| Myelodysplastic syndromes (MDS) are clonal stem cell disorders and they can be divided into two groups based on the clinical prognosis: low-risk MDS [refractory anemia (RA) and RA with ring sideroblasts (RAS)] and high-risk MDS [RA with excess of blasts (RAEB) and RAEB in transformation (RAEB-t)]. Recently, there are a few reports abroad and at home about that the p15INK4B gene inactivation may play an important role in the pathogenesis of MDS and during disease progression. The p15INK4B protein is a cell cycle regulator involved in the inhibitation of GI phase progression. It associates with cyclin-dependent kinase (CDK) 4 and CDK 6, and inhibits their kinase activities. Hypermethylation in CpG islands of the p15INK4B promoter region seems to be an important way in resulting gene silencing. The DNA methylation is catalyzed by C5 DNA methyltransferases (DNMTS), including DNMT,, DNMT3A, and DNMT3B, which transfer methyl groups proved by S-adenosylmethionine (SAM) to the carbon-5 position of cytosine. Hypermethylation of genes has a tendency to show significantly high expressivelevels of DNMTS. There are a few reports abroad about that the up-regulated DNMTS might contribute to the pathogenesis of acute myeloid leukemia (AML) by inducing aberrant regional hypermethylation of suppressor genes, which has yet not been reported in MDS.Arsenic trioxide (AS2O3) is the chief compound of "Ailing 1', which is a kind of traditional Chinese agent. The drug has been found to be effective in the treatment of acute promyelocytic leukemia (APL), especially in the treatment of relapsed and refractory APL. It has been reported that AS2O3 can inhibit the growth of some tumor cells in vitro by inducing apoptosis and differentiation, down-regulating of telomerase activity and inhibiting of angiogenesis. Since AS2O3 is detoxified via methylation and it consumes methyl groups that deplete the SAM methyl donor pool. The lack of methyl groups would result in inability to properly maintain methylate cytosine in DNA. It has been reported that AS2O3 can alter methylation patterns of the promoter of the tumor suppressor gene p53 in human lung cells.There is no report about AS2O3's antitumor effects on myelodysplasia cells. In this study, we tried to explode the p15TNK4B gene methylation status in myelodysplasia cells to verify the role of methylation as a gene-silencing mechanism involved in the pathogenesis of MDS, and to elucidate the antitumor mechanisms of AS2O3 in myelodysplasia cells in order to expend the train of thought of the clinical application of AS2O3 in MDS and to some extent, to provide a theoretical and experimental basis for designing new antitumor strategies.We studied the mononuclear cells (MNCs) from bone marrow of 20 cases of MDS by RT-PCR, Western blot, and methylation specific PCR (MSP). Twenty cases of acute leukemia (AL) were studied as positive controls. Of the 40 patients, 10 cases were low-risk MDS, 10 cases were high-risk MDS, 10 cases were acute myeloid leukemia (AML), and 10 cases were acute lymphocytic leukemia (ALL). Ten normal persons were studied as nective controls. The results showed that the incidence of p!5INK4B methylation in cells of high-risk MDS was higher than that in low-risk MDS (60% VS 10%), and the p15INK4B methylation was found to be associated with the down-regulation of the expressions of p15INK4B gene on both mRNA and protein levels, which indicated that the silencing of p15INK4B gene was in conjunction withhypermethylation in MDS. The expressions of p15INK4B on mRNA level and protein levels were almost detected in the MNCs from bone marrow of normal persons without the p15INK4B methylation. We also found high-risk myelodysplasia cells with methylated p15INK4B tended to express high levels of DNA methyltransferases DNMT3A and DNMT3B. The expression level of DNMT] was higher in both low-risk and high-risk MDS, which indicated up-regulated DNMTS might contribute to the hypermethylation of p15INK4B, and the higher expressions of de novo methyltransferases DNMT3A and...
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