The class III histone deacetylase SIRT1 (sir2) is important in epigenetic gene silencing. Inhibition of SIRT1 reactivates silenced genes, suggesting a possible therapeutic approach of targeted reversal of aberrantly silenced genes. In addition, SIRT1 may be involved in the well-known link between obesity, cellular energy balance and cancer. However, a comprehensive study of SIRT1 using human cancer tissue with clinical outcome data is currently lacking, and its prognostic significance is uncertain. Using the database of 485 colorectal cancers in two independent prospective cohort studies, we detected SIRT1 overexpression in 180 (37%) tumors by immunohistochemistry. We examined its relationship to the CpG island methylator phenotype (CIMP), related molecular events, clinical features including body mass index, and patient survival. We quantified DNA methylation in eight CIMP-specific promoters (CACNA1G, CDKN2A, CRABP1, IGF2, MLH1, NEUROG1, RUNX3, and SOCS1) and eight other CpG islands (CHFR, HIC1, IGFBP3, MGMT, MINT1, MINT31, p14, and WRN) by MethyLight. SIRT1 overexpression was associated with CIMP-high (6 of 8 methylated CIMP-specific promoters, P0.002) and microsatellite instability (MSI)-high phenotype (P0.0001). In both univariate and multivariate analyses, SIRT1 overexpression was significantly associated with the CIMP-high MSI-high phenotype (multivariate odds ratio, 3.20; 95% confidence interval, 1.35-7.59; P0.008). In addition, mucinous component (P0.01), high tumor grade (P0.02), and fatty acid synthase overexpression (P0.04) were significantly associated with SIRT positivity in multivariate analysis. SIRT1 was not significantly related with age, sex, tumor location, stage, signet ring cells, cyclooxygenase-2 (COX-2), LINE-1 hypomethylation, KRAS, BRAF, BMI, PIK3CA, HDAC, p53, Β-catenin, COX-2, or patient prognosis. In conclusion, SIRT1 expression is associated with CIMP-high MSI-high colon cancer, suggesting involvement of SIRT1 in gene silencing in this unique tumor subtype.
Bibliographical noteFunding Information:
We thank the Nurses’ Health Study and Health Professionals Follow-up Study cohort participants who generously agreed to provide us with biological specimens and information through responses to questionnaires. We also thank Frank Speizer, Walter Willett, Susan Hankinson, Graham Colditz, Meir Stampfer, and many other staff members who implemented and have maintained the cohort studies. This work was supported by US National Institute of Health (NIH) grants P01 CA87969, P01 CA55075, P50 CA127003 (to CSF) and K07 CA122826 (to SO), and in part by grants from the Bennett Family Fund and from the Entertainment Industry Foundation through the National Colorectal Cancer Research Alliance (NCCRA). KN was supported by a fellowship grant from the Japan Society for Promotion of Science. The content is solely the responsibility of the authors and does not necessarily represent the official views of NCI or NIH. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the paper.
- Colon cancer