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Mol. Cell. Biol., Jan 1998, 546-557, Vol 18, No. 1
V Dulic, GH Stein, DF Far and SI Reed
Cell cycle arrest in G1 in response to ionizing radiation or senescence is
believed to be provoked by inactivation of G1 cyclin-cyclin- dependent
kinases (Cdks) by the Cdk inhibitor p21(Cip1/Waf1/Sdi1). We provide
evidence that in addition to exerting negative control of the G1/S phase
transition, p21 may play a role at the onset of mitosis. In nontransformed
fibroblasts, p21 transiently reaccumulates in the nucleus near the
G2/M-phase boundary, concomitant with cyclin B1 nuclear translocation, and
associates with a fraction of cyclin A-Cdk and cyclin B1-Cdk complexes.
Premitotic nuclear accumulation of cyclin B1 is not detectable in cells
with low p21 levels, such as fibroblasts expressing the viral human
papillomavirus type 16 E6 oncoprotein, which functionally inactivates p53,
or in tumor-derived cells. Moreover, synchronized E6-expressing fibroblasts
show accelerated entry into mitosis compared to wild-type cells and exhibit
higher cyclin A- and cyclin B1-associated kinase activities. Finally,
primary embryonic fibroblasts derived from p21-/- mice have significantly
reduced numbers of premitotic cells with nuclear cyclin B1. These data
suggest that p21 promotes a transient pause late in G2 that may contribute
to the implementation of late cell cycle checkpoint controls.
Copyright © 1998, American Society for Microbiology
Nuclear accumulation of p21Cip1 at the onset of mitosis: a role at the G2/M-phase transition
CNRS-UMR 134, Universite de Nice-Sophia Antipolis, Nice, France. dulic@vega.crbm.cnrs-mop.fr
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