title: Differential responses of skin cancer-chemopreventive agents silibinin, quercetin, and epigallocatechin 3-gallate on mitogenic signaling and cell cycle regulators in human epidermoid carcinoma A431 cells.
abstract: Silibinin, quercetin, and epigallocatechin 3-gallate (EGCG) have been shown to be skin cancer-preventive agents, albeit by several different mechanisms. Here, we assessed whether these agents show their cancer-preventive potential by a differential effect on mitogenic signaling molecules and cell cycle regulators. Treatment of human epidermoid carcinoma A431 cells with these agents inhibited the activation of the epidermal growth factor receptor and the downstream adapter protein Shc, but only silibinin showed a marked inhibition of mitogen-activated protein kinase-extracellular signal-regulated kinase-1 and -2 activation. In terms of cell cycle regulators, silibinin treatment showed an induction of Cip1/p21 and Kip1/p27 together with a significant decrease in cyclin-dependent kinase (CDK)-4, CDK2, and cyclin D1. Quercetin treatment, however, resulted in a moderate increase in Cip1/p21 with no change in Kip1/p27 and a decrease in CDK4 and cyclin D1. EGCG treatment also led to an induction of Cip1/p21 but no change in Kip1/27, CDK2, and cyclin D1 and a decrease in CDK4 only at low doses. Treatment of cells with these agents resulted in a strong dose- and time-dependent cell growth inhibition. A high dose of silibinin and low and high doses of quercetin and EGCG also led to cell death by apoptosis, suggesting that a lack of their inhibitory effect on mitogen-activated protein kinase-extracellular signal-regulated kinase-1 and -2 activation possibly "turns on" an apoptotic cell death response associated with their cancer-preventive and anticarcinogenic effects. Together, these results suggest that silibinin, quercetin, and EGCG exert their cancer-preventive effects by differential responses on mitogenic signaling and cell cycle regulators.
authors.affiliation: AMC Cancer Research Center, Center for Cancer Causation and Prevention, Denver, CO 80214, USA.
authors.forename: N
authors.initials: N
authors.lastname: Bhatia
authors.forename: C
authors.initials: C
authors.lastname: Agarwal
authors.forename: R
authors.initials: R
authors.lastname: Agarwal
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D016588:Anticarcinogenic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D042846:CDC2-CDC28 Kinases; D002294:Carcinoma, Squamous Cell / Q000378:metabolism* / Q000473:pathology; D002392:Catechin / Q000031:analogs & derivatives / Q000494:pharmacology*; D002453:Cell Cycle / Q000187:drug effects; D018797:Cell Cycle Proteins / Q000096:biosynthesis; D019938:Cyclin D1 / Q000378:metabolism; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D016213:Cyclins / Q000096:biosynthesis; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066246:ErbB Receptors / Q000037:antagonists & inhibitors; D006801:Humans; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors; D008934:Mitogens; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011506:Proteins / Q000037:antagonists & inhibitors; D011518:Proto-Oncogene Proteins; D011794:Quercetin / Q000494:pharmacology*; D055765:Shc Signaling Adaptor Proteins; D015398:Signal Transduction / Q000187:drug effects; D012838:Silymarin / Q000494:pharmacology*; D012878:Skin Neoplasms / Q000517:prevention & control*; D000071425:Src Homology 2 Domain-Containing, Transforming Protein 1; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins / Q000096:biosynthesis
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D016588:Anticarcinogenic Agents; C493956:CDKN1A protein, human; D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004791:Enzyme Inhibitors; D008934:Mitogens; D011506:Proteins; D011518:Proto-Oncogene Proteins; C528024:SHC1 protein, human; D055765:Shc Signaling Adaptor Proteins; D012838:Silymarin; D000071425:Src Homology 2 Domain-Containing, Transforming Protein 1; D025521:Tumor Suppressor Proteins; D019938:Cyclin D1; D050760:Cyclin-Dependent Kinase Inhibitor p27; D002392:Catechin; D011794:Quercetin; C045651:epigallocatechin gallate; D066246:ErbB Receptors; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; C495900:CDK4 protein, human; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases