Cyclic adenosine monophosphate-mediated protection against bile acid-induced apoptosis in cultured rat hepatocytes

Intracellular cAMP Sensor EPAC: Physiology, Pathophysiology, and Therapeutics Development

This review focuses on one family of the known cAMP receptors, the exchange proteins directly activated by cAMP (EPACs), also known as the cAMP-regulated guanine nucleotide exchange factors (cAMP-GEFs). Although EPAC proteins are fairly new additions to the growing list of cAMP effectors, and relatively "young" in the cAMP discovery timeline, the significance of an EPAC presence in different cell systems is extraordinary. The study of EPACs has considerably expanded the diversity and adaptive nature of cAMP signaling associated with numerous physiological and pathophysiological responses. This review comprehensively covers EPAC protein functions at the molecular, cellular, physiological, and pathophysiological levels; and in turn, the applications of employing EPAC-based biosensors as detection tools for dissecting cAMP signaling and the implications for targeting EPAC proteins for therapeutic development are also discussed.

Mechanisms of bile acid mediated inflammation in the liver

Bile acids are synthesized in the liver and are the major component in bile. Impaired bile flow leads to cholestasis that is characterized by elevated levels of bile acid in the liver and serum, followed by hepatocyte and biliary injury. Although the causes of cholestasis have been extensively studied, the molecular mechanisms as to how bile acids initiate liver injury remain controversial. In this chapter, we summarize recent advances in the pathogenesis of bile acid induced liver injury. These include bile acid signaling pathways in hepatocytes as well as the response of cholangiocytes and innate immune cells in the liver in both patients with cholestasis and cholestatic animal models. We focus on how bile acids trigger the production of molecular mediators of neutrophil recruitment and the role of the inflammatory response in this pathological process. These advances point to a number of novel targets where drugs might be judged to be effective therapies for cholestatic liver injury.

Methanol extract of Nymphaea lotus ameliorates carbon tetrachloride-induced chronic liver injury in rats via inhibition of oxidative stress

BACKGROUND

Nymphaea lotus (NL) is an aquatic perennial plant used traditionally in the management of various liver diseases. In this study, the protective effect of methanol extract of NL against carbon tetrachloride (CCl4)-induced chronic hepatotoxicity in rats was investigated.

METHODS

Male Wistar rats were assigned into six groups of five rats each. Group I received corn oil (0.5 mL p.o.) and served as control, group II received CCl4 (1 mL/kg i.p., 1:3 in corn oil), group III received NL (200 mg/kg), and groups IV, V, and VI received CCl4+NL (50, 100, and 200 mg/kg, respectively) for 6 weeks. Twenty-four hours after the last exposure, rats were bled and killed.

RESULTS

The activities of alanine aminotransaminase (ALT), aspartate aminotransferase (AST), and levels of total bilirubin (TB) in the serum, thiobarbituric acid reactive substances (TBARS), superoxide dismutase, catalase, glutathione peroxidase (GPx) and glutathione (GSH) in the liver, and histopathology of the liver were determined using standard procedures. NL significantly (p<0.05) lowered the levels of ALT, AST, and TB and exhibited antioxidant potentials in rats exposed to CCl4 relative to the control values. Specifically, NL at 100 and 200 mg/kg significantly (p<0.05) increased CCl4-induced decrease in hepatic GSH and GPx and also decreased the level of hepatic TBARS in CCl4-intoxicated rats. Histopathological findings revealed cellular infiltration and fibrosis in rats that received CCl4 only, which were ameliorated in rats that received NL+CCl4.

CONCLUSIONS

The data suggest that NL exhibited hepatoprotective effects in CCl4-intoxicated rats via antioxidative mechanism.

The Emerging Role of Soluble Adenylyl Cyclase in Primary Biliary Cholangitis

BACKGROUND

Primary biliary cholangitis (PBC; previously referred to as primary biliary cirrhosis) is a chronic fibrosing cholangiopathy with the signature of an autoimmune disease and features of intrahepatic cholestasis. Immunosuppressing treatments are largely unsuccessful. Responsiveness to ursodeoxycholic acid and reduced expression of anion exchanger 2 (AE2) on canalicular membranes and small bile ducts underline the importance of bicarbonate transportation in its disease mechanism. Soluble adenylyl cyclase (sAC; ADCY10) is an evolutionarily conserved bicarbonate sensor that regulates apoptosis, barrier function and TNF signaling. Key Messages: The biliary epithelium defends against the toxic bile by bicarbonate secretion and by maintaining a tight barrier. Passive diffusion of weak acid conjugates (e.g. bile salts and other toxins) across plasma membrane is pH-dependent. Reduced AE2 expression results in both reduced bicarbonate secretion and accumulation of bicarbonate in the cells. Increased intracellular bicarbonate leads to increased sAC activity, which regulates bile salt-induced apoptosis. Reduced bicarbonate secretion causes more bile salts to enter cells, which further increase sAC activity by releasing intracellular Ca2+ store. In vitro studies demonstrate that inhibition of sAC not only corrects sensitization to bile salt-induced apoptosis as a result of AE2 down-regulation but also prevents bile salt-induced apoptosis altogether. Targeting sAC is also likely to slow down disease progression by strengthening the barrier function of biliary epithelia and by reducing oxidative stress as a result of chronic inflammation.

CONCLUSIONS

sAC is a potential therapeutic target for PBC. More in vitro and in vivo studies are needed to understand how sAC regulates bile salt-induced apoptosis and to establish its therapeutic value in PBC and other cholestatic cholangiopathies.

Hydrophobic bile acid apoptosis is regulated by sphingosine-1-phosphate receptor 2 in rat hepatocytes and human hepatocellular carcinoma cells

The hepatotoxic bile acid glycochenodeoxycholate (GCDC) modulates hepatocyte cell death through activation of JNK, Akt, and Erk. The nonhepatotoxic bile acid taurocholate activates Akt and Erk through the sphingosine-1-phosphate receptor 2 (S1PR2). The role of the S1PR2 in GCDC-mediated apoptosis and kinase activation is unknown. Studies were done in rat hepatocytes, HUH7 cells, and HUH7 cells stably transfected with rat Ntcp (HUH7-Ntcp). Cells were treated with GCDC and apoptosis was monitored morphologically by Hoechst staining and biochemically by immunoblotting for the active cleaved fragment of caspase 3. Kinase activation was determined by immunoblotting with phospho-specific antibodies. JTE-013, an inhibitor of S1PR2, significantly attenuated morphological evidence of GCDC-induced apoptosis and prevented caspase 3 cleavage in rat hepatocytes and HUH7-Ntcp cells. In hepatocytes, JTE-013 mildly suppressed, augmented, and had no effect on GCDC-induced JNK, Akt, and Erk phosphorylation, respectively. Similar results were seen in HUH7-Ntcp cells except for mild suppression of JNK and Erk phosphorylation. Knockdown of S1PR2 in HUH7-Ntcp augmented Akt, inhibited JNK, and had no effect on Erk phosphorylation. GCDC failed to induce apoptosis or kinase activation in HUH7 cells. In conclusion, SIPR2 inhibition attenuates GCDC-induced apoptosis and inhibits and augments GCDC-induced JNK and Akt phosphorylation, respectively. In addition, GCDC must enter hepatocytes to mediate cell death or activate kinases. These results suggest that SIPR2 activation is proapoptotic in GCDC-induced cell death but that this effect is not due to direct ligation of the S1PR2 by the bile acid.

BBT improves glucose homeostasis by ameliorating β-cell dysfunction in type 2 diabetic mice

Impaired glucose-stimulated insulin secretion (GSIS) and increasing β-cell death are two typical dysfunctions of pancreatic β-cells in individuals that are destined to develop type 2 diabetes, and improvement of β-cell function through GSIS enhancement and/or inhibition of β-cell death is a promising strategy for anti-diabetic therapy. In this study, we discovered that the small molecule, N-(2-benzoylphenyl)-5-bromo-2-thiophenecarboxamide (BBT), was effective in both potentiating GSIS and protecting β-cells from cytokine- or streptozotocin (STZ)-induced cell death. Results of further studies revealed that cAMP/PKA and long-lasting (L-type) voltage-dependent Ca(2) (+) channel/CaMK2 pathways were involved in the action of BBT against GSIS, and that the cAMP/PKA pathway was essential for the protective action of BBT on β-cells. An assay using the model of type 2 diabetic mice induced by high-fat diet combined with STZ (STZ/HFD) demonstrated that BBT administration efficiently restored β-cell functions as indicated by the increased plasma insulin level and decrease in the β-cell loss induced by STZ/HFD. Moreover, the results indicated that BBT treatment decreased fasting blood glucose and HbA1c and improved oral glucose tolerance further highlighting the potential of BBT in anti-hyperglycemia research.

Anti-fibrotic effect of Holothuria arenicola extract against bile duct ligation in rats

BACKGROUND

Holothuria arenicola is the most important and abundant sea cucumber species in the Mediterranean Sea on the Egyptian coast. The present study aims to assess the anti-oxidative and anticholestatic effects of the sea cucumber Holothuria arenicola extract (HaE) in a model of bile duct ligation in male albino rats.

METHODS

Fifty four male Wistar albino rats were assigned into two main groups, the Sham-operated control and bile duct ligated (BDL) group. After 14 days of surgery, the animals of the group I (Sham control) received distilled water only for 7, 14 and 28 days. Second group (BDL group) was divided into 2 subgroups, animals of these subgroups treated for 7, 14 and 28 consecutive days as follow: subgroup I (BDL), rats of this subgroup administered distilled water orally. Subgroup II (HaE), animals of this subgroup treated orally with HaE (200 mg/kg body weight).

RESULTS

The HaE revealed significant antifibrotic effect as evident by decreasing the levels of total conjugated and unconjugated bilirubin and the activities of serum aminotransferases (ASAT and ALAT) and alkaline phosphatase (ALP) as well as malondialdehyde (MDA) level, and increasing the serum albumin, glutathione reduced (GSH) levels. Treatment with HaE normalized the antioxidant enzyme, glutathione-S-transferase (GST), superoxide dismutase (SOD) and catalase (CAT) activities activities.

CONCLUSION

The present prospective study correlated the antifibrotic effect of HaE to its direct antioxidant effect that can be related to its contents of phenolic compounds specially chlorogenic acid, pyrogallol, rutin and coumaric acid.

Decreasing mitochondrial fission prevents cholestatic liver injury

Mitochondria frequently change their shape through fission and fusion in response to physiological stimuli as well as pathological insults. Disrupted mitochondrial morphology has been observed in cholestatic liver disease. However, the role of mitochondrial shape change in cholestasis is not defined. In this study, using in vitro and in vivo models of bile acid-induced liver injury, we investigated the contribution of mitochondrial morphology to the pathogenesis of cholestatic liver disease. We found that the toxic bile salt glycochenodeoxycholate (GCDC) rapidly fragmented mitochondria, both in primary mouse hepatocytes and in the bile transporter-expressing hepatic cell line McNtcp.24, leading to a significant increase in cell death. GCDC-induced mitochondrial fragmentation was associated with an increase in reactive oxygen species (ROS) levels. We found that preventing mitochondrial fragmentation in GCDC by inhibiting mitochondrial fission significantly decreased not only ROS levels but also cell death. We also induced cholestasis in mouse livers via common bile duct ligation. Using a transgenic mouse model inducibly expressing a dominant-negative fission mutant specifically in the liver, we demonstrated that decreasing mitochondrial fission substantially diminished ROS levels, liver injury, and fibrosis under cholestatic conditions. Taken together, our results provide new evidence that controlling mitochondrial fission is an effective strategy for ameliorating cholestatic liver injury.

Adenylyl cyclases in the digestive system

Adenylyl cyclases (ACs) are a group of widely distributed enzymes whose functions are very diverse. There are nine known transmembrane AC isoforms activated by Gαs. Each has its own pattern of expression in the digestive system and differential regulation of function by Ca(2+) and other intracellular signals. In addition to the transmembrane isoforms, one AC is soluble and exhibits distinct regulation. In this review, the basic structure, regulation and physiological roles of ACs in the digestive system are discussed.

Cell death sensitization of leukemia cells by opioid receptor activation

Cyclic AMP (cAMP) regulates a number of cellular processes and modulates cell death induction. cAMP levels are altered upon stimulation of specific G-protein-coupled receptors inhibiting or activating adenylyl cyclases. Opioid receptor stimulation can activate inhibitory G_i-proteins which in turn block adenylyl cyclase activity reducing cAMP. Opioids such as D,L-methadone induce cell death in leukemia cells. However, the mechanism how opioids trigger apoptosis and activate caspases in leukemia cells is not understood. In this study, we demonstrate that downregulation of cAMP induced by opioid receptor activation using the opioid D,L-methadone kills and sensitizes leukemia cells for doxorubicin treatment. Enhancing cAMP levels by blocking opioid-receptor signaling strongly reduced D,L-methadone-induced apoptosis, caspase activation and doxorubicin-sensitivity. Induction of cell death in leukemia cells by activation of opioid receptors using the opioid D,L-methadone depends on critical levels of opioid receptor expression on the cell surface. Doxorubicin increased opioid receptor expression in leukemia cells. In addition, the opioid D,L-methadone increased doxorubicin uptake and decreased doxorubicin efflux in leukemia cells, suggesting that the opioid D,L-methadone as well as doxorubicin mutually increase their cytotoxic potential. Furthermore, we found that opioid receptor activation using D,L-methadone alone or in addition to doxorubicin inhibits tumor growth significantly in vivo. These results demonstrate that opioid receptor activation via triggering the downregulation of cAMP induces apoptosis, activates caspases and sensitizes leukemia cells for doxorubicin treatment. Hence, opioid receptor activation seems to be a promising strategy to improve anticancer therapies.

INTRACELLULAR SIGNALING BY BILE ACIDS

Bile acids, synthesized from cholesterol, are known to produce beneficial as well as toxic effects in the liver. The beneficial effects include choleresis, immunomodulation, cell survival, while the toxic effects include cholestasis, apoptosis and cellular toxicity. It is believed that bile acids produce many of these effects by activating intracellular signaling pathways. However, it has been a challenge to relate intracellular signaling to specific and at times opposing effects of bile acids. It is becoming evident that bile acids produce different effects by activating different isoforms of phosphoinositide 3-kinase (PI3K), Protein kinase Cs (PKCs), and mitogen activated protein kinases (MAPK). Thus, the apoptotic effect of bile acids may be mediated via PI3K-110γ, while cytoprotection induce by cAMP-GEF pathway involves activation of PI3K-p110α/β isoforms. Atypical PKCζ may mediate beneficial effects and nPKCε may mediate toxic effects, while cPKCα and nPKCδ may be involved in both beneficial and toxic effects of bile acids. The opposing effects of nPKCδ activation may depend on nPKCδ phosphorylation site(s). Activation of ERK1/2 and JNK1/2 pathway appears to mediate beneficial and toxic effects, respectively, of bile acids. Activation of p38α MAPK and p38β MAPK may mediate choleretic and cholestatic effects, respectively, of bile acids. Future studies clarifying the isoform specific effects on bile formation should allow us to define potential therapeutic targets in the treatment of cholestatic disorders.

Ursodeoxycholyl lysophosphatidylethanolamide inhibits lipoapoptosis by shifting fatty acid pools toward monosaturated and polyunsaturated fatty acids in mouse hepatocytes

Ursodeoxycholyl lysophosphatidylethanolamide (UDCA-LPE) is a hepatoprotectant in inhibiting apoptosis, inflammation, and hyperlipidemia in mouse models of nonalcoholic steatohepatitis (NASH). We studied the ability of UDCA-LPE to inhibit palmitate (Pal)-induced apoptosis in primary hepatocytes and delineate cytoprotective mechanisms. We showed that lipoprotection by UDCA-LPE was mediated by cAMP and was associated with increases in triglycerides (TGs) and phospholipids (PLs). An inhibitor of cAMP-effector protein kinase A partially reversed the protective effects of UDCA-LPE. Lipidomic analyses of fatty acids and PL composition revealed a shift of lipid metabolism from saturated Pal to monounsaturated and polyunsaturated fatty acids, mainly, oleate, docosapentaenoate, and docosahexaenoate. The latter two ω-3 fatty acids were particularly found in phosphatidylcholine and phosphatidylserine pools. The catalysis of Pal by stearoyl-CoA desaturase-1 (SCD-1) is a known mechanism for the channeling of Pal away from apoptosis. SCD-1 protein was upregulated during UDCA-LPE lipoprotection. SCD-1 knockdown of Pal-treated cells showed further increased apoptosis, and the extent of UDCA-LPE protection was reduced. Thus, the major mechanism of UDCA-LPE lipoprotection involved a metabolic shift from toxic saturated toward cytoprotective unsaturated fatty acids in part via SCD-1. UDCA-LPE may thus be a therapeutic agent for treatment of NASH by altering distinct pools of fatty acids for storage into TGs and PLs, and the latter may protect lipotoxicity at the membrane levels.

Serotonin and the 5-HT7 receptor: the link between hepatocytes, IGF-1 and small intestinal neuroendocrine tumors

Platelet-derived serotonin (5-HT) is involved in liver regeneration. The liver is also the metastatic site for malignant enterochromaffin (EC) cell "carcinoid" (neuroendocrine) neoplasms, the principal cellular source of 5-HT. We hypothesized that 5-HT produced by metastatic EC cells played a role in the hepatic tumor-microenvironment principally via 5-HT₇ receptor-mediated activation of hepatocyte IGF-1 synthesis and secretion. Using isolated rat hepatocytes, we evaluated 5-HT₇ receptor expression (using PCR, sequencing and western blot). ELISA, cell transfection and western blots delineated 5-HT-mediated signaling pathways (pCREB, AKT and ERK). IGF-1 synthesis/secretion was evaluated using QPCR and ELISA. IGF-1 was tested on small intestinal neuroendocrine neoplasm proliferation, while IGF-1 production and 5-HT₇ expression were examined in an in vivo SCID metastasis model. Our results demonstrated evidence for a functional 5-HT₇ receptor. 5-HT activated cAMP/PKA activity, pCREB (130-205%, P < 0.05) and pERK/pAKT (1.2-1.75, P < 0.05). Signaling was reversed by the 5-HT₇ receptor antagonist SB269970. IGF-1 significantly stimulated proliferation of two small intestinal neuroendocrine neoplasm cell lines (EC₅₀: 7-70 pg/mL) and could be reversed by the small molecule inhibitor BMS-754807. IGF-1 and 5-HT were elevated (40-300×) in peri-tumoral hepatic tissue in nude mice, while 5-HT₇ was increased fourfold compared to sham-operated animals. We conclude that hepatocytes express a cAMP-coupled 5-HT₇ receptor, which, at elevated 5-HT concentrations that occur in liver metastases, signals via CREB/AKT and is linked to IGF-1 synthesis and secretion. Because IGF-1 regulates NEN proliferation, identification of a role for 5-HT₇ in the hepatic metastatic tumor microenvironment suggests the potential for novel therapeutic strategies for amine-producing mid-gut tumors.

The effects of hyperbaric oxygen application against cholestatic oxidative stress and hepatic damage after bile duct ligation in rats

BACKGROUND

The aim of this study was to evaluate the preventive and therapeutic potential of hyperbaric oxygen therapy (HBO) on the liver tissue against bile duct ligation (BDL)-induced oxidative damage and fibrosis in rats.

MATERIALS AND METHODS

We divided 32 adult male Sprague Dawley rats into four groups: sham, sham plus HBO, BDL, and BDL plus HBO; each group contained eight animals. We placed the sham plus HBO and BDL plus HBO groups in an experimental hyperbaric chamber in which we administered pure oxygen at 2.5 atmospheres absolute 100% oxygen for 90 min on 14 consecutive days.

RESULTS

The application of BDL clearly increased the tissue malondialdehyde level, myeloperoxidase activity, and hydroxyproline content and decreased the antioxidant enzymes (superoxide dismutase and catalase activities) and glutathione level. Hyperbaric oxygen therapy treatment significantly decreased the elevated tissue malondialdehyde level, myeloperoxidase activity, and hydroxyproline content and increased the reduced superoxide dismutase and catalase activities and glutathione level in the tissues. The changes demonstrating the bile duct proliferation and fibrosis in expanded portal tracts include the extension of proliferated bile ducts into lobules, mononuclear cells, and neutrophil infiltration into the widened portal areas were observed in BDL group. Treatment of BDL with HBO attenuated alterations in liver histology. Alpha smooth muscle actin, cytokeratin-positive ductular proliferation, and the activity of terminal deoxynucleotidyl transferase 2'-deoxyuridine, 5'-triphosphate nick end labeling in the BDL decreased with HBO treatment.

CONCLUSIONS

The data indicate that HBO attenuates BDL-induced oxidative injury, hepatocytes damage, bile duct proliferation, and fibrosis. The hepatoprotective effect of HBO is associated with antioxidative potential.

Artemisia capillaris extract protects against bile duct ligation-induced liver fibrosis in rats

Artemisia capillaris has been widely used as a traditional herbal medicine in the treatment of liver diseases. However, no previous study has investigated whether A. capillaries alone is effective in treating pathological conditions associated with cholestatic liver injury. In the present study, we evaluated the anti-hepatofibrotic effects of A. capillaris (aqueous extract, WAC) in a bile duct ligation (BDL)-induced cholestatic fibrosis model. After BDL, rats were given WAC (25 or 50 mg/kg) or urosodeoxycholic acid (UDCA, 25 mg/kg) orally for 2 weeks (once per day). The serum cholestatic markers, malondialdehyde, and liver hydroxyproline levels were drastically increased in the BDL group, while administering WAC significantly reduced these alterations. Administering WAC also restored the BDL-induced depletion of glutathione content and glutathione peroxidase activity. Cholestatic liver injury and collagen deposition were markedly attenuated by WAC treatment, and these changes were paralleled by the significantly suppressed expression of fibrogenic factors, including hepatic alpha-smooth muscle actin (α-SMA), platelet-derived growth factor (PDGF), and transforming growth factor beta (TGF-β). The beneficial effects of WAC administration are associated with antifibrotic properties via both upregulation of antioxidant activities and downregulation of ECM protein production in the rat BDL model.

Aqueous extract of Artemisia iwayomogi Kitamura attenuates cholestatic liver fibrosis in a rat model of bile duct ligation

Cholestatic liver fibrosis, characterized by excessive accumulation of extracellular matrix (ECM) proteins, is associated with bile acid-induced oxidative stress and lipid peroxidation. We evaluated the therapeutic or protective effect of an aqueous extract of Artemisia iwayomogi Kitamura (WAI) in a rat bile duct ligation (BDL)-induced hepatic fibrogenesis model. After BDL, rats were treated once daily with 25 or 50 mg/kg of WAI for 2weeks. The serum bilirubin, aspartate transaminase, alanine transaminase, malondialdehyde, and liver hydroxyproline levels were drastically increased in the BDL group. WAI administration significantly reduced these markers and restored BDL-induced depletion of glutathione content and glutathione peroxidase activity. Cholestatic liver injury and collagen deposition were markedly attenuated by WAI treatment, and these changes were paralleled by significantly suppressed gene and protein expression of fibrogenic factors, including hepatic alphasmooth muscle actin, platelet-derived growth factor, and transforming growth factor β. Our data suggest that WAI may have antifibrotic properties via both improvement of antioxidant activities and inhibition of ECM protein production in the rat model of BDL.

Cryptotanshinone from Salviae miltiorrhizae radix inhibits sodium-nitroprusside-induced apoptosis in neuro-2a cells

The root of Salvia miltiorrhiza (Salviae miltiorrhizae radix), a herbal medicine has widely been used for the treatment of pain, miscarriage and oedema. In this study, we evaluated the neuroprotective effect of cryptotanshinone (CRT) from Salviae miltiorrhizae radix on sodium-nitroprusside (SNP)-induced apoptosis in neuro-2a (N2a) cells, and further investigated its action mechanism in signalling pathways. The effects of CRT against SNP-induced toxicity, mitochondrial membrane potential (MMP) changes, and oxidants/antioxidant defences and apoptotic signalling pathways were investigated in N2a cells. Cryptotanshinone significantly inhibited SNP-induced cell toxicity and the generation of reactive oxygen and nitrogen species (RONS), and improved MMP in N2a cells. Cryptotanshinone significantly suppressed SNP-induced peroxidation of lipid and protein, and the expression of Gclc mRNA. In the signalling pathway, CRT effectively blocked SNP-induced activation of NF-κB and ERK1/2 and JNK MAPK pathways through the elevation of Akt and cyclic AMP response element binding protein. Furthermore, CRT remarkably reduced the increase of mitochondrial Bax/Bcl-2 ratio, the release of cytochrome c from mitochondria to cytosol, and the activations of cytosolic procaspase-3 and nuclear inactive poly ADP (adenosine diphosphate)-ribose polymerase by SNP-induced apoptosis. These results indicate that CRT has neuroprotective effects against SNP-induced apoptosis in neuronal cells via the regulation of mitochondrial apoptotic cascades and antiapoptotic cellular signalling pathways.

Liver X receptor α and farnesoid X receptor are major transcriptional regulators of OATP1B1

Organic anion transporting polypeptide 1B1 (OATP1B1) is a liver-enriched transporter involved in the hepatocellular uptake of many endogenous molecules and several structurally divergent drugs in clinical use. Although OATP1B1 coding region polymorphisms are known to make an impact on substrate drug disposition in humans, little is known regarding the mechanisms underlying the transcriptional regulation of this transporter. In this study, we note that messenger RNA (mRNA) expression of OATP1B1 in a large human liver bank exhibited marked interindividual variability that was not associated with coding region polymorphisms. Accordingly, we hypothesized that such variability in expression is reflective of nuclear receptor-mediated transcriptional regulation of this transporter. We tested prototypical ligands for the nuclear receptors pregnane X receptor (PXR), constitutive androstane receptor (CAR), liver X receptor (LXR) α, and farnesoid X receptor (FXR) in a human hepatoma-derived cell line and noted induction of OATP1B1 mRNA when the cells were treated with LXRα or FXR ligands. To confirm a direct role for LXRα and FXR to OATP1B1 expression, we performed detailed promoter analysis and cell-based reporter gene assays resulting in the identification of two functional FXR response elements and one LXRα response element. The direct interaction between nuclear receptors with the identified response elements was assessed using chromatin immunoprecipitation assays. Using isolated primary human hepatocytes, we show that LXRα or FXR agonists, but not PXR or CAR agonists, are capable of OATP1B1 induction.

CONCLUSION

We note that OATP1B1 transcriptional regulation is under dual nuclear receptor control through the oxysterol sensing LXRα and the bile acid sensor FXR. Accordingly, the interplay between OATP1B1 and nuclear receptors may play an important and heretofore unrecognized role during cholestasis, drug-induced liver injury, and OATP1B1 induction-related drug interactions.

Akt-mediated signaling is induced by cytokines and cyclic adenosine monophosphate and suppresses hepatocyte inducible nitric oxide synthase expression independent of MAPK P44/42

Cyclic AMP inhibits the expression of nitric oxide synthase (Harbrecht et al., 1995 [1]) in hepatocytes but the mechanism for this effect is incompletely understood. Cyclic AMP can activate several intracellular signaling pathways in hepatocytes including Protein Kinase A (PKA), cAMP regulated guanine nucleotide exchange factors (cAMP-GEFs), and calcium-mediated Protein Kinases. There is considerable overlap and cross-talk between many of these signaling pathways, however, and how these cascades regulate hepatocyte iNOS is not known. We hypothesized that Akt mediates the effect of cAMP on hepatocyte iNOS expression. Hepatocytes cultured with cytokines and dbcAMP increased Akt phosphorylation up to 2h of culture. Akt phosphorylation was inhibited by the PI3K inhibitor LY294002 (10μM), farnyltranferase inhibitor FTI-276, or transfection with a dominant negative Akt. The cyclic AMP-induced suppression of cytokine-stimulated iNOS was partially reversed by LY294002 and FTI-276. LY294002 also increased NFκB nucleus translocation by Western blot analysis in nuclear extracts. Cyclic AMP increased phosphorylation of Raf1 at serine 259 which was blocked by LY294002 and associated with decreased MAPK P44/42 phosphorylation. However, inhibition of MAPK P44/42 signaling with PD98059 failed to suppress cytokine-induced hepatocyte iNOS expression and did not enhance the inhibitory effect of dbcAMP on iNOS production. A constitutively active MAPK P44/42 plasmid had no effect on cytokine-stimulated NO production. These data demonstrate that dbcAMP regulates hepatocyte iNOS expression through an Akt-mediated signaling mechanism that is independent of MAPK P44/42.

Antithrombin-III Attenuates Hepatocyte Apoptosis in Bile Duct Ligated Rat: A Striking Cellular Change

Background and purpose: Retention and accumulation of toxic hydrophobic bile salts within hepatocyte may cause hepatocyte toxicity by inducing apoptosis. This study was designed with the purpose of evaluating the possible effect of antithrombin-III on hepatocyte apoptosis in bile duct ligated rat. Materials and methods: The rats were randomized to 3 groups: group 1 (control, C) underwent sham operation; group 2 (obstructive jaundice, OB) underwent common bile duct ligation; and group 3 (obstructive jaundice with antithrombin-III, OBAT-III) underwent common bile duct ligation and simultaneously were treated with antithrombin-III. Liver tissues were harvested on the fifth postoperative day. Results: Hepatocyte apoptosis was significantly increased in bile duct ligated group when compared with the sham operation group. The administration of antithrombin-III effectively attenuates such phenomenon in obstructive jaundice with antithrombin-III group. Conclusion: Bile duct ligation significantly increased hepatocyte apoptosis and the administration of antithrombin-III effectively attenuates such phenomenon.

Synergistic effect of cAMP and palmitate in promoting altered mitochondrial function and cell death in HepG2 cells

Saturated free fatty acids (FFAs), e.g. palmitate, have long been shown to induce toxicity and cell death in various types of cells. In this study, we demonstrate that cAMP synergistically amplifies the effect of palmitate on the induction of cell death in human hepatocellular carcinoma cell line, HepG2 cells. Elevation of cAMP level in palmitate-treated cells led to enhanced mitochondrial fragmentation, mitochondrial reactive oxygen species (ROS) generation and mitochondrial biogenesis. Mitochondrial fragmentation precedes mitochondrial ROS generation and mitochondrial biogenesis, and may contribute to mitochondrial ROS overproduction and subsequent mitochondrial biogenesis. Fragmentation of mitochondria also facilitated the release of cytotoxic mitochondrial proteins, such as Smac, from the mitochondria and subsequent activation of caspases. However, cell death induced by palmitate and cAMP was caspase-independent and mainly necrotic.

Hepatoprotective effect of water soluble extract of Coleus barbatus on cholestasis on young rats

PURPOSE

To test the effects of water extract of Coleus barbatus (WEB) on liver damage in biliary obstruction in young rats.

METHODS

Forty 21 day-old male Wistar rats were divided into four groups of ten 21 day old (P21) submitted to sham or actual operation (S or L) combined with WEB or Water (B or A). At P48 pentobarbital sleeping time (ST) was measured. At P49 they were submitted to euthanasia to determine of serum activities of aspartate aminotransferase (AST) and alanine aminotransferase (ALT), liver wet weight (PFF) and, on hepatic histological slides, the frequency of mitoses (FM), the number of necrotic areas (NN), intensity of fibrosis (IF) and intensity of ductal proliferation (IPD). Two Way ANOVA, the S.N.K. test and the Wilcoxon test for paired multiple comparisons were employed to study the effects of cholestasis and those of EAB and their interactions. The Pearson's coefficient of linear correlation of between paired histological variables separately for the groups LA and LD was determined. The test results were considered statistically significant when the p of alpha error <0.05.

RESULTS

Cholestasis increased the TS, ALT, AST, PFF, MI, NN, IF and IPD. The EAB decreased the TS and IM in the animals without cholestasis (sham operated animals). The EAB decreased the TS, ALT, AST, PFF, MI, NN and IF of the cholestatic animals. In the LA group there was a positive correlation between the IPD and the IF, a negative correlation between the IPD and the FM and a negative correlation between the IF and the FM. In the LD group there was a negative correlation between the NN and the IPD.

CONCLUSIONS

In the absence of cholestasis the EAB reduces the pentobarbital sleeping time and decreases the frequency of mitoses. The EAB has a hepatoprotective effect on the biliary cirrhosis secondary to extra-hepatic biliary obstruction.

Z-LLY-FMK can attenuate hepatocyte apoptosis after bile duct ligation in rat

BACKGROUND

Cholestasis leading to retention and accumulation of toxic hydrophobic bile salts within hepatocytes may cause hepatocyte toxicity by inducing apoptosis. Calpains have been found to be involved in apoptosis of many cell systems. This study is designed with the aim of evaluating the possible effect of Z-LLY-FMK (a calpain inhibitor) on hepatocyte apoptosis after bile duct ligation in rat.

MATERIALS AND METHODS

Male Sprague-Dawley rats were randomized to five groups. Group 1 (C) underwent sham operation. Group 2 (CDMSO) underwent Sham operation and simultaneous treatment with dimethylsulfoxide (DMSO). Group 3 (OB) underwent common bile duct ligation. Group 4 (OBZLLY) underwent common bile duct ligation and simultaneous treatment with Z-LLY-FMK. Group 5 (OBZFA) underwent common bile duct ligation and simultaneous treatment with ZFA-FMK. After 3 days, liver tissue was harvested for histopathologic analysis and apoptosis measurements.

RESULTS

When compared with sham operation groups, increased hepatocyte apoptosis (P < 0.001) and ductular proliferation (P < 0.001) occurred after common bile duct ligation. Following administration of Z-LLY-FMK, the increased hepatocyte apoptosis and ductular proliferation after common bile duct ligation were significantly diminished (P < 0.001 and P < 0.001). Moreover, administration of ZFA failed to show the same phenomenon (P = 0.9 and 0.987).

CONCLUSION

Significantly increased hepatocyte apoptosis and ductular proliferation occurred after common bile duct ligation. The administration of Z-LLY-FMK could effectively diminish the hepatocyte apoptosis and ductular proliferation after common bile duct ligation, whereas the administration of ZFA-FMK failed to show the same effect.

Effect of Boc-D-Fmk on hepatocyte apoptosis after bile duct ligation in rat and survival rate after endotoxin challenge

BACKGROUND AND AIM

Retention and accumulation of toxic hydrophobic bile salts within hepatocytes may cause hepatocyte toxicity by inducing apoptosis. Apoptosis is a pathway of cell death orchestrated by a family of proteases called caspases. Boc-D-FMK is a cell-permeable irreversible inhibitor of caspase and recent data suggest that it might block the processing of many caspases. The purpose of the present study was to evaluate the possible effect of Boc-D-FMK on hepatocyte apoptosis and on survival rate after bile duct ligation in the rat.

METHODS

Male Sprague-Dawley rats, weighing 280-300 g were randomized to three groups of eight rats each. Group 1 (OBBOC-D) underwent common bile duct ligation and simultaneous treatment with Boc-D-FMK-fmk (dissolved in dimethylsulfoxide [DMSO]). Group 2 (OBZFA) underwent common bile duct ligation and simultaneous treatment with ZFA-fmk (dissolved in DMSO). Group 3 (SHAM) underwent sham operation and simultaneous treatment with the same amount of dimethylsulfoxide (DMSO, n = 4) or the same amount of normal saline (n = 4). After 3 days, liver tissue was harvested for histopathological analysis and measurements of apoptosis. Survival rates were measured in a separate experiment in which animals underwent the same protocol. The animals received endotoxin (15 mg/kg) in the afternoon of the third postoperative day. Animals were observed for 48 h and the survival rates were recorded.

RESULTS

When compared with sham operation, common bile duct ligation with ZFA-fmk (placebo) significantly increased hepatocyte apoptosis (P < 0.001). When compared with the OBZFA group, Boc-D-FMK significantly diminished the increased hepatocyte apoptosis in the OBBOC-D group (P < 0.001). There is no difference in hepatocyte apoptosis (P = 0.05) between OBBOC-D and SHAM groups. After endotoxin challenge, the 48 h survival rates were 100%, 87.5% and 62.5% for the SHAM, OBBOC-D and OBZFA groups, respectively.

CONCLUSIONS

Boc-D-FMK-fmk effectively attenuated the hepatocyte apoptosis in bile duct-ligated rats and may improve the survival rates after endotoxin challenge.

Protein kinase Cdelta mediates cyclic adenosine monophosphate-stimulated translocation of sodium taurocholate cotransporting polypeptide and multidrug resistant associated protein 2 in rat hepatocytes

Cyclic adenosine monophosphate (cAMP) stimulates translocation of Na(+)-taurocholate (TC) cotransporting polypeptide (Ntcp) and multidrug resistant associated protein 2 (Mrp2) to the plasma membrane. Because cAMP activates phosphoinositide-3-kinase (PI3K) and protein kinase C (PKC) activation is PI3K-dependent, the aim of the current study was to determine whether cAMP activates conventional and novel PKCs in hepatocytes and whether such activation plays a role in cAMP-stimulated Ntcp and Mrp2 translocation. The effect of cAMP on PKCs, TC uptake, and Ntcp and Mrp2 translocation was studied in isolated rat hepatocytes using a cell-permeable cAMP analog, CPT-cAMP. The activity of PKCs was assessed from membrane translocation of individual PKCs, and phospho-specific antibodies were used to determine PKCdelta phosphorylation. TC uptake was determined from time-dependent uptake of (14)C-TC, and a cell surface biotinylation method was used to determine Ntcp and Mrp2 translocation. CPT-cAMP stimulated nPKCdelta but not cPKCalpha or nPKCepsilon, and induced PI3K-dependent phosphorylation of nPKCdelta at Thr(505). Rottlerin, an inhibitor of nPKCdelta, inhibited cAMP-induced nPKCdelta translocation, TC uptake, and Ntcp and Mrp2 translocation. Bistratene A, an activator of nPKCdelta, stimulated nPKCdelta translocation, TC uptake, and Ntcp and Mrp2 translocation. The effects of cAMP and bistratene A on TC uptake and Ntcp and Mrp2 translocation were not additive.

CONCLUSION

These results suggest that cAMP stimulates Ntcp and Mrp2 translocation, at least in part, by activating nPKCdelta via PI3K-dependent phosphorylation at Thr(505).

Ursodeoxycholic acid: Mechanism of action and novel clinical applications

Ursodeoxycholic acid (UDCA) is used in the treatment of cholestatic liver diseases, gallstone dissolution, and for patients with hepatitis C virus infection to ameliorate elevated alanine aminotransferase levels. The efficacy of UDCA treatment has been debated and the mechanisms of action in humans have still not defined. Suggested mechanisms include the improvement of bile acid transport and/or detoxification, cytoprotection, and anti-apoptotic effects. In this review, we summarize the proposed molecular mechanisms for the action of UDCA, especially in hepatocytes, and also discuss the putative future clinical usage of this unique drug.

Novel interaction of bile acid and neural signaling in the regulation of cholangiocyte function

Cholangiocytes, the epithelial cells that line the intrahepatic biliary tree, are the target of cholangiopathies, a wide array of chronic disorders that are characterized by the progressive vanishing of bile ducts, leading to ductopenia and liver failure. The loss of bile ducts is a consequence of cholangiocyte death by apoptosis and impaired proliferative response of these cells to injury. The factors that regulate cholangiocyte proliferation and survival are poorly understood. In this regard, a major role is played by the interaction between bile acids and the autonomic nervous system. It has been shown that adrenergic and cholinergic denervation of the liver results in the induction of cell death and impaired proliferative responses of the biliary epithelium to cholestasis. In addition,bile acids have been shown to enter cholangiocytes through the apical, Na(+)-dependent bile acid transporter, ASBT, which has a marked impact on cholangiocyte pathobiology. Recent evidence shows that bile acids and autonomic innervation interact in modulating cholangiocyte response to liver injury. In this review, we describe the recent advances in understanding the molecular mechanisms by which such events occur.

CD95 activation in the liver: ion fluxes and oxidative signaling

Apoptosis is characterized by typical features as cell shrinkage, nuclear condensation, DNA fragmentation, and apoptotic body formation. Whereas some signs of apoptosis are cell type-and death signal-dependent, apoptotic cell volume decrease is an early and ubiquitous event and little is known about the signalling events, which are localized upstream of the plasma membrane transport steps leading to apoptotic cell volume decrease and the proapoptotic events, which are induced by osmolyte loss and cell shrinkage. Ion fluxes and oxidative signaling were recently shown to play an important role in signal transduction with respect to apoptotic cell death within the liver, as a ceramide-dependent activation of the NADPH oxidase was identified as the source of reactive oxygen species generation in rat hepatocytes upon treatment with CD95 ligand, hydrophobic bile salts or hyperosmolarity. The NADPH oxidase-derived ROS signal then allows via Yes, JNK, and EGFR activation for CD95 tyrosine phosphorylation as a prerequisite for CD95 targeting to the plasma membrane and formation of the death inducing signalling complex. Other covalent modifications such as CD95-tyrosine-nitration or CD95-serine/threonine-phosphorylation can interfere with the CD95 activation process. The findings not only provide a mechanistic explanation for the high susceptibility of dehydrated cells for apoptosis, but also give insight into the role of ion fluxes and oxidative signaling with respect to apoptotic cell death within the liver.

Hyperosmotic Activation of the CD95 System

Cell shrinkage, nuclear condensation, DNA fragmentation, and apoptotic body formation are hallmarks of programmed apoptotic cell death. Herein, apoptotic volume decrease (AVD) is an early and ubiquitous event. Conversely, in hepatocytes, hyperosmotic cell shrinkage leads to an activation of the CD95 death receptor system, which involves CD95 tyrosine phosphorylation, CD95 oligomerization, and subsequent trafficking of the CD95 to the plasma membrane, and sensitizes hepatocytes toward CD95 ligand (CD95L)-induced apoptosis. Early signaling events leading to CD95 activation by hyperosmolarity have been identified. In hepatocytes, hyperosmotic exposure induces an almost instantaneous acidification of an acidic sphingomyelinase (ASM) containing endosomal compartment, which is followed by an increase in the intracellular ceramide concentration. Inhibition of anion channels or the vacuolar-type H(+)-ATPase abolishes not only endosomal acidification and subsequent ceramide generation, but also the otherwise observed hyperosmotically induced generation of reactive oxygen species (ROS) by NADPH oxidase isoforms. Hyperosmolarity-induced ROS formation then leads to a Src-family kinase Yes-mediated activation of the epidermal growth factor receptor (EGFR) and to an activation of the c-Jun-N-terminal kinase (JNK). JNK then provides a signal for CD95/EGFR association and subsequent CD95 tyrosine phosphorylation, which is mediated by the EGFR tyrosine kinase activity. CD95 tyrosine phosphorylation then allows for CD95 receptor oligomerization, translocation of the CD95/EGFR protein complex to the plasma membrane, and formation of the death inducing signaling complex (DISC). Mild hyperosmotic exposure, that is, 405 mosmol/liter, does not lead to a reduction of cell viability, even if DISC formation and subsequent caspase 8 and 3 activation occur, but sensitizes hepatocytes to CD95L-induced apoptosis. However, activation of the CD95 system by a more severe hyperosmotic challenge (>505 mosmol/liter) is followed by execution of the apoptotic cell death. Other covalent modifications of CD95, such as CD95 tyrosine nitration or CD95 serine/threonine phosphorylation, were shown to inhibit the CD95 activation process.

Glycochenodeoxycholate (GCDC) inhibits cytokine induced iNOS expression in rat hepatocytes

BACKGROUND

Although the accumulation of hydrophobic bile acid (e.g., glycine conjugated chenodeoxycholic acid, GCDC) is considered to be an important factor contributing to cholestatic liver dysfunction, its pathogenesis is poorly understood. The purpose of this study was to examine the effect of the bile salt GCDC on the regulation of iNOS expression, a key immune modulator during liver inflammation.

MATERIALS AND METHODS

GCDC significantly decreased cytokine-stimulated iNOS promoter activity, and both iNOS mRNA and protein expression. GCDC decreased iNOS promoter activity by preventing IkappaB degradation and inhibiting NF-kappaB DNA-binding activity. To explore the role of iNOS in bile salt induced apoptosis, we also examined the effect of NO on caspase-3 activity.

RESULTS

GCDC strongly induced caspase-3 activity, and this increase was abrogated by both exogenous NO exposure and endogenous NO synthesis. Furthermore, adenoviral iNOS (AdiNOS) pre-treatment decreased acute cholestatic-induced liver injury in a rat bile duct ligation model.

CONCLUSIONS

These findings indicate a novel signaling pathway where potentially toxic bile salts down-regulate hepatic iNOS expression. This blockade of the iNOS mediated antiapoptotic phenotype may have important implications in certain liver disorders.

Cyclic AMP and cyclic GMP suppress TNFalpha-induced hepatocyte apoptosis by inhibiting FADD up-regulation via a protein kinase A-dependent pathway

Cyclic AMP (cAMP) and cyclic GMP (cGMP) suppress apoptosis in many cell types, including hepatocytes. We have previously shown that membrane-permeable cAMP and cGMP analogs attenuate tumor necrosis factor alpha plus actinomycin D (TNFalpha/ActD)-induced apoptosis in hepatocytes at a step upstream of caspase activation and cytochrome c release. Recently we have also shown that FADD levels increase 10 folds in response to TNFalpha/ActD. Therefore we hypothesized that cAMP and cGMP would inhibit FADD upregulation. We show here that cyclic nucleotide analogs dibutyryl cAMP (db-cAMP) and 8-bromo-cGMP (Br-cGMP) inhibit cell death and the cleavages of multiple caspases including caspase-10, -9, -8, -3, and -2, as well as suppress FADD protein up-regulation in TNFalpha/ActD-induced apoptosis. The inhibitory effects of cAMP were seen at lower concentrations than cGMP. Both cAMP and cGMP prevented FADD overexpression and cell death in hepatocytes transfected with the FADD gene. A protein kinase A (PKA) inhibitor, KT 5720, reversed the inhibition of FADD protein levels induced by cAMP or cGMP. In conclusion, our findings indicate that cAMP and cGMP prevent TNFalpha/ActD-induced apoptosis in hepatocytes and that this occurs in association with a near complete inhibition of the upregulation of FADD via a PKA-dependent mechanism.

Glial-derived neurotrophic factor (GDNF) prevents ethanol (EtOH) induced B92 glial cell death by both PI3K/AKT and MEK/ERK signaling pathways

We investigated the neuroprotective effect of glial-derived neurotrophic factor (GDNF) upon alcohol-exposed B92 cultures, as well as the role of the cytoskeleton and mitogen-activated protein kinase (MAPK) pathways in this effect. Ethanol (EtOH) was added to cultures, either alone or in combination with 30 ng/ml GDNF. Exposure to EtOH (86 and 172 mM; 60 and 120 min) increased the frequency of apoptotic cells identified by nuclear DNA staining with 4,6-diamidino-2-phenylindole (DAPI). Cultures treated with GDNF showed a decrease in ethanol-induced apoptosis. A jun N-terminal kinase (JNK) pathway is activated by EtOH and their pharmacological inhibition (by SP600125) neutralized ethanol-induced apoptosis, suggesting a role for JNK in EtOH neurotoxicity. Immunocytochemically detected phospho-JNK (p-JNK) showed an unusual filamental expression, and localized together with actin stress fibers. Examination of the cytoskeleton showed that EtOH depolymerized actin filaments, inducing p-JNK dissociation and translocation to the nucleus, which suggests that released p-JNK may contribute to glial cell death after EtOH exposure. Treatment with GDNF, in turn, may neutralize the ethanol-induced cell death pathway. Either a phosphatidylinositol 3-kinase (PI3K)/AKT pathway inhibitor (LY294002) or an inhibitor of the extracellular signal-regulated kinase (ERK) 1, 2 pathways (UO126) failed to neutralize GDNF protective effects. However, the simultaneous use of both inhibitors blocked the protective effect of GDNF, suggesting a role for both signaling cascades in the GDNF protection. These findings provide further insight into the mechanism involved in ethanol-induced apoptosis and the neurotrophic protection of glial cells.

Oxidative stress induces actin-cytoskeletal and tight-junctional alterations in hepatocytes by a Ca2+ -dependent, PKC-mediated mechanism: protective effect of PKA

Oxidative stress elevates Ca2+ and, presumably, activates Ca2+ -dependent PKCs. We analyzed the participation of Ca2+ -dependent PKCs in actin disorganization and tight-junctional impairment induced by the pro-oxidant tert-butylhydroperoxide (tBOOH) in isolated rat hepatocyte couplets. tBOOH (100 microM) augmented radical oxygen species (ROS), as indicated by increased lipid peroxidation (+217%, p < 0.05) and intracellular production of 2',7'-dichlorofluorescein (+36%, p < 0.05). Cytosolic Ca2+ and PKCalpha translocation to membrane, an indicator of PKCalpha activation, were also elevated by tBOOH (+100 and +79%, respectively, p < 0.05). tBOOH increased the number of couplets displaying membrane blebs (+278%, p < 0.001) and caused redistribution of F-actin. tBOOH induced tight-junctional impairment, as indicated by a reduction in the percentage of couplets retaining presecreted cholyllysylfluorescein in their canalicular vacuoles (-54%, p < 0.001). tBOOH induced redistribution of the tight-junctional-associated protein ZO-1. All these events were prevented by the panspecific PKC inhibitors H7 and staurosporine, the Ca2+ -dependent PKC inhibitor Gö6976, the intracellular Ca2+ chelator BAPTA/AM, and the PKA activator dibutyryl-cyclic AMP. Furthermore, PKC inhibition and PKA activation not only prevented but also fully reversed tBOOH-induced blebbing. Conversely, tBOOH-induced ROS formation and Ca2+ elevation remained unchanged. We conclude that ROS induce hepatocellular actin-cytoskeleton rearrangement and tight-junctional impairment by a PKC-mediated, Ca2+ -dependent mechanism, which is counteracted by PKA.

Hyperosmotic activation of the CD95 death receptor system

Apoptosis is characterized by cell shrinkage, nuclear condensation, DNA fragmentation and apoptotic body formation. These features distinguish apoptosis from other types of cell death, such as necrosis. Whereas some signs of apoptosis, such as externalization of phosphatidylserine, altered mitochondrial function or activation of caspases are cell type- and death signal-dependent, apoptotic cell volume decrease (AVD) is an early and ubiquitous event and little is known about the signalling events, which are localized upstream of the plasma membrane transport steps leading to AVD and the proapoptotic events, which are induced by osmolyte loss and cell shrinkage. In hepatocytes hyperosmotic shrinkage sensitizes the cells towards CD95 ligand-induced apoptosis by activating the CD95 system. This complex process with a NADPH oxidase-derived reactive oxygen species signal as an important upstream event, allows via Yes, JNK and epidermal growth factor-receptor activation for CD95 tyrosine phosphorylation as a prerequisite for CD95 targeting to the plasma membrane and formation of the death inducing signalling complex. Other covalent modifications such as CD95-tyrosine-nitration or CD95-serine/threonine-phosphorylation can interfere with the CD95 activation process. The findings not only provide a mechanistic explanation for the high susceptibility of dehydrated cells for apoptosis, but also give insight into the role of AVD.

3,5,3'-triiodothyronine (T3) is a survival factor for pancreatic beta-cells undergoing apoptosis

3,5,3'-triiodothyronine (T3) is essential for the growth and the regulation of metabolic functions, moreover, the growth-stimulatory effect of T3 has largely been demonstrated and the pathways via which T3 promotes cell growth have been recently investigated. Type 1 diabetes (T1D) is due to the destruction of beta-cells, which occurs even through apoptosis. Aim of our study was to analyze whether T3 could have an antiapoptotic effect on cultured beta-cells undergoing apoptosis. We have demonstrated that T3 promotes cell proliferation in islet beta-cell lines (rRINm5F and hCM) provoking an increment in cell number (up to 55%: rRINm5F and 45%: hCM), cell viability, and BrdU incorporation, and regulating the cell cycle-related molecules (cyc A, D1, E, and p27(kip1)). T3 inhibited the apoptotic process induced by streptozocin, S-Nitroso-N-Acetylpenicylamine (SNAP), and H2O2 via regulation of the pro- and anti-apoptotic factors Bcl-2, Bcl-XL, Bad, Bax, and Caspase 3. The T3 protective effect was PI-3 K-, but not MAPK- or PKA-mediated, involving pAktThr308. Thus, T3 could be considered a survival factor protecting islet beta-cells from apoptosis.

Oxidative Stress Induces Internalization of the Bile Salt Export Pump, Bsep, and Bile Salt Secretory Failure in Isolated Rat Hepatocyte Couplets: A Role for Protein Kinase C and Prevention by Protein Kinase A

We have shown that Ca2+-mediated protein kinase C (PKC) activation induces impairment of bile salt secretory function and F-actin redistribution in hepatocyte couplets. Because oxidative stress induces Ca2+ elevation, we tested here whether PKC inhibition or protein kinase A (PKA) activation, which often counteracts PKC-dependent effects, can prevent and reverse these alterations. The pro-oxidant compounds tert-butylhydroperoxide (tBOOH, 100 microM) and 2,3-dimethoxy-1,4-naphthoquinone (30 microM), reduced by -41% and -29%, respectively, the percentage of couplets accumulating the fluorescent bile salt analog, cholyl-lysylfluorescein in their canalicular vacuoles (p < 0.01). tBOOH-induced bile salt secretory failure was accompanied by internalization of the canalicular bile salt export pump (Bsep), and disarrangement of cytoskeletal F-actin. All these deleterious effects were fully prevented by the intracellular Ca2+ chelator BAPTA/AM (20 microM), the pan-specific PKC inhibitors H7 (100 microM) and staurosporine (1 microM), the inhibitor of Ca2+-dependent PKCs, Gö6976 (2 microM), and the PKA activator dibutyryl-cAMP (500 microM). H7, Gö6976, and dibutyryl-cAMP not only prevented but also fully reversed the decrease in the cholyl-lysyl-fluorescein accumulation. In conclusion, these results suggest that low levels of oxidative stress impair bile salt secretion by internalizing Bsep through a Ca2+-dependent, PKC-mediated mechanism, and that inhibition of PKC, or activation of PKA, prevents and reverses these effects. Alterations in actin organization may be a causal factor.

The inhibitory effect of dibutyryl cyclic AMP on docosahexaenoic acid-induced apoptosis in HL-60 cells through activation of the phosphatidylinositol-3 kinase pathway

OBJECTIVE

Docosahexaenoic acid (DHA) is known as a chemopreventive substance for cancers. Previously we reported that DHA induces apoptosis in HL-60 cells. The aim of this study was to clarify the role of phosphatidylinositol 3-kinase (PI3-kinase)/Akt signaling during DHA-induced apoptosis in HL-60 cells.

METHODS

The inhibitory effects of dibutyryl cAMP (db-cAMP) or LY294002 (a specific inhibitor of the PI3-kinase/Akt pathway) on DHA-induced apoptosis in HL-60 cells were evaluated by the appearance of apoptosis, and from the activities of caspases (3 and 8), the phospholylation of Akt, and cleavage of Bid using DNA indexes, emzymatic measurement of fragmented substrates, and Western blotting, respectively.

RESULTS

The pre-incubation of db-cAMP reduced the activation of caspasses (3 and 8) during the occurrence of DHA-induced apoptosis in HL-60. However, the inhibition of PI3-kinase/Akt signaling by LY294002 resulted in recovery of the caspases' activities, appearance of apoptotic cells, and cleavage of the Bid molecule when LY294002 was co-treated with db-cAMP before the occurrence of DHA-induced apoptosis in HL-60. It was also confirmed that LY294002 strongly inhibited phospholylation of Akt during db-cAMP induced-reduction of DHA-induced apoptosis in HL-60.

CONCLUSION

We demonstrated that DHA-induced apoptosis was sensitive to the modulation of PI3-kinase activity by treatment with db-cAMP or LY294002. These results may provide new insights into the mechanisms of the anti-cancer activity of DHA.

Effect of ZVAD-fmk on hepatocyte apoptosis after bile duct ligation in rat

AIM: Retention and accumulation of toxic hydrophobic bile salts within hepatocyte may cause hepatocyte toxicity by inducing apoptosis. Apoptosis is a pathway of cell death orchestrated by a family of proteases called caspases. Z-Val-Ala-Asp (OMe)-fluoromethyl ketone (ZVAD-fmk) is a cell-permeable irreversible inhibitor of caspase. The purpose of this study was to evaluate the possible effect of ZVAD-fmk on hepatocyte apoptosis after bile duct ligation in the rat.

METHODS: Male Sprague-Dawley rats, weighing 250-300 g, were randomized to five groups of five rats each. Group 1 underwent common bile duct ligation and simultaneous treatment with ZVAD-fmk (dissolved in dimethylsulfoxide (DMSO)). Group 2 underwent common bile duct ligation and simultaneous treatment with Z-Phe-Ala-fluoromethyl ketone ( ZFA-fmk, dissolved in DMSO). Group 3 underwent sham operation and simultaneous treatment with the same amount of DMSO. Group 4 underwent sham operation and simultaneous treatment with the same amount of normal saline. Group 5 underwent common bile duct ligation without other manipulation. After three days, liver tissue was harv-ested for histopathologic analysis and measurements of apoptosis.

RESULTS: When compared with sham operation, common bile duct ligation significantly increased hepatocyte apoptosis (P = 0.008) and ductular proliferation (P = 0.007). ZVAD-fmk significantly diminished the increased hepatocyte apoptosis and ductular proliferation after common bile duct ligation (P = 0.008 and P = 0.007, respectively). ZFA did not show the same effects.

CONCLUSION: Hepatocyte apoptosis and ductular proliferation significantly increased after common bile duct ligation. ZVAD-fmk effectively diminished the increased hepatocyte apoptosis and ductular proliferation after common bile duct ligation, whereas ZFA-fmk did not.

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

We have examined the significance of the activation of c-Jun N-terminal kinase (JNK) and p42/44 mitogen-activated protein kinase (MAPK) by ethanol and acetaldehyde in rat hepatocyte apoptosis. Acetaldehyde induced rapid and transient (15 min) activation of p42/44 MAPK followed by activation of JNK, which remained above control up to 1 h. Ethanol activated JNK for up to 4 h. Both ethanol and acetaldehyde caused apoptosis as determined by DNA fragmentation, caspase-3 activation and 2'[4-ethoxyphenyl]-5-[4-methyl-piperazinyl]-2,5'-bi-1H-benzimidazole (Hoechst 33342) staining. Ethanol-induced apoptosis was blocked by JNK inhibitor 1,9-pyrazoloanthrone (SP600125), indicating that JNK activation is pro-apoptotic. In contrast, acetaldehyde-induced apoptosis was not suppressed by this inhibitor. In fact, SP600125 potentiated acetaldehyde-induced apoptosis, suggesting that JNK activation is anti-apoptotic. Inhibition of p42/44 MAPK by MAPK kinase (MKK1) inhibitor, 1,4-diamino-2,3-dicyano-1,4-bis(2-aminophenylthio)butadiene (U0126), potentiated apoptosis by acetaldehyde or ethanol, suggesting anti-apoptotic role of p42/44 MAPK. The activation of JNK by ethanol or acetaldehyde was insensitive to the genistein (tyrosine kinase inhibitor), GF109203X (2-[1-(3-dimethylaminopropyl)-1H-indol-3-yl]-3-(1H-indol-3-yl)maleimide, protein kinase C [PKC] inhibitor) and N-acetylcysteine (N-AC) (antioxidant), whereas p42/44 MAPK activation by acetaldehyde was inhibited by genistein and GF109203X. Furthermore, p42/44 MAPK activation is not necessary for the JNK activation. In summary, transient activation of JNK by acetaldehyde is anti-apoptotic, whereas sustained activation of JNK by ethanol is pro-apoptotic. The activation of p42/44 MAPK appears to be anti-apoptotic for both ethanol and acetaldehyde. Thus, JNK activation by ethanol and acetaldehyde can be both pro- and anti-apoptotic in hepatocytes.

HIP/PAP, a C-type lectin overexpressed in hepatocellular carcinoma, binds the RII alpha regulatory subunit of cAMP-dependent protein kinase and alters the cAMP-dependent protein kinase signalling

HIP/PAP is a C-type lectin overexpressed in hepatocellular carcinoma (HCC). Pleiotropic biological activities have been ascribed to this protein, but little is known about the function of HIP/PAP in the liver. In this study, therefore, we searched for proteins interacting with HIP/PAP by screening a HCC cDNA expression library. We have identified the RII alpha regulatory subunit of cAMP-dependent protein kinase (PKA) as a partner of HIP/PAP. HIP/PAP and RII alpha were coimmunoprecipitated in HIP/PAP expressing cells. The biological relevance of the interaction between these proteins was established by demonstrating, using fractionation methods, that they are located in a same subcellular compartment. Indeed, though HIP/PAP is a protein secreted via the Golgi apparatus we showed that a fraction of HIP/PAP escaped the secretory apparatus and was recovered in the cytosol. Basal PKA activity was increased in HIP/PAP expressing cells, suggesting that HIP/PAP may alter PKA signalling. Indeed, we showed, using a thymidine kinase-luciferase reporter plasmid in which a cAMP responsive element was inserted upstream of the thymidine kinase promoter, that luciferase activity was enhanced in HIP/PAP expressing cells. Thus our findings suggest a novel mechanism for the biological activity of the HIP/PAP lectin.

Involvement of the Src family kinase yes in bile salt-induced apoptosis

BACKGROUND AND AIMS

Hydrophobic bile acids induce CD95 (Fas, APO-1)-dependent hepatocyte apoptosis, which involves epidermal growth factor receptor (EGFR)-catalyzed CD95 tyrosine phosphorylation. The mechanisms underlying bile salt-induced EGFR activation remain unclear.

METHODS

Bile acid-induced EGFR activation was studied in 24-hour cultured rat hepatocytes and perfused rat liver.

RESULTS

The proapoptotic bile salts taurolithocholate-3-sulfate (TLCS), glycochenodesoxycholate (GCDC) and taurochenodeoxycholate (TCDC), but not taurocholate (TC), activate within 1 minute the Src kinase family member Yes, followed by an association of Yes with EGFR and subsequent EGFR activation. EGFR phosphorylation by TLCS involves tyrosines 845 and 1173 but not 1045. Yes/EGFR association and EGFR activation were sensitive to inhibition by SU6656 but not by PP-2. cAMP had no effect on TLCS and GCDC-induced Yes activation but induced Ser/Thr phosphorylation of Yes and prevented Yes/EGFR association and subsequent EGFR activation. Both SU6656 and cAMP had no effect on bile salt-induced c-Jun N-terminal kinase activation, but blocked bile salt-induced CD95 tyrosine phosphorylation, membrane trafficking of CD95, formation of the death-inducing signaling complex, and apoptosis. In 4-day cultured hepatocytes, knockdown of either Yes or EGFR strongly attenuated bile salt-induced CD95 activation and apoptosis.

CONCLUSIONS

The data identify the Src kinase Yes as an upstream target of proapoptotic bile acids, which triggers EGFR activation, subsequent CD95 tyrosine phosphorylation, and apoptosis. The antiapoptotic effect of cAMP involves a protein kinase A-dependent inhibition of Yes/EGFR association, thereby preventing EGFR activation, which is required for CD95 activation.

Activation of cAMP-guanine exchange factor confers PKA-independent protection from hepatocyte apoptosis

cAMP has previously been shown to promote cell survival in a variety of cell types, but the downstream signaling pathway(s) of this antiapoptotic effect is unclear. Thus the role of cAMP signaling through PKA and cAMP-regulated guanine nucleotide exchange factors (cAMP-GEFs) in cAMP's antiapoptotic action was investigated in the present study. cAMP's protective effect against bile acid-, Fas ligand-, and TNF-alpha-induced apoptosis in rat hepatocytes was largely unaffected by the selective PKA inhibitor, Rp-8-(4-chlorophenylthio)-cAMP (Rp-cAMP). In contrast, a novel cAMP analog, 8-(4-chlorophenylthio)-2'-O-methyl (CPT-2-Me)-cAMP, which activated cAMP-GEFs in hepatocytes without activating PKA, protected hepatocytes against apoptosis induced by bile acids, Fas ligand, and TNF-alpha. The role of cAMP-GEF and PKA on activation of Akt, a kinase implicated in cAMP survival signaling, was investigated. Inhibition of PKA with RP-cAMP had no effect on cAMP-mediated Akt phosphorylation, whereas CPT-2-Me-cAMP, which did not activate PKA, induced phosphatidylinositol 3-kinase (PI3-kinase)-dependent activation of Akt. Pretreatment of hepatocytes with the PI3-kinase inhibitor, Ly-294002, prevented CPT-2-Me-cAMP's protective effect against bile acid and Fas ligand, but not TNF-alpha-mediated apoptosis. Glucagon, CPT-cAMP, and CPT-2-Me-cAMP all activated Rap 1, a downstream effector of cAMP-GEF. These results suggest that a PKA-independent cAMP/cAMP-GEF/Rap pathway exists in hepatocytes and that activation of cAMP-GEFs promotes Akt phosphorylation and hepatocyte survival. Thus a cAMP/cAMP-GEF/Rap/PI3-kinase/Akt signaling pathway may confer protection against bile acid- and Fas-induced apoptosis in hepatocytes.

MAP kinase signaling in diverse effects of ethanol

Chronic ethanol abuse is associated with liver injury, neurotoxicity, hypertension, cardiomyopathy, modulation of immune responses and increased risk for cancer, whereas moderate alcohol consumption exerts protective effect on coronary heart disease. However, the signal transduction mechanisms underlying these processes are not well understood. Emerging evidences highlight a central role for mitogen activated protein kinase (MAPK) family in several of these effects of ethanol. MAPK signaling cascade plays an essential role in the initiation of cellular processes such as proliferation, differentiation, development, apoptosis, stress and inflammatory responses. Modulation of MAPK signaling pathway by ethanol is distinctive, depending on the cell type; acute or chronic; normal or transformed cell phenotype and on the type of agonist stimulating the MAPK. Acute exposure to ethanol results in modest activation of p42/44 MAPK in hepatocytes, astrocytes, and vascular smooth muscle cells. Acute ethanol exposure also results in potentiation or prolonged activation of p42/44MAPK in an agonist selective manner. Acute ethanol treatment also inhibits serum stimulated p42/44 MAPK activation and DNA synthesis in vascular smooth muscle cells. Chronic ethanol treatment causes decreased activation of p42/44 MAPK and inhibition of growth factor stimulated p42/44 MAPK activation and these effects of ethanol are correlated to suppression of DNA synthesis, impaired synaptic plasticity and neurotoxicity. In contrast, chronic ethanol treatment causes potentiation of endotoxin stimulated p42/44 MAPK and p38 MAPK signaling in Kupffer cells leading to increased synthesis of tumor necrosis factor. Acute exposure to ethanol activates pro-apoptotic JNK pathway and anti-apoptotic p42/44 MAPK pathway. Apoptosis caused by chronic ethanol treatment may be due to ethanol potentiation of TNF induced activation of p38 MAPK. Ethanol induced activation of MAPK signaling is also involved in collagen expression in stellate cells. Ethanol did not potentiate serum stimulated or Gi-protein dependent activation of p42/44 MAPK in normal hepatocytes but did so in embryonic liver cells and transformed hepatocytes leading to enhanced DNA synthesis. Ethanol has a 'triangular effect' on MAPK that involve direct effects of ethanol, its metabolically derived mediators and oxidative stress. Acetaldehyde, phosphatidylethanol, fatty acid ethyl ester and oxidative stress, mediate some of the effects seen after ethanol alone whereas ethanol modulation of agonist stimulated MAPK signaling appears to be mediated by phosphatidylethanol. Nuclear MAPKs are also affected by ethanol. Ethanol modulation of nuclear p42/44 MAPK occurs by both nuclear translocation of p42/44 MAPK and its activation in the nucleus. Of interest is the observation that ethanol caused selective acetylation of Lys 9 of histone 3 in the hepatocyte nucleus. It is plausible that ethanol modulation of cross talk between phosphorylation and acetylations of histone may regulate chromatin remodeling. Taken together, these recent developments place MAPK in a pivotal position in relation to cellular actions of ethanol. Furthermore, they offer promising insights into the specificity of ethanol effects and pharmacological modulation of MAPK signaling. Such molecular signaling approaches have the potential to provide mechanism-based therapy for the management of deleterious effects of ethanol or for exploiting its beneficial effects.

Inhibition of bile salt-induced apoptosis by cyclic AMP involves serine/threonine phosphorylation of CD95

BACKGROUND AND AIMS

Cyclic AMP (cAMP) inhibits bile salt-induced hepatocyte apoptosis; the underlying mechanisms are unclear.

METHODS

The effects of cAMP on taurolithocholate-3-sulfate-(TLCS)- or glycochenodesoxycholate (GCDC)-induced CD95 (Fas/APO-1) activation and apoptosis were studied in 24-hour cultured rat hepatocytes and in perfused rat liver.

RESULTS

TLCS induced a rapid oxidative stress response, c-Jun-N-terminal kinase (JNK) and epidermal growth factor (EGF) receptor (EGF-R) activation, subsequent EGF-R/CD95 association and CD95 tyrosine phosphorylation, CD95 membrane targeting, death-inducing signal complex (DISC) formation and hepatocyte apoptosis. None of these responses was triggered by cAMP; however, cAMP induced H89-sensitive serine/threonine phosphorylation of CD95. Similar data were obtained with GCDC, another proapoptotic bile acid. cAMP did not prevent the TLCS-induced oxidative stress response, JNK activation and EGF-R/CD95 association, however abolished EGF-R activation and subsequent CD95 tyrosine phosphorylation, CD95 membrane trafficking, and DISC formation in a H89-sensitive way. Also in presence of TLCS, cAMP induced rapid Ser/Thr phosphorylation of CD95 within 10 min. The effects of cAMP on the various steps of CD95 activation were also found in the intact perfused rat liver. Evidence is given that a cAMP-induced Ser/Thr phosphorylation favors internalization of CD95.

CONCLUSIONS

Inhibition of bile salt-induced apoptosis by cAMP involves both PKA-dependent Ser/Thr phosphorylation of the CD95 and inhibition of EGF-R activation, which results in an inhibition of CD95 tyrosine phosphorylation, CD95 membrane targeting, and DISC formation. CD95 regulation involves complex phosphorylations with CD95-tyrosine phosphorylation favoring CD95 membrane trafficking and DISC formation, whereas CD95 Ser/Thr phosphorylation inhibits these processes.

HIP/PAP stimulates liver regeneration after partial hepatectomy and combines mitogenic and anti-apoptotic functions through the PKA signaling pathway

The HIP/PAP (=human Reg-2) C-type lectin encoding gene is activated in primary liver cancers. In normal liver, the protein is undetectable in normal mature hepatocytes and found only in some ductular cells, representing potential hepatic progenitor cells. The aim of this study was to examine the consequences of human HIP/PAP expression in the liver of transgenic mice. We demonstrated that HIP/PAP stimulated liver regeneration after partial hepatectomy. To further investigate the enhanced liver regeneration observed in vivo, primary cultures of hepatocytes were used to evaluate the mitogenic and anti-apoptotic properties of HIP/PAP. HIP/PAP increased hepatocyte DNA synthesis and protected hepatocytes against TNF-alpha plus actinomycin-D-induced apoptosis. HIP/PAP anti-apoptotic effects against TNF-alpha were clearly demonstrated when protein kinase A activity was specifically inhibited by KT5720, and HIP/PAP stimulated PKA-dependent phosphorylation of the proapoptotic Bad protein at Ser-112, suggesting that HIP/PAP may compete with cAMP to stimulate PKA activity. Overall, our results led us to propose a new role for a C-type lectin, HIP/PAP, as a hepatic cytokine that combines mitogenic and anti-apoptotic functions regarding hepatocytes, and consequently acts as a growth factor in vivo to enhance liver regeneration.

Mechanisms by which cAMP increases bile acid secretion in rat liver and canalicular membrane vesicles

Bile acid secretion induced by cAMP and taurocholate is associated with recruitment of several ATP binding cassette (ABC) transporters to the canalicular membrane. Taurocholate-mediated bile acid secretion and recruitment of ABC transporters are phosphatidylinositol 3-kinase (PI3K) dependent and require an intact microtubular apparatus. We examined mechanisms involved in cAMP-mediated bile acid secretion. Bile acid secretion induced by perfusion of rat liver with dibutyryl cAMP was blocked by colchicine and wortmannin, a PI3K inhibitor. Canalicular membrane vesicles isolated from cAMP-treated rats manifested increased ATP-dependent transport of taurocholate and PI3K activity that were reduced by prior in vivo administration of colchicine or wortmannin. Addition of a PI3K lipid product, phosphoinositide 3,4-bisphosphate, but not its isomer, phosphoinositide 4,5-bisphosphate, restored ATP-dependent taurocholate in these vesicles. Addition of a decapeptide that activates PI3K to canalicular membrane vesicles increased ATP-dependent transport above baseline activity. In contrast to effects induced by taurocholate, cAMP-stimulated intracellular trafficking of the canalicular ABC transporters was unaffected by wortmannin, and recruitment of multidrug resistance protein 2, but not bile salt excretory protein (bsep), was partially decreased by colchicine. These studies indicate that trafficking of bsep and other canalicular ABC transporters to the canalicular membrane in response to cAMP is independent of PI3K activity. In addition, PI3K lipid products are required for activation of bsep in the canalicular membrane. These observations prompt revision of current concepts regarding the role of cAMP and PI3K in intracellular trafficking, regulation of canalicular bsep, and bile acid secretion.

cFLIP-L inhibits p38 MAPK activation: an additional anti-apoptotic mechanism in bile acid-mediated apoptosis

In cholestasis, toxic bile acids accumulate within the liver inducing hepatocyte apoptosis, which exacerbates liver injury. Although bile acids activate both death receptors and mitogen-activated kinase (MAPK) pathways, the mechanistic link between death receptor signaling and MAPK activation in bile acid apoptosis remains unclear. The aim of this study was to ascertain if MAPKs contribute to bile acid cytotoxicity. Although deoxycholate induced apoptosis and activated all three classic mediators of the MAPK pathways including JNK 1/2, p38, and p42/44, only p38 MAPK inhibition attenuated apoptosis. Suppressing FADD expression with siRNA or employing a caspase inhibitor, zVAD-fmk, did not block p38 MAPK activation suggesting its activation was not death receptor-dependent. Unexpectedly, expression of cFLIP-L in a stably transfected cell line blocked apoptosis and p38 MAPK phosphorylation. Based on these data we postulated a direct effect of cFLIP on p38 MAPK activation. The nonphosphorylated but not the phosphorylated/active form of p38 MAPK co-immunoprecipitated with cFLIP-L. In reverse immunoprecipitation experiments, cFLIP-L long but not cFLIP-S co-immunoprecipitate with p38 MAPK. In conclusion, these data suggest that cFLIP-L exerts its anti-apoptotic activity, in part, by inhibiting p38 MAPK activation, an additional anti-apoptotic effect for this protein.