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Analysis of competing risks in the burr XII model in presence of progressive type-II censoring
A. Pourdarvish,R. Hashemi,J. Azar 장전수학회 2012 Proceedings of the Jangjeon mathematical society Vol.15 No.1
In reliability and survival analysis, it is quite common that the failure of any individual or any item may be attributable to more than one cause (competing risks). In this paper, we will study the competing risks in the Burr XII model in the presence of progressive type II censoring scheme. We study the model under the assumption of independent causes of failure. The maximum likelihood estimator was developed to estimate the unknown parameters. The asymptotic distribution of the maximum likelihood estimators is used to construct approximate confidence interval. We also present a simulation study to illustrate the results.
Methyl Donor Status Influences DNMT Expression and Global DNA Methylation in Cervical Cancer Cells
Poomipark, Natwadee,Flatley, Janet E,Hill, Marilyn H,Mangnall, Barbara,Azar, Elnaz,Grabowski, Peter,Powers, Hilary J Asian Pacific Journal of Cancer Prevention 2016 Asian Pacific journal of cancer prevention Vol.17 No.7
Background: Methyl donor status influences DNA stability and DNA methylation although little is known about effects on DNA methyltransferases. The aim of this study was to determine whether methyl-donor status influences DNA methyltransferase (Dnmt) gene expression in cervical cancer cells, and if so, whether there are associated effects on global DNA methylation. Materials and Methods: The human cervical cancer cell line, C4-II, was grown in complete medium and medium depleted of folate (F-M+) and folate and methionine (F-M-). Growth rate, intracellular folate, intracellular methionine and homocysteine in the extracellular medium were measured to validate the cancer cell model of methyl donor depletion. Dnmt expression was measured by qRT-PCR using relative quantification and global DNA methylation was measured using a flow cytometric method. Results: Intracellular folate and methionine concentrations were significantly reduced after growth in depleted media. Growth rate was also reduced in response to methyl donor depletion. Extracellular homocysteine was raised compared with controls, indicating disturbance to the methyl cycle. Combined folate and methionine depletion led to a significant down-regulation of Dnmt3a and Dnmt3b; this was associated with an 18% reduction in global DNA methylation compared with controls. Effects of folate and methionine depletion on Dnmt3a and 3b expression were reversed by transferring depleted cells to complete medium. Conclusions: Methyl donor status can evidently influence expression of Dnmts in cervical cancer cells, which is associated with DNA global hypomethylation. Effects on Dnmt expression are reversible, suggesting reversible modulating effects of dietary methyl donor intake on gene expression, which may be relevant for cancer progression.