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Aims: Aberrant overactivation/overexpression of NRF2 is implicated as a driving event in tumor progression, which has been attributed to its mutation or inactivation of the inhibitory protein, KEAP1. However, alternative mechanisms responsible for sustained activation of NRF2 are less understood., Main Methods: Human colon cancer cell lines and tissues obtained from colorectal cancer (CRC) patients were used. To examine the expression levels of ARD1 and NRF2, Western blot and immunofluorescence analyses were performed. To investigate the potential relevance of NRF2 and ARD1 to human CRC, NRF2 and ARD1 were individually silenced in human colon cancer cells (HCT-116) by transfection with their specific small interfering RNA (siRNA). To determine the functional role of ARD1 in NRF2 regulation, in situ proximate ligation, co-immunoprecipitation, nano-LC-ESI MS/MS, and in vitro acetylation assays were performed., Key Findings: ARD1 knockdown in human colon cancer cell lines significantly reduced the protein levels of NRF2 without affecting its mRNA expression; however, silencing of NRF2 did not alter ARD1 protein expression. In addition, these two proteins were co-localized and physically interacted with each other both in human colon cancer cells (HCT-116) and human colon tumor tissues. Mechanistically, ARD1 overexpression increased the acetylation levels of NRF2. Moreover, an in vitro acetylation assay and mass spectrometric analysis demonstrated that ARD1 could directly acetylate NRF2. Ectopic expression of mutant forms of ARD1 with defective acetyltransferase activity reduced the stability of NRF2., Significance: In conclusion, ARD1 may potentiate the oncogenic function of NRF2 in human colon cancer by stabilizing this transcription factor., Competing Interests: Declaration of competing interest The authors declare no competing financial interests., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Sirtuin 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 malignancy, including colorectal cancer. In the present study, we found that both SIRT1 and SIRT1 phosphorylated on serine 27 were coordinately upregulated in colon cancer patients' tissues and human colon cancer cell lines. This prompted us to investigate a role of phospho-SIRT1 in the context of colon cancer progression. A phosphorylation-defective mutant form of SIRT1, in which serine 27 was substituted by alanine (SIRT1-S27A), exhibited lower protein stability compared to that of wild-type SIRT1. Notably, human colon cancer (HCT-116) cells harboring the SIRT1-S27A mutation showed decreased cell proliferation and reduced capability to form xenograft tumor in athymic nude mice, which was accompanied by diminished transcriptional activity of Snail. HCT-116 cells carrying SIRT1-S27A were less capable of deacetylating the Snail protein, with a concomitant decrease in the levels of interleukin (IL)-6 and IL-8 mRNA transcripts. Taken together, these observations suggest that SIRT1 stabilized through phosphorylation on serine 27 exerts oncogenic effects at least partly through deacetylation-dependent activation of Snail and subsequent transcription of IL-6 and IL-8 in human colon cancer cells., (© 2021 The Authors. Molecular Oncology published by John Wiley & Sons Ltd on behalf of Federation of European Biochemical Societies.)

SIRT1 is a mammalian NAD + -dependent deacetylase, which is known to be involved in various physiological events, such as adaptive response to environmental stresses including caloric restriction, as well as in aging and cellular senescence. However, recent studies have revealed overexpression of SIRT1 in many different types of human malignancies, particularly colon cancer. Interleukin-1β (IL-1β) is a proinflammatory cytokine that plays a major role in invasiveness, stemness and progression of colon cancer. However, the interaction between IL-1β and SIRT1 in the tumor development and progression remains elusive. In this study, we found that IL-1β induces SIRT1 protein expression in human colon cancer HCT-116 cells. IL-1β-induced SIRT1 upregulation led to enhanced expression of mRNA transcripts of pro-inflammatory cytokines, IL-6 and IL-8 as well as that of IL-1β. Knockdown of SIRT1 prevented IL-1β-induced phosphorylation and nuclear accumulation of c-Jun. Furthermore, pharmacologic inhibition of SIRT1 abrogated clonogenicity and migrative capability of human colon cancer cells stimulated with IL-1β. In summary, IL-1β-induced SIRT1 upregulation stimulates production of proinflammatory cytokines via a nuclear accumulation of c-Jun, leadng to colon cancer growth and progression., (Copyright © 2021 Elsevier Inc. All rights reserved.)

SIRT1, an NAD + -dependent histone/protein deacetylase, has diverse physiological actions. Recent studies have demonstrated that SIRT1 is overexpressed in colorectal cancer, suggesting its oncogenic potential. However, the molecular mechanisms by which overexpressed SIRT1 induces the progression of colorectal cancer and its inhibition remain largely unknown. Curcumin (diferuloymethane), a major component of the spice turmeric derived from the plant Curcuma longa L., has been reported to exert chemopreventive and anti-carcinogenic effects on colon carcinogenesis. In the present study, we found that curcumin reduced the expression of SIRT1 protein without influencing its mRNA expression in human colon cancer cells, suggesting posttranslational regulation of SIRT1 by this phytochemical. Notably, ubiquitination and subsequent proteasomal degradation of SIRT1 were induced by curcumin treatment. Results of nano-LC-ESI-MS/MS revealed the direct binding of curcumin to cysteine 67 of SIRT1. In line with this result, the protein stability and clonogenicity of a mutant SIRT1 in which cysteine 67 was substituted by alanine were unaffected by curcumin. Taken together, these observations suggest that curcumin facilitates the proteasomal degradation of oncogenic SIRT1 through covalent modification of SIRT1 at the cysteine 67 residue., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Leptin, a representative adipokine secreted from the white adipose tissue, is considered as a potential linker between obesity and cancer. SIRT1 is an NAD + -dependent histone/protein deacetylase speculated to function as an oncogene. In the present study, we found that leptin signaling-defective ob/ob and db/db mice had lower colonic expression of SIRT1 compared with leptin signaling-intact C57BL/6J mice, implying that leptin signaling is crucial for SIRT1 expression in vivo. Moreover, leptin induced up-regulation of SIRT1 in human colon cancer (HCT-116) cells. Leptin stimulated migration and invasion of cultured HCT-116 cells and tumor growth in the xenograft assay, and these effects were abrogated by a SIRT1 inhibitor sirtinol, suggesting that SIRT1 plays a role in leptin-induced colon carcinogenesis. Leptin-induced SIRT1 expression was regulated by the redox-sensitive transcription factor NF-E2-related factor 2 (Nrf2). Leptin stimulated nuclear accumulation of Nrf2 as well as its binding to the antioxidant response elements located in the SIRT1 promoter. Moreover, siRNA knockdown of Nrf2 abrogated the leptin-induced SIRT1 expression. Notably, SIRT1 was significantly reduced in colon tissues of Nrf2-null mice, lending further support to Nrf2-dependent SIRT1 expression. Expression of leptin, Nrf2 and SIRT1 was coordinately increased in human colon tumor tissues. In conclusion, leptin might play a role in colon carcinogenesis by inducing Nrf2-dependent SIRT1 overexpression., (Copyright © 2018 Elsevier Inc. All rights reserved.)