CpG island promoter hypermethylation of the Ras-effector gene NORE1A occurs in the context of a wild-type K-ras in lung cancer.
Imbalance of the Ras signaling pathway is a major hallmark of human cancer. In this context, activating point mutations of the K-ras oncogene are a common feature of many tumor types. The discovery of methylation-mediated silencing of the Ras-effector homologue RASSF1A has revealed another way by which this cellular pathway may be altered. Inactivation by hypermethylation of a RASSF1A homologue, NORE1A, has recently been observed in human cancers. If both K-ras and NORE1A act in the same pathway, simultaneous molecular lesions in the two genes in the same tumor should be a rare event. To test whether this inverse association exists, we have analysed the K-ras mutational status and NORE1A CpG island hypermethylation of 61 non-small-cell lung carcinomas and the methylation status of the two other Ras effectors, RASSF1A and HRASLS. No association was found between the methylation status of NORE1A, RASSF1A and HRASLS or the status of K-ras with respect to the latter two genes. However, our results demonstrate that the epigenetic alteration of NORE1A is confined to lung tumors with a wild-type K-ras: 88% (15 of 17) of the tumors with NORE1 hypermethylation did not harbor a K-ras mutation (P=0.008, Fisher's exact test). Thus, the mutual exclusivity of the epigenetic and genetic alterations in the two genes of the Ras pathway suggests that they play a critical and cooperative role in human tumorigenesis.
Irimia
Manuel
M
Molecular Pathology Program, Cancer Epigenetics Laboratory, Spanish National Cancer Centre (CNIO), Melchor Fernandez Almagro 3, Madrid 28029, Spain.
Fraga
Mario F
MF
Sanchez-Cespedes
Montserrat
M
Esteller
Manel
M
D048868:Adaptor Proteins, Signal Transducing; D051017:Apoptosis Regulatory Proteins; D001483:Base Sequence; D018899:CpG Islands / Q000235:genetics*; D019175:DNA Methylation; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008175:Lung Neoplasms / Q000235:genetics* / Q000378:metabolism; D020559:Monomeric GTP-Binding Proteins / Q000235:genetics*; D009154:Mutation / Q000235:genetics; D010741:Phospholipases A; D011401:Promoter Regions, Genetic / Q000235:genetics*; D011506:Proteins / Q000235:genetics; D016283:Proto-Oncogene Proteins p21(ras) / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D025521:Tumor Suppressor Proteins / Q000235:genetics
D048868:Adaptor Proteins, Signal Transducing; D051017:Apoptosis Regulatory Proteins; D011506:Proteins; C411762:RASSF1 protein, human; C454042:RASSF5 protein, human; D025521:Tumor Suppressor Proteins; C433809:PLAAT1 protein, human; D010741:Phospholipases A; C501009:HRAS protein, human; D020559:Monomeric GTP-Binding Proteins; D016283:Proto-Oncogene Proteins p21(ras)