Direct Activation of the Stress-activated Protein Kinase (SAPK) and Extracellular Signal-regulated Protein Kinase (ERK) Pathways by an Inducible Mitogen-activated Protein Kinase/ERK Kinase Kinase 3 (MEKK) Derivative

Heidrun Ellinger-Ziegelbauer,Keith Brown,Kathy Kelly,Ulrich Siebenlist

doi:10.1074/jbc.272.5.2668

Abstract

The extracellular signal-regulated kinase (ERK) pathway, the stress-activated protein kinase (SAPK) pathway, and the p38 pathway are three major mitogen-activated protein kinase (MAPK) cascades known to participate in the regulation of cellular responses to a variety of extracellular signals. Upstream regulatory components of these kinase cascades, the MAPK/ERK kinase kinases (MEKK), have been described in several systems. We have isolated a cDNA encoding human MEKK3. Transfected MEKK3 has the ability to activate both SAPK and ERK pathways, but does not induce p38 activity, in agreement with a previous report on murine MEKK3 (Blank, J. L., Gerwins, P., Elliott, E. M., Sather, S., and Johnson, G. L. (1996) J. Biol. Chem. 271, 5361-5368). We now demonstrate that MEKK3 activates SEK and MEK, the known kinases targeting SAPK and ERK, respectively. Utilizing an estrogen ligand-activated MEKK3 derivative, we furthermore demonstrate that MEKK3 regulates the SAPK and the ERK pathway directly. Consistent with the fact that several SAPK-inducing agents activate the transcription factor NFkappaB, we now show that MEKK3 also enhances transcription from an NFkappaB-dependent reporter gene in cotransfection assays. The ability of MEKK3 to simultaneously activate the SAPK and ERK pathways is remarkable, given that they have divergent roles in cellular homeostasis.

Highlights

The extracellular signal-regulated kinase (ERK) pathway, the stress-activated protein kinase (SAPK) pathway, and the p38 pathway are three major mitogenactivated protein kinase (MAPK) cascades known to participate in the regulation of cellular responses to a variety of extracellular signals
Our findings suggest that MEKK3- and MEKK1-activated MAPK cascades may participate in transducing signals leading to activation of NF␬B, actual intervening molecular steps are unknown since none of the kinases in these cascades are likely to phosphorylate I␬B␣ directly [56]
The biochemical characterization of human MEKK3 presented here clearly demonstrates the ability of MEKK3 to directly regulate two of the three currently identified mammalian MAPK cascades, namely the SAPK and the ERK pathways

Summary

Introduction

The extracellular signal-regulated kinase (ERK) pathway, the stress-activated protein kinase (SAPK) pathway, and the p38 pathway are three major mitogenactivated protein kinase (MAPK) cascades known to participate in the regulation of cellular responses to a variety of extracellular signals. One of the major signaling systems by which cells transduce extracellular signals into intracellular responses are the mitogen-activated protein kinase (MAPK) cascades. Three MAPK subfamilies have so far been clearly identified, more are believed to exist These are (i) the extracellular signal regulated kinases ERK1 and ERK2 ( referred to as p44/42MAPK) [9]; ii) the c-Jun-Nterminal/stress-activated protein kinases (JNK/SAPK), including human JNK1/rat SAPK␥, human JNK2/rat SAPK␣, and human JNK3, probably the human homologue of rat SAPK␤ (p54␤) (10 –12); and (iii) the p38 kinase, which is similar to the yeast high osmolarity glycerol response (HOG) kinase [14, 15]. A MEKK for the p38 pathway has not yet been identified, evidence suggests that it may be related to the transforming growth factor-␤-activated kinase 1 [27, 28]

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Conclusion