Inhibition of c-Abl with STI571 attenuates stress-activated protein kinase activation and apoptosis in the cellular response to 1-beta-D-arabinofuranosylcytosine

The response of myeloid leukemia cells to treatment with 1-beta-D-arabinofuranosylcytosine (ara-C) includes activation of the c-Abl protein tyrosine kinase and the stress-activated protein kinase (SAPK). The present studies demonstrate that treatment of human U-937 leukemia cells with ara-C is associated with translocation of SAPK to mitochondria. STI571 (imatinib mesylate), an inhibitor of c-Abl, blocked both activation and mitochondrial targeting of SAPK in the ara-C response. In concert with these effects of STI571, similar findings were obtained in c-Abl-deficient cells. The results further show that STI571 inhibits ara-C-induced loss of mitochondrial transmembrane potential, caspase-3 activation, and apoptosis. These findings demonstrate that STI571 down-regulates c-Abl-mediated signals that target the mitochondria in the apoptotic response to ara-C.     

Chronic ethanol consumption increases homocysteine accumulation in hepatocytes.

Results of previous studies have shown that chronic ethanol administration impairs methionine synthetase activity and decreases S-adenosylmethionine levels in the liver, indicating interference with homocysteine remethylation. The purpose of the present study was to investigate the effects of chronic ethanol feeding on the accumulation of homocysteine (Hcy), a potentially toxic agent. The research was divided into two experiments. In Experiment A, hepatocytes were isolated from pair-fed control and ethanol-fed rats after 2 weeks of feeding, and the release of Hcy into the medium was determined. Hepatocytes obtained from ethanol-fed rats released twice as much Hcy into the medium as did those obtained from controls. When hepatocytes were challenged by a methionine load, a marked increase in Hcy generation was observed, and the increase was further enhanced in hepatocytes obtained from ethanol-fed rats. In Experiment B, hepatocytes were isolated from pair-fed control and ethanol-fed rats after 4 weeks of feeding (the feeding time required for significant formation of alcoholic fatty liver in rats). In this experiment, similar results were obtained with Hcy generation as in Experiment A. In Experiment B, supplementation of the incubation medium with betaine prevented the increase in generation of Hcy by methionine-treated control cells as well as the generation of Hcy by cells of ethanol-treated rats. These results indicate that betaine may have the potential as a therapeutic agent against toxic Hcy formation.     

Activation of protein kinase Cdelta in human myeloid leukemia cells treated with 1-beta-D-arabinofuranosylcytosine

Treatment of human myeloid leukemia cells with 1-beta-D- arabinofuranosylcytosine (ara-C) is associated with induction of protein kinase activity and early-response gene expression. The present studies in ara-C-treated U-937 cells extend these findings by demonstrating activation of a protein kinase that phosphorylates myelin basic protein (MBP). Purification by sequential ion-exchange chromatography and gel filtration supports the detection of a 40-kD MBP kinase. Substrate and inhibitor studies further support a pattern similar to that of protein kinase C (PKC) isozymes. Results of N- terminal amino acid sequencing and immunoblot analysis demonstrate detection of a 40-kD catalytic fragment of PKCdelta. The results also demonstrate the activation and cleavage of PKCdelta (1) is inhibited by expression of antiapoptotic proteins, and (2) is induced by camptothecin (CAM) and mitomycin C (MMC). These findings support proteolytic activation of PKCdelta in the cellular response to ara-C and other DNA-damaging agents.     

β-catenin is essential for ethanol metabolism and protection against alcohol-mediated liver steatosis in mice

The liver plays a central role in ethanol metabolism, and oxidative stress is implicated in alcohol-mediated liver injury. β-Catenin regulates hepatic metabolic zonation and adaptive response to oxidative stress. We hypothesized that β-catenin regulates the hepatic response to ethanol ingestion. Female liver-specific β-catenin knockout (KO) mice and wild-type (WT) littermates were fed the Lieber-Decarli liquid diet (5% ethanol) in a pairwise fashion. Liver histology, biochemistry, and gene-expression studies were performed. Plasma alcohol and ammonia levels were measured using standard assays. Ethanol-fed (EtOH) KO mice exhibited systemic toxicity and early mortality. KO mice exhibited severe macrovesicular steatosis and 5 to 6-fold higher serum alanine aminotransferase and aspartate aminotransferase levels. KO mice had a modest increase in hepatic oxidative stress, lower expression of mitochondrial superoxide dismutase (SOD2), and lower citrate synthase activity, the first step in the tricarboxylic acid cycle. N-Acetylcysteine did not prevent ethanol-induced mortality in KO mice. In WT livers, β-catenin was found to coprecipitate with forkhead box O3, the upstream regulator of SOD2. Hepatic alcohol dehydrogenase and aldehyde dehydrogenase activities and expression were lower in KO mice. Hepatic cytochrome P450 2E1 protein levels were up-regulated in EtOH WT mice, but were nearly undetectable in KO mice. These changes in ethanol-metabolizing enzymes were associated with 30-fold higher blood alcohol levels in KO mice. CONCLUSION: β-Catenin is essential for hepatic ethanol metabolism and plays a protective role in alcohol-mediated liver steatosis. Our results strongly suggest that integration of these functions by β-catenin is critical for adaptation to ethanol ingestion in vivo.     

Role of alcohol in pathogenesis of hepatitis B virus infection

Hepatitis B virus(HBV)and alcohol abuse often contribute to the development of end-stage liver disease.Alcohol abuse not only causes rapid progression of liver disease in HBV infected patients but also allows HBV to persist chronically.Importantly,the mechanism by which alcohol promotes the progression of HBVassociated liver disease are not completely understood.Potential mechanisms include a suppressed immune response,oxidative stress,endoplasmic reticulum and Golgi apparatus stresses,and increased HBV replication.Certainly,more research is necessary to gain a better understanding of these mechanisms such that treatment(s)to prevent rapid liver disease progression in alcohol-abusing HBV patients could be developed.In this review,we discuss the aforementioned factors for the higher risk of liver diseases in alcohol-induced HBV pathogenies and suggest the areas for future studies in this field.