22, 2.88, 2.32, 7.04 and 3.47 folds, respectively.

Figure 5 Effects of DNMT1 silencing on gene methylation and mRNA expression of seven tumor suppressor genes in Siha cells assayed by MeDIP combined with Real-Time PCR. Except for FHIT and CHFR, the rest five suppressor genes CCNA1, PTEN, PAX1, SFRP4 and TSLC1 in transfected group displayed lower level of methylation with increased mRNA expression when compared with control group. (n = 3, **P < 0.01). Discussion DNMT1 silencing in cervical cancer cells could induce re-expression of most tumor suppressor genes by demethylating its promoter region, and co-silencing of DNMT1 and DNMT3b might perform a greater inhibitory effect on tumorigenesis [3]. Sowinska AZD3965 order [4] demonstrated that combined DNMT1 and DNMT3b selleck screening library siRNAs could enhance promoter demethylation and re-expression of

CXCL12 in MCF-7 breast cancer as well as AsPC1 in pancreatic carcinoma cell lines, and suggested that they acted synergistically in inhibiting CpG island hypermethylation of tumor suppressor genes. Rhee et al [5] reported that DNMT3b deletion in a colorectal cancer cell line reduced global DNA methylation by less than 3%, but co-silencing of both DNMT1 and DNMT3b nearly eliminated methyltransferase activity, and reduced genomic DNA methylation by greater than 95%. Thus, DNMT1 and DNMT3b play the significant role in promoter methylation of tumor suppressor genes and tumorigenesis in its early status. for Currently, functions and mechanisms of DNMTs in cervical cancer cells remained unclear, and whether DNMT1 and DNMT3b act synergistically or through other ways exploration efforts were still required study. In human bladder cancer cells, selective depletion of DNMT1 with siRNA induced demethylation and reactivation of the silenced tumor-suppressor gene CDKN2A [6]. RNAi-mediated knockdown of DNMT1 resulted in significant reduction of promoter methylation and re-expression of RASSF1A, p16, and HPP1 in HCC1954 breast cancer cells

[7]. In ovarian cancer cell line CP70, DNMT1 siRNA treatment led to a partial removal of DNA methylation from three inactive promoter CpG islands, TWIST, RASSF1A, and HIN-1, and restored the expression of these genes [8]. Thus, RNAi-mediated DNMT1 depletion in different tumor cells could induce demethylation of various tumor suppressor genes and enhance re-expression. However, contradictory results were reported even in the same cell line. Ting et al [9] found that hypermethylation of CDKN2A, SFPR1, GATA4 and GATA5 were still maintained in HCT116 colorectal cancer cells after transiently or stably depleted of DNMT1, and suggested that DNMT1 might not play the dominant effect which caused hypermethylation of CpG islands in tumor suppressor genes. Knockout of DNMT1 in HCT116 cells by homologous recombination only reduced global DNA methylation by 20% and p16 maintained completely methylated status.