CUHK electronic theses & dissertations collection

"Epigenetic" refers to a heritable change in the gene expression pattern that is not mediated by any alterations in the primary nucleotide sequence of a gene in the genome. This change involves methylation of DNA in the gene promoter regions, modification of histone residues and chromatin remodeling. Among them, methylation of DNA promoter region is an essential step in epigenetic gene silencing and is known to be closely related to carcinogenesis and cancer progression.Our preliminary study on effect of treatments of some potential anti-cancer drug candidates, namely Pheophorbide A (Pa), Pa combining with photodynamic therapy, Polyphyllin D (designated as HK-18), and its derivative designated as HK-27 on human breast cancer cell lines MCF-7 and MDA-MB-231 showed that the promoter methylation of CDH1 was decreased in response to treatments of Pa, HK-18, and HK-27 in MDA-MB-231 cells.The aim of this study was to explore whether any methylation of DNA promoters mechanism is involved in drug resistance of a doxorubicin-induced human multidrug resistant hepatocellular carcinoma sub-linage R-HepG2 which was established from the doxorubicin sensitive HepG2 cell line in our laboratory. In this project, it was observed that the DNA promoter methylations of ESR1, Rassf2A, CDH1 and MDR1 in R-HepG2 were higher than those in HepG2 cells respectively by methylation specific polymerase chain reaction method. Bisulfite sequencing showed that the total 32 CpGs of CDH1 promoter region in R-HepG2 cells were hypermethylated while they were hypomethylated in HepG2 cells. CDH1 is the encoding gene of E-cadherin. The promoter hypermethylation induced CDH1 silencing in R-HepG2 cells was confirmed by reverse transcription polymerase chain reaction and Western blotting that CDH1 transcription and E-cadherin expression were maintained in HepG2 cells but both were lost in R-HepG2 cells. RT-PCR of 10 multidrug resistant related genes revealed that transcription of MDR1 was obviously increased in R-HepG2 cells, transcription of MRP1 and MRP5 were slightly increased in R-HepG2 cells, transcription of MRP6 and BCRP were slightly decreased in R-HepG2 cells comparing to those in the parental HepG2 cells. This result suggests that up-regulation of P-glycoprotein expression which is the protein product of MDR1 may be one of the major causes of multidrug resistance in R-HepG2 cells. Transient transfection of CDH1 cDNA increased the CDH1 transcription and E-cadherin expression in R-HepG2 cells. I also found that the CDH1 transfected R-HepG2-CDH1 cells showed increased amount of doxorubicin uptake, increased apoptotic population of cells exposed to doxorubicin, suppressed cell migration, and decreased P-glycoprotein expression comparing to those in R-HepG2 cells. It was also found that the transcription levels of SNAI2, TWIST1, ASNA1 and FYN were obviously higher in R-HepG2 cells than those in HepG2 cells. The transcription of FYN and TWIST1 were obviously decreased in CDH1 cDNA transfected R-HepG2-CDH1 cells which displayed a negative correlation with the transcription level of CDH1 and these results imply a suppressive role of CDH1 in regulating these genes which were involved in cancer metastasis and multidrug resistance.Jiang, Lei.Adviser: Kwok-Pui, Fang.Source: Dissertation Abstracts International, Volume: 73-02, Section: B, page: .Thesis (Ph.D.)--Chinese University of Hong Kong, 2010.Includes bibliographical references (leaves 144-171).Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web.Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web.Abstract also in Chinese