ABSTRACT
Colorectal cancer (CRC) is one of the most malignant type of cancers and its incidence is steadily increasing, due to life style factors that include western diet. Abnormal activation of canonical Wnt/β-catenin signaling pathway plays an important role in colorectal carcinogenesis. Therefore, targeting Wnt/β-catenin signaling has been considered a crucial strategy in the discovery of small molecules for CRC. In the present study, we found that Nodosin, an ent-kaurene diterpenoid isolated from Isodon serra, effectively inhibits the proliferation of human colon cancer HCT116 cells. Mechanistically, Nodosin effectively inhibited the overactivated transcriptional activity of β-catenin/T-cell factor (TCF) determined by Wnt/β-catenin reporter gene assay in HEK293 and HCT116 cells. The expression of Wnt/β-catenin target genes such as Axin2, cyclin D1, and survivin were also suppressed by Nodosin in HCT116 cells. Further study revealed that a longer exposure of Nodosin induced the G 2/M phase cell cycle arrest and subsequently apoptosis in HCT116 cells. These findings suggest that the anti-proliferative activity of Nodosin in colorectal cancer cells might in part be associated with the regulation of Wnt/β-catenin signaling pathway.
ABSTRACT
BACKGROUND: 15,16-dihydrotanshinone I (DHTS) is a natural abietane diterpenoid that is mainly found in the roots of Salvia miltiorrhiza Bunge (Labiatae). DHTS exhibits a potential anti-proliferative effect in various human cancer cells. However, the mechanisms of action of DHTS as an anti-cancer agent have not been fully elucidated. Therefore, the present study investigated the anti-cancer effect of DHTS in terms of cell cycle regulation and the regulation of the AMP-activated protein kinase (AMPK)/Akt/mTOR signaling pathway in SK-HEP-1 human hepatocellular carcinoma cells. METHODS: The anti-proliferative effects of DHTS were evaluated by the sulforhodamine B assay in SK-HEP-1 cells. Cell cycle distribution was analyzed by flow cytometry. The elucidation of mechanisms of action such as the AMPK/AKT/mTOR and mitogen-activated protein kinase (MAPK) pathway was assessed by Western blot analysis. RESULTS: DHTS showed a significant anti-proliferative activity against SK-HEP-1 cells. DHTS induced cell cycle arrest in the G0/G1 phase, which was mediated by downregulation of cyclin D1, cyclin A, cyclin E, CDK4, CDK2, c-Myc and p-Rb expression and with increased expression of the CDK inhibitor p21. DHTS also activated the AMPK signaling. In addition, DHTS downregulated the Akt/mTOR and MAPK signaling pathways. CONCLUSIONS: Our results suggest that the anti-proliferative activity of DHTS might be associated with the induction of G0/G1 phase cell cycle arrest and regulation of AMPK/Akt/mTOR and MAPK signaling pathways in SK-HEP-1 cells.