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J. Cell Biol.,
Volume 142, Number 6, September 21, 1998 1547-1558


* Department of Microbiology and Cancer Center and To investigate possible involvement of the
mitogen-activated protein (MAP) kinases ERK1 and
ERK2 (extracellular signal-regulated kinases) in somatic cell mitosis, we have used indirect immunofluorescence with a highly specific phospho-MAP kinase
antibody and found that a portion of the active MAP
kinase is localized at kinetochores, asters, and the midbody during mitosis. Although the aster labeling was
constant from the time of nuclear envelope breakdown,
the kinetochore labeling first appeared at early
prometaphase, started to fade during chromosome congression, and then disappeared at midanaphase. At
telophase, active MAP kinase localized at the midbody.
Based on colocalization and the presence of a MAP kinase consensus phosphorylation site, we identified the
kinetochore motor protein CENP-E as a candidate mitotic substrate for MAP kinase. CENP-E was phosphorylated in vitro by MAP kinase on sites that are
known to regulate its interactions with microtubules and was found to associate in vivo preferentially with
the active MAP kinase during mitosis. Therefore, the
presence of active MAP kinase at specific mitotic structures and its interaction with CENP-E suggest that
MAP kinase could play a role in mitosis at least in part
by altering the ability of CENP-E to mediate interactions between chromosomes and microtubules.
Department of Cell Biology, University of Virginia, Health Sciences
Center, Charlottesville, Virginia 22908; and § The Fox Chase Cancer Institute, Philadelphia, Pennsylvania 19111
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