Differential Changes in MAP Kinases, Histone Modifications and Liver Injury in Rats Acutely Treated With Ethanol

Alcoholic liver disease (ALD) is the most common hepatic disease in the western countries. More than 18 million adults in the United States abuse alcohol (Lucey et al., 2009, Purohit et al., 2009) and its chronic consumption causes liver damage leading to steatosis, alcoholic hepatitis, fibrosis, cirrhosis and leads to the development of hepatocellular carcinoma in susceptible individuals (Lucey et al., 2009, Purohit et al., 2009). Acute liver injury induced by ethanol is also drawing attention because the incidence of acute alcoholism or binge drinking is on the rise worldwide (Mathurin and Deltenre, 2009). Moreover, liver is sensitized to injury after acute ethanol in burn injury (Emanuele et al., 2009). Although mechanisms and mediators of chronic alcoholic liver injury have been extensively studied, little is known about the mechanisms underlying acute alcoholic liver injury. The mitogen-activated protein kinase (MAPK) pathways represent a converging point for many signaling pathways, including tyrosine and serine/threonine kinases, G proteins, and calcium signaling (Roux et al., 2004). The most common MAPKs are the extracellular signal-regulated kinases ERK1 and ERK2 (also known as p44 and p42MAPK, respectively), p38MAPK, and c-Jun-N-terminal kinase/stress-activated protein kinases (JNK/SAPK). MAPKs regulate a variety of biologic processes, eg. cell growth and proliferation, chemotaxis, inflammation, steatosis, necrosis and apoptosis (Boutrous, 2008; Brown and Sacks, 2008). The activated MAP kinases translocate into nucleus and then phosphorylate transcription factors, and thereby regulate transcription. In addition to phosphorylating specific transcriptional factors, MAP kinases and their downstream kinases are implicated in alterations in chromatin environment by modulating the phosphorylation and acetylation of nucleosomal and chromatin proteins (Bartova et al., 2008, Delcuve et al., 2009). Histone H3 at ser-10 and ser-28 are rapidly and transiently phosphorylated during immediate-early response of mammalian cells to extracellular stimuli (Delcuve et al., 2009). There are a few kinases identified as histone H3 kinase, eg, mitogen-and stress-activated kinase-1 (MSK1), ribosomal S6 kinase 2 (RSK2), aurora B, and IkB kinase α (Bartova et al., 2008). RSK2, a downstream kinase of ERK1/2, is shown to be required for epidermal growth factor (EGF)-stimulated phosphorylation of histone H3 (Sassone-Corsi, et al., 1999). Histone H3 phosphorylation by p38 MAPK involves downstream kinase MSK-1 (Cheung, et al., 2000; Zhong et al., 2001). Acetylation of histone is also closely related to regulation of transcriptional activity (Delcuve et al., 2009). The regulation of histone acetylation may be indirect through phosphorylation of histone H3 by MAPKs (Sassone-Corsi, et al., 2000) or direct through phosphorylation of histone acetyltransfearses by MAPKs (Ait-Si-Ali S et al., 1999; Kawasaki et al., 2000; Merienne et al., 2001). A role for MAPKs and epigenetic histone modifications in alcoholic organ damage is emerging (Aroor and Shukla, 2004; Shukla et al., 2008). However, the relationship between MAPK signaling and epigenetic histone modifications in acute alcoholic liver injury is not known. In primary culture of rat hepatocytes, ethanol caused moderate activation of ERK1/2 and marked activation of JNK (Lee et al., 2002). Although phospho-p38 MAPK was not affected in the cytosol, nuclear p38 MAPK phosphorylation was increased by ethanol (Lee and Shukla, 2007). Previously we have reported histone H3 lys 9 acetylation and histone H3 ser-10 and ser-28 phosphorylation in primary cultures of hepatocytes (Park et al., 2005; Lee and Shukla, 2007). In hepatocytes, histone H3 lys 9 acetylation was decreased by inhibition of ERK1/2 and JNK whereas histone H3 ser-10 and ser-28 phosphorylations were reduced by inhibition of p38 MAPK (Park et al., 2005; Lee and Shukla, 2007). Although the activation of MAPKs and histone modifications by ethanol have been studied in vitro, very little is known about the activation of MAPKs and their relationship to histone acetylation and phosphorylation in liver acutely exposed to ethanol in vivo. This was investigated here.