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Human methyl purine DNA glycosylase and DNA polymerase beta expression collectively predict sensitivity to temozolomide.

ABSTRACT: Overexpression of N-methylpurine DNA glycosylase (MPG) has been suggested as a possible gene therapy approach to sensitize tumor cells to the cell-killing effects of temozolomide, an imidazotetrazine-class chemotherapeutic alkylating agent. In the present study, we show that both elevated MPG expression and short hairpin RNA-mediated loss of DNA polymerase beta (Pol beta) expression in human breast cancer cells increases cellular sensitivity to temozolomide. Resistance to temozolomide is restored by complementation of either wild-type human Pol beta or human Pol beta with an inactivating mutation specific to the polymerase active site yet functional for 5'-deoxyribose-phosphate (5'dRP) lyase activity. These genetic and cellular studies uniquely demonstrate that overexpression of MPG causes an imbalance in base excision repair (BER), leading to an accumulation of cytotoxic 5'dRP lesions, and that the 5'dRP lyase activity of Pol beta is required to restore resistance to temozolomide. These results imply that Pol beta-dependent 5'dRP lyase activity is the rate-limiting step in BER in these cells and suggests that BER is a tightly balanced pathway for the repair of alkylated bases such as N7-methylguanine and N3-methyladenine. Furthermore, we find that 5'dRP-mediated cell death is independent of caspase-3 activation and does not induce the formation of autophagosomes, as measured by green fluorescent protein-light chain 3 localization. The experiments presented herein suggest that it will be important to investigate whether an active BER pathway could be partially responsible for the temozolomide-mediated resistance seen in some tumors and that balanced BER protein expression and overall BER capacity may help predict sensitivity to temozolomide.

SUBMITTER: Trivedi RN

PROVIDER: S-EPMC3909956 | biostudies-literature | 2008 Aug

REPOSITORIES: biostudies-literature

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Human methyl purine DNA glycosylase and DNA polymerase beta expression collectively predict sensitivity to temozolomide.

Trivedi Ram N RN Wang Xiao-hong XH Jelezcova Elena E Goellner Eva M EM Tang Jiang-bo JB Sobol Robert W RW

Molecular pharmacology 20080513 2

Overexpression of N-methylpurine DNA glycosylase (MPG) has been suggested as a possible gene therapy approach to sensitize tumor cells to the cell-killing effects of temozolomide, an imidazotetrazine-class chemotherapeutic alkylating agent. In the present study, we show that both elevated MPG expression and short hairpin RNA-mediated loss of DNA polymerase beta (Pol beta) expression in human breast cancer cells increases cellular sensitivity to temozolomide. Resistance to temozolomide is restore ...[more]

PMID: 18477668

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Project description:DNA damage that stalls replicative polymerases can be bypassed with the Y-family polymerases. These polymerases have more open active sites that can accommodate modified nucleotides. The lack of protein-DNA interactions that select for Watson-Crick base pairs correlate with the lowered fidelity of replication. Interstrand hydrogen bonds appear to play a larger role in dNTP selectivity. The mechanism by which purine-purine mispairs are formed and extended was examined with Solfolobus solfataricus DNA polymerase IV, a member of the RAD30A subfamily of the Y-family polymerases, as is pol eta. The structures of the purine-purine mispairs were examined by comparing the kinetics of mispair formation with adenine versus 1-deaza- and 7-deazaadenine and guanine versus 7-deazaguanine at four positions in the DNA, the incoming dNTP, the template base, and both positions of the terminal base pair. The time course of insertion of a single dNTP was examined with a polymerase concentration of 50 nM and a DNA concentration of 25 nM with various concentrations of dNTP. The time courses were fitted to a first-order equation, and the first-order rate constants were plotted against the dNTP concentration to produce k pol and K d (dNTP) values. A decrease in k pol/ K d (dNTP) associated with the deazapurine substitution would indicate that the position is involved in a crucial hydrogen bond. During correct base pair formation, the adenine to 1-deazaadenine substitution in both the incoming dNTP and template base resulted in a >1000-fold decrease in k pol/ K d (dNTP), indicating that interstrand hydrogen bonds are important in correcting base pair formation. During formation of purine-purine mispairs, the k pol/ K d (dNTP) values for the insertion of dATP and dGTP opposite 7-deazaadenine and 7-deazaguanine were decreased >10-fold with respect to those of the unmodified nucleotides. In addition, the rate of incorporation of 1-deaza-dATP opposite guanine was decreased 5-fold. These results suggest that during mispair formation the newly forming base pair is in a Hoogsteen geometry with the incoming dNTP in the anti conformation and the template base in the syn conformation. These results indicate that Dpo4 holds the incoming dNTP in the normal anti conformation while allowing the template nucleotide to change conformations to allow reaction to occur. This result may be functionally relevant in the replication of damaged DNA in that the polymerase may allow the template to adopt multiple configurations.

Project description:BackgroundAlthough intrinsic immune-evasion is important in cancer proliferation, metastasis and response to treatment, it is unclear whether intrinsic immune-evasion patterns of gliomas can aid in predicting clinical prognosis and determining treatment.MethodsA total of 182 immune-evasion genes intrinsic to cancer were subjected to consensus clustering to identify immune-evasion patterns in 1421 patients with lower-grade glioma (LGG). The levels of each cancer hallmark were determined by the Gene Set Variant Analysis (GSVA) method, and immune cell infiltrations were quantified using two algorithms, the single-sample Gene Set Enrichment Analysis (ssGSEA) and the Cell-type Identification By Estimating Relative Subsets Of RNA Transcripts (CIBERSORT) methods. IEVscore was determined by a method that combined univariate Cox regression analysis, least absolute shrinkage and selection operator (LASSO) regression and principal component analysis (PCA).ResultsTranscriptional and genomic analysis showed that most immune evasion genes (IEVGs) were upregulated in LGGs, with aberrant expression driven by alterations in copy number variants (CNV). Based on the mRNA expression profiles of cancer-intrinsic IEVGs could be divided into three LGG subgroups with distinct prognosis, clinicopathological features and immune infiltrations. A combined scoring scheme designed to assess the immune-evasion levels of LGGs divided these 1421 patients into two subgroups that differed in IEVscores. LGG patients with low-IEVscore had a better prognosis, would be more likely to benefit from immune check-point inhibitors and would be more susceptible to temozolomide (TMZ) chemotherapy.ConclusionIntrinsic immune evasion in the tumor microenvironment (TME) has a crucial effect on glioma formation. Quantitatively assessing the IEV scores of individual LGG patients could enhance knowledge about the intra-glioma microenvironment and lead to the development of individualized therapeutic strategies for patients with LGG.

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Human methyl purine DNA glycosylase and DNA polymerase beta expression collectively predict sensitivity to temozolomide.

Publications

Human methyl purine DNA glycosylase and DNA polymerase beta expression collectively predict sensitivity to temozolomide.

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