DNMT1 mediates chemosensitivity by reducing methylation of miRNA-20a promoter in glioma cells

Although methyltransferase has been recognized as a major element that governs the epigenetic regulation of the genome during temozolomide (TMZ) chemotherapy in glioblastoma multiforme (GBM) patients, its regulatory effect on glioblastoma chemoresistance has not been well defined. This study investigated whether DNA methyltransferase (DNMT) expression was associated with TMZ sensitivity in glioma cells and elucidated the underlying mechanism. DNMT expression was analyzed by western blotting. miR-20a promoter methylation was evaluated by methylation-specific PCR. Cell viability and apoptosis were assessed using the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT) and TdT-mediated dUTP-biotin nick end labeling assays, respectively. The results showed that compared with parental U251 cells, DNMT1 expression was downregulated, miR-20a promoter methylation was attenuated and miR-20a levels were elevated in TMZ-resistant U251 cells. Methyltransferase inhibition by 5-aza-2\'-deoxycytidine treatment reduced TMZ sensitivity in U251 cells. In U251/TM cells, DNMT1 expression was negatively correlated with miR-20a expression and positively correlated with TMZ sensitivity and leucine-rich repeats and immunoglobulin-like domains 1 expression; these effects were reversed by changes in miR-20a expression. DNMT1 overexpression induced an increase in U251/TM cell apoptosis that was inhibited by the miR-20a mimic, whereas DNMT1 silencing attenuated U251/TM cell apoptosis in a manner that was abrogated by miR-20a inhibitor treatment. Tumor growth of the U251/TM xenograft was inhibited by pcDNA-DNMT1 pretreatment and boosted by DNMT1-small hairpin RNA pretreatment. In summary, DNMT1 mediated chemosensitivity by reducing methylation of the microRNA-20a promoter in glioma cells.

In vitro amplification and biological characterization of rabbit corneal limbal epithelial stem cells / 中国组织工程研究

BACKGROUND: How to establish a stable in vitro culture system, including location of corneal limbal epithelial stem cells, in vitro sample harvest, in vitro culture, vector selection, as well as identification methods, play a key role in corneal limbal epithelial stem cells culture. OBJECTIVE: To culture the isolated rabbit corneal limbal epithelial stem cells and to identify the biological properties of cultured cells. METHODS: The primary rabbit cornel limbal epithelial stem cells were isolated and cultured with tissue inoculation using human amniotic membrane as vector. The growth features of cells were observed under an inverted microscope. The morphology of cells was observed by hematoxylin-eosin staining and a scanning electron microscope. Furthermore, the monoclonal antibody AE5 and P63 two-step immunohistochemical staining were used to identify limbal epithelial stem cell protein expression. RESULTS AND CONCLUSION: The rabbit corneal limbal epithelial stem cells could be successfully cultured and maintained a relatively high value-added potential in vitro. Rabbit corneal limbal epithelial stem cells cultured on the amniotic membrane pull netted cellular layer. The AE5 monoclonal antibody positive rate of primary cultured cells was about 5% and P63 monoclonal antibody positive up to 90%. AE5-positive rate increased and P63-positive rate decreased with the increase in the number of subculture. The rabbit limbal epithelial stem cells can be successful culture and amplified on human amniotic membrane in vitro by limbal tissue culture method. The cultured cells maintain the characteristics of corneal epithelial cells. The rabbit corneal limbal epithelial stem cells can form grafts on the amniotic membrane.