The mixed lineage kinase SPRK phosphorylates and activates the stress-activated protein kinase activator, SEK-1 - PubMed (original) (raw)

. 1996 Aug 9;271(32):19025-8.

doi: 10.1074/jbc.271.32.19025.

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The mixed lineage kinase SPRK phosphorylates and activates the stress-activated protein kinase activator, SEK-1

A Rana et al. J Biol Chem. 1996.

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Abstract

SPRK (also called PTK-1 and MLK-3), a member of the mixed lineage kinase subfamily of (Ser/Thr) protein kinases, encodes an amino-terminal SH3 domain followed by a kinase catalytic domain, two leucine zippers interrupted by a short spacer, a Rac/Cdc42 binding domain, and a long carboxyl-terminal proline-rich region. We report herein that SPRK activates the stress-activated protein kinases (SAPKs) but not ERK-1 during transient expression in COS cells; the p38 kinase is activated modestly (1.3-2 fold) but consistently. SPRK also activates cotransfected SEK-1/MKK-4, a dual specificity kinase which phosphorylates and activates SAPK. Reciprocally, expression of mutant, inactive SEK-1 inhibits completely the basal and SPRK-activated SAPK activity. Immunoprecipitated recombinant SPRK is able to phosphorylate and activate recombinant SEK-1 in vitro to an extent comparable to that achieved by MEK kinase-1. These results identify SPRK as a candidate upstream activator of the stress-activated protein kinases, acting through the phosphorylation and activation of SEK-1.

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