SIRT1 and malignant colon neoplasm: Finally, SIRT1 protein levels were also reduced in RKO colon cancer cells and SIRT1was found to maintain silencing of TSGs including the mismatch repair gene, MLH1 (Figure 1E), for which epigenetic silencing and loss of function produces the microsatellite instability (MIN+) colon cancer phenotype [32,33] .