H. Ellinger-ziegelbauer et al., Ste20-like kinase (SLK), a regulatory kinase for polo-like kinase (Plk) during the G2/M transition in somatic cells, GENES CELLS, 5(6), 2000, pp. 491-498
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 dur
ing mitosis, but a kinase upstream of Plk is still unknown.
Results: We show here that human Ste20-like kinase (SLK), which is a ubiqui
tously expressed mammalian protein related to xPlkk1, can phosphorylate and
activate murine Plk1. During progression through the G2 phase of the mamma
lian 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 a
ctivity.
Conclusions: We propose that SLK has a role in the regulation of Plk1 activ
ity in actively dividing cells during the somatic cell cycle. SLK itself is
suggested to be regulated by phosphorylation.