Methylation of the p15INK4b Gene in Myelodysplastic Syndromes Is Frequent and Acquired During Disease Progression

Abstract

p15INK4b gene is an inhibitor of cyclin-dependent kinase (CDK) 4 and CDK6 whose expression is induced by transforming growth factor (TGF)β. Recent reports suggest frequent methylation of the p15INK4b gene promoter in leukemias, and it has been proposed that this methylation could be necessary for leukemic cells to escape TGFβ regulation. We investigated the methylation status of p15INK4b gene in 53 myelodysplastic syndromes (MDS) cases, including nine that had progressed to acute myeloid leukemia (AML), using a recently described sensitive method where polymerase chain reaction (PCR) is preceded by bisulfite modification of DNA (methylation specific PCR). p15INK4b methylation was observed in 20 of 53 (38%) of the cases. Twenty of the 24 patients with greater than 10% bone marrow blasts had p15INK4bmethylation (including all nine patients who had progressed to AML) as compared with none of MDS patients with <10% bone marrow blasts. No correlation between karyotypic abnormalities and methylation status was found. Patients with p15INK4b methylation had a worse prognosis, but the prognostic significance of p15INK4bmethylation was no more found by multivariate analysis, due to its strong correlation to the percentage of marrow blasts. In 10 MDS cases, sequential DNA samples were available. In five of them, methylation of the p15INK4b gene was detected at leukemic transformation, but not at diagnosis. Our results showed that methylation of the p15INK4b gene in MDS is correlated with blastic bone marrow involvement and increases with disease evolution toward AML. It suggests that proliferation of leukemic cells might require an escape of regulation of the G1 phase of the cell cycle, and possibly of TGFβ inhibitory effect.