title: Cyclin D1 is necessary for tamoxifen-induced cell cycle progression in human breast cancer cells.
abstract: Despite the success of tamoxifen in treating hormone-responsive breast cancer, its use is limited by the development of resistance to the drug. Understanding the pathways involved in the growth of tamoxifen-resistant cells may lead to new ways to treat tamoxifen-resistant breast cancer. Here, we investigate the role of cyclin D1, a mediator of estrogen-dependent proliferation, in growth of tamoxifen-resistant cells using a cell culture model of acquired resistance to tamoxifen. We show that tamoxifen and 4-hydroxytamoxifen (OHT) promoted cell cycle progression of tamoxifen-resistant cells after growth-arrest mediated by the estrogen receptor down-regulator ICI 182,780. Down-regulation of cyclin D1 with small interfering RNA blocked basal cell growth of tamoxifen-resistant cells and induction of cell proliferation by OHT. In addition, pharmacologic inhibition of phosphatidylinositol 3-kinase/Akt or mitogen-activated protein kinase/extracellular signal-regulated kinase 1/2 pathways decreased basal cyclin D1 expression and impaired OHT-mediated cyclin D1 induction and cell cycle progression. These findings indicate that cyclin D1 expression is necessary for proliferation of tamoxifen-resistant cells and for tamoxifen-induced cell cycle progression. These results suggest that therapeutic strategies to block cyclin D1 expression or function may inhibit development and growth of tamoxifen-resistant tumors.
authors.affiliation: Department of Pharmacology, Penn State College of Medicine, Hershey, Pennsylvania 17033, USA.
authors.forename: Robin L
authors.initials: RL
authors.lastname: Kilker
authors.forename: Maricarmen D
authors.initials: MD
authors.lastname: Planas-Silva
mesh_terms: D015153:Blotting, Western; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D002453:Cell Cycle / Q000187:drug effects* / Q000502:physiology; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002867:Chromones / Q000494:pharmacology; D019938:Cyclin D1 / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D019008:Drug Resistance, Neoplasm; D004965:Estrogen Antagonists / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D006801:Humans; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D009025:Morpholines / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000235:genetics; D016196:S Phase / Q000187:drug effects / Q000502:physiology; D015398:Signal Transduction / Q000235:genetics; D013629:Tamoxifen / Q000031:analogs & derivatives / Q000494:pharmacology*; D013997:Time Factors
chemical_list: D002867:Chromones; D019938:Cyclin D1; D004965:Estrogen Antagonists; D005419:Flavonoids; D020928:Mitogen-Activated Protein Kinases; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D051057:Proto-Oncogene Proteins c-akt; D034741:RNA, Small Interfering; D013629:Tamoxifen; C016601:afimoxifene; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one