Prostate-derived sterile 20-like kinases (PSKs/TAOKs) are activated in mitosis and contribute to mitotic cell rounding and spindle positioning.

Prostate-derived sterile 20-like kinases (PSKs) 1-α, 1-β, and 2 are members of the germinal-center kinase-like sterile 20 family of kinases. Previous work has shown that PSK 1-α binds and stabilizes microtubules whereas PSK2 destabilizes microtubules. Here, we have investigated the activation and autophosphorylation of endogenous PSKs and show that their catalytic activity increases as cells accumulate in G(2)/M and declines as cells exit mitosis. PSKs are stimulated in synchronous HeLa cells as they progress through mitosis, and these proteins are activated catalytically during each stage of mitosis. During prophase and metaphase activated PSKs are located in the cytoplasm and at the spindle poles, and during telophase and cytokinesis stimulated PSKs are present in trans-Golgi compartments. In addition, small interfering RNA (siRNA) knockdown of PSK1-α/β or PSK2 expression inhibits mitotic cell rounding as well as spindle positioning and centralization. These results show that PSK catalytic activity increases during mitosis and suggest that these proteins can contribute functionally to mitotic cell rounding and spindle centralization during cell division.