p16/MTS1/INK4A gene is frequently inactivated by hypermethylation in childhood acute lymphoblastic leukemia with 11q23 translocation

The p16 gene encoding a specific inhibitor of cyclin-dependent kinases 4 an d 6 has been reported to be inactivated at a variety of rates in malignant tumors. We studied frequency and mechanism of inactivation of the p16 gene in various types of childhood acute lymphoblastic leukemia (ALL) using 36 l eukemic cell lines established from children (B precursor-ALL, 28; B-ALL/Bu rkitt's lymphoma, 3; and T-ALL, 5). On Southern blot, homozygous deletions or hemizygous deletions with rearrangement were detected in 14 cell lines. The expression of p16 protein was not observed on Western blot in 18 of 22 cell lines with intact p16 gene, but induced in 16 cell lines after treatme nt with the demethylating agent, indicating the silencing of the p16 gene b y hypermethylation. Of note, the p16 gene was inactivated by hypermethylati on of the 5' CpG island in nine of nine cell lines with 11q23 translocation , but was restored with the treatment of the demethylating agent. Partial m ethylation of the p16 gene was also demonstrated in three of eight primary leukemia samples with this translocation, suggesting that the p16 gene inac tivation by hypermethylation might play a role in the leukemogenesis and di sease progression of ALL with 11q23 translocation.