The JNK-interacting protein-1 scaffold protein targets MAPK phosphatase-7 to dephosphorylate JNK

The c-Jun N-terminal kinase (JNK) group of mitogen-activated protein kinases (MAPKs) are activated by pleiotropic signals including environmental stresses, growth factors, and hormones. A subset of JNK can bind to distinct scaffold proteins that also bind upstream kinases of the JNK pathway, allowing sequential kinase activation within a signaling module. The JNK-interacting protein-1 (JIP-1) scaffold protein specifically binds JNK, MAP kinase kinase 7, and members of the MLK family and is essential for stress-mediated JNK activation in neurones. Here we report that JIP-1 also binds the dual-specificity phosphatases MKP7 and M3/6 via a region independent of its JNK binding domain. The C-terminal region of MKP7, homologous to that of M3/6 but not other DSPs, is required for interaction with JIP-1. When MKP7 is bound to JIP-1 it reduces JNK activation leading to reduced phosphorylation of the JNK target c-Jun. These results indicate that the JIP-1 scaffold protein modulates JNK signaling via association with both protein kinases and protein phosphatases that target JNK.     

Ceramide promotes apoptosis in chronic myelogenous leukemia-derived K562 cells by a mechanism involving caspase-8 and JNK

Ceramide is a sphingolipid that activates stress kinases such as p38 and c-JUN N-Terminal Kinase (JNK). Though Chronic Myelogenous Leukemia (CML) derived K562 cells resist killing by short chain C2-ceramide, we report here that longer chain C6-ceramide promotes apoptosis in these cells. C6-ceramide induces cleavage of Caspase-8 and Caspase-9, but only Caspase-8 is required for apoptosis. The sphingolipid killed CML derived KBM5 cells and, to a lesser extent, imatinib-resistant KBM5-STI cells suggesting that BCR-ABL can not completely block C6-ceramide-induced apoptosis but the kinase may regulate the process. BCR-ABL is known to suppress Protein Phosphatase 2A (PP2A) in CML cells. While C6-ceramide can activate PP2A in acute leukemia cells, the sphingolipid did not activate the phosphatase in K562 cells. C6-ceramide did not activate p38 kinase but did promote JNK activation and phosphorylation of JUN. Inhibition of JNK by pharmacological agent protected K562 cells from C6-ceramide suggesting that JNK plays an essential role in C6-ceramide mediated apoptosis. Furthermore, the sphingolipid promoted MCL-1 phosphorylation by a mechanism that, at least in part, involves JNK. The findings presented here suggest that Caspase-8, JNK, and perhaps MCL-1 may play important roles in regulating cell death and may represent new targets for therapeutic strategies for CML.     

JNK信号通路对蜂胶抑制白血病K562细胞增殖的调控作用

目的探讨JNK信号通路对蜂胶抑制K562细胞增殖过程的调控作用。方法体外培养K562细胞,用不同浓度蜂胶、c—Jun氨基末端激酶（c—JanN—terminalkinase,JNK）特异性抑制剂SP600125对白血病K562细胞进行处理,用MTT法检测细胞增殖抑制率,流式细胞术（FCM）检测细胞凋亡率,Western印迹检测JNK下游分子c—Jun以及磷酸化c—Jan（p-c-Jun）的变化。结果蜂胶作用K562细胞后,增殖抑制率、凋亡率显著升高,具有时间和剂量依赖性,并伴随p-c-Jun蛋白水平上调;加入SP600125能下调p-c-Jun的水平,显著提高蜂胶对K562细胞的增殖抑制率和凋亡率。结论JNK信号通路参与了蜂胶抑制K562细胞增殖过程的调控。抑制JNK活性可增强蜂胶对K562细胞的增殖抑制、凋亡诱导作用。     

Involvement of a Rho-ROCK-JNK pathway in arsenic trioxide-induced apoptosis in chronic myelogenous leukemia cells

The apoptotic signals activated by As(2)O(3) in the chronic myelogenous leukemia (CML) cell lines K562 and KCL22 were investigated. As(2)O(3) was found to induce apoptosis in these cells via the intrinsic pathway. As(2)O(3) also induced a sustained c-Jun NH2-terminal kinase (JNK) activation which preceded and was necessary for caspase-9 activation. We established that Rho and its effector, the kinase ROCK, are activated by As(2)O(3). Inhibition of either Rho or ROCK prevented JNK activation and protected against apoptosis. Thus, in CML cells, apoptosis induced by As(2)O(3) is mediated, at least in part, via a Rho-ROCK-JNK axis. These findings define a novel signaling pathway for As(2)O(3)-induced apoptosis.     

Induction of apoptosis by shikonin through a ROS/JNK-mediated process in Bcr/Abl-positive chronic myelogenous leukemia （CML） cells

This study examined the signaling events induced by shikonin that lead to the induction of apoptosis in Bcr/ Abl-positive chronic myelogenous leukemia （CML） cells （e.g., K562, LAMA84）. Treatment of K562 cells with shikonin （e.g., 0.5 pM） resulted in profound induction of apoptosis accompanied by rapid generation of reactive oxygen species （ROS）, striking activation of c-Jun-N-terminal kinase （JNK） and p38, marked release of the mitochondrial proteins cytochrome c and Smac/DIABLO, activation of caspase-9 and -3, and cleavage of PARP. Scavenging of ROS completely blocked all of the above-mentioned events （i.e., JNK and p38 phosphorylation, cytochrome c and Smac/DIABLO release, caspase and PARP cleavage, as well as the induction of apoptosis） following shikonin treatment. Inhibition of JNK and knock-down of JNK1 significantly attenuated cytochrome c release, caspase cleavage and apoptosis, but did not affect shikonin-mediated ROS production. Additionally, inhibition of caspase activation completely blocked shikonin-induced apoptosis, but did not appreciably modify shikonin-mediated cytochrome c release or ROS generation. Altogether, these findings demonstrate that shikonin-induced oxidative injury operates at a proximal point in apoptotic signaling cascades, and subsequently activates the stress-related JNK pathway, triggers mitochondrial dysfunction, cytochrome c release, and caspase activation, and leads to apoptosis. Our data also suggest that shikonin may be a promising agent for the treatment of CML, as a generator of ROS.     

Reactive oxygen species-mediated activation of JNK and down-regulation of DAXX are critically involved in penta-O-galloyl-beta-d-glucose-induced apoptosis in chronic myeloid leukemia K562 cells

Although 1,2,3,4,6-penta-O-galloyl-beta-d-glucose (PGG) was well known to have antitumor activities in breast, prostate, kidney, liver cancers and HL-60 leukemia via regulation of caspase 3, p53, S-phase kinase-associated protein 2 (Skp2) and insulin receptor signaling, the underlying mechanism of PGG-induced apoptosis linked with reactive oxygen species (ROS) mediated c-Jun N-terminal kinase (JNK) and DAXX was never elucidated in chronic myeloid leukemia (CML) K562 cells until now. Herein PGG significantly decreased the viability of CML cell lines such as K562 and KBM-5 without hurting normal peripheral blood lymphocytes (PBLs). PGG increased the number of TUNEL-positive cells and the sub-G1 cell population as well as activated caspase cascades including caspase-8, -9 and -3 in K562 cells. Interestingly, a significant activation of JNK by PGG was observed by MULTIPLEX assay and Western blotting. Conversely, JNK inhibitor D-JNKi suppressed the cleavages of caspase 3 and PARP induced by PGG in K562 cells. Also, PGG dramatically enhanced generation of ROS and reduced the expression of death-domain-associated protein (DAXX). Of note, ROS inhibitor acetyl-l-cysteine (NAC) reversed JNK-dependent apoptosis and DAXX inhibition induced by PGG. Overall, these findings suggest that ROS-dependent JNK activation and DAXX downregulation are critically involved in PGG-induced apoptosis in K562 cells.     

Caspase-activated DNase (CAD)-independent oligonucleosomal DNA fragmentation in chronic myeloid leukaemia cells; a requirement for serine protease and Mn2+-dependent acidic endonuclease activity

We have previously reported that the pro-apoptotic pyrrolobenzoxazepine, PBOX-6, induces apoptosis in chronic myelogenous leukaemia (CML) cells which is accompanied by oligonucleosomal DNA fragmentation. In this study we show that PBOX-6-induced oligonucleosomal DNA fragmentation occurs in the absence of caspase and CAD activation in CML cells. Dissection of the signalling pathway has revealed that induction of apoptosis requires the upstream activation of a trypsin-like serine protease that promotes the phosphorylation and inactivation of anti-apoptotic Bcl-2. In addition, in this system chymotrypsin-like serine proteases are dispensable for high molecular weight DNA fragmentation, however are required for the activation of a relatively small manganese-dependent acidic endonuclease that is responsible for oligonucleosomal fragmentation of DNA. Furthermore, we demonstrate mitochondrial involvement during PBOX-6-induced apoptosis and suggest the existence of unidentified mitochondrial effectors of apoptosis. This work was supported by the Irish Research Council for Science, Technology and Engineering (IRCSET).     

JNK and p38 MAPK are independently involved in tributyltin-mediated cell death in rainbow trout (Oncorhynchus mykiss) RTG-2 cells

Mitogen-activated protein kinases (MAPKs) are a family of Ser/Thr protein kinases that transmit various extracellular signals to the nucleus inducing gene expression, cell proliferation, and apoptosis. Recent studies have revealed that organotin compounds induce apoptosis and MAPK phosphorylation/activation in mammal cells. In this study, we elucidated the cytotoxic mechanism of tributyltin (TBT), a representative organotin compound, in rainbow trout (Oncorhynchus mykiss) RTG-2 cells. TBT treatment resulted in significant caspase activation, characteristic morphological changes, DNA fragmentation, and consequent apoptotic cell death in RTG-2 cells. TBT exposure induced the rapid and sustained accumulation of phosphorylated MAPKs, including extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 MAP kinase (p38 MAPK). Further analysis using pharmacological inhibitors against caspases and MAPKs showed that TBT also induced cell death in a caspase-independent manner and that p38 MAPK is involved in TBT-induced caspase-independent cell death, whereas JNK is involved in the caspase-dependent apoptotic pathway. Thus, TBT employs at least two independent signaling cascades to mediate cell death in RTG-2 cells. To our knowledge, this is the first study revealing the relationship between MAPK activation and TBT cytotoxicity in RTG-2 cells.     

c-Jun N-terminal kinase regulates apoptosis in endometrial cancer cells

c-Jun N-terminal kinases (JNKs) are important regulators of cell proliferation and apoptosis that have been implicated in tumorigenesis. We investigated the role of JNKs in apoptotic responses in Ishikawa and HEC-50 cells, models of type I and type II endometrial cancer, respectively. Etoposide treatment or UV irradiation resulted in sustained activation of JNK, correlating with the induction of apoptosis. Inhibition of JNK, or MAP kinase kinase 4 (MKK4), selectively suppressed apoptotic responses in both Ishikawa and HEC-50 cells. Knockdown of protein kinase C δ (PKCδ) also attenuated apoptosis in endometrial cancer cells and inhibited the sustained, UV-mediated JNK activation in HEC-50, but not Ishikawa cells. Etoposide-induced JNK phosphorylation was unaffected by PKCδ knockdown, implying that JNK can regulate apoptosis by PKCδ-dependent and independent pathways, according to stimulus and cell type. Thus, expression and activity of JNK and PKCδ in endometrial cancer cells modulate apoptosis and sensitivity to chemotherapeutic agents and may function as tumor suppressors in the endometrium. Elaine M. Reno and James M. Haughian are first authors.     

Vinblastine-induced phosphorylation of Bcl-2 and Bcl-XL is mediated by JNK and occurs in parallel with inactivation of the Raf-1/MEK/ERK cascade

Microtubule-damaging agents arrest cells at G(2)/M and induce apoptosis in association with phosphorylation of the anti-apoptotic proteins Bcl-2 and Bcl-X(L). Because microtubule inhibitors activate JNK, we sought to determine whether JNK was responsible for Bcl-2/Bcl-X(L) phosphorylation in KB-3 cells treated with vinblastine. Two major endogenous forms of JNK, p46(JNK1) and p54(JNK2), were present in KB-3 cells, and both isoforms were activated by vinblastine as determined by Mono Q chromatography. We used antisense oligonucleotides (AS) to specifically inhibit their expression. A combination of AS-JNK1 with AS-JNK2 inhibited by 80% vinblastine-induced phosphorylation of two known JNK substrates, c-Jun and ATF-2. In addition, AS-JNK1/2 inhibited vinblastine-induced phosphorylation of Bcl-2 by 85% and that of Bcl-X(L) by 65%. Stable expression of the JNK scaffold protein JIP-1 blocked vinblastine-induced phosphorylation of c-Jun and ATF-2, but did not affect Bcl-2/Bcl-X(L) phosphorylation, confirming a bifurcation in JNK signaling involving both nuclear and non-nuclear substrates. Vinblastine-induced phosphorylation of Raf-1 was unaffected by AS-JNK1/2 and was associated with loss of activity for MEK substrate in vitro and inactivation of ERK in vivo. These results provide evidence for a direct role of the JNK pathway in apoptotic regulation through Bcl-2/Bcl-X(L) phosphorylation.     

Apoptosis induced by domoic acid in mouse cerebellar granule neurons involves activation of p38 and JNK MAP kinases

In mouse cerebellar granule neurons (CGNs) the marine neurotoxin domoic acid (DomA) induces neuronal cell death, either by apoptosis or by necrosis, depending on its concentration, with apoptotic damage predominating in response to low concentrations (100 nM). DomA-induced apoptosis is due to selective activation of AMPA/kainate receptors, and is mediated by DomA-induced oxidative stress, leading to mitochondrial dysfunction and activation of caspase-3. The p38 MAP kinase and the c-Jun NH2-terminal protein kinase (JNK) have been shown to be preferentially activated by oxidative stress. Here we report that DomA increases p38 MAP kinase and JNK phosphorylation, and that this effect is more pronounced in CGNs from Gclm (-/-) mice, which lack the modifier subunit of glutamate-cysteine ligase, have very low glutathione (GSH) levels, and are more sensitive to DomA-induced apoptosis than CGNs from wild-type mice. The increased phosphorylation of JNK and p38 kinase was paralleled by a decreased phosphorylation of Erk 1/2. The AMPA/kainate receptor antagonist NBQX, but not the NMDA receptor antagonist MK-801, prevents DomA-induced activation of p38 and JNK kinases. Several antioxidants (GSH ethyl ester, catalase and phenylbutylnitrone) also prevent DomA-induced phosphorylation of JNK and p38 MAP kinases. Inhibitors of p38 (SB203580) and of JNK (SP600125) antagonize DomA-induced apoptosis. These results indicate the importance of oxidative stress-activated JNK and p38 MAP kinase pathways in DomA-induced apoptosis in CGNs.