CpG island promoter hypermethylation of a novel Ras-effector gene RASSF2A is an early event in colon carcinogenesis and correlates inversely with K-ras mutations

Oncogene. 2005 Jun 2;24(24):3987-94. doi: 10.1038/sj.onc.1208566.


We report in silico identification and characterisation of a novel member of the ras association domain family 1 (RASSF1)/NORE1 family, namely, RASSF2, located at chromosomal region 20p13. It has three isoforms, all contain a ras association domain in the C-terminus. The longest isoform RASSF2A contains a 5' CpG island. RASSF2A was cloned from a brain cDNA library and directly sequenced, confirming the genomic gene structure. In previous reports, we and others have demonstrated that RASSF1A is epigenetically inactivated in a variety of cancers, including sporadic colorectal cancer (CRC). In the present report, we analysed the methylation status of RASSF2A promoter region CpG island in sporadic CRC and compared it to K-ras mutation status. RASSF2A promoter region CpG island was hypermethylated in a majority of colorectal tumour cell lines (89%) and in primary colorectal tumours (70%), while DNA from matched normal mucosa was found to be unmethylated (tumour-specific methylation). RASSF2A expression was reactivated in methylated tumour cell lines after treatment with 5-aza 2-deoxycytidine. RASSF2A methylation is an early event, detectable in 7/8 colon adenomas. Furthermore, 75% of colorectal tumours with RASSF2A methylation had no K-ras mutations (codons, 12 and 13) (P=0.048), Fisher's exact test). Our data demonstrate that RASSF2A is frequently inactivated in CRCs by CpG island promoter hypermethylation, and that epigenetic (RASSF2A) and genetic (K-ras) changes are mutually exclusive and provide alternative pathways for affecting Ras signalling.

MeSH terms

  • Base Sequence
  • Brain / physiology
  • Cell Line, Tumor
  • Cloning, Molecular
  • Colonic Neoplasms / genetics*
  • Colonic Neoplasms / pathology
  • Colorectal Neoplasms / genetics
  • Colorectal Neoplasms / pathology
  • DNA Primers
  • Female
  • Gene Expression Regulation, Neoplastic*
  • Gene Library
  • Humans
  • Male
  • Mutation*
  • Neoplasm Staging
  • Promoter Regions, Genetic*
  • Proteins / genetics*
  • Sulfites / pharmacology
  • Tumor Suppressor Proteins


  • DNA Primers
  • Proteins
  • RASSF2 protein, human
  • Sulfites
  • Tumor Suppressor Proteins
  • sodium bisulfite