We propose to understand how the mitotic kinase PLK1 drives chromosome segregation errors, with a specific focus on Gravin, a PLK1 scaffold. In both three-dimensional primary prostate cancer cell cultures that are prone to Gravin depletion and Gravin short hairpin RNA (shRNA)–treated cells, an increase in cells containing micronuclei was noted in comparison with controls. To examine whether the loss of Gravin affected PLK1 distribution and activity, we utilized photokinetics and a PLK1 activity biosensor. Gravin depletion resulted in an increased PLK1 mobile fraction, causing the redistribution of active PLK1, which leads to increased defocusing and phosphorylation of the mitotic centrosome protein CEP215 at serine-613. Gravin depletion further led to defects in microtubule renucleation from mitotic centrosomes, decreased kinetochore-fiber integrity, increased incidence of chromosome misalignment, and subsequent formation of micronuclei following mitosis completion. Murine Gravin rescued chromosome misalignment and micronuclei formation, but a mutant Gravin that cannot bind PLK1 did not. These findings suggest that disruption of a Gravin–PLK1 interface leads to inappropriate PLK1 activity contributing to chromosome segregation errors, formation of micronuclei, and subsequent DNA damage.
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