Down-regulation of p21 (CDKN1A/CIP1) is inversely associated with microsatellite instability and CpG island methylator phenotype (CIMP) in colorectal cancer

• Published in: The Journal of pathology 2006-10, Vol.210 (2), p.147-154
• Main Authors: Ogino, S, Kawasaki, T, Kirkner, GJ, Ogawa, A, Dorfman, I, Loda, M, Fuchs, CS
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; BRAF; CIMP; colon cancer; Colorectal Neoplasms - genetics; Colorectal Neoplasms - metabolism; CpG Islands - genetics; Cyclin-Dependent Kinase Inhibitor p21 - metabolism; Databases as Topic; DNA Methylation; Down-Regulation; Female; Gastroenterology. Liver. Pancreas. Abdomen; Gene Expression Regulation, Neoplastic - genetics; Humans; Investigative techniques, diagnostic techniques (general aspects); KRAS; Male; Medical sciences; MethyLight; Microsatellite Instability; MSI; Mutation; p21; p53; Pathology. Cytology. Biochemistry. Spectrometry. Miscellaneous investigative techniques; Polymerase Chain Reaction - methods; Prospective Studies; Protein Array Analysis - methods; Proto-Oncogene Proteins - genetics; Proto-Oncogene Proteins B-raf - genetics; Proto-Oncogene Proteins p21(ras); ras Proteins - genetics; Stomach. Duodenum. Small intestine. Colon. Rectum. Anus; Tumor Suppressor Protein p53 - metabolism; Tumors; WAF1
• ISSN: 0022-3417; 1096-9896
• DOI: 10.1002/path.2030

p21 (CDKN1A/CIP1/WAF1), one of the cyclin‐dependent kinase inhibitors, plays a key role in regulating the cell cycle and is transcriptionally regulated by p53. Down‐regulation of p21 is caused by TP53 mutations in colorectal cancer. CpG island methylator phenotype (CIMP) appears to be a distinct subtype of colorectal cancer with concordant methylation of multiple gene promoters and is associated with a high degree of microsatellite instability (MSI‐H) and BRAF mutations. However, no study to date has evaluated the relationship between p21 expression and CIMP in colorectal cancer. The purpose of this study was to examine the inter‐relationships between p21, p53, CIMP, MSI and KRAS/BRAF status in colorectal cancer. We utilized 737 relatively unbiased samples of colorectal cancers from two large prospective cohort studies. Using quantitative real‐time PCR (MethyLight), we measured DNA methylation in five CIMP‐specific gene promoters [CACNA1G, CDKN2A (p16/INK4A), CRABP1, MLH1 and NEUROG1]. CIMP‐high (≥4/5 methylated promoters) was diagnosed in 118 (16%) of the 737 tumours. We also assessed expression of p21 and p53 by immunohistochemistry. Among the 737 tumours, 371 (50%) showed p21 loss. Both p21 loss and p53 positivity were inversely associated with CIMP‐high, MSI‐H and BRAF mutations. The associations of p21 with these molecular features were still present after tumours were stratified by p53 status. In contrast, the associations of p53 positivity with the molecular features were no longer present after tumours were stratified by p21 status. When CIMP‐high and non‐CIMP‐high tumours were stratified by MSI or KRAS/BRAF status, CIMP‐high and MSI‐H (but not BRAF mutations) were still inversely associated with p21 loss. In conclusion, down‐regulation of p21 is inversely correlated with CIMP‐high and MSI‐H in colorectal cancer, independent of TP53 and BRAF status. Copyright © 2006 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.