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
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Research Support, Non-U.S. Gov't
MeSH terms
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Animals
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Antineoplastic Agents, Phytogenic / pharmacology*
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Apoptosis / drug effects*
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CDC2 Protein Kinase
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Carcinoma, Hepatocellular / drug therapy*
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Carcinoma, Hepatocellular / enzymology
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Carcinoma, Hepatocellular / genetics
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Carcinoma, Hepatocellular / pathology
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Cyclin B / metabolism
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Cyclin B1 / metabolism
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Cyclin-Dependent Kinase Inhibitor p21 / metabolism
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Cyclin-Dependent Kinases
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Diterpenes, Kaurane / pharmacology*
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Dose-Response Relationship, Drug
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Down-Regulation
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G2 Phase Cell Cycle Checkpoints / drug effects*
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Hep G2 Cells
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Humans
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JNK Mitogen-Activated Protein Kinases / antagonists & inhibitors
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JNK Mitogen-Activated Protein Kinases / metabolism*
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Liver Neoplasms / drug therapy*
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Liver Neoplasms / enzymology
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Liver Neoplasms / genetics
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Liver Neoplasms / pathology
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Male
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Mice
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Mice, Inbred BALB C
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Mice, Nude
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Phosphorylation
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Protein Kinase Inhibitors / pharmacology
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Proto-Oncogene Mas
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Proto-Oncogene Proteins c-jun / metabolism*
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Reactive Oxygen Species / metabolism*
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S-Phase Kinase-Associated Proteins / genetics
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S-Phase Kinase-Associated Proteins / metabolism*
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Signal Transduction / drug effects*
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Time Factors
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Transfection
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Tumor Burden / drug effects
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Xenograft Model Antitumor Assays
Substances
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Antineoplastic Agents, Phytogenic
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CCNB1 protein, human
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CDKN1A protein, human
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Cyclin B
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Cyclin B1
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Cyclin-Dependent Kinase Inhibitor p21
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Diterpenes, Kaurane
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MAS1 protein, human
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Protein Kinase Inhibitors
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Proto-Oncogene Mas
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Proto-Oncogene Proteins c-jun
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Reactive Oxygen Species
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S-Phase Kinase-Associated Proteins
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longikaurin A
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CDC2 Protein Kinase
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CDK1 protein, human
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Cyclin-Dependent Kinases
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JNK Mitogen-Activated Protein Kinases