Raf kinase inhibitor protein: mechanism of loss of expression and association with genomic instability.
OBJECTIVE
Raf kinase inhibitory protein (RKIP; also known as PEBP, for phosphatidylethanolamine-binding protein) is an endogenous inhibitor of the Raf- MAPK kinase (MEK)-MAP kinase pathway. It has emerged as a significant metastasis suppressor in a variety of human cancers including colorectal cancer (CRC) and was recently shown to regulate the spindle checkpoint in cultured cells. This study aims at correlating RKIP expression with chromosomal instability in colorectal cancer samples and identifies possible mechanisms of RKIP loss.


METHODS
Chromosomal instability was assessed using metaphase-based comparative genomic hybridisation (CGH) and loss of heterozygosity (LOH) in 65 cases with microsatellite stable CRC and correlated with RKIP expression. Methyl-specific PCR was used on DNA extracted from 82 cases with CRC to determine CpG methylation status at the RKIP promoter and the results correlated with RKIP protein expression.


RESULTS
We demonstrate for the first time that in microsatellite stable (MSS) CRC, the number of chromosomal losses is inversely proportional to RKIP expression levels. We also show that methylation of the RKIP promoter is a major mechanism by which RKIP expression is silenced in CRC.


CONCLUSIONS
RKIP loss by hypermethylation of its promoter could have a significant influence on colorectal cancer aneuploidy, which might explain its association with metastatic progression.
Al-Mulla
F
F
Department of Pathology, Molecular Pathology Unit, Faculty of Medicine, Kuwait University, Kuwait. fahd@al-mulla.org
Hagan
S
S
Al-Ali
W
W
Jacob
S P
SP
Behbehani
A I
AI
Bitar
M S
MS
Dallol
A
A
Kolch
W
W
D000368:Aged; D015331:Cohort Studies; D015179:Colorectal Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D018899:CpG Islands / Q000235:genetics; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D042822:Genomic Instability; D006801:Humans; D007124:Immunoenzyme Techniques / Q000379:methods; D019656:Loss of Heterozygosity; D008297:Male; D008875:Middle Aged; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D009367:Neoplasm Staging; D009693:Nucleic Acid Hybridization / Q000379:methods; D049488:Phosphatidylethanolamine Binding Protein / Q000235:genetics / Q000378:metabolism*; D016133:Polymerase Chain Reaction / Q000379:methods; D011401:Promoter Regions, Genetic; D047428:Protein Kinase Inhibitors / Q000378:metabolism
D009363:Neoplasm Proteins; D049488:Phosphatidylethanolamine Binding Protein; D047428:Protein Kinase Inhibitors