Calmodulin And Polo-like Kinase 1 Regulate Mitotic Entry In Mammalian Cells

The cell-division cycle in mammalian cells has to be regulated in both time and space. Ordered and tightly controlled molecular events by activation and deactivation of a series of proteins that act at each stage ensure normal cellular progression. Calmodulin is a universal signaling molecule and thought to be involved in regulating mitotic transitions, but the essential targets of Ca2+/CaM-dependent pathways required for cell proliferation remain elusive. Polo-like kinase is a Ser/Thr kinase and regulates a wide variety of mitotic events from the beginning to the end of mitosis. Bioinformation suggest that Plkl has three potential CaM binding sites, one is the polo-box domain and the other two is in the kinase domain. More and more evidence suggest that timely activation and dynamic subcellular localization of Plkl are critical for regulating Plkl function. Our result suggest a mechanism that the spatio-temporal distribution of calmodulin with Plkl will active Plk1 and promote mitotic entry.1. In metaphase, CaM co-localization with polo-like kinase 1 (Plk1) at centrosome. Immunofluoresence suggest that CaM co-localized with Plk1 at spindle pole body and immunoprecipitation results also shows that they can co-immunoprecipitation with each other in metaphase cell lysate.2. CaM can regulate Plkl activity. Plkl activity was high at G2/M transition. Plkl activity can be inhibit by CaM antagonist in synchronized HeLa cells. Compared with the control cells, CaM stable cell line has higher Plkl activity. Overexpression of mutant CaM in HEK293 cell will not elevate Plkl activity.