IDENTIFICATION OF A 102-KDA PROTEIN (CYTOCENTRIN) IMMUNOLOGICALLY RELATED TO KERATIN-19, WHICH IS A CYTOPLASMICALLY DERIVED COMPONENT OF THE MITOTIC SPINDLE POLE
Eca. Paul et A. Quaroni, IDENTIFICATION OF A 102-KDA PROTEIN (CYTOCENTRIN) IMMUNOLOGICALLY RELATED TO KERATIN-19, WHICH IS A CYTOPLASMICALLY DERIVED COMPONENT OF THE MITOTIC SPINDLE POLE, Journal of Cell Science, 106, 1993, pp. 967-981
The mAb RK7, previously shown to recognize keratin 19, was also found
to cross-react with a biologically unrelated 102 kDa protein, which be
comes associated with the poles of the mitotic apparatus. This newly i
dentified protein, called cytocentrin, is a stable cellular component,
may be at least in part phosphorylated, and displays a cell cycle-dep
endent cellular localization. In interphase cells, it is diffusely dis
tributed in the cytosol and shows no affinity for cytoplasmic microtub
ules. It becomes localized to the centrosome in early prophase, prior
to nuclear envelope breakdown, separation of replicated centrosomes, a
nd nucleation of mitotic apparatus microtubules. During metaphase, cyt
ocentrin is located predominately at the mitotic poles, often appearin
g as an aggregate of small globular sub-components; it also associates
with some polar microtubules. In late anaphase/early telophase cytoce
ntrin dissociates entirely from the mitotic apparatus and becomes temp
orarily localized with microtubules in the midbody, from which it disa
ppears by late telophase. In taxol-treated cells cytocentrin was assoc
iated with the center of the miniasters but also showed affinity for s
ome cytoplasmic microtubules. Studies employing G2-synchronized cells
and nocodazole demonstrated that cytocentrin can become associated wit
h mitotic centrosomes independently of tubulin polymerization and that
microtubules regrow from antigen-containing foci. We interpret these
results to suggest that cytocentrin is a cytoplasmic protein that beco
mes specifically activated or modified at the onset of mitosis so that
it can affiliate with the mitotic poles where it may provide a link b
etween the pericentriolar material and other components of the mitotic
apparatus.