title: α-Lipoic acid prevents p53 degradation in colon cancer cells by blocking NF-κB induction of RPS6KA4.
abstract: α-Lipoic acid (α-LA) is a biogenic antioxidant that has been used successfully in the treatment of diabetic polyneuropathy and its application to many oxidative stress-associated chronic diseases has increased. In this study, we investigated the effect of α-LA on colorectal cancer cell growth and its underlying mechanism. α-LA treatment resulted in a marked reduction in the growth of HCT116 colon cancer cells in a dose-dependent manner through the G1 arrest of the cell cycle and apoptosis induction. α-LA treatment significantly increased tumor cell response to various apoptotic stresses, such as etoposide, 5-fluorouracil, UVC, γ-irradiation, hypoxia, and tumor necrosis factor α (TNFα). Interestingly, α-LA increased p53 protein stability and its apoptosis-enhancing effect was more evident in wild-type p53-carrying cells compared with p53-deficient cells, suggesting that the proapoptotic role of α-LA is associated with its p53-stabilizing function. On the basis of our microarray data showing α-LA downregulation of the ribosomal protein p90S6K (RPS6KA4), which has been reported to inhibit p53 function, we tested whether α-LA regulation of RPS6KA4 is associated with its proapoptotic function. α-LA treatment led to a marked reduction in the RPS6KA4 mRNA level in multiple colorectal cancer cells and restoration of RPS6KA4 expression markedly attenuated α-LA induction of apoptosis in a p53-dependent manner. In addition, we observed that RPS6KA4 expression is activated by TNFα whereas both basal and TNFα induction of RPS6KA4 are inhibited by the nuclear factor-κB (NF-κB) inhibitor BAY11-7082 or transfection of a dominant-negative mutant of NF-κB, indicating that NF-κB plays a crucial role in RPS6KA4 gene expression. Finally, we found that α-LA exerts an inhibitory effect on the nuclear translocation of NF-κB triggered by TNFα. Collectively, our study shows that α-LA suppresses colorectal tumor cell growth at least partially by preventing RPS6KA4-mediated p53 inhibition through blockade of NF-κB signaling.
authors.affiliation: Department of Life Sciences, School of Life Sciences and Biotechnology, Korea University, Seoul, Republic of Korea.
authors.forename: Tae-Hyoung
authors.initials: TH
authors.lastname: Yoo
authors.forename: Jin-Hee
authors.initials: JH
authors.lastname: Lee
authors.forename: Hyang-Sook
authors.initials: HS
authors.lastname: Chun
authors.forename: Sung-Gil
authors.initials: SG
authors.lastname: Chi
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D000975:Antioxidants / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D059585:G1 Phase Cell Cycle Checkpoints / Q000187:drug effects; D045325:HCT116 Cells; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology; D016328:NF-kappa B / Q000037:antagonists & inhibitors*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000096:biosynthesis*; D008063:Thioctic Acid / Q000494:pharmacology*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; D000975:Antioxidants; D016328:NF-kappa B; D014409:Tumor Necrosis Factor-alpha; D016159:Tumor Suppressor Protein p53; D008063:Thioctic Acid; C115634:RPS6KA4 protein, human; D038744:Ribosomal Protein S6 Kinases, 90-kDa