Inhibition of cytokinesis and akt phosphorylation by chaetoglobosin K in ras-transformed epithelial cells.

Abstract

PURPOSE:

Chaetoglobosin K (ChK), a bioactive natural product previously shown to have anti-tumor promoting activity in glial cells and growth inhibitory effects in ras-transformed fibroblasts, inhibited anchorage-dependent and anchorage-independent growth in ras-transformed liver epithelial cells. The purpose of this study was to identify cellular targets of ChK that mediate its anti-tumor effects.

METHODS:

Anchorage-independent cell growth assays, using soft agar-coated dishes, and anchorage-dependent growth assays were performed on transformed WB- ras1 cells. Phase/contrast and fluorescent microscopy were used to visualize cell morphological changes and DAPI-stained nuclei. Analyses of p21 Ras membrane versus cytosolic forms, p44/42 mitogen-activated protein kinase (MAPK) phosphorylation, Akt kinase phosphorylation and connexin 43 phosphorylation were performed by Western blotting. Gap junction-mediated cellular communication was measured by fluorescent dye transfer.

RESULTS:

Treatment of WB- ras1 cells with a non-cytotoxic dose of ChK inhibited both anchorage-dependent and anchorage-independent growth. Inhibited cells were generally larger and less spindle-shaped in morphology than vehicle-treated cells, many of which were multinucleate. Removal of ChK induced cytokinesis and a return to predominantly single-nucleate cells, suggesting that ChK inhibits cytokinesis. The proportion of membrane-associated versus cytosolic forms of p21 Ras was unchanged by ChK treatment, suggesting that ChK does not act as a farnesylation inhibitor. ChK treatment decreased the level of phosphorylation of Akt kinase, a key signal transducer of the Phosphatidylinositol 3-kinase pathway. In contrast, ChK had no effect on phosphorylation of p44/42 MAPK, which mediates the MAPK/ERK Ras effector pathway. Phosphorylation of the gap junction protein, connexin 43, shown previously to increase following treatment with other anti-Ras compounds, was also not altered by ChK, which correlated with its lack of effect on gap junction-mediated cellular communication.

CONCLUSIONS:

Our results demonstrate that ChK inhibits Akt kinase phosphorylation and cytokinesis in ras-transformed cells, which likely contribute to its ability to inhibit tumorigenic growth.

• Authors: Diane F Matesic, Kimberly N Villio, Stacey L Folse, Erin L Garcia, Stephen J Cutler, Horace G Cutler
• Journal: Cancer chemotherapy and pharmacology (Cancer Chemother Pharmacol) Vol. 57 Issue 6 Pg. 741-54 (Jun 2006) ISSN: 0344-5704 [Print] Germany
• PMID: 16254733 (Publication Type: Journal Article)

Chemical References

• Antineoplastic Agents
• Indole Alkaloids
• chaetoglobosins
• Proto-Oncogene Proteins c-akt
• Proto-Oncogene Proteins p21(ras)

Topics

• Animals
• Antineoplastic Agents (pharmacology)
• Cell Line, Transformed
• Cell Proliferation (drug effects)
• Cytokinesis (drug effects)
• Epithelial Cells (cytology, drug effects, metabolism)
• Indole Alkaloids (pharmacology)
• Liver
• Phosphorylation (drug effects)
• Proto-Oncogene Proteins c-akt (metabolism)
• Proto-Oncogene Proteins p21(ras) (genetics, metabolism)
• Rats