title: Cyclin D1 degradation is sufficient to induce G1 cell cycle arrest despite constitutive expression of cyclin E2 in ovarian cancer cells.
abstract: D- and E-type cyclins mediate G(1)-S phase cell cycle progression through activation of specific cyclin-dependent kinases (cdk) that phosphorylate the retinoblastoma protein (pRb), thereby alleviating repression of E2F-DP transactivation of S-phase genes. Cyclin D1 is often overexpressed in a variety of cancers and is associated with tumorigenesis and metastasis. Loss of cyclin D can cause G(1) arrest in some cells, but in other cellular contexts, the downstream cyclin E protein can substitute for cyclin D and facilitate G(1)-S progression. The objective of this study was to determine if a flexible heteroarotinoid anticancer compound, SHetA2, regulates cell cycle proteins and cell cycle progression in ovarian cancer cells. SHetA2 induced cyclin D1 phosphorylation, ubiquitination, and proteasomal degradation, causing G(1) arrest in ovarian cancer cells despite continued cyclin E2 expression and independently of p53 and glycogen synthase kinase-3beta. Cyclin D1 loss inhibited pRb S780 phosphorylation by cyclin D1-cdk4/6 and released p21 from cyclin D1-cdk4/6-p21 protein complexes to form cyclin E2-cdk2-p21 complexes, which repressed phosphorylation of pRb S612 by cyclin E2-cdk2 and ultimately E2F-DP transcriptional activity. G(1) arrest was prevented by overexpression or preventing degradation of cyclin D1 but not by restoration of pRb S612 phosphorylation through p21 knockdown. In conclusion, we show that loss of cyclin D1 in ovarian cancer cells treated with SHetA2 is sufficient to induce G(1) cell cycle arrest and this strategy is not impeded by the presence of cyclin E2. Therefore, cyclin D1 is a sufficient therapeutic target in ovarian cancer cells.
authors.affiliation: Departments of Biochemistry and Molecular Biology, University of Oklahoma Health Sciences Center, Oklahoma City, 73104, USA.
authors.forename: Chioniso Patience
authors.initials: CP
authors.lastname: Masamha
authors.forename: Doris Mangiaracina
authors.initials: DM
authors.lastname: Benbrook
mesh_terms: D017209:Apoptosis / Q000187:drug effects / Q000235:genetics; D049109:Cell Proliferation / Q000187:drug effects; D002839:Chromans / Q000494:pharmacology; D019938:Cyclin D1 / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D016213:Cyclins / Q000235:genetics*; D004353:Drug Evaluation, Preclinical; D005260:Female; D016193:G1 Phase / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects / Q000502:physiology; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism / Q000502:physiology; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D010051:Ovarian Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D010766:Phosphorylation / Q000187:drug effects; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011499:Protein Processing, Post-Translational / Q000187:drug effects / Q000502:physiology; D013871:Thiones / Q000494:pharmacology; D014162:Transfection; D014407:Tumor Cells, Cultured; D054875:Ubiquitination / Q000187:drug effects
chemical_list: C476105:(((4-nitrophenyl)amino)(2,2,4,4-tetramethyl thiochroman-6-yl)amino) methane-1-thione; C503688:CCNE2 protein, human; D002839:Chromans; D016213:Cyclins; D013871:Thiones; D019938:Cyclin D1; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; D038362:Glycogen Synthase Kinase 3; D046988:Proteasome Endopeptidase Complex