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Selective variegated methylation of the p15 CpG island in acute myeloid leukemia
J E Dodge1, A F List, B W Futscher
1Department of Pharmacology and Toxicology, University of Arizona, Tucson, USA.
Abstract:
Both p15 and p16 are tumor suppressor genes that have 5' CpG islands; aberrant cytosine methylation of these islands has been associated with silencing of their expression. Deoxycytidine kinase (dCK) converts prodrugs to their cytotoxic form, has a 5' CpG island and is a candidate gene for inactivation by hypermethylation. In our study, we used sodium bisulfite sequencing to generate high resolution maps of 5-methylcytosine in the CpG islands associated with p15, p16 and dCK in normal human bone marrow (BM), peripheral blood lymphocytes (PBL) and cytosine arabinoside (ara-C)-resistant acute myeloid leukemia (AML) patients, and established human hematopoietic tumor cell lines. In normal cells the p15, p16 and dCK CpG islands were largely unmethylated. The p16 and dCK CpG islands were also unmethylated in the 8 AML specimens. In contrast, the p15 CpG island was aberrantly methylated in 6 of the 8 AML specimens. Furthermore, bisulfite sequencing revealed that the p15 CpG island is heterogeneously methylated in AML, with large intra-individual and inter-individual variability.
Insights
Aberrant methylation of the p15 tumor suppressor gene CpG island was observed in acute myeloid leukemia (AML) patients, unlike p16 and deoxycytidine kinase (dCK). This aberrant p15 methylation in AML shows significant variability.
Area of Science:
- Oncology
- Epigenetics
- Molecular Biology
Background:
- p15 and p16 are tumor suppressor genes with 5' CpG islands, susceptible to silencing via aberrant cytosine methylation.
- Deoxycytidine kinase (dCK) is crucial for prodrug activation and also possesses a 5' CpG island, making it a candidate for hypermethylation-induced inactivation.
Purpose of the Study:
- To investigate the methylation status of CpG islands in p15, p16, and dCK in normal hematopoietic cells, acute myeloid leukemia (AML), and related cell lines.
- To determine if hypermethylation contributes to gene silencing in AML, particularly for the p15 gene.
Main Methods:
- Sodium bisulfite sequencing was employed to create high-resolution maps of 5-methylcytosine.
- Analysis was performed on normal human bone marrow (BM), peripheral blood lymphocytes (PBL), ara-C-resistant AML specimens, and hematopoietic tumor cell lines.
Main Results:
- In normal BM and PBL, the CpG islands of p15, p16, and dCK were predominantly unmethylated.
- The p16 and dCK CpG islands remained unmethylated in the analyzed AML specimens.
- Aberrant methylation of the p15 CpG island was detected in 6 out of 8 AML specimens, exhibiting significant intra-individual and inter-individual heterogeneity.
Conclusions:
- Aberrant methylation of the p15 CpG island is a frequent event in AML, contrasting with p16 and dCK.
- The heterogeneous methylation pattern of p15 in AML suggests complex regulatory mechanisms and potential variability in gene silencing.