Abstract 1250: Curcumin inhibits migration and growth of human colon cancer cells through covalent modification of oncogenic SIRT1: Cysteine 67 as a potential binding site
Authors: Lee Yeon-Hwa , Song Na-Young , Kim Do-Hee , Na Hye-Kyung , Surh Young-Joon 
Published: July 2017

Abstract
Silent mating type information regulator 2 homolog 1 (SIRT1), an NAD+-dependent histone/protein deacetylase, has diverse physiological functions, including metabolic regulation and stress response. Despite extensive research, however, the role of SIRT1 in tumorigenesis remains controversial. Recent studies have demonstrated that SIRT1 is abnormally overexpressed in several human malignancies, and elevated levels of SIRT1 are correlated with the tumor invasion and metastasis. Curcumin (diferuloymethane), a major component of the spice turmeric (Curcuma longa L.), has been reported to possess anti-inflammatory and anti-carcinogenic properties. In the present study, we found that SIRT1 is predominantly overexpressed in the cytoplasm of several colorectal cancer cells as well as colon tumors. Curcumin abrogated migration and colony forming capability of human colon cancer (HCT-116) cells. This prompted us to investigate the effect of curcumin on the expression of SIRT1 and underlying molecular mechanisms in the context of its inhibition of the migration and growth of these cells. 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. The curcumin-induced suppression of SIRT1 protein expression was abrogated by the proteasomal inhibitor, MG-132. When HCT-116 cells were treated with curcumin, ubiquitination of SIRT1 was elevated. Notably, tetrahydrocurcumin, a non-electrophilic analogue of curcumin that lacks the α,β-unsaturated carbonyl moiety, failed to ubiquitinate and degrade SIRT1. Nano-LC-ESI-MS/MS analysis revealed the modification of the SIRT1 cysteine 67 residue. 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 barely inhibited by curcumin compared with those in cells harbouring wild-type SIRT1. Lysates of HCT-116 cells incubated with curcumin-conjugated Sepharose 4B beads exhibited covalent binding of curcumin to SIRT1. However, such direct interaction was markedly reduced in cells with SIRT1 cysteine 67 mutation. Taken together, these findings suggest that curcumin exerts inhibitory effects on progression of colon cancer through destabilization of oncogenic SIRT1. The electrophilic α,β-unsaturated carbonyl group present in curcumin can covalently modify SIRT1, preferentially at the cysteine 67 residue, facilitating its degradation via the ubiquitin-proteasome pathway in HCT-116 cells.
Citation Format: Yeon-Hwa Lee, Na-Young Song, Do-Hee Kim, Hye-Kyung Na, Young-Joon Surh. Curcumin inhibits migration and growth of human colon cancer cells through covalent modification of oncogenic SIRT1: Cysteine 67 as a potential binding site [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1250. doi:10.1158/1538-7445.AM2017-1250