Regulation of Nuclear Transport and Degradation of the Xenopus Cyclin-dependent Kinase Inhibitor, p27Xic1

The regulation of the vertebrate cell cycle is controlled by the function of cyclin-dependent kinases (CDKs), cyclins, and CDK inhibitors. The Xenopus laevis kinase inhibitor, p27Xic1 (Xic1) is a member of the p21Cip1/p27Kip1/p57Kip2 CDK inhibitor family and inhibits CDK2-cyclin E in vitro as well a...

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Bibliographic Details
Published in:The Journal of biological chemistry 2001-01, Vol.276 (2), p.1610-1617
Main Authors: Chuang, Li-Chiou, Yew, P. Renee
Format: Article
Language:English
Subjects:
Animals
Binding Sites
CDC2-CDC28 Kinases
Cell Cycle Proteins
Cell Nucleus - physiology
Cell-Free System
Chromatin - physiology
Cyclin E - metabolism
Cyclin-Dependent Kinase 2
Cyclin-Dependent Kinase Inhibitor p27
Cyclin-Dependent Kinases - antagonists & inhibitors
Cyclin-Dependent Kinases - metabolism
DNA Replication
Enzyme Inhibitors - metabolism
Female
Interphase
Male
Microtubule-Associated Proteins - metabolism
Mutagenesis, Site-Directed
Oocytes - cytology
Oocytes - physiology
Point Mutation
Protein-Serine-Threonine Kinases - metabolism
Recombinant Proteins - metabolism
Spermatozoa - physiology
Tumor Suppressor Proteins
Ubiquitins
Xenopus laevis
Xenopus Proteins
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Summary:The regulation of the vertebrate cell cycle is controlled by the function of cyclin-dependent kinases (CDKs), cyclins, and CDK inhibitors. The Xenopus laevis kinase inhibitor, p27Xic1 (Xic1) is a member of the p21Cip1/p27Kip1/p57Kip2 CDK inhibitor family and inhibits CDK2-cyclin E in vitro as well as DNA replication in Xenopus egg extracts. Xic1 is targeted for degradation in interphase extracts in a manner dependent on both the ubiquitin conjugating enzyme, Cdc34, and nuclei. Here we show that ubiquitination of Xic1 occurs exclusively in the nucleus and that nuclear localization of Xic1 is necessary for its degradation. We find that Xic1 nuclear localization is independently mediated by binding to CDK2-cyclin E and by nuclear localization sequences within the C terminus of Xic1. Our results also indicate that binding of Xic1 to CDK2-cyclin E is dispensable for Xic1 ubiquitination and degradation. Moreover, we show that amino acids 180–183 of Xic1 are critical determinants of Xic1 degradation. This region of Xic1 may define a motif of Xic1 essential for recognition by the ubiquitin conjugation machinery or for binding an alternate protein required for degradation.
ISSN:0021-9258
1083-351X
DOI:10.1074/jbc.M008896200