Epigallocatechin-3-gallate and trichostatin A synergistically inhibit human lymphoma cell proliferation through epigenetic modification of p16INK4a.

DNA methylation and histone deacetylation play important roles in the occurrence and development of cancers by inactivating the expression of tumor suppressors, including p16(INK4a), a cyclin-dependent kinase inhibitor. The present study investigated the effect of epigallocatechin-3-gallate (EGCG) alone or in combination with trichostatin A (TSA) on p16(INK4a) gene expression and growth in human malignant lymphoma CA46 cells. CA46 cell viability and cell cycle were analyzed; methylation of the p16(INK4a) gene was assessed by nested methylation-specific PCR (n-MSP). p16(INK4a )mRNA and protein expression was determined by real-time quantitative PCR and western blot analyses, respectively. Both EGCG and TSA alone inhibited CA46 cell proliferation; the combined treatment (6 µg/ml EGCG and 15 ng/ml TSA) significantly reduced CA46 cell proliferation from 24 to 96 h (all P<0.001). Cells treated with 24 µg/ml EGCG or the combination treatment (6 µg/ml EGCG and 15 ng/ml TSA) had lower proliferative indices when compared to the other groups. Co-treatment with EGCG and TSA decreased p16(INK4a) gene methylation, which coincided with increased p16(INK4a) mRNA and protein expression. Thus, EGCG and TSA synergistically reactivate p16(INK4a) gene expression in part through reducing promoter methylation, which may decrease CA46 cell proliferation.

[Effect of epigallocatechin-3-galate on human acute monocytic leukemia cell line U937 and its relevant mechanism].

The purpose of this study was to explore the effect of epigallocatechin-3-galate (EGCG) on acute monocytic leukemia cell line U937 and its relevant mechanism. The viability of U937 cells were assayed by SRB method. The cell cycle of U937 cells was analyzed by flow cytometry. The mRNA and protein expression of p16 gene were detected by RT-PCR and Western blot, respectively. Methylation level of U937 cells was analyzed by n-MSP. The mRNA expression of DNA methyltransferase 1 (DNMT1), DNMT3A and DNMT3B genes were analyzed by RT-PCR. The results showed that EGCG could inhibit the growth of U937 cells significantly in dose-and time-dependent manners (r=0.71), and induce the G0/G1 arrest of U937 cells in dose-dependent manner. EGCG could up-regulate the mRNA and protein expression of P16 gene in U937 cells in dose-dependent manner. EGCG could down-regulate the methylation level of p16 gene in U937 cells in dose-dependent manner. EGCG could down-regulate the mRNA expression of DNMT3A, DNMT3B genes, while did not influence the mRNA expression of DNMT1 gene. It is concluded that EGCG can up-regulate the mRNA and protein expression of p16 gene by demethylation or/and by inhibiting DNMT3A and DNMT3B genes, leading, in turn, to G0/G1 arrest and growth inhibition of U937 cells.

[Detection of APC gene promoter methylation in hematological malignant cell lines by nested-methylation specific polymerase chain reaction].

This study was aimed to investigate the efficiency of nested methylation specific polymerase chain reaction (nMS-PCR) for detecting the APC gene promoter methylation and to clarify the roles of methylation in genesis and development of hematologic malignancies, as well as to screen the hematologic malignant cell lines with hypermethylation of APC gene promoter to use as an ideal cell model for exploring the relationship between gen methylation and gene expression. The genome DNA of 10 cell lines modified with bisulfide was amplified and the methylation status of APC gene promoter was detected by using nMS-PCR. The results showed that the methylation of APC gene promoter was detected in Jurkat cells, while could not be detected in CA46, U266, Molt4, K562, HL-60, CEM, AKR, U937 and Raji cell lines. In conclusion, APC gene methylation in hematological malignant cell lines can be accurately detected by nMS-PCP method, which is simple method for detecting methylation status of various hematological malignant cell lines.

[Demethylation and transcription of p16 gene in malignant lymphoma cell line CA46 induced by EGCG].

The study was purposed to investigate the possible mechanism of epigallocatechin-3-gallate (EGCG) induced p16 gene demethylation and transcription regulation in the malignant lymphoma cell line-CA46. The induced growth inhibition of CA46 cells was assayed by growth curve and MTT; the DNA content of CA46 cells was analyzed by flow cytometry after being exposed to EGCG; the methylation status of the p16 gene in CA46 cell line before and after treatment with EGCG was detected by the nested-methylation specific PCR and DNA sequencing; the mRNA of p16 and DNA methyltransferases (DNMT3A and DNMT3B) gene were determined by RT-PCR. The results showed that in comparison with the control, all the 3 different concentration of EGCG were able to inhibit the growth of malignancy cell lines and increase the cell number in G(0)/G(1) phase. After treatment with EGCG for 48 hours, the methylation level was apparently attenuated in a concentration-dependent manner. Expression of p16 gene in untreated group was mild while in the treated groups it had been greatly strengthened, as compared with untreated group, the gray scale ratio of p16 to beta-actin 1 treated with EGCG (6, 12, 24) microg/ml was increased from (0.05 +/- 0. 01) to (0.19 +/- 0.03), (0.39 +/- 0.10), (0.85 +/- 0.09) respectively, exhibiting a significant difference (p < 0.05); as compared with the untreated group, after treatment with EGCG for 48 hours, the expressions of DNMT3A and DNMT3B were obviously down-regulated. It is concluded that EGCG can activate and up-regulate the expression of p16 gene mRNA which inhibits the proliferation of CA46 cell through inducing the G(0)/G(1) arrest by demethylation and/or by inhibiting DNMT3A and DNMT3B gene.

[Detection of p16 gene methylation status in adult patients with acute leukemia by using n-MSP].

The study was aimed to explore the relationship between patterns of methylation or deletion and the development of acute leukemia, and further to clarify the possible mechanism in the development of adult acute leukemia. Nested methylation-specific polymerase chain reaction (n-MSP) was adopted to analyze p16 gene methylation or deletion patterns in 82 adult acute leukemia patients with different subtypes and stages. The results indicated that rate of p16 gene methylation was 39.0% in 82 adult acute leukemia patients, among them, 41.4% in acute myelogenous leukemia (AML) and 33.3% in acute lymphoblastic leukemia (ALL). It were found that 36.6% of de novo AL patients and 54.5% of relapsed AL patients developed the hypermethylation of p16 gene. Out of the 82 patients, 6 seemed to have deletion of p16 gene, including 1 AML (1.7%) and 5 ALL (20.8%). There were no hypermethylation or deletion of p16 gene in the 16 controls. It is concluded that methylation of p16 gene may play a more important role than homozygous deletion of p16 gene in the leukemogenesis and progression of adult acute leukemia.