Abstract
Emi1 promotes mitotic entry in Xenopus laevis embryos by inhibiting the APC(Cdc20) ubiquitination complex to allow accumulation of cyclin B. We show here that human Emi1 (hEmi1) functions to promote cyclin A accumulation and S phase entry in somatic cells by inhibiting the APC(Cdh1) complex. At the G1-S transition, hEmi1 is transcriptionally induced by the E2F transcription factor, much like cyclin A. hEmi1 overexpression accelerates S phase entry and can override a G1 block caused by overexpression of Cdh1 or the E2F-inhibitor p105 retinoblastoma protein (pRb). Depleting cells of hEmi1 through RNA interference prevents accumulation of cyclin A and inhibits S phase entry. These data suggest that E2F can activate both transcription of cyclin A and the hEmi1-dependent stabilization of APC(Cdh1) targets, such as cyclin A, to promote S phase entry.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Anaphase-Promoting Complex-Cyclosome
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Animals
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Cell Cycle Proteins / genetics
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Cell Cycle Proteins / metabolism*
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Cyclin A / metabolism
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DNA-Binding Proteins / metabolism
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E2F Transcription Factors
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F-Box Proteins
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Fibroblasts / metabolism
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HeLa Cells
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Humans
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Ligases / metabolism*
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Recombinant Fusion Proteins / metabolism
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S Phase / physiology*
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Transcription Factors / metabolism*
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Tumor Cells, Cultured
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Ubiquitin / metabolism
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Ubiquitin-Protein Ligase Complexes*
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Xenopus Proteins
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Xenopus laevis / embryology
Substances
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Cell Cycle Proteins
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Cyclin A
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DNA-Binding Proteins
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E2F Transcription Factors
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F-Box Proteins
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FBXO5 protein, Xenopus
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FBXO5 protein, human
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Recombinant Fusion Proteins
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Transcription Factors
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Ubiquitin
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Xenopus Proteins
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Ubiquitin-Protein Ligase Complexes
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Anaphase-Promoting Complex-Cyclosome
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Ligases