Activation Of JNKs Research Articles

UVA Induces Ser381 Phosphorylation of p90RSK/MAPKAP-K1 via ERK and JNK Pathways

UVA exposure plays an important role in the etiology of skin cancer. The family of p90-kDa ribosomal S6 kinases (p90(RSK)/MAPKAP-K1) are activated via phosphorylation. In this study, results show that UVA-induced phosphorylation of p90(RSK) at Ser(381) through ERKs and JNKs, but not p38 kinase pathways. We provide evidence that UVA-induced p90(RSK) phosphorylation and kinase activity were time- and dose-dependent. Both PD98059 and a dominant negative mutant of ERK2 blocked ERKs and p90(RSK) Ser(381) phosphorylation, as well as p90(RSK) activity. A dominant negative mutant of p38 kinase blocked UVA-induced phosphorylation of p38 kinase, but had no effect on UVA-induced Ser(381) phosphorylation of p90(RSK) or kinase activity. UVA-induced p90(RSK) phosphorylation and kinase activity were markedly attenuated in JnK1(-/-) and JnK2(-/-) cells. A dominant negative mutant of JNK1 inhibited UVA-induced JNKs and p90(RSK) phosphorylation and kinase activity, but had no effect on ERKs phosphorylation. PD169316, a novel inhibitor of JNKs and p38 kinase, inhibited phosphorylation of p90(RSK), JNKs, and p38 kinase, but not ERKs. However, SB202190, a selective inhibitor of p38 kinase, had no effect on p90(RSK) or JNKs phosphorylation. Significantly, ERKs and JNKs, but not p38 kinase, immunoprecipitated with p90(RSK) when stimulated by UVA and p90(RSK) was a substrate for ERK2 and JNK2, but not p38 kinase. These data indicate clearly that p90(RSK) Ser(381) may be phosphorylated by activation of JNKs or ERKs, but not p38 kinase.

Activation of mitogen-activated protein kinases in the non-ischemic myocardium of an acute myocardial infarction in rats.

As one of the signal transduction pathways related to myocardial remodeling, mitogen-activated protein kinases (MAPKs) possibly play an important role in ischemic heart disease, but it is still unknown whether myocardial MAPKs are activated in the non-ischemic region of an acute myocardial infarction (AMI). Therefore, the present study investigated the myocardial activity of extracellular signal-regulated kinases (ERKs), c-Jun NH2 terminal kinases (JNKs) and p38MAPK during the acute phase of an infarction of the rat heart, and measured the geometrical ventricular changes by echocardiography. All MAPKs were significantly activated in the ischemic myocardium (IM), non-ischemic septal wall (SW), and right ventricular wall (RV). Furthermore, the activation patterns of MAPKs differed in each region. The activation of p44ERK, JNKs and p38MAPK in the IM occurred rapidly after myocardial ischemia, followed by those in the SW and RV. The activator protein-1 DNA binding activities of the IM, SW and RV increased significantly at I day after coronary ligation. Echocardiography showed increased SW motion and RV dilatation. In conclusion, this is the first in vivo evidence that myocardial MAPKs are activated in the non-ischemic region of an AMI. Echocardiographic results suggest that acceleration of workload and/or stretch may partially induce the activation of MAPKs.

KiSS-1 Represses 92-kDa Type IV Collagenase Expression by Down-regulating NF-κB Binding to the Promoter as a Consequence of IκBα-induced Block of p65/p50 Nuclear Translocation

The 92-kDa type IV collagenase (MMP-9) plays a critical role in tissue remodeling. We undertook a study to determine whether the KiSS-1 gene, previously shown to suppress cancer spread (metastases), negatively regulates MMP-9 expression. Six cell lines positive for MMP-9 mRNA were deficient in KiSS-1 mRNA. One of these cell lines, HT-1080, stably transfected with a KiSS-1 expression construct, demonstrated substantially lower MMP-9 enzyme activity/protein and in vitro invasiveness. The lower MMP-9 enzyme activity reflected reduced steady-state mRNA levels which, in turn, was due to attenuated transcription. Activation of ERKs and JNKs by phorbol 12-myristate 13-acetate and tumor necrosis factor alpha, respectively, leading to increased MMP-9 amounts was not antagonized by KiSS-1 expression, suggesting that MAPK pathways modulating MMP-9 synthesis are not the target of KiSS-1. Although MMP-9 expression is regulated by AP-1, Sp1, and Ets transcription factors, KiSS-1 did not alter the binding of these factors to the MMP-9 promoter. However, NF-kappaB binding to the MMP-9 promoter required for expression of this collagenase was reduced by KiSS-1 expression. Diminished NF-kappaB binding reflected less p50/p65 in the nucleus secondary to increased IkappaBalpha levels in the cytosols of the KiSS-1 transfectants. Thus, KiSS-1 diminishes MMP-9 expression by effecting reduced NF-kappaB binding to the promoter.

PI3 Kinase mediates transformation of hematopoietic cells by the V816 c-kit mutant

Abstract C-Kit is a receptor tyrosine kinase that binds stem cell factor. Substitution of valine for aspartic acid 816 (V816) constitutively activates human c-Kit and this mutation is found in patients with mastocytosis, leukemia and germ cells tumors. Transduction of immortalized murine progenitor cells with wild-type c-Kit (MIHC-Kit) results in stem cell factor-induced growth (SCF), while cells expressing V816 c-Kit (MIHC-V816) are factor-independent and tumorigenic. The mechanisms mediating transformation by V816 c-Kit are unknown. SCF activates Erk 1, Erk2 and P13 kinase in MIHC-Kit cells, and P13 kinase contributes to activation of Akt and Jnks. In MIHC-V816 cells, P13 kinase, Jnk 1 and Jnk 2 were activated, but Akt, Erk 1 and Erk 2 were not. Thus, V816 c-Kit constitutively activates P13 kinase, but not all signaling pathways activated by wild-type c-Kit. Further, pathways downstream of P13 kinase are altered in MIHC-V816 cells. Studies with a P13 kinase inhibitor and V816/F721 c-Kit, a mutant incapable of recruiting P13 kinase, indicate that constitutive activation of P13 kinase plays a role in factor-independent growth mediated by V816 c-Kit and is critical for tumorigenicity of MIHC. These data are the first to demonstrate the role of P13 kinase in transformation of hematopoietic cells by this oncogenic c-Kit mutant.

Prolactin Stimulates Activation of c-jun N-Terminal Kinase (JNK)

In recent years the mitogen-activated protein (MAP) kinase family has expanded to include both c-jun N-terminal kinases (JNKs), and the p38/HOG1 family in addition to the extracellular regulated kinase (ERK) family. These kinases are activated by a variety of growth factors, as well as extra- and intracellular insults such as osmotic stress, UV light, and chemotherapeutic agents. Stimulation of the PRL-dependent Nb2 cell line with PRL results in the rapid activation of JNK as determined by the glutathione-S-transferase (GST)-jun kinase assay. Activation was maximal 30 min after stimulation with 50 nM rat PRL (rPRL) and decreased after that time. Dose response studies indicated that concentrations as low as 10 nM rPRL resulted in maximal activation. The interleukin-3 (IL-3)-dependent myeloid progenitor cell line 32Dcl3 was transfected with the long, Nb2, and short forms of the rat PRL receptor (rPRLR), as well as the long form of the human PRLR (hPRLR). The long and Nb2 forms of the PRLR were able to stimulate activation of JNK; however, the short form of the rPRLR was not. This corresponds with the inability of the short form of the rPRLR to stimulate proliferation of 32Dcl3 cells. Activation of JNK in 32Dcl3 cells expressing the long form of the hPRLR was maximal at 30 min after stimulation with 100 nM ovine PRL (oPRL) and declined after that time. Dose response studies indicated that activation of JNK was maximal after 30 min at a concentration of 10 nM, and the amount of activated JNK declined at the highest concentration of oPRL, 100 nM. Immunoblot analysis with an antibody that recognizes the activated (phosphorylated) forms of JNK1 and JNK2 indicated that both JNK1 and JNK2 isoforms were activated in 32D/hPRLR cells stimulated with oPRL. A recombinant human adenovirus expressing a kinase-inactive mutant of JNK1 (APF mutant) was used to determine the biological effect of blocking JNK activity in Nb2 cells. Expression of the JNK1-APF mutant inhibited cellular proliferation and induced DNA fragmentation typical of cells undergoing apoptosis. These data suggest that activation of JNKs may be important in mitogenic signaling and/or suppression of apoptosis in Nb2 cells.

Mitogen-Activated Protein Kinases Are Differently Activated in Early Hypertrophic Response to Acute Pressure Overload in Rat Myocardium

P55 Mitogen-activated protein kinases (MAPKs) have been reported as important signaling molecules mediating cardiomyocyte hypertrophic response to various stimuli. Four subfamilies of MAPKs have been described in mammalian cells: c-jun NH2 terminal kinases (JNKs), p38-MAPKs (p38), extracellular response kinases (ERKs) and big MAP-kinase (BMK). Our objective was to study the activation of these kinases in the early phases of hypertrophic response, which is currently obscure. Transverse aorta constriction (TAC) was performed in male Wistar rats (160-200g) and left ventricles were studied up to 3 h following the surgery. To study the activation of ERKs, JNKs and p38, heart homogenates were separated into cytosolic (C) and nuclear (N) fractions and their kinase activities were determined by Western Blot using anti p-ERK, p-JNK and p-p38 antibodies. The membranes were then stripped and blotted with anti-ERK, anti-JNK and anti-p38 to determine the protein contents. The amount of BMK was studied in total homogenates using anti-BMK antibody and its activity was studied by measuring its in vitro autophosphorylation. ERK1/2 were transiently activated in both subcellular fractions, reaching a maximum 30 min after TAC (ERK1 - 236% in C and 196% in N; ERK2 - 280% in C and 248% in N) and returning toward basal levels after 1 h. p38 showed a sustained increase in its activity only in C (to 259%) but not in N after 1 h of TAC. JNKs showed a biphasic response with an early and major increase in their activities after 10 min (to 313% for JNK1 and to 288% for JNK2 in C) and a second and minor one following 3 h of TAC. In parallel, TAC induced a significant nuclear translocation of JNK1. The total amount of BMK remained stable during the studied period. We observed a progressive increase in its kinase activity which was directly related to TAC time course (45% in 10 min; 159% in 1 h and 173 % in 2h). These results indicate that pressure overload induces an early activation of the four subfamilies of MAPKs. Differences in their time course activation suggest that they might play different roles in the early hypertrophic response in adult rat myocardium.

Mitogen-Activated Protein Kinases Are Differently Activated in Early Hypertrophic Response to Acute Pressure Overload in Rat Myocardium

P55 Mitogen-activated protein kinases (MAPKs) have been reported as important signaling molecules mediating cardiomyocyte hypertrophic response to various stimuli. Four subfamilies of MAPKs have been described in mammalian cells: c-jun NH2 terminal kinases (JNKs), p38-MAPKs (p38), extracellular response kinases (ERKs) and big MAP-kinase (BMK). Our objective was to study the activation of these kinases in the early phases of hypertrophic response, which is currently obscure. Transverse aorta constriction (TAC) was performed in male Wistar rats (160-200g) and left ventricles were studied up to 3 h following the surgery. To study the activation of ERKs, JNKs and p38, heart homogenates were separated into cytosolic (C) and nuclear (N) fractions and their kinase activities were determined by Western Blot using anti p-ERK, p-JNK and p-p38 antibodies. The membranes were then stripped and blotted with anti-ERK, anti-JNK and anti-p38 to determine the protein contents. The amount of BMK was studied in total homogenates using anti-BMK antibody and its activity was studied by measuring its in vitro autophosphorylation. ERK1/2 were transiently activated in both subcellular fractions, reaching a maximum 30 min after TAC (ERK1 - 236% in C and 196% in N; ERK2 - 280% in C and 248% in N) and returning toward basal levels after 1 h. p38 showed a sustained increase in its activity only in C (to 259%) but not in N after 1 h of TAC. JNKs showed a biphasic response with an early and major increase in their activities after 10 min (to 313% for JNK1 and to 288% for JNK2 in C) and a second and minor one following 3 h of TAC. In parallel, TAC induced a significant nuclear translocation of JNK1. The total amount of BMK remained stable during the studied period. We observed a progressive increase in its kinase activity which was directly related to TAC time course (45% in 10 min; 159% in 1 h and 173 % in 2h). These results indicate that pressure overload induces an early activation of the four subfamilies of MAPKs. Differences in their time course activation suggest that they might play different roles in the early hypertrophic response in adult rat myocardium.

Differential Requirement for the Stress-Activated Protein Kinase/c-Jun NH2-Terminal Kinase in RNA Damage-Induced Apoptosis in Primary and in Immortalized Fibroblasts

Onconase, an anticancer ribonuclease, damages cellular tRNA and causes caspase-dependent apoptosis in targeted cells (M. S. Iordanov, O. P. Ryabinina, J. Wong, T. H. Dinh, D. L. Newton, S. M. Rybak, and B. E. Magun. Cancer Res. 60, 1983–1994, 2000). The proapoptotic action of onconase depends on its RNase activity, but the molecular mechanisms leading to RNA damage-induced caspase activation are completely unknown. In this study, we have investigated whether onconase activates two signal-transduction pathways commonly stimulated by conventional chemo- and radiotherapy, namely the stress-activated protein kinase (SAPK) cascade and the pathway leading to the activation of nuclear factor-kappa B (NF-κB). We found that, in all cell types tested, onconase is a potent activator of SAPK1 (JNK1 and JNK2) and SAPK2 (p38 MAP kinase), but that it is incapable of activating NF-κB. Inhibition of p38 MAP kinase activity with a pharmacological inhibitor, SB203580, demonstrated that p38 MAP kinase is not required for onconase cytotoxicity. Using explanted fibroblasts from mice that contain targeted disruption of both jnk1 and jnk2 alleles, we found that JNKs are important mediators of onconase-induced cytotoxicity. Surprisingly, following the immortalization of these same cells with human papilloma virus (HPV16) gene products E6 and E7, additional proapoptotic pathways (exclusive of JNK) were provoked by onconase. Our results demonstrate that onconase may activate proapoptotic pathways in tumor cells that are not able to be accessed in normal cells. These results present the possibility that the cytotoxic activity of onconase in normal cells may be reduced by blocking the activity of JNKs.

Requirement for Protein-tyrosine Phosphatase SHP-2 in Insulin-induced Activation of c-Jun NH2-terminal Kinase

Mitogen-activated protein kinases, including extracellular signal-regulated kinases and c-Jun NH(2)-terminal kinases (JNKs), are activated by insulin. Although the mechanism by which the insulin receptor activates extracellular signal-regulated kinases is relatively well defined, the pathway that leads to JNK activation is poorly understood. Overexpression of a catalytically inactive mutant (SHP-2C/S) of the protein-tyrosine phosphatase SHP-2 in Rat-1 fibroblasts that also express human insulin receptors has now revealed that activation of JNKs by insulin and epidermal growth factor, but not that by anisomycin or sorbitol, requires SHP-2. A dominant negative mutant (RasN17) of Ha-Ras blocked insulin-induced JNK activation, whereas a dominant negative mutant (RacN17) of Rac1 or a specific inhibitor (LY294002) of phosphoinositide 3-kinase did not, indicating a role for Ras, but not for Rac or phosphoinositide 3-kinase, in this effect. SHP-2C/S markedly inhibited Ras activation in response to insulin without affecting insulin-induced tyrosine phosphorylation of cellular substrates or the dissociation of the Crk-p130(Cas) complex. In contrast, SHP-2C/S did not inhibit activation of JNKs induced by a constitutively active mutant (RasV12) of Ha-Ras. Furthermore, expression of myristoylated SOS, which functions as a potent activator of Ras, induced JNK activation even when SHP-2 was inactivated. These results suggest that SHP-2 contributes to JNK activation in response to insulin by positively regulating the Ras signaling pathway at the same level as, or upstream from, SOS.

Induction of signal transduction pathways in rat gastric epithelial cells stimulated with interleukin-1beta.

Interleukin-1beta (IL-1beta) participates in cell growth, differentiation and apoptosis via activation of several kinases in a variety of cells. Mitogen-activated protein (MAP) kinases are important intermediates of the signal transduction pathway from the cell surface to the nucleus, leading to activation of transcription factors. There are no reports on the effect of IL-1beta on these pathways in gastric epithelial cells. To investigate whether IL-1beta activates MAP kinases [extracellular signal-regulated kinases (ERKs), c-Jun NH2-terminal kinases (JNKs) and p38 MAP kinase (p38 MAPK)] and nuclear factor (NF)-kappaB. a transcription factor, in gastric epithelial cells (RGM1). The activities of ERKs and JNKs were estimated by in-gel kinase assay, and p38 MAPK activity was measured by in vitro kinase assay at various time points (0-40 min) after addition of IL-1beta (100 pg/mL) for 20 min. The activity of NF-kappaB was analysed using gel mobility shift assay at times from 0 to 4 h after addition of IL-1beta. Activity of ERKs was detectable at 10 min, peaked at 20 min, and continued at increased levels until 40 min. Activity of both JNKs and p38 MAPK were detectable during 5-20 min, and then decreased within 40 min. Activation of NF-kappaB occurred at 30 min, and increased activity continued for 6 h. Interleukin-1beta activated MAP kinases and NF-kappaB in RGM1 cells. The activation induced by this cytokine may play an important role in the initiation of the inflammatory process in gastric mucosa.

Downregulation of p53 by sustained JNK activation during apoptosis.

In a previous study, we prepared short-chain fatty acid (SCFA) mixtures mimicking the composition of the digested fibers from wheat bran, oat bran, pectin, and cellulose and tested the products on U4 cells, a cell-line model for normal colonocytes. These SCFA mixes induced the cyclin-dependent kinase (cdk) inhibitors p21 and p27, which bound to cdk2/cyclin E and cdk4/cyclin D1 complexes, blocking their kinase activity and arresting cell growth. SCFAs from digested fiber may control intestinal crypt height in vivo by inducing apoptosis in growth-arrested cells at the top of the crypt. In the present study, we report that SCFA mixes induced apoptosis of U4 cells and unexpectedly caused both a sustained activation of the stress-activated protein kinase c-jun N-terminal kinase 1 (JNK1) and downregulation of the tumor suppressor protein p53. JNK1 bound to p53, and the amount of JNK1-bound p53 accurately reflected the amount of total cellular p53. After activation by SCFAs, JNK1 phosphorylated its bound p53. This phosphorylation is likely to have converted p53 into an apoptotic target because p53 breakdown correlated with caspase-3 activity, was inhibited by a caspase-3 inhibitor in a dose-dependent manner, and was inhibited by transfection of dominant-negative JNK1. Because JNK1 activation was sustained in SCFA-treated U4 cells, JNK1 can bind, phosphorylate, and release p53 for proteolysis and then continue this cycle until many p53 molecules have been phosphorylated. Loss of p53 protein was likely due to proteolysis and not to transcriptional changes because a sixfold decrease in p53 protein occurred within 3-24 h of SCFA treatment, whereas p53 mRNA levels were downregulated as much only after 2-3 d. SCFA mixes targeted p53 and possibly other cellular proteins for degradation during apoptosis by causing a sustained activation of JNKs.

Pro-inflammatory Cytokines Stimulate Mitogen-activated Protein Kinase Subfamilies, Increase Phosphorylation of c-Jun and ATF2 and Upregulate c-Jun Protein in Neonatal Rat Ventricular Myocytes

A. Clerk, J. G. Harrison, C. S. Long and P. H. Sugden. Pro-inflammatory Cytokines Stimulate Mitogen-activated Protein Kinase Subfamilies, Increase Phosphorylation of c-Jun and ATF2 and Upregulate c-Jun Protein in Neonatal Rat Ventricular Myocytes. Journal of Molecular and Cellular Cardiology (1999) 31, 2087–2099. Pro-inflammatory cytokines may be important in the pathophysiological responses of the heart. We investigated the activation of the three mitogen-activated protein kinase (MAPK) subfamilies [c-Jun N-terminal kinases (JNKs), p38-MAPKs and extracellularly-responsive kinases (ERKs)] by interleukin-1 β (IL-1 β) or tumour necrosis factorα (TNF α) in primary cultures of myocytes isolated from neonatal rat ventricles. Both cytokines stimulated a rapid (maximal within 10 min) increase in JNK activity. Although activation of JNKs by IL-1 β was transient returning to control values within 1 h, the response to TNF α was sustained. IL-1 β and TNFα also stimulated p38-MAPK phosphorylation, but the response to IL-1 β was consistently greater than TNFα . Both cytokines activated ERKs, but to a lesser degree than that induced by phorbol esters. The transcription factors, c-Jun and ATF2, are phosphorylated by the MAPKs and are implicated in the upregulation of c-Jun. IL-1 β and TNF α stimulated the phosphorylation of c-Jun and ATF2. However, IL-1 β induced a greater increase in c-Jun protein. Inhibitors of protein kinase C (PKC) (Ro318220, GF109203X) and the ERK cascade (PD98059) attenuated the increase in c-Jun induced by IL-1 β, but LY294002 (an inhibitor of phosphatidylinositol 3′ kinase) and SB203580 (an inhibitor of p38-MAPK, which also inhibits certain JNK isoforms) had no effect. These data illustrate that some of the pathological effects of IL-1 β and TNF α may be mediated through the MAPK cascades, and that the ERK cascade, rather than JNKs or p38-MAPKs, are implicated in the upregulation of c-Jun by IL-1 β.

JNK Activation Is Required for JB6 Cell Transformation Induced by Tumor Necrosis Factor-α but Not by 12-O-Tetradecanoylphorbol-13-Acetate

Signal transduction via mitogen-activated protein kinase pathways plays a key role in a variety of cellular responses, including cell proliferation, differentiation, tumor promotion, and cell death. c-Jun N-terminal kinases (JNKs) are identified as members of the mitogen-activated protein kinase family and are known to phosphorylate and activate several transcription factors, including c-Jun, ATF, and Elk-1. However, the role of JNK activation in tumor promotion is not yet defined. Because previous studies have indicated that exposure of JB6 Cl 41 cells to either 12-O-tetradecanoylphorbol-13-acetate (TPA) or tumor necrosis factor-alpha (TNF-alpha) results in cell transformation, we investigated the role of JNKs in this biological process by using dominant negative JNK(1) and the cell transformation model JB6 Cl 41 cells. Incubation of Cl 41 cells with TNF-alpha led to cell transformation and activation of JNKs. Introduction of the dominant negative mutant of JNK(1) into JB6 Cl 41 cells specifically inhibited TNF-alpha-induced activation of JNKs, but not Erks and p38 kinases. Most importantly, expressing dominant negative mutant JNK(1) inhibited TNF-alpha-induced cell transformation but not TPA-induced cell transformation. Our results directly demonstrated for the first time that JNK activation is required for TNF-alpha- but not TPA-induced cell transformation.

Translocation of Protein Kinase Cε and Protein Kinase Cδ to Membrane Is Required for Ultraviolet B-induced Activation of Mitogen-activated Protein Kinases and Apoptosis

UV-induced signal transduction may be involved in tumor promotion and induction of apoptosis. The role of protein kinase C (PKC) in UVB-induced signal transduction is not well understood. This study showed that UVB markedly induced translocation of membrane-associated PKCepsilon and PKCdelta, but not PKCalpha, from cytosol to membrane. Dominant negative mutant (DNM) PKCepsilon or PKCdelta inhibited UVB-induced translocation of PKCepsilon and PKCdelta, respectively. UVB-induced activation of extracellular signal-regulated protein kinases (Erks) and c-Jun NH2-terminal kinases (JNKs) was strongly inhibited by DNM PKCepsilon and PKCdelta, whereas the DNM of PKCalpha was less effective on the UVB-induced phosphorylation of Erks and JNKs. Among the PKC inhibitors used only rottlerin, a selective inhibitor of PKCdelta, markedly inhibited the UVB-induced activation of Erks and JNKs, but not p38 kinases. Safingol, a selective inhibitor for PKCalpha, did not show any inhibitory effect on UVB-induced mitogen-activated protein kinase activation. GF109203X is a stronger inhibitor of classical PKC than novel PKC. Lower concentrations of GF109203X (<10 microM) had no effect on UVB-induced activation of Erks or JNKs. However, at higher concentrations (over 20 microM), GF109203X inhibited UVB-induced activation of JNKs, Erks, and even p38 kinases. Meanwhile, rottlerin and GF109203X markedly inhibited UVB-induced apoptosis of JB6 cells, whereas safingol had little inhibitory effect. DNM-Erk2 cells and PD98059, a selective inhibitor for mitogen-activated protein kinase/extracellular signal-regulated kinase 1 that directly activates Erks, inhibited UVB-induced apoptosis. DNM-JNK1 cells also blocked UVB-induced apoptosis, whereas SB202190, a specific inhibitor for p38 kinases, did not produce the inhibitory effect. These data demonstrate that PKCdelta and PKCepsilon, but not PKCalpha, mediate UVB-induced signal transduction and apoptosis in JB6 cells through activation of Erks and JNKs.

Etoposide-induced activation of c-jun N-terminal kinase (JNK) correlates with drug-induced apoptosis in salivary gland acinar cells.

We have examined the ability of etoposide to induce apoptosis in two recently established rat salivary acinar cell lines. Etoposide induced apoptosis in the parotid C5 cell line as evidenced by the appearance of cytoplasmic blebbing and nuclear condensation, DNA fragmentation and cleavage of PARP. Etoposide also induced activation of c-jun N-terminal kinase (JNK) in parotid C5 cells by 4 h after treatment, with maximal activation at 8 - 10 h. Coincident with activation of JNK, the amount of activated ERK1 and ERK2 decreased in etoposide-treated parotid C5 cells. In contrast to the parotid C5 cells, the vast majority of submandibular C6 cells appeared to be resistant to etoposide-induced apoptosis. Likewise, activation of JNKs was not observed in etoposide-treated submandibular C6 cells, and the amount of activated ERK1 and ERK2 decreased only slightly. Etoposide treatment of either cell line had no effect upon the activation of p38. Treatment of the parotid C5 cells with Z-VAD-FMK, a caspase inhibitor, inhibited etoposide-induced activation of JNK and DNA fragmentation. These data suggest that etoposide may induce apoptosis in parotid C5 cells by activating JNKs and suppressing the activation of ERKs, thus creating an imbalance in these two signaling pathways.

Mitogen-activated protein kinases: specific messages from ubiquitous messengers.

Mitogen-activated protein kinases: specific messages from ubiquitous messengers.

Activation of Mitogen-Activated Protein Kinases in Cardiovascular Hypertrophy and Remodeling

Extracellular signal-regulated kinases (ERKs) and c-jun NH2-terminal kinases (JNKs), which belong to the family of mitogen-activated protein kinases (MAPKs), play a key role in the regulation of cell growth or apoptosis or various gene expressions. In spite of the critical importance of MAPKs for cell function in vitro, the role of MAPKs in the pathophysiology of the cardiovascular system in vivo is poorly understood. Recently, we have examined the activities of MAPKs in various cardiovascular disease models. JNKs activity is chronically enhanced in cardiac hypertrophy of hypertensive rats or angiotensin II-infused rats, which is followed by the increase in activator protein-1 (AP-1) activity composed of c-Fos and c-Jun proteins. In chronic hypertensive rats, vascular ERKs and JNKs activities are continuously increased compared with normotensive rats, with the development of vascular thickening. Furthermore, balloon injury rapidly and transiently activates vascular ERKs and JNKs, followed by the activation of AP-1. This activation of ERKs and JNKs in injured artery is in part mediated by angiotensin AT1 receptor. Thus, the enhanced activation of JNKs or ERKs occurs in various cardiovascular disease models, supporting the notion that MAPKs may be a useful target for treatment of cardiovascular hypertrophy and remodeling.

Expression of Polyglutamine-expanded Huntingtin Activates the SEK1-JNK Pathway and Induces Apoptosis in a Hippocampal Neuronal Cell Line

Huntington's disease is one of a growing number of hereditary neurodegenerative disorders caused by expansion of a polyglutamine stretch at the NH2 terminus of huntingtin. To explore whether polyglutamine-expanded huntingtin induces neuronal toxicity, I examined the expression of the full-length of huntingtin with 16, 48, or 89 polyglutamine repeats in a rat hippocampal neuronal cell (HN33). Expression of mutated huntingtin with 48 or 89 polyglutamine repeats stimulated c-Jun amino-terminal kinases (JNKs) activity and induced apoptotic cell death in HN33 cells while expression of normal huntingtin with 16 polyglutamine repeats had no toxic effect. The JNK activation precedes apoptotic cell death and co-expression of a dominant negative mutant form of stress-signaling kinase (SEK1) nearly completely blocked activation of JNKs and neuronal apoptosis mediated by mutated huntingtin. Taken together, my studies demonstrate that expression of polyglutamine-expanded huntingtin induces neuronal apoptosis via activation of the SEK1-JNK pathway.

Activation of p38 MAP Kinase and JNK But Not ERK Is Required for Erythropoietin-Induced Erythroid Differentiation

p38 MAP kinase (p38) and JNK have been described as playing a critical role in the response to a variety of environmental stresses and proinflammatory cytokines. It was recently reported that hematopoietic cytokines activate not only classical MAP kinases (ERK), but also p38 and JNK. However, the physiological function of these kinases in hematopoiesis remains obscure. We found that all MAP kinases examined, ERK1, ERK2, p38, JNK1, and JNK2, were rapidly and transiently activated by erythropoietin (Epo) stimulation in SKT6 cells, which can be induced to differentiate into hemoglobinized cells in response to Epo. Furthermore, p38-specific inhibitor SB203580 but not MEK-specific inhibitor PD98059 significantly suppressed Epo-induced differentiation and antisense oligonucleotides of p38, JNK1, and JNK2, but neither ERK1 nor ERK2 clearly inhibited Epo-induced hemoglobinization. However, in Epo-dependent FD-EPO cells, inhibition of either ERKs, p38, or JNKs suppressed cell growth. Furthermore, forced expression of a gain-of-function MKK6 mutant, which specifically activated p38, induced hemoglobinization of SKT6 cells without Epo. These results indicate that activation of p38 and JNKs but not of ERKs is required for Epo-induced erythroid differentiation of SKT6 cells, whereas all of these kinases are involved in Epo-induced mitogenesis of FD-EPO cells.© 1998 by The American Society of Hematology.

"Stress-responsive" mitogen-activated protein kinases (c-Jun N-terminal kinases and p38 mitogen-activated protein kinases) in the myocardium.

The best-characterized subfamilies of the mitogen-activated protein kinase (MAPK) superfamily are the extracellularly responsive kinases (ERKs) and the two “stress-responsive” MAPK subfamilies, namely, the c-Jun N-terminal kinases (JNKs) and the p38-MAPKs.1 2 3 4 5 As yet, no single nomenclature has been determined, and the synonyms currently in use are summarized in Table 1⇓. The ERK cascade is the most thoroughly studied of the MAPK cascades, and it is activated principally by G protein–coupled receptor (GPCR) agonists in cardiac myocytes. We have reviewed this topic recently,6 and we will not discuss it in any depth here. The regulation of the JNK and p38-MAPK cascades in the myocardium (Figure 1⇓) forms the principal subject of this review. Figure 1. A scheme for the activation of stress-responsive MAPK cascades. Exposure of cultured cardiac myocytes and whole hearts to stresses or GPCR agonists leads to activation of the JNKs and p38-MAPKs. Cellular stresses induce reorganization of the cytoskeleton and activation of the small G proteins, Rac and Cdc42. GPCR agonists activate the small G protein, Ras, through a PKC-dependent mechanism. Ras is recognized to participate in the activation of the ERK cascade and, either directly or indirectly, may activate the stress-responsive MAPKs (JNKs and p38-MAPKs). The JNKs are activated by MKK4 and MKK7, whereas p38-MAPKs are activated by MKK3 and MKK6 (see Table 2⇓). The upstream activators (the MKKKs) of the stress-responsive MKKs have not been clearly defined but possibly include MEKKs (MAPK or ERK kinase kinases), mixed lineage kinases (MLKs), and/or p21-activated kinases (PAKs). Substrates for the stress-responsive MAPKs include transcription factors, which regulate the transcriptional changes, and MAPKAPK2, which phosphorylates Hsp25/27 and may thereby confer cytoprotection. CHOP indicates C/EBP homologous protein; MEF2C myocyte enhancer factor 2C. View this table: Table 1. Mitogen-Activated Protein Kinase (MAPK) Subfamilies An ever-increasing number of isoforms of …