Silibinin inhibits hypoxia-inducible factor-1alpha and mTOR/p70S6K/4E-BP1 signalling pathway in human cervical and hepatoma cancer cells: implications for anticancer therapy.
The hypoxia-inducible factor 1 (HIF-1) plays a critical role for tumour adaptation to microenvironmental hypoxia, and represents an appealing chemotherapeutic target. Silibinin is a nontoxic flavonoid reported to exhibit anticancer properties. However, the mechanisms by which silibinin inhibits tumour growth are not fully understood. In this study, silibinin was found to inhibit hypoxia-induced HIF-1alpha accumulation and HIF-1 transcriptional activity in human cervical (HeLa) and hepatoma (Hep3B) cells. Neither HIF-1alpha protein degradation rate nor HIF-1alpha steady-state mRNA level was affected by silibinin. Rather, we found that suppression of HIF-1alpha accumulation by silibinin correlated with strong dephosphorylation of mammalian target of rapamycin (mTOR) and its effectors ribosomal protein S6 kinase (p70S6K) and eukaryotic initiation factor 4E-binding protein-1 (4E-BP1), a pathway known to regulate HIF-1alpha expression at the translational level. Silibinin also activated Akt, a mechanistic feature exhibited by established mTOR inhibitors in many tumour cells. Moreover, silibinin reduced hypoxia-induced vascular endothelial growth factor (VEGF) release by HeLa and Hep3B cells, and this effect was potentiated by the PI3K/Akt inhibitor LY294002. Finally, silibinin was found to be a potent inhibitor of cell proliferation. These results show that silibinin is an effective inhibitor of HIF-1 and provide new perspectives into the mechanism of its anticancer activity.
García-Maceira
P
P
Department of Regenerative Cardiology, Centro Nacional de Investigaciones Cardiovasculares (CNIC), Madrid, Spain.
Mateo
J
J
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D000975:Antioxidants / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D006528:Carcinoma, Hepatocellular / Q000188:drug therapy; D018797:Cell Cycle Proteins; D015687:Cell Hypoxia; D049109:Cell Proliferation / Q000187:drug effects; D005260:Female; D006367:HeLa Cells / Q000187:drug effects; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000037:antagonists & inhibitors* / Q000235:genetics; D047468:Immunoprecipitation; D008156:Luciferases / Q000378:metabolism; D020944:Silybum marianum / Q000737:chemistry; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism*; D011494:Protein Kinases / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects*; D000077385:Silybin; D012838:Silymarin / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; D000975:Antioxidants; D018797:Cell Cycle Proteins; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D008156:Luciferases; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D011494:Protein Kinases; D051057:Proto-Oncogene Proteins c-akt; D012333:RNA, Messenger; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D000077385:Silybin; D012838:Silymarin; D058570:TOR Serine-Threonine Kinases; D042461:Vascular Endothelial Growth Factor A; C087000:EIF4EBP1 protein, human; C497442:HIF1A protein, human; C467484:VEGFA protein, human; C546842:MTOR protein, human