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.
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.
Hesson
Luke B
LB
Section of Medical and Molecular Genetics, Division of Reproductive and Child Health, Institute of Biomedical Research, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK.
Wilson
Robin
R
Morton
Dion
D
Adams
Clare
C
Walker
Mike
M
Maher
Eamonn R
ER
Latif
Farida
F
D001483:Base Sequence; D001921:Brain / Q000502:physiology; D045744:Cell Line, Tumor; D003001:Cloning, Molecular; D003110:Colonic Neoplasms / Q000235:genetics* / Q000473:pathology; D015179:Colorectal Neoplasms / Q000235:genetics / Q000473:pathology; D017931:DNA Primers; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D015723:Gene Library; D006801:Humans; D008297:Male; D009154:Mutation; D009367:Neoplasm Staging; D011401:Promoter Regions, Genetic; D011506:Proteins / Q000235:genetics*; D013447:Sulfites / Q000494:pharmacology; D025521:Tumor Suppressor Proteins
D017931:DNA Primers; D011506:Proteins; C425300:RASSF2 protein, human; D013447:Sulfites; D025521:Tumor Suppressor Proteins; C009279:sodium bisulfite