Assessing of the methylation status of p15 and MGMT genes may allow stratification of patients with AML into distinct groups with potentially different prognosis.
Furthermore, two patients with PBC-ALL and 11 acute myeloblastic leukemia (AML) were quantitatively examined for p15 gene methylation using bisulfite genomic sequencing.
Methylation of E-cadherin and RARbeta occurs preferentially in AMLs with high methylation index (MI), while epigenetic lesions in SOCS1, DAP-kinase, and p15 appear to be independent.
At diagnosis, p15 methylation occurred in 29 (58%) AML patients, and 10 (40.0%) ALL patients. p16 methylation occurred in two (4%) AML and two (8%) ALL patients.
At presentation, 93 % of cases of AML (8 of 8 M1, 10 of 11 M2, 2 of 2 M4, 5 of 6 M5, and 2 of 2 M6; French-American-British classification system) showed p15 methylation, but none showed p16 methylation.
These results revealed the frequent methylation of p16 and p15 genes in B-ALL and AML despite a low frequency of p16 and p15 deletions and mutations in these leukemias.
We also demonstrated for the first time concomitant p16 and p15 methylation in 22% (8/37) of adults with AML or ALL, exclusively in those with M2, M4, or L2 subtypes.
Furthermore, bisulfite sequencing revealed that the p15 CpG island is heterogeneously methylated in AML, with large intra-individual and inter-individual variability.
We identified homozygous deletion of p16 and p15 genes in five (19%) of 27 acute lymphoblastic leukemias (ALLs) and in two (11%) of 19 acute myeloid leukemias (AMLs).
In order to determine whether these genes are more widely involved in haematological malignancies, we have investigated a total of 84 samples that did not have homozygous p16 or p15 deletions from patients with acute lymphoid leukaemia (n=13), acute myeloid leukaemia (n=24) and chronic myeloid leukaemia in blast crisis (n=43) as well as four haemopoietic cell lines. p15 and p16 exon 1 and exon 2 were amplified by polymerase chain reaction (PCR), analysed by single-stranded conformation polymorphism (SSCP) and subsequently by sequencing.
We have examined the genomic status of two recently isolated p16-related CDK inhibitors, p15 and p18, in 15 normal and 73 tumor-derived cell lines established from 23 different tissues, as well as 26 invasive primary breast cancers and 20 acute myelogenous leukemias. p15 was found to be homozygously deleted in 22% of the tumor derived cell lines, but no point mutations were found in either the cultured cells or the two types of primary tumors.
Alterations of the p16 or p15 gene only occurred in primary acute myeloid leukaemia samples that were of mixed myeloid/lymphoid lineage (CD19/CD20-positive acute myeloid leukaemia [AML], CD2/CD19-positive AML, and lymphoid blastic crisis of chronic myeloid leukaemia).