Variable Expression and Hypermethylation of p16 Gene in Patients with T-ALL and Cell Lines

The multi tumor suppressor genes MTS1 (CDKN2, p16INK4A) and MTS2 (CDKN1, p15INK4B) located at 9p21-22 are inactivated in some human cancers via several mechanisms including deletion and hypermethylation. In hematological malignancies, deletion of p16/p15 locus has been shown to be highly specific to lymphoid malignancies, and more particularly to T-cell acute lymphoblastic leukemia (TALL). We have investigated the deletion, methylation and p16 protein expression status of MTS1 in Tcell childhood acute lymphoblastic leukemia (19 cases) and cell lines[11]. On Southern blot homozygous deletions or hemizygous deletion with rearangement were detected in 4/19 T-ALL. The expression of p16 protein was not observed on Western blot in 4/15 T-ALL with intact p16 gene. The p16 gene was methylated 3/15 in T-ALL. Only one of three expressed p16 protein. The other 11/15 T-ALL had p16 protein expression but different level. Loss of MTS1 was observed in 3/11 cell lines. Cell line with MTS1 gene had p16 protein expression in 6/8. After treatment with the demethylating agent (5-AzoCyt) RD cell line showed p16 expression. This has not been observed with the other cell lines. Thus hypermethylation of MTS1 is rare in childhood T-ALL. Although inactivation of MTS1 by deletion is common in T-ALL and cell lines. Furthermore our data show that the p16 gene inactivation by hypermethylation and deletion may play a role in the leukemogenesis.