De novo methylation of tumor suppressor gene p16/INK4a is a frequent finding in multiple myeloma patients at diagnosis

The p16 gene competes with cyclin D for binding to CDK4/CDK6 and therefore inhibits CDK4/6 complex kinase activity, resulting in dephosphorylation of pRb and related GI growth arrest. Inactivation of this gene has been involv ed in a variety of tumors by different mechanisms: homozygous/hemyzygous de letions, point mutations and methylation of a 5' CpG island into exon E1 al pha of the p16 gene. Homozygous deletions have been rarely found in multipl e myeloma (MM) and no point mutations have been reported. Two recent studie s have reported a high prevalence of methylation in the exon E1 alpha of th e p16 gene, but included only a small number of cases. We have analyzed the methylation pattern of exon E1 alpha of the pie gene in 101 untreated MM a nd five primary plasma cell leukemias (PCL). A PCR assay, relying on the in ability of some restriction enzymes to digest methylated sequences, was use d to analyze the methylation status. Southern blot analysis was used to con firm these results. Forty-one of 101 MM patients (40.5%) as well as four of the five (80%) primary PCL patients had shown methylation of the exon E1 a lpha. Our study confirms that hypermethylation of the pie gene is a frequen t event in MM.