Distinct regulators for Plk1 activation in starfish meiotic and early embryonic cycles

Abstract

The Polo-like kinase, Plk, has multiple roles in regulating mitosis. In particular, Plk1 has been postulated to function as a trigger kinase that phosphorylates and activates Cdc25C prior to the activation of cyclin B-Cdc2 and thereby initiates its activation. However, the upstream regulation of Plk1 activation remains unclear. Here we have studied the interplay between Plk1 and Cdc2 through meiotic and early embryonic cycles in starfish. Distinct kinases, cyclin B-Cdc2, MAPK along with cyclin B- and/or cyclin A-Cdc2 and cyclin A-Cdc2, were unique upstream regulators for Plk1 activation at meiosis I, meiosis II and embryonic M-phase, respectively, indicating that Plk1 is not the trigger kinase at meiotic reinitiation. When Plk1 was required for cyclin B-Cdc2 activation, the action of Plk1 was mediated primarily through suppression of Myt1 rather than through activation of Cdc25. We propose that Plk1 can be activated by either cyclin A- or cyclin B-Cdc2, and its primary target is Myt1.

Molecular and structural basis of polo-like kinase 1 substrate recognition: Implications in centrosomal localization

“…Indeed, Plk1 can phosphorylate and thereby regulate both Cdc25C (12) and the Cdk1 inhibitor Myt1 (13,14). This would seem consistent with the hypothesis that Plk1 is the ''trigger'' kinase for the activation of Cdk1.…”

Plk1 inhibition leads to a failure of mitotic division during the first mitotic division in pig embryos

“…It is involved in regulating multiple biological events in cancer cell proliferation [14]. In recent years, Plk1 has been discovered to also play regulatory roles in germ cells and oocytes, such as mouse [18], porcine [19], and starfish [20]. The recent focus of research has been on some Bexperimental or model^animals, such as Drosophila melanogaster [21], zebrafish [2], and mice [1].…”

B23/Nucleophosmin Serine 4 Phosphorylation Mediates Mitotic Functions of Polo-like Kinase 1

“…However, more recent studies (42,43) have shown that Plk1 is implicated in a positive feedback loop that consists of both Plk1 and CDK1, and it does not function as the initial activator, rather its activation depends upon CDK1 activity. Our study seems to shed new light on this controversial issue, as the inhibitory effect of olomoucine on Plk1-mediated B23 Ser-4 phosphorylation that we observed here strongly implies that the B23 phosphorylation activity of Plk1 during M-phase is dependent upon CDK1 activation.…”