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Updated: Jul 2, 2026

Identification of Cyclin-dependent Kinase 1 Specific Phosphorylation Sites by an In Vitro Kinase Assay
Published on: May 3, 2018
Bacterial cyclomodulin Cif blocks the host cell cycle by stabilizing the cyclin-dependent kinase inhibitors p21 and
Ascel Samba-Louaka1, Jean-Philippe Nougayrède, Claude Watrin
1INRA, UMR 1225, F-31076 Toulouse, France.
Abstract:
The cycle inhibiting factor (Cif) is a cyclomodulin produced by enteropathogenic and enterohemorrhagic Escherichia coli. Upon injection into the host cell by the bacterial type III secretion system, Cif inhibits the G2/M transition via sustained inhibition of the mitosis inducer CDK1 independently of the DNA damage response. In this study, we show that Cif induces not only G2, but also G1 cell cycle arrest depending on the stage of cells in the cell cycle during the infection. In various cell lines including differentiated and untransformed enterocytes, the cell cycle arrests are correlated with the accumulation of the cyclin-dependent kinase inhibitors p21(waf1/cip1) and p27(kip1). Cif-induced cyclin-dependent kinase inhibitor accumulation is independent of the p53 pathway but occurs through inhibition of their proteasome-mediated degradation. Our results provide a direct link between the mode of action of Cif and the host cell cycle control.
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