The forkhead-associated domain of Ki-67 antigen interacts with the novel kinesin-like protein Hklp2

The Ki-67 antigen (pKi-67) is widely used as a cell proliferation marker pr otein. Its actual role in the cell cycle progression, however, is presently unclear. Using a two-hybrid screening in yeast, a novel protein, termed Hk lp2 (human kinesin-like protein 2), was identified and shown to interact wi th the forkhead-associated (FHA) domain of pKi-67, Hklp2 has 1388 amino aci ds and shows a striking similarity (a 53% identity in amino acids) to Xklp2 , a plus-end directed kinesin-like motor found in Xenopus, The interaction domain of Hklp2 was mapped to the portion that comprised residues 1017-1237 and that was phosphorylated in vitro by incubating with mitotic but not in terphasic HeLa cell extracts. That the interaction was striking in the mito tic extract was also verified. In addition, immunofluorescence using specif ic antibodies revealed an association between pKi-67 and Hklp2 at the perip hery of mitotic chromosomes, largely in close proximity to the centromeres, These findings suggest that pKi-67 is involved in the progression of mitos is via its interaction with Hklp2.