Abstract
Centrobin/NIP2 is a centrosomal protein that is required for centrosome duplication. It is also critical for microtubule organization in both interphase and mitotic cells. In the present study, we observed that centrobin is phosphorylated in a cell cycle stage-specific manner, reaching its maximum at M phase. PLK1 is a kinase that is responsible for M phase-specific phosphorylation of centrobin. The microtubule forming activity of centrobin was enhanced by PLK1 phosphorylation. Furthermore, mitotic spindles were not assembled properly with the phospho-resistant mutant of centrobin. Based on these results, we propose that centrobin functions as a microtubule stabilizing factor and PLK1 enhances centrobin activity for proper spindle formation during mitosis.
Highlights
A global change in microtubule dynamics is observed in cells entering M phase [6, 7]
Microtubule polymerization recovers during prometaphase and returns to interphase levels by the end of metaphase. Protein kinases such as CDK1 and MAP4/microtubule affinity-regulating kinase are known to regulate microtubule dynamics during this period
We propose that PLK1 phosphorylation is required for centrobin function in spindle assembly during mitosis
Summary
A global change in microtubule dynamics is observed in cells entering M phase [6, 7]. The results showed that centrobin phosphorylation was reduced in PLK1-suppressed cells; centrobin protein levels remained constant, suggesting that PLK1 may be responsible for phosphorylation of centrobin at the M phase (Fig. 1B). Centrobin fusion proteins (GST-CBN) were used as substrates, and PLK1 was prepared from 293T cells in which wild-type (WT), kinase-dead (KD), or constitutively active (CA) FLAG-PLK1 proteins were ectopically expressed [25].
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