Different Properties of SEK1 and MKK7 in Dual Phosphorylation of Stress-induced Activated Protein Kinase SAPK/JNK in Embryonic Stem Cells

Abstract

Stress-activated protein kinase/c-Jun NH 2 -terminal kinase (SAPK/JNK), belonging to the mitogen-activated protein kinase family, plays an important role in stress signaling. SAPK/JNK activation requires the phosphorylation of both Thr and Tyr residues in its Thr-Pro-Tyr motif, and SEK1 and MKK7 have been identified as the dual specificity kinases. In this study, we generated The SAPK/JNK 1 is a member of the family of mitogen-activated protein kinase (MAPK). This MAPK is activated not only by many types of cellular stresses, including changes in osmolarity, heat shock, and UV irradiation, but also by serum, lysophosphatidic acid, and inflammatory cytokines (interleukin-1␤ and tumor necrosis factor-␣). The activated SAPK/JNK phosphorylates transcription factors c-Jun, Jun D, and activating transcription factor-2 to regulate gene expression for the stress response. Activation of SAPK/JNK requires the phosphorylation of Tyr and Thr residues located in a Thr-Pro-Tyr motif in the activation loop between VII and VIII of the kinase domain. The phosphorylation is catalyzed by the dual specificity kinases SEK1 (also known as MKK4) and MKK7 (SEK2), which are capable of catalyzing the phosphorylation of both Thr and Tyr residues in vitro (1, 2).Targeted gene-disruption experiments in mice demonstrate that both SEK1 and MKK7 are required for embryonic development. Sek1 Ϫ/Ϫ embryos die between embryonic day 10.5 (E10.5) and E12.5 with impaired liver formation (3-5). Furthermore, we have recently reported that SEK1 is crucial for hepatocyte growth factor-induced activation of SAPK/JNK in developing hepatoblasts of mouse embryos. On the other hand, mkk7 Ϫ/Ϫ embryos die between E11.5 and E12.5 with similar impairment of liver formation and SAPK/JNK activation (6). These results clearly show that both SEK1 and MKK7 play indispensable roles in hepatoblast proliferation during mouse embryogenesis. Distinct biochemical properties between SEK1 and MKK7 may be critical for the indispensable roles of the two activators of SAPK/JNK in vivo.In this regard, several in vitro experiments have shown that SAPK/JNK is activated synergistically by SEK1 and MKK7 (7-9). The synergistic activation may be related to the enzymatic properties of the two MAPKKs: SEK1 prefers the Tyr residue and MKK7 prefers the Thr residue of the MAPK. We have also reported that the synergistic activation of SAPK/JNK in response to stress signals is attenuated with a decreased level of its Tyr phosphorylation in sek1 Ϫ/Ϫ mouse ES cells that retain MKK7 at the same level as the wild-type cells (10).

Stress-Activated Protein Kinase MKK7 Regulates Axon Elongation in the Developing Cerebral Cortex

“…Comparison of MKK4 and MKK7 in the developing brain MKK7 and MKK4 are both JNK activators, and complete activation of JNK requires the activities of both of these kinases (Kishimoto et al, 2003). In our Mkk7 flox/flox Nestin-Cre mice, phosphorylated JNK was markedly reduced despite an upregulation of MKK4 (Fig.…”

Role of mitogen-activated protein kinase kinase 4 in cancer

“…This is supported by studies demonstrating that TNFa and IL-1 preferentially activate MKK7 in vitro and in cells (Finch et al, 1997;Lawler et al, 1997;Moriguchi et al, 1997;Tournier et al, 2001). In contrast, it was observed in Mkk4À/À and Mkk7À/À ES cells and MEFs that both MKK4 and MKK7 make similar contributions to JNK activation in response to a number of environmental stresses including UV radiation, heat shock and osmotic shock (Tournier et al, 2001;Kishimoto et al, 2003). Although the studies described above provided strong genetic evidence to support the role of MKK4 as a JNK activator in vivo, it had been less clear whether MKK4 could regulate p38 activity in vivo.…”

“…These observations led to the hypothesis that JNK isoforms are activated synergistically by MKK4 and MKK7 (Lawler et al, 1998;Fleming et al, 2000;Lisnock et al, 2000). Some in vivo evidence to support this model has come from studies using mouse embryonic stem (ES) cells and mouse embryonic fibroblasts (MEFs) that feature targeted deletions of the Mkk4 and Mkk7 genes (Tournier et al, 2001;Wada et al, 2001;Kishimoto et al, 2003). These studies also demonstrated that distinct stimuli might differentially utilize MKK4 and MKK7.…”

Involvement of Stress Kinase Mitogen-activated Protein Kinase Kinase 7 in Regulation of Mammalian Circadian Clock

“…JNK is activated by many types of external stresses, including changes in osmolarity, heat shock, and UV irradiation, and this activity is regulated via the phosphorylation of particular tyrosine and threonine residues located in the kinase domain. JNK phosphorylation is catalyzed by two dual-specificity kinases, MKK4 3 and MKK7, that act in a synergistic manner (3,4). Although most often activated in response to stress, phosphorylated JNK has been detected in unstressed cultured cells and in isolated mouse tissues, such as the brain (5,6), indicating the importance of JNK signaling in physiological processes other than cellular stress responses.…”