Gigantol Targets MYC for Ubiquitin-proteasomal Degradation and Suppresses Lung Cancer Cell Growth
CANCER GENOMICS & PROTEOMICS
Authors: Losuwannarak, Nattanan; Roytrakul, Sittiruk; Chanvorachote, Pithi
Background: Gigantol is a pharmacologically active bibenzyl compound exerting potential anticancer activities. At non-toxic concentrations, it reduces cancer stem cell properties and tumorigenicity. The mechanisms of the effects of gigantol on cancer cell growth are largely unknown. This study aimed to unravel the molecular profile and identify the prominent molecular mechanism of the effects of gigantol in controlling lung cancer cell proliferation. Materials and Methods: Proteomics and bioinformatics analysis were used accompanied by experimental molecular pharmacology approaches. Results: Gigantol exhibited antiproliferative effects on human lung cancer cells confirmed by 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide proliferation assay and colony growth assay. The protein profile in response to gigantol treatment associated with regulation of cell proliferation was analyzed to determine the prominent protein targets. Among the significant hub proteins, MYC, an important proto-oncogene and proliferation-promoting transcription factor, was down-regulated with the highest number of protein-protein interactions. MYC downregulation was confirmed by western blot analysis. The upstream regulator of MYC, Glycogen synthase kinase 3 beta (GSK3 beta) was found to be responsible for MYC destabilization mediated by gigantol. Gigantol facilitated GSK3 beta function and resulted in the increase of MYC-ubiquitin complex as evaluated by immunoprecipitation. Conclusion: Gigantol was found to inhibit lung cancer proliferation through induction of GSK3 beta-mediated MYC ubiquitin-proteasome degradation. These data suggest gigantol to be a promising candidate for novel strategy in inhibition of lung cancer.
Monounsaturated oleic acid modulates autophagy flux and upregulates angiogenic factor production in human retinal pigment epithelial ARPE-19 cells
Authors: Chang, Yo-Chen; Lin, Chia-Wei; Chang, Yuh-Shin; Chen, Po-Han; Li, Chia-Yang; Wu, Wen-Chuan; Kao, Ying-Hsien
Aims: Dyslipidemia-associated diabetic retinopathy is featured by macular edema and retinal angiogenesis. This study investigated the in vitro lipotoxicity of free fatty acids and their modulatory roles in regulation of au-tophagy and angiogenic factor production in cultured human retinal pigment epithelium (RPE) ARPE-19 cells. Main methods: ARPE-19 cells were exposed to monounsaturated oleic acid (OA), saturated palmitic acid (PA), or both. Cell viability, cell cycle distribution, migration, and autophagy of the treated cells were monitored. Angiogenic factor production was determined by RT-qPCR and ELISA. Key findings: OA, but not PA, at doses higher than 500 mu M significantly induced cytostasis and lipotoxicity in ARPE-19 cells. OA exposure not only markedly enhanced autophagy flux, but also enhanced cell migration, while PA suppressed motility of RPE cells. Meanwhile, OA stimulated de novo synthesis of angiogenic factors including VEGF and bFGF in ARPE-19 cells. Mechanistically, OA treatment stimulated not only AMPK/mTOR/p70S6K signaling, but also induced hyperphosphorylation of MAPK pathway mediators, including ERK, JNK and p38 MAPK, as well as NF-kappa B activation. Kinase inhibition assays showed that blockade of PI3K/Akt, MAPK and NF-kappa B pathways prevented the OA-upregulated VEGF transcription and its peptide release. Comparatively, only NF-kappa B inhibition significantly suppressed bFGF peptide release from ARPE-19 cells. Significance: Out findings support the OA-exhibited cytostasis, autophagy modulation and angiogenic factor production in RPE cells. This study sheds light on the interrelationship between metabolic disorder and retinopathy and provides molecular strategies for preventing and treating choroidal neovascularization in diabetic retinopathy.