein. These results indicate that retention of either DNA-binding or Setd1 association of Cfp1 is required to rescue hypersensitivity to DNA damaging agents, plating efficiency, cytosine and histone methylation, and in vitro differentiation. In contrast, confocal immunofluorescence analysis revealed that full-length Cfp1 is required to restrict Setd1A and histone H3K4me3 to euchromatic regions.