Pro- and anti-apoptotic roles of c-Jun N-terminal kinase (JNK) in ethanol and acetaldehyde exposed rat hepatocytes

Involvement of p42/44 MAPK in the effects of ethanol on secretion of insulin-like growth factor (IGF)-I and insulin-like growth factor binding protein (IGFBP)-1 in primary cultured rat hepatocytes

This article investigates the effects of ethanol on Insulin-like growth factor (IGF)-I secretion, p42/44 mitogen-activated protein kinase (MAPK) activity, and IGF binding protein (IGFBP-1 secretion) in primary cultured rat hepatocytes. The p42/44 MAPK activity increased with the ethanol concentration compared to control after ethanol treatment. The secretion of IGF-I significantly increased compared to control, but IGFBP-1 secretion was inhibited. Treatment with 4-methylpyrazole blocked the IGF-I and IGFBP-1 secretion and p42/44 MAPK activity. Increased IGF-I secretion and inhibited IGFBP-1 secretion due to ethanol-induced p42/44 MAPK activity (at 30 min) was blocked by treatment with PD98059. Taken together, these results suggest that ethanol is involved in the modulation of the secretion of IGF-I and IGFBP-1 by p42/44 MAPK in primary cultured rat hepatocytes. In addition, inhibition of p42/44 MAPK activity by ethanol occurs via the activity of ADH.

Inhibitive effects of anti-oxidative vitamins on mannitol-induced apoptosis of vascular endothelial cells

OBJECTIVE

Study blood vessel injury and gene expression indicating vascular endothelial cell apoptosis induced by mannitol with and without administration of anti-oxidative vitamins.

METHODS

Healthy rabbits were randomly divided into four groups. Mannitol was injected into the vein of the rabbit ear in each animal. Pre-treatment prior to mannitol injection was performed with normal saline (group B), vitamin C (group C) and vitamin E (group D). Blood vessel injury was assessed under electron and light microscopy. In a second experiment, cell culture specimen of human umbilical vein endothelial cells were treated with mannitol. Pre-treatment was done with normal saline (sample B), vitamin C (sample C) and vitamin E (sample D). Total RNA was extracted with the original single step procedure, followed by hybridisation and analysis of gene expression.

RESULTS

In the animal experiment, serious blood vessel injury was seen in group A and group B. Group D showed light injury only, and normal tissue without pathological changes was seen in group C. Of all 330 apoptosis-related genes analysed in human cell culture specimen, no significant difference was seen after pre-treatment with normal saline, compared with the gene chip without pre-treatment. On the gene chip pre-treated with vitamin C, 45 apoptosis genes were down-regulated and 34 anti-apoptosis genes were up-regulated. Pre-treatment with vitamin E resulted in the down-regulation of 3 apoptosis genes.

CONCLUSION

Vitamin C can protect vascular endothelial cells from mannitol-induced injury.

Differential regulation of the JNK/AP-1 pathway by S-adenosylmethionine and methylthioadenosine in primary rat hepatocytes versus HuH7 hepatoma cells

S-adenosylmethionine (AdoMet) and 5'-methylthioadenosine (MTA) exert a protective action on apoptosis induced by okadaic acid in primary rat hepatocytes but not in human transformed HuH7 cells. In the present work, we analyzed the role played by the JNK/activator protein (AP)-1 pathway in this differential effect. Okadaic acid induced the phosphorylation of JNK and c-Jun and the binding activity of AP-1 in primary hepatocytes, and pretreatment with either AdoMet or MTA prevented those effects. In HuH7 cells, pretreatment with either AdoMet or MTA did not affect JNK and c-Jun activation or AP-1 binding induced by okadaic acid. In both cell types, p38 was activated by okadaic acid, but neither AdoMet nor MTA presented a significant effect on its activity. Therefore, the differential effect of both AdoMet and MTA on the JNK/AP-1 pathway could explain their antiapoptotic effect on primary hepatocytes and the lack of protection they show against okadaic acid-induced apoptosis in hepatoma cells.

S-adenosyl-methionine decreases ethanol-induced apoptosis in primary hepatocyte cultures by a c-Jun N-terminal kinase activity-independent mechanism

AIM: To determine the role of c-Jun N-terminal kinase (JNK) activity in ethanol-induced apoptosis and the modulation of this signaling cascade by S-Adenosyl-methionine (AdoMet).

METHODS: Primary hepatocyte cultures were pretreated with 100 µmol/L SP600125, a selective JNK inhibitor, 1 mL/L DMSO or 4 mmol/L AdoMet and then exposed to 100 mmo/L ethanol. Hepatocyte apoptosis was determined by the TUNEL and DNA ladder assays. JNK activity and its inhibition by SP600125 and AdoMet were determined by Western blot analysis of c-jun phosphorylation and Bid fragmentation. SP600125 and AdoMet effects on the apoptotic signaling pathway were determined by Western blot analysis of cytochrome c release and pro-caspase 3 fragmentation. The AdoMet effect on glutathione levels was measured by Ellman’s method and reactive oxygen species (ROS) generation by cell cytometry.

RESULTS: The exposure of hepatocytes to ethanol induced JNK activation, c-jun phosphorylation, Bid fragmentation, cytochrome c release and pro-caspase 3 cleavage; these effects were diminished by SP600125, and caused a significant decrease in ethanol-induced apoptosis (P< 0.05). AdoMet exerted an antioxidant effect maintaining glutathione levels and decreasing ROS generation, without a significant effect on JNK activity, and prevented cytochrome c release and pro-caspase 3 cleavage.

CONCLUSION: The JNK signaling cascade is a key component of the proapoptotic signaling pathway induced by ethanol. JNK activation may be independent from ROS generation, since AdoMet which exerted antioxidant properties did not have a significant effect on JNK activity. JNK pathway modulator agents and AdoMet may be components of promising therapies for alcoholic liver disease (ALD) treatment.

ERK regulation upon contact inhibition in fibroblasts

Despite the understanding of the importance of mitogen-activated protein (MAP) kinase activation in the stimulation of growth, little is known about the role of MAP kinase regulation during contact inhibited growth control. To investigate the role of the MAP kinase extracellular signal-regulated kinase (ERK) during the transition to a contact inhibited state, cultures of normal fibroblasts (BJ) were grown to different stages of confluency. The levels of MAP kinase phosphatase (MKP) expression and the amount of active ERK and MAP ERK kinase (MEK) in these cultures were assessed through western blot analysis and were compared to fibrosarcoma cell cultures (HT-1080), which lack contact inhibition. In normal fibroblasts, the amounts of active MEK and ERK decline at contact inhibition, concurrently with a rise in MKP-1, MKP-2, and MKP-3 protein levels. In contrast, fibrosarcoma cells appear to lack density-dependent regulation of the ERK pathway. Additionally, altering the redox environment of fibrosarcoma cells to a less reducing state, as seen during contact inhibition, results in increased MKP-1 expression. Taken together, these results suggest that the altered redox environment upon contact inhibition may contribute to the regulation of ERK inactivation by MKPs.

Suppression of survival kinases and activation of JNK mediate ethanol-induced cell death in the developing rat brain

Administration of ethanol to immature rat pups during the period in which synaptogenesis occurs triggers extensive apoptotic cell death in the brain. This ethanol-induced cell death is known to be mediated by Bax activation, which is caused by mitochondrial dysfunction. However, little data is available regarding the regulation of survival signaling pathways and their downstream events that lead to Bax activation. Thus, in the present study, we aimed to investigate the effect of ethanol on survival signaling pathways and their downstream events that lead to cell death in the rat brain during the brain developmental period. Ethanol (3 g/kg, 20% in saline) was administered subcutaneously to post-natal 7-day-old rat pups twice at 2-h intervals and the pups were sacrificed at 4 h following the first ethanol injection. Ethanol treatment suppressed the activation of survival kinases, particularly Akt, Erk1/2 and PKAalpha, whereas it increased the activation of JNK. Moreover, dissociation of dephosphorylated Bad from 14-3-3 and the interaction of activated JNK with Bcl-2 were elevated by ethanol treatment. The present study demonstrated that ethanol treatment during the brain developmental period induced mitochondrial dysfunction, which led to cell death by the suppression of survival kinases, Bad release from 14-3-3 and inactivation of Bcl-2 by activated JNK.

Involvement of histone acetyltransferase (HAT) in ethanol-induced acetylation of histone H3 in hepatocytes: potential mechanism for gene expression

Ethanol treatment increases gene expression in the liver through mechanisms that are not clearly understood. Histone acetylation has been shown to induce transcriptional activation. We have investigated the characteristics and mechanisms of ethanol-induced histone H3 acetylation in rat hepatocytes. Immunocytochemical and immunoblot analysis revealed that ethanol treatment significantly increased H3 acetylation at Lys9 with negligible effects at Lys14, -18, and -23. Acute in vivo administration of alcohol in rats produced the same results as in vitro observations. Nuclear extracts from ethanol-treated hepatocytes increased acetylation in H3 peptide to a greater extent than extracts from untreated cells, suggesting that ethanol either increased the expression level or the specific activity of histone acetyltransferases (HAT). Use of different H3 peptides indicated that ethanol selectively modulated HAT(s) targeting H3-Lys9. Treatment with acetate, an ethanol metabolite, also increased acetylation of H3-Lys9 and modulated HAT(s) in the same manner as ethanol, suggesting that acetate mediates the ethanol-induced effect on HAT. Inhibitors of MEK (U0126) and JNK (SP600125), but not p38 MAPK inhibitor (SB203580), suppressed ethanol-induced H3 acetylation. However, U0126 and SP600125 did not significantly affect ethanol-induced effect on HAT, suggesting that ERK and JNK regulate histone acetylation through a separate pathway(s) that does not involve modulation of HAT. Chromatin immunoprecipitation assay demonstrated that ethanol treatment increased the association of the class I alcohol dehydrogenase (ADH I) gene with acetylated H3-Lys9. These data provide first evidence that ethanol increases acetylation of H3-Lys9 through modulation of HAT(s) and that histone acetylation may underlie the mechanism for ethanol-induced ADH I gene expression.

Mitogen-activated protein kinase contributes to elevated basal tone in aortic smooth muscle from hypertensive rats

The role of mitogen-activated protein kinase (MAPK) in increased basal tone -spontaneous resistance in vascular muscle strips- was clarified in aortic smooth muscle from deoxycorticosterone acetate (DOCA)-salt hypertensive rats. The MAPK/extracellular signal-regulated protein kinase (ERK) kinase inhibitor, PD098059 (2'-amino-3'-methoxyflavone), significantly inhibited basal tone in a dose-dependent manner. The basal level of ERK1/2 activation was inhibited by PD098059 and was significantly greater in hypertensive rats than in sham-operated rats. In contrast, inhibition with PD098059 was not observed in sham-operated rats. GF109203X (2-[1-(3-dimethylaminopropyl)-1H-indol-3-yl]-3-(1H-indol-3-yl)maleimide), an inhibitor of protein kinase C (PKC), decreased both basal tone and ERK1/2 activity in the hypertensive rats. In contrast, Y27632 ((R)-(+)-trans-N-(4-Pyridyl)-4-(1-aminoethyl)cyclohexanecarboxamide) and verapamil, inhibitors of Rho kinase and voltage-dependent Ca2+ channels, respectively, significantly inhibited basal tone but not ERK1/2 activity. Thus, basal vascular tone is elevated by the altered activation of MAPK in DOCA-salt hypertensive rats, and this is regulated by PKC, but not by Rho or intracellular Ca2+.