Premium
Regulation of cyclin E stability in Xenopus embryos
Author(s) -
Brandt Yekaterina,
Mitchell Therese,
Wu Yuehan,
Hartley Rebecca
Publication year - 2010
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.24.1_supplement.840.1
Subject(s) - cyclin b , cyclin d , cyclin , xenopus , cyclin e , cyclin a , cyclin b1 , microbiology and biotechnology , biology , cell cycle , cyclin dependent kinase , proteasome , cyclin a2 , phosphorylation , cytoplasm , cyclin dependent kinase 1 , biochemistry , cell , gene
Cyclin E associates with Cdk2 to mediate the G1/S cell cycle transition and is overexpressed in many cancers. We are studying how cyclin E is downregulated in Xenopus laevis embryos to ask if similar mechanisms are disrupted during tumorigenesis. In Xenopus embryos, cyclin E level is constant until its abrupt destabilization by an undefined mechanism after the12th cell cycle, corresponding to midblastula transition (MBT). Degradation of mammalian cyclin E is regulated by the ubiquitin proteasome system and is phosphorylation dependent. To examine the role of phosphorylation in cyclin E turnover in Xenopus, we generated a series of threonine/serine mutations. Western blot analysis showed that mutation of threonine 394 to alanine (T394A) and both T394A/S398A increased cyclin E stability. T75A mutation had only a minor effect. Immunofluorescence analysis showed that cyclin E re‐localized from the cytoplasm to the nucleus preceding degradation. When cyclin E nuclear import was inhibited, its stability was markedly increased after MBT. We conclude from these studies that cyclin E destruction is facilitated by phosphorylation and requires nuclear import. Treatment of embryos with a proteasome inhibitor caused progressive cytoplasmic accumulation of cyclin E after MBT, suggesting that it may be exported back to the cytoplasm for destruction by the proteasome. This work was supported by NIH grant R01CA095898 to RSH. Grant Funding Source : NIH