Kinetochore localization and microtubule interaction of the human spindle checkpoint kinase Mps1

Members of the Mps1 protein kinase family have been implicated in the regulation of the kinetochore-mediated spindle assembly checkpoint in species ranging from yeast to man. However, conflicting data have been reported on the subcellular localization of vertebrate Mps1 kinases and their possible roles in centrosome duplication. Moreover, little is presently known about the regulation of Mps1 kinases during the cell cycle. Here, we have used immunofluorescence microscopy, immunoblotting and siRNA-mediated depletion of hMps1 to re-investigate the subcellular localization of this kinase. Our data confirm the kinetochore association of hMps1 but suggest that the centrosome staining produced by some anti-hMps1 antibodies could be due to cross-reactivity with other proteins. We also show that the kinetochore association of hMps1 is mediated by the amino-terminal, non-catalytic domain and specifically requires the presence of the Hec1/Ndc80-Nuf2 complex at the kinetochore. Finally, we have combined in vitro binding studies and kinase assays to explore the influence of microtubules on hMps1 activity. Our data indicate that the catalytic domain of hMps1 displays affinity for microtubules and that microtubule binding could contribute to the regulation of kinase activity.