Activated JNK Phosphorylates the C-terminal Domain of MLK2 That Is Required for MLK2-induced Apoptosis

Abstract

One mechanism by which cells respond to extracellular stimuli is the recruitment of signaling networks that regulate changes in the internal environment and control gene transcription (reviewed in Refs. 1 and 2). A group of signaling pathways that are highly conserved through evolution are collectively known as mitogen-activated protein kinase (MAPK) 1 pathways (3, 4). The classical MAPK pathway is triggered by growth factors binding to cell surface receptors leading to the activation of the GTPase, Ras. This pathway results in activation of the extracellular signal-regulated kinases (ERKs) leading to gene transcription and cellular proliferation. A parallel MAPK pathway triggered by stress factors such as osmotic shock, UV irradiation, cytotoxic drugs, and inflammatory cytokines results in activation of the stress-activated protein kinase/c-Jun N-terminal kinases (SAPK/JNKs) (2). A second stress-activated pathway leads to activation of p38 MAPK. Effects of stress activation vary from proliferation, differentiation, and gene transcription to cell cycle arrest and apoptosis depending on cell type and stimulus (2).All MAPK pathways utilize a "three-kinase cascade" mechanism to modulate incoming signals. Thus, each MAPK has upstream-activating kinases (MAPKKs) that are in turn regulated by MAPKK kinases (MAPKKKs) (reviewed in Ref. 5). Some of the upstream kinases appear to be highly specific for a particular cascade, whereas others link to more than one MAPK. The MAPKKs for the ERKs are the MAP/ERK kinases (MEKs) (6 -8), whereas activators for JNKs are the SAPK/ERK kinase/JNK kinase (SEK1/JNKK), also known as MAPK kinase 4 (MKK4) (9 -11), and the more recently discovered MKK7 (12)(13)(14). In the case of p38, the main upstream-activating kinases are MKK3 and MKK6 (11,15,16), but p38 can also be activated by JNKK/MKK4 (11), providing crossover between the JNK and the p38 pathways. MAPKKKs are a larger group of kinases that have overlapping specificities for MAPKKs and are themselves activated by an array of interactions in response to extracellular and internal stimuli (reviewed in Ref. 17). As more upstream activators of the MAPKs are identified, the picture of how these three parallel pathways are regulated becomes more complex.Recently it has become clear that MAPKs not only control downstream signals to transcription factors but also exert effects upstream on their activators. In budding yeast, the three components of the pheromone-induced MAPK cascade are Ste11 f Ste7 f Fus3/KSS (18). Errede and co-workers (19) coined the term "feedback phosphorylation" to describe upstream phosphorylation of Ste7 by Fus3. In mammalian cells, Xu and Cobb (20) report that JNK binds to and phosphorylates

Regulation of mixed-lineage kinase activation in JNK-dependent morphogenesis

“…Extensive phosphorylation of the C-termini of MLK2 and MLK3 suggest that this region might serve a regulatory role as a substrate for proline-directed kinases engaged in feedback or crosstalk control (Phelan et al, 2001;Vacratsis et al, 2002). Thus, it was surprising to find that the SKLC-WT transgenic protein, lacking the Cterminus of Slpr, rescued slpr mutants to adulthood nearly as well as the epitope-tagged full-length version ( Fig.…”

“…The C-terminal half of MLK proteins is the least conserved among homologs although it tends to be rich in serine, threonine and proline residues (Phelan et al, 2001;Vacratsis et al, 2002). Yet, there are no recognizable protein domains to suggest a function.…”

Induction of apoptosis in retinoid-refractory acute myelogenous leukemia by a novel AHPN analog

“…JNK activation has been found to be an essential component of the apoptotic process in a number of systems. 53,[76][77][78] JNK protein kinases are encoded by 3 genes. 56 JNK1 and JNK2 are expressed ubiquitously while expression of JNK 3 is predominantly restricted to the brain; simultaneous loss of expression of JNK1 and JNK2 is associated with defects in neuronal apoptosis.…”

Stimulation of NeuroD activity by huntingtin and huntingtin-associated proteins HAP1 and MLK2

“…The HA-MLK2 expression plasmid has been described in ref. 31. The pCS2ϩHA vector was generated by cloning the fragment of pKH3 (the HA-MLK2 vector backbone) containing three copies of the HA epitope tag into the pCS2ϩ vector.…”