Abstract LB-243: Curcumin suppresses oncogenicity of human colon cancer cells through covalent modification of oncogenic SIRT1

Silent mating type information regulator 2 homolog 1 (SIRT1), an NAD+-dependent histone/protein deacetylase, has multifaceted functions in various biological events such as inflammation, aging and energy metabolism. The role of SIRT1 in carcinogenesis, however, is still under debate. Recent studies have indicated that aberrant overexpression of SIRT1 is correlated with metastasis and poor prognosis in several types of cancer, suggesting that it may act as a tumor promoter. In our present study, 27 out of 35 human colorectal cancer specimens exhibit significantly elevated expression of SIRT1 compared with corresponding adjacent normal tissues. siRNA knock down of SIRT1 in human colon cancer (HCT-116) cells significantly reduced the volume and the weight of the xenograft tumors when these cells were injected subcutaneously into the flanks of BALB/c nude mice. Curcumin (diferuloymethane), a substance present in the spice turmeric (Curcuma longa L., Zingiberaceae) has been known to possess the beneficial effects on pathological conditions such as inflammation and cancer. Curcumin abrogated migration and colony forming capability of HCT-116 cells. This prompted us to investigate the effect of curcumin on the expression of SIRT1 and underlying molecular mechanisms. When HCT-116 cells were treated with curcumin, the protein expression of SIRT1 was significantly reduced, but the level of its mRNA transcript remained unchanged. Notably, the ubiquitination of SIRT1 was elevated by curcumin treatment. Nano-LC-ESI-MS/MS analysis revealed the modification of the SIRT1 cysteine 67 residue by curcumin. In line with this observation, the protein stability of a mutant SIRT1 in which cysteine 67 was replaced by alanine (SIRT1-C67A) was unaffected by curcumin treatment. Furthermore, migration and anchorage-independent growth of cells expressing SIRT1-C67A were affected by curcumin to a lesser extent than those of cells expressing wild-type SIRT1. It has been reported that c-Jun N-terminal kinases 2 (JNK2) phosphorylates SIRT1 at the serine 27 residue, thereby enhancing the protein stability of SIRT1 in HCT-116 cells. Based on these report, we speculated that binding of curcumin to SIRT1 at cysteine 67 may disrupt the interaction between JNK and SIRT1, leading to blockade of the phosphorylation-dependent stabilization of SIRT1. Binding of phosphorylated JNK to SIRT1 in cells expressing SIRT1-C67A was barely inhibited by curcumin compared with that in cells harbouring wild-type SIRT1, lending support to the above supposition. Taken together, cysteine 67 modification of SIRT1 by curcumin is a prerequisite for proteasomal degradation of oncogenic SIRT1, which accounts for anti-cancer effects of curcumin. Supported by the Global Core Research Center (GCRC) grant (No. 2011-0030001) from the National Research Foundation (NRF) of Republic of Korea. Citation Format: Yeon-Hwa Lee, Na-Young Song, Do-Hee Kim, Hye-Kyung Na, Young-Joon Surh. Curcumin suppresses oncogenicity of human colon cancer cells through covalent modification of oncogenic SIRT1 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr LB-243.