CAMP (C13orf8, ZNF828) is a novel regulator of kinetochore-microtubule attachment.

Proper attachment of microtubules to kinetochores is essential for accurate chromosome segregation. Here, we report a novel protein involved in kinetochore-microtubule attachment, chromosome alignment-maintaining phosphoprotein (CAMP) (C13orf8, ZNF828). CAMP is a zinc-finger protein containing three characteristic repeat motifs termed the WK, SPE, and FPE motifs. CAMP localizes to chromosomes and the spindle including kinetochores, and undergoes CDK1-dependent phosphorylation at multiple sites during mitosis. CAMP-depleted cells showed severe chromosome misalignment, which was associated with the poor resistance of K-fibres to the tension exerted upon establishment of sister kinetochore bi-orientation. We found that the FPE region, which is responsible for spindle and kinetochore localization, is essential for proper chromosome alignment. The C-terminal region containing the zinc-finger domains negatively regulates chromosome alignment, and phosphorylation in the FPE region counteracts this regulation. Kinetochore localization of CENP-E and CENP-F was affected by CAMP depletion, and by expressing CAMP mutants that cannot functionally rescue CAMP depletion, placing CENP-E and CENP-F as downstream effectors of CAMP. These data suggest that CAMP is required for maintaining kinetochore-microtubule attachment during bi-orientation.

Nucleoporin Nup188 is required for chromosome alignment in mitosis.

Most cancer cells are aneuploid, which could be caused by defects in chromosome segregation machinery. Nucleoporins (Nup) are components of the nuclear pore complex, which is essential for nuclear transport during interphase, but several nucleoporins are also known to be involved in chromosome segregation. Here we report a novel function of Nup188, one of the nucleoporins regulating chromosome segregation. Nup188 localizes to spindle poles during mitosis, through the C-terminal region of Nup188. In Nup188-depleted mitotic cells, chromosomes fail to align to the metaphase plate, which causes mitotic arrest due to the spindle assembly checkpoint. Both the middle and the C-terminal regions were required for chromosome alignment. Robust K-fibers, microtubule bundles attaching to kinetochores, were hardly formed in Nup188-depleted cells. Significantly, we found that Nup188 interacts with NuMA, which plays an instrumental role in focusing microtubules at centrosomes, and NuMA localization to spindle poles is perturbed in Nup188-depleted cells. These data suggest that Nup188 promotes chromosome alignment through K-fiber formation and recruitment of NuMA to spindle poles.