Ste20-like kinase (SLK), a regulatory kinase for polo-like kinase (Plk) during the G2/M transition in somatic cells.
BACKGROUND
Activation of the cyclin-dependent kinase cdc2-cyclin B1 at the G2/M transition of the cell cycle requires dephosphorylation of threonine-14 and tyrosine-15 in cdc2, which in higher eukaryotes is brought about by the Cdc25C phosphatase. In Xenopus, there is evidence that a kinase cascade comprised of xPlkk1 and Plx1, the Xenopus polo-like kinase 1, plays a key role in the activation of Cdc25C during oocyte maturation. In the mammalian somatic cell cycle, a polo-like kinase homologue (Plk1) also functions during mitosis, but a kinase upstream of Plk is still unknown.


RESULTS
We show here that human Ste20-like kinase (SLK), which is a ubiquitously expressed mammalian protein related to xPlkk1, can phosphorylate and activate murine Plk1. During progression through the G2 phase of the mammalian cell cycle, the activity of endogenous SLK is increased. The amount of SLK protein is decreased in quiescent and differentiating cells. Treatment with okadaic acid induces a phosphorylation-dependent enhancement of SLK activity.


CONCLUSIONS
We propose that SLK has a role in the regulation of Plk1 activity in actively dividing cells during the somatic cell cycle. SLK itself is suggested to be regulated by phosphorylation.
Ellinger-Ziegelbauer
H
H
Department of Biophysics, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.
Karasuyama
H
H
Yamada
E
E
Tsujikawa
K
K
Todokoro
K
K
Nishida
E
E
D016475:3T3 Cells; D000818:Animals; D015153:Blotting, Western; D019556:COS Cells; D018797:Cell Cycle Proteins; D002455:Cell Division / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D016195:G2 Phase / Q000187:drug effects / Q000502:physiology*; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D008938:Mitosis / Q000187:drug effects / Q000502:physiology*; D019319:Okadaic Acid / Q000494:pharmacology; D009928:Organ Specificity; D010766:Phosphorylation / Q000187:drug effects; D011233:Precipitin Tests; D011494:Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D011518:Proto-Oncogene Proteins; D014162:Transfection; D014981:Xenopus; D029867:Xenopus Proteins; D000097869:Polo-Like Kinase 1; D000099317:Hippo Kinases
D018797:Cell Cycle Proteins; D004791:Enzyme Inhibitors; D019319:Okadaic Acid; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D029867:Xenopus Proteins; D000097869:Polo-Like Kinase 1; C485733:SLK protein, human; D000099317:Hippo Kinases; C115856:stk10-a protein, Xenopus; C402650:SLK protein, mouse