Aberrant promoter methylation and silencing of the RASSF1A gene in pediatric tumors and cell lines

Aberrant promoter methylation of tumor suppressor genes has not been fully investigated in pediatric tumors. Therefore, we examined the methylation status of nine genes (p16(Ink4a), MGMT, GSTP1, RASSF1A, APC, DAPK, RARbeta, CDH1 and CDH13) in 175 primary pediatric tumors and 23 tumor cell lines using methylation-specific PCR. We studied the major forms of pediatric tumors - Wilms' tumor, neuroblastoma, hepatoblastoma, medulloblastoma, rhabdomyosarcoma, osteosarcoma, Ewing's sarcoma, retinoblastoma and acute leukemia. The most frequently methylated gene in both primary tumors and cell lines was RASSF1A (40, 86%, respectively). However, the rates of RASSF1A methylation in individual tumor types varied from 0 to 88%. RASSF1A methylation was tumor specific and was absent in adjacent non-malignant tissues. Methylation of the other genes was relatively rare in tumors and nonmalignant tissues (less than 5%). Neuroblastoma patients with methylation of RASSF1A were significantly older than patients without methylation (P=0.008). There was no relationship between methylation status and other clinico-pathologic parameters. We treated six cell lines lacking RASSF1A mRNA with 5-aza-2'deoxycytidine to examine the relationship between methylation and transcriptional silencing. In five of six cell lines, restoration of RASSF1A mRNA was confirmed by RT-PCR. Our findings indicate that aberrant promoter methylation of RASSF1A may contribute to the pathogenesis of many different forms of pediatric tumors.