Abstract
Expression and activity of the germinal center kinase, Ste20-like kinase (SLK), are increased during kidney development and recovery from ischemic acute renal failure. In this study, we characterize the activation and functional role of SLK. SLK underwent dimerization via the C-terminal domain, and dimerization enhanced SLK activity. In contrast, the C-terminal domain of SLK did not dimerize with a related kinase, Mst1, and did not affect Mst1 activity. Phosphorylation/dephosphorylation of SLK were not associated with changes in kinase activity. SLK induced phosphorylation of apoptosis signal-regulating kinase-1 (ASK1) and increased ASK1 activity, indicating that ASK1 is a substrate of SLK. Moreover, SLK stimulated phosphorylation of p38 mitogen-activated protein kinase via ASK1, but not c-Jun N-terminal kinase nor extracellular signal-regulated kinase. Chemical anoxia and recovery during re-exposure to glucose (ischemia-reperfusion injury in cell culture) stimulated SLK activity. Overexpression of SLK enhanced anoxia/recovery-induced apoptosis, release of cytochrome c, and activities of caspase-8 and -9, and apoptosis was reduced significantly with p38 and caspase-9 inhibitors. Induction of the endoplasmic reticulum stress response by anoxia/recovery or tunicamycin (monitored by induction of Bip or Grp94 expression, phosphorylation of eukaryotic translation initiation factor 2alpha subunit, expression of CHOP, and activation of caspase-12) was attenuated in cells that overexpress SLK. Thus, SLK is an anoxia/recovery-dependent kinase that is activated via homodimerization and that signals via ASK1 and p38 to promote apoptosis. Attenuation of the protective aspects of the endoplasmic reticulum stress response by SLK may contribute to its proapoptotic effect.
Highlights
FEBRUARY 10, 2006 VOLUME 281 NUMBER 6 c-Jun N-terminal kinase (JNK) pathway but not extracellular signalregulated (ERK) or p38 pathways
The present study demonstrates that Ste20-like kinase (SLK) is an ischemia-reperfusion-dependent protein kinase that may be activated via homodimerization and that signals via apoptosis signalregulating kinase-1 (ASK1) and p38 mitogenactivated protein kinase (MAPK) to promote apoptosis
Expression and activity of the renal epithelial protein kinase, SLK, were increased during kidney development and following ischemiareperfusion injury, and stable overexpression of SLK in cultured cells increased apoptosis and exacerbated cell death after cells were subjected to chemical anoxia/recovery [16]
Summary
FEBRUARY 10, 2006 VOLUME 281 NUMBER 6 c-Jun N-terminal kinase (JNK) pathway but not extracellular signalregulated (ERK) or p38 pathways. To determine whether SLK-induced phosphorylation of ASK1 leads to an increase in ASK1 activity, COS cells were transiently transfected with Myc-His-SLK and/or HA-ASK1. Anoxia/recovery increased expression of Grp94 in control MDCK cells but not in MDCK cells that stably overexpress SLK (Fig. 7, C and D).
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