title: Genetic reevaluation of the role of F-box proteins in cyclin D1 degradation.
abstract: D-type cyclins play a pivotal role in G(1)-S progression of the cell cycle, and their expression is frequently deregulated in cancer. Cyclin D1 has a half-life of only ~30 min as a result of its ubiquitylation and proteasomal degradation, with various F-box proteins, including Fbxo4, Fbxw8, Skp2, and Fbxo31, having been found to contribute to its ubiquitylation. We have now generated Fbxo4-deficient mice and found no abnormalities in these animals. Cyclin D1 accumulation was thus not observed in Fbxo4(-/-) mouse tissues. The half-life of cyclin D1 in mouse embryonic fibroblasts (MEFs) prepared from Fbxo4(-/-), Fbxw8(-/-), and Fbxo4(-/-); Fbxw8(-/-) mice also did not differ from that in wild-type MEFs. Additional depletion of Skp2 and Fbxo31 in Fbxo4(-/-); Fbxw8(-/-) MEFs by RNA interference did not affect cyclin D1 stability. Although Fbxo31 depletion in MEFs increased cyclin D1 abundance, this effect appeared attributable to upregulation of cyclin D1 mRNA. Furthermore, abrogation of the function of the Skp1-Cul1-F-box protein (SCF) complex or the anaphase-promoting complex/cyclosome (APC/C) complexes did not alter the half-life of cyclin D1, whereas cyclin D1 degradation was dependent largely on proteasome activity. Our genetic analyses thus do not support a role for any of the four F-box proteins examined in cyclin D1 degradation during normal cell cycle progression. They suggest the existence of other ubiquitin ligases that target cyclin D1 for proteolysis.
authors: Department of Molecular and Cellular Biology, Medical Institute of Bioregulation, Kyushu University, Fukuoka, Japan.
authors: Tomoharu
authors: T
authors: Kanie
authors: Ichiro
authors: I
authors: Onoyama
authors: Akinobu
authors: A
authors: Matsumoto
authors: Masanori
authors: M
authors: Yamada
authors: Hirokazu
authors: H
authors: Nakatsumi
authors: Yuki
authors: Y
authors: Tateishi
authors: So
authors: S
authors: Yamamura
authors: Ryosuke
authors: R
authors: Tsunematsu
authors: Masaki
authors: M
authors: Matsumoto
authors: Keiichi I
authors: KI
authors: Nakayama
mesh_terms: D064173:Anaphase-Promoting Complex-Cyclosome; D000818:Animals; D002453:Cell Cycle; D044842:Cullin Proteins / Q000378:metabolism; D019938:Cyclin D1 / Q000378:metabolism*; D044783:F-Box Proteins / Q000235:genetics*; D005260:Female; D005347:Fibroblasts / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D055550:Protein Stability; D059748:Proteolysis; D034622:RNA Interference; D044786:S-Phase Kinase-Associated Proteins / Q000378:metabolism; D043743:Ubiquitin-Protein Ligase Complexes / Q000378:metabolism
chemical_list: C530105:Ccnd1 protein, mouse; C100318:Cullin 1; D044842:Cullin Proteins; D044783:F-Box Proteins; C515213:Fbx4 protein, mouse; C570599:Fbxo31 protein, mouse; C513332:Fbxw8 protein, mouse; D044786:S-Phase Kinase-Associated Proteins; D019938:Cyclin D1; D043743:Ubiquitin-Protein Ligase Complexes; D064173:Anaphase-Promoting Complex-Cyclosome; D046988:Proteasome Endopeptidase Complex