title: Cell cycle regulators cyclin D1 and CDK4/6 have estrogen receptor-dependent divergent functions in breast cancer migration and stem cell-like activity.
abstract: Cyclin D1 and its binding partners CDK4/6 are essential regulators of cell cycle progression and are implicated in cancer progression. Our aim was to investigate a potential regulatory role of these proteins in other essential tumor biological characteristics. Using a panel of breast cancer cell lines and primary human breast cancer samples, we have demonstrated the importance of these cell cycle regulators in both migration and stem-like cell activity. siRNA was used to target cyclin D1 and CDK4/6 expression, having opposing effects on both migration and stem-like cell activity dependent upon estrogen receptor (ER) expression. Inhibition of cyclin D1 or CDK4/6 increases or decreases migration and stem-like cell activity in ER-ve (ER-negative) and ER+ve (ER-positive) breast cancer, respectively. Furthermore, overexpressed cyclin D1 caused decreased migration and stem-like cell activity in ER-ve cells while increasing activity in ER+ve breast cancer cells. Treatment of breast cancer cells with inhibitors of cyclin D1 and CDK4/6 (Flavopiridol/PD0332991), currently in clinical trials, mimicked the effects observed with siRNA treatment. Re-expression of ER in two ER-ve cell lines was sufficient to overcome the effects of either siRNA or clinical inhibitors of cyclin D1 and CDK4/6.   In conclusion, cyclin D1 and CDK4/6 have alternate roles in regulation of migration and stem-like cell activity. Furthermore, these effects are highly dependent upon expression of ER. The significance of these results adds to our general understanding of cancer biology but, most importantly, could be used diagnostically to predict treatment response to cell cycle inhibition in breast cancer.
authors.affiliation: Breakthrough Breast Cancer Unit; Institute of Cancer Sciences; Paterson Institute for Cancer Research; University of Manchester; Manchester, UK.
authors.forename: Rebecca
authors.initials: R
authors.lastname: Lamb
authors.forename: Sophie
authors.initials: S
authors.lastname: Lehn
authors.forename: Lynsey
authors.initials: L
authors.lastname: Rogerson
authors.forename: Robert B
authors.initials: RB
authors.lastname: Clarke
authors.forename: Göran
authors.initials: G
authors.lastname: Landberg
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D001943:Breast Neoplasms / Q000188:drug therapy / Q000201:enzymology* / Q000473:pathology; D002453:Cell Cycle; D045744:Cell Line, Tumor; D002465:Cell Movement; D049109:Cell Proliferation; D019938:Cyclin D1 / Q000037:antagonists & inhibitors / Q000502:physiology*; D051358:Cyclin-Dependent Kinase 4 / Q000037:antagonists & inhibitors / Q000502:physiology*; D051361:Cyclin-Dependent Kinase 6 / Q000502:physiology*; D005260:Female; D005419:Flavonoids / Q000494:pharmacology; D055785:Gene Knockdown Techniques; D006801:Humans; D014411:Neoplastic Stem Cells / Q000201:enzymology* / Q000502:physiology; D010880:Piperidines / Q000494:pharmacology; D034741:RNA, Small Interfering / Q000235:genetics; D011960:Receptors, Estrogen / Q000378:metabolism; D018874:Spheroids, Cellular / Q000201:enzymology / Q000502:physiology
chemical_list: D000970:Antineoplastic Agents; C530104:CCND1 protein, human; D005419:Flavonoids; D010880:Piperidines; D034741:RNA, Small Interfering; D011960:Receptors, Estrogen; D019938:Cyclin D1; C077990:alvocidib; C495900:CDK4 protein, human; C495911:CDK6 protein, human; D051358:Cyclin-Dependent Kinase 4; D051361:Cyclin-Dependent Kinase 6
keywords: breast cancer; cell cycle; estrogen receptor; migration; stem cell