Longikaurin A, a natural ent-kaurane, induces G2/M phase arrest via downregulation of Skp2 and apoptosis induction through ROS/JNK/c-Jun pathway in hepatocellular carcinoma cells

Cell Death Dis. 2014 Mar 20;5(3):e1137. doi: 10.1038/cddis.2014.66.

Abstract

Hepatocellular carcinoma (HCC) is the most common form of primary liver cancer, and is also highly resistant to conventional chemotherapy treatments. In this study, we report that Longikaurin A (LK-A), an ent-kaurane diterpenoid isolated from the plant Isodon ternifolius, induced cell cycle arrest and apoptosis in human HCC cell lines. LK-A also suppressed tumor growth in SMMC-7721 xenograft models, without inducing any notable major organ-related toxicity. LK-A treatment led to reduced expression of the proto-oncogene S phase kinase-associated protein 2 (Skp2) in SMMC-7721 cells. Lower Skp2 levels correlated with increased expression of p21 and p-cdc2 (Try15), and a corresponding decrease in protein levels of Cyclin B1 and cdc2. Overexpression of Skp2 significantly inhibited LK-A-induced cell cycle arrest in SMMC-7721 cells, suggesting that LK-A may target Skp2 to arrest cells at the G2/M phase. LK-A also induced reactive oxygen species (ROS) production and apoptosis in SMMC-7721 cells. LK-A induced phosphorylation of c-Jun N-terminal kinase (JNK), but not extracellular signal-regulated kinase and P38 MAP kinase. Treatment with, the JNK inhibitor SP600125 prevented LK-A-induced apoptosis in SMMC-7721 cells. Moreover, the antioxidant N-acetylcysteine prevented phosphorylation of both JNK and c-Jun. Taken together, these data indicate that LK-A induces cell cycle arrest and apoptosis in cancer cells by dampening Skp2 expression, and thereby activating the ROS/JNK/c-Jun signaling pathways. LK-A is therefore a potential lead compound for development of antitumor drugs targeting HCC.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antineoplastic Agents, Phytogenic / pharmacology*
  • Apoptosis / drug effects*
  • CDC2 Protein Kinase
  • Carcinoma, Hepatocellular / drug therapy*
  • Carcinoma, Hepatocellular / enzymology
  • Carcinoma, Hepatocellular / genetics
  • Carcinoma, Hepatocellular / pathology
  • Cyclin B / metabolism
  • Cyclin B1 / metabolism
  • Cyclin-Dependent Kinase Inhibitor p21 / metabolism
  • Cyclin-Dependent Kinases
  • Diterpenes, Kaurane / pharmacology*
  • Dose-Response Relationship, Drug
  • Down-Regulation
  • G2 Phase Cell Cycle Checkpoints / drug effects*
  • Hep G2 Cells
  • Humans
  • JNK Mitogen-Activated Protein Kinases / antagonists & inhibitors
  • JNK Mitogen-Activated Protein Kinases / metabolism*
  • Liver Neoplasms / drug therapy*
  • Liver Neoplasms / enzymology
  • Liver Neoplasms / genetics
  • Liver Neoplasms / pathology
  • Male
  • Mice
  • Mice, Inbred BALB C
  • Mice, Nude
  • Phosphorylation
  • Protein Kinase Inhibitors / pharmacology
  • Proto-Oncogene Proteins c-jun / metabolism*
  • Reactive Oxygen Species / metabolism*
  • S-Phase Kinase-Associated Proteins / genetics
  • S-Phase Kinase-Associated Proteins / metabolism*
  • Signal Transduction / drug effects*
  • Time Factors
  • Transfection
  • Tumor Burden / drug effects
  • Xenograft Model Antitumor Assays

Substances

  • Antineoplastic Agents, Phytogenic
  • CCNB1 protein, human
  • CDKN1A protein, human
  • Cyclin B
  • Cyclin B1
  • Cyclin-Dependent Kinase Inhibitor p21
  • Diterpenes, Kaurane
  • Protein Kinase Inhibitors
  • Proto-Oncogene Proteins c-jun
  • Reactive Oxygen Species
  • S-Phase Kinase-Associated Proteins
  • longikaurin A
  • CDC2 Protein Kinase
  • CDK1 protein, human
  • Cyclin-Dependent Kinases
  • JNK Mitogen-Activated Protein Kinases