Frequent Methylation Silencing of P15(INK4b) (MTS2) and P16(INK4a) (MTS1) in B-cell and T-cell Lymphomas

The methylation status of p15(INK4b) (MTS2), p16(INK4a) (MTS1) and p14(ARF) (p16beta) was analyzed in 56 lymphomas by restriction-enzyme related polymerase chain reaction (PCR) (REP), methylation-specific PCR (MSP), and bisulfite genomic sequencing (BGS). Methylation of the p15 and p16 genes was detected, respectively, in 64% and 32% of the B-cell lymphomas, in 44% and 22% of the T-cell lymphomas, and in none of the 5 reactive lymph nodes analyzed. Both p15 and p16 genes were methylated more often in the high-grade (78% and 50%, respectively) than in the low-grade B-cell lymphomas (55% and 21%, respectively). For 5 cases, mapping of the methylated CpGs of the p16 promoter region confirmed the results of REP and MSP. In addition, a large variation in the methylation patterns of p16 exon 1 was observed, not only from one lymphoma to another, but also within a given tumor. Methylation of p15 and p16 was associated with an absence of gene expression, as assessed by reverse transcription-PCR. The p14 gene was unmethylated and normally expressed in all 56 tumors. We found no mutations of p15, p16, or p14 in any of the 56 lymphomas. Our results suggest a role for p15 and p16 gene methylation during lymphomagenesis and a possible association between p15 and p16 inactivation and aggressive transformation in B-cell and T-cell lymphomas.