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Biochem Pharmacol. 2014 Jun 1;89(3):361-9. doi: 10.1016/j.bcp.2014.03.008. Epub 2014 Mar 26.

Constitutive activation of the ATM/BRCA1 pathway prevents DNA damage-induced apoptosis in 5-azacytidine-resistant cell lines.

Author information

1
Institute for Medical Science, Tokyo Medical University, 6-7-1 Nishi-shinjuku, Shinjuku, Tokyo 160-0023, Japan. Electronic address: s-ima@tokyo-med.ac.jp.
2
Institute for Medical Science, Tokyo Medical University, 6-7-1 Nishi-shinjuku, Shinjuku, Tokyo 160-0023, Japan; Department of Molecular Science, Tokyo Medical University, 6-7-1 Nishi-shinjuku, Shinjuku, Tokyo 160-0023, Japan.
3
Institute for Medical Science, Tokyo Medical University, 6-7-1 Nishi-shinjuku, Shinjuku, Tokyo 160-0023, Japan; First Department of Internal Medicine, Tokyo Medical University, 6-7-1 Nishi-shinjuku, Shinjuku, Tokyo 160-0023, Japan.
4
First Department of Internal Medicine, Tokyo Medical University, 6-7-1 Nishi-shinjuku, Shinjuku, Tokyo 160-0023, Japan.
5
Institute for Medical Science, Tokyo Medical University, 6-7-1 Nishi-shinjuku, Shinjuku, Tokyo 160-0023, Japan.

Abstract

5-Azacytidine (AZA) exerts its anti-tumor effects by exerting cytotoxicity via its incorporation into RNA and DNA, which causes the reactivation of aberrantly silenced growth-regulatory genes by promoter demethylation, as well as DNA damage. AZA is used for patients with myelodysplastic syndrome and acute myeloid leukemia. However, some patients demonstrate resistance to AZA, the mechanisms of which are not fully elucidated. We therefore sought to better characterize the molecular mechanism of AZA resistance using an in vitro model of AZA resistance. We established AZA-resistant cell lines by exposing the human leukemia cell lines U937 and HL-60 to clinical concentrations of AZA, and characterized these cells. AZA-resistant cells showed a down-regulation of the DNMT3A protein, in correlation with their marked genome-wide DNA hypomethylation. Furthermore, genes involved in pyrimidine metabolism were down-regulated in both AZA-resistant cell lines; AZA sensitivity was restored by inhibition of CTP synthase. Of note is that the DNA damage response pathway is constitutively activated in the AZA-resistant cell lines, but not in the parental cell lines. Inhibition of the DNA damage response pathway canceled the AZA resistance, in association with an increase in apoptotic cells. We found that the molecular mechanism underlying AZA resistance involves pyrimidine metabolism and the DNA damage response through ATM kinase. This study therefore sheds light on the mechanisms underlying AZA resistance, and will enable better understanding of AZA resistance in patients undergoing AZA treatment.

KEYWORDS:

2-desoxy-5-azacytidine (PubChem CID: 451668); 3-deazauridine (PubChem CID: 3000824); 5-Azacytidine; 5-Azacytidine (PubChem CID: 9444); DNA damage; DNA demethylation; KU55933 (PubChem CID: 5278396); RG108 (PubChem CID: 702558); caffeine (PubChem CID: 2519); cisplatin (PubChem CID: 441203); etoposide (PubChem CID: 36462); mitomycin C (PubChem CID: 5746)

PMID:
24680865
DOI:
10.1016/j.bcp.2014.03.008
[Indexed for MEDLINE]
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