During cell division, the mitotic spindle consists mainly of microtubules (MTs) and is essential for accurate distribution of the genetic material to the two daughter cells. Errors in spindle formation can lead to incorrect separation of chromosomes that is associated with tumorigenesis or developmental disorders; however, the molecular mechanisms of mitotic spindle assembly are incompletely understood.
In the present study, we show that Chk1, a kinase involved in the cellular response to DNA damage, is essential for optimal density and effective polymerization of spindle MTs in human cells. Chk1 localizes to the centrosomes (the main centers of MT-organization in animal cells) in mitosis by confocal microscopy. Chk1 phosphorylates purified β-tubulin in kinase reactions in vitro at several conserved residues which were identified by mass ,spectrometry. Furthermore, reduced microtubule density in Chk1-deficient cells associates with formation of disorganized spindles. We propose that Chk1 phosphorylates β-tubulin to promote optimal spindle MT polymerization and spindle assembly.
In conclusion, these findings describe a novel mechanism that could protect against tumorigenesis, through regulating mitotic spindle formation.