p14^ARF,p15^INK4b, and p16^INK4amethylation status in chronic myelogenous leukemia

The promoters of the p16^INK4aand p15^INK4b genes located at chromosome band 9p21 are frequently silenced by CpG island methylation in hematologic malignancies and solid tumors.1 In chronic myelogenous leukemia (CML) the situation is confused because 2 reports have produced contradictory results on p15^INK4bmethylation, possibly because of the sensitivity of the techniques used for these studies. By use of restriction endonuclease–based Southern blot, methylation of the 5′ region of p15^INK4bwas not detected on 21 samples in contrast to other leukemia types.2 In another study with the more sensitive methylation-specific polymerase chain reaction (MSP) technique, methylation of p15^INK4b was detected in 24% (8/34) of CML cases and was associated with progression.3 

In the present report, we used MSP4 to study p15^INK4b- andp16^INK4a-promoter hypermethylation status in 76 cases of CML at various phases of the disease: chronic (50), accelerated (11), myeloblastic transformation (5), and complete cytogenetic remission (10) upon interferon-base regimen5 or imatinib treatment.6 In addition, we tested p14^ARF promoter methylation, as this study has not been described yet.

Partial p15^INK4b hypermethylation was found for 4 patients (5%), 2 in chronic phase and 2 in blast crisis (patients 11, 12, 15, and 19 in Figure 1), consistent with previous data on a smaller series.2 In all cases, the intensity of the unmethylated bands greatly exceeded that of methylated ones. While the technique is only semiquantitative, this suggests that only a minor part of the leukemic cells was implicated in the hypermethylation process. Patient 19 in myeloid transformation showed slight hypermethylation of thep14^ARF promoter (Figure 1). For all the other patients, the p14^ARF promoter was unmethylated. The p16^INK4a promoter was found unmethylated for all patients (not shown), again in agreement with Herman et al's data.2 

On the basis of these data, negative regulation by hypermethylation of p14^ARF,p15^INK4b, and p16^INK4a,which contributes to the cell cycle, does not appear to be a frequent inactivating event in CML. This is in contrast with other hematopoietic malignancies, particularly acute myelogenous leukemia (AML), in which p15^INK4bhypermethylation is frequent.8 Perhaps more interestingly, in myelodysplastic syndromes hypermethylation ofp15^INK4b has been reported to increase with the phase of the disease.9 

Supported by Association pour la Recherche Contre le Cancer et Ligue Nationale Contre le Cancer.