pregna-4-17-diene-3-16-dione and Colonic-Neoplasms

Besides its essential role in controlling bile acid and lipid metabolism, the farnesoid X receptor (FXR) protects against intestinal tumorigenesis by promoting apoptosis and inhibiting cell proliferation. However, the mechanisms underlying these anti-proliferative actions of FXR remain to be elucidated. In the present study, we examined the effects of FXR activation (FXR overexpression and treatment with an FXR agonist GW4064) and inactivation (treatment with FXR siRNA and an FXR antagonist guggulsterone) on colon cancer cell proliferation in vitro using human colon cancer cell lines (H508, SNU-C4 and HT-29) and in vivo using xenografts in nude mice. Blocking FXR activity with guggulsterone stimulated time- and dose-dependent EGFR (Tyr845) phosphorylation and ERK activation. In contrast, FXR overexpression and activation with GW4064 attenuated cell proliferation by down-regulating EGFR (Tyr845) phosphorylation and ERK activation. Treatment with guggulsterone and GW4064 also caused dose-dependent changes in Src (Tyr416) phosphorylation. In stably-transfected human colon cancer cells, overexpression of FXR reduced EGFR, ERK, Src phosphorylation and cell proliferation, and in nude mice attenuated the growth of human colon cancer xenografts (64% reduction in tumor volume; 47% reduction in tumor weight; both P<0.01). Moreover, guggulsterone-induced EGFR and ERK phosphorylation and cell proliferation were abolished by inhibiting activation of Src, EGFR and MEK. Collectively these data support the novel conclusion that in human colon cancer cells Src-mediated cross-talk between FXR and EGFR modulates ERK phosphorylation, thereby regulating intestinal cell proliferation and tumorigenesis.

Topics: Animals; Cell Line, Tumor; Cell Proliferation; Cell Transformation, Neoplastic; Colonic Neoplasms; Epithelial Cells; ErbB Receptors; Gene Expression; Gene Knockdown Techniques; Humans; Intestinal Mucosa; Isoxazoles; Mice; Mice, Nude; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Phosphorylation; Pregnenediones; Receptors, Cytoplasmic and Nuclear; RNA Interference; Signal Transduction; src-Family Kinases; Transplantation, Heterologous

The plant sterol guggulsterone has been shown to exert anti-tumor effects, making it a candidate chemotherapeutic agent. We investigated the anti-tumor effects of guggulsterone on colon cancer cells and elucidated the underlying molecular mechanisms related to angiogenesis. The apoptotic effects of guggulsterone were examined by cell survival assay. Western blot analysis was used to determine the levels of various down-stream intracellular proteins involved in angiogenesis, including signal transducer and activator of transcription 3 (STAT3), vascular endothelial growth factor (VEGF), hypoxia-inducible factor-1alpha (HIF-1alpha) and aryl hydrocarbon receptor nuclear translocator (ARNT). Using chromatin immunoprecipitation assay, we tested whether guggulsterone affects the recruitment of STAT3, ARNT and HIF-1alpha to the human VEGF promoter. To investigate the effect of guggulsterone on vascular endothelial cell migration and invasion, tube formation and migration assays were conducted using human umbilical vein endothelial cells (HUVECs). Matrix metalloproteinase (MMP)-2 and -9 activities were measured by gelatin zymography. Guggulsterone significantly reduced cell viability in colon cancer cells in a dose-dependent manner and blocked VEGF, ARNT and STAT3 expression prominently in hypoxic conditions. The recruitment of STAT3 and ARNT, but not HIF-1alpha, to the VEGF promoter was inhibited by guggulsterone treatment. HUVECs produced much foreshortened and severely broken tubes and showed decreased migration activity under guggulsterone effects. In addition, zymography revealed that MMP-2 and -9 enzyme activities were markedly lower in the presence of guggulsterone. The results of this study suggest that guggulsterone not only induces apoptosis, but also inhibits angiogenesis and metastasis in colon cancer cells by blocking STAT3 and VEGF expression, suggesting its therapeutic potential in the treatment of colorectal cancer.

Topics: Angiogenesis Inhibitors; Cell Line, Tumor; Cell Movement; Colonic Neoplasms; Endothelium, Vascular; Gene Expression Regulation, Neoplastic; Humans; Models, Biological; Neoplasm Metastasis; Neovascularization, Pathologic; Pregnenediones; Promoter Regions, Genetic; STAT3 Transcription Factor; Tetrazolium Salts; Thiazoles; Vascular Endothelial Growth Factor A