Alterations of the p53, p21, p16, p15 and RAS genes in childhood T-cell acute lymphoblastic leukemia

We investigated the alterations of the p53, p21, p16, p15 and RAS genes in childhood T-cell acute lymphoblastic leukemia (T-ALL) and T-ALL cell lines by polymerase chain reaction-single strand conformation polymorphism (PCR-S SCP) analysis and direct sequencing. Mutations of the p53 gene were found i n three of 57 (5%) patients at diagnosis, one of 14 (7%) patients at relaps e and in 12 of 18 (67%) cell lines. In these 12 cell lines, four had more t han two mutations of the p53 gene. The p53 mutations were found in four of five cell lines whose original fresh leukemic cells were simultaneously exa mined original fresh leukemic cells. However, only one of the four fresh le ukemic cells had the same mutation. All patients with p53 mutations in the course of disease died. Mutations of the p21 gene were not identified in 71 fresh samples and in 18 cell lines. N-RAS mutations were found in two of 5 7 (4%) fresh T-ALL patients at diagnosis, and four of 18 cell lines (22%), whereas no mutations were detected in any samples at relapse. Alterations o f the p16 gene were found in 18 of 47 (38%) patients at diagnosis and in se ven of 14 (50%) at relapse. These differences were not statistically signif icant. There were no differences in the frequency of alteration of the p16 and p15 genes between event-free patients and the remaining patients. Furth ermore, we found the methylation of p16 gene in three of seven patients lac king homozygous deletions, suggesting higher frequency of p16 inactivation than previous reports in T-ALL. Interestingly, we found that one allele is inactivated by methylation and another allele had nonsense mutation in one cell line (KOPT-K1), resulting in loss of protein expression of p16. This t ype of p16 inactivation has not been so far reported in leukemia. We conclu de that, (1) p53 mutations are infrequent at diagnosis but tend to be assoc iated with poor clinical outcome; (2) RAS and p21 mutations may not be invo lved in the pathogenesis of T-ALL; (3) not only frequent alterations of p16 and p15 genes but also methylation of p16 gene are involved in initiating the leukemogenesis of T-ALLs, and (4) these 5 genes are independently invol ved in T-ALL. (C) 1999 Elsevier Science Ltd. All rights reserved.