Downregulated SIRT6 and upregulated NMNAT2 are associated with the presence, depth and stage of colorectal cancer.

Colorectal cancer (CRC) is an important cause of morbidity and mortality worldwide, and is difficult to detect in its early stages. Diagnostic and prognostic biomarkers are required, which may also be the basis for improving the targeted therapy for CRC. Sirtuin 6 (SIRT6) is a member of the sirtuin family of gene regulators, which have specific functions in genomic stability, gene transcription and energy metabolism in tumorigenesis. Nicotinamide mononucleotide adenylyltransferase 2 (NMNAT2) is a metabolic enzyme which can be deacetylated by sirtuins. In this study, tissue samples from 29 patients with histologically confirmed CRC of varying grade and stage were studied for SIRT6 and NMNAT2 expression by western blotting and reverse transcription-quantitative polymerase chain reaction. Immunohistochemistry was performed for SIRT6 and NMNAT2 expression in 113 paired (CRC and adjacent) tissue sections. SIRT6 protein and mRNA expression levels were significantly reduced in CRC tissues; NMNAT2 protein and mRNA expression levels were significantly increased in CRC tissues (P<0.01). A negative correlation between the expression of SIRT6 and NMNAT2 in CRC tissue samples was identified (r=-0.246, P<0.01). The reduced expression of SIRT6 and increased expression of NMNAT2 were associated with the tumor depth invasion, stage, differentiation grade (SIRT6 only) and the presence of lymph node metastasis (P<0.05). In conclusion, the findings of the present preliminary study demonstrated that the increased expression of NMNAT2 and reduced expression of SIRT6 may be associated with the progression of CRC. The downregulation of SIRT6 may promote the expression of NMNAT2. Further studies are indicated on the role of NMNAT2 and SIRT6 as potential diagnostic and prognostic biomarkers and as targets for therapy in CRC and other malignant tumors.