Plk1 regulates PICH, a centromere-associated SNF2 family tranlocase that is required for the spindle checkpoint

To investigate the requirements of mitotic, kinetochore-associated
proteins for human chromosome segregation we analyzed the human
Ndc80 complex, a core structural component of the outer
kinetochore. The Ndc80 complex contains Hec1 and Nuf2 that interact
via their N-termini and a smaller subcomplex of Spc24 and Spc25 is
linked to Hec1. The complex is required for faithful chromosome
congression and the recruitment of several proteins of the outer
kinetochore, including the mitotic regulatory kinase Plk1. Pull
down experiments with Plk1 identified a novel
kinetochore/centromere associated DNA translocase, which we termed
PICH, as an interactor of Plk1. The localization of PICH to
kinetochores and centromeres is controlled by Plk1; and moreover,
Plk1 phosphorylation on PICH negatively regulates its localization
/ chromatin association. PICH associates with conspicuous threads
that persist into anaphase where Topoisomerase II causes their
resolution. Moreover, PICH is a novel component of the spindle
assembly checkpoint and PICH-dependent checkpoint signaling is
likely to be mediated via kinetochore associated Mad2. This study
raises questions as to the fate of centromeric DNA in sister
chromatid separation and its timing of decatenation. We speculate
that this enzyme associates with catenated, centromeric DNA from
prometaphase where it may be required to sense the tension between
sister kinetochores.