Cytokines increase CRE binding but decrease CRE-mediated reporter activity in rat hepatocytes by increasing c-Jun

Abstract

The cyclic AMP response element (CRE) has been implicated in the regulation of the expression of many genes and cellular processes important in hepatocyte function. CRE sites exist in the promoter regions of several genes expressed during inflammation. Numerous studies on the role of CRE in hepatocyte gene expression have been performed in resting hepatocytes, but the role of CRE during inflammation is unknown. To evaluate the regulation of CRE-mediated transcription during sepsis, cultured hepatocytes were exposed to proinflammatory cytokines and lipopolysaccharide (LPS) was injected into rats. Nuclear proteins were collected and CRE binding activity measured by electromobility shift assay (EMSA) using a consensus CRE oligonucleotide. CRE binding activity was increased in vitro by cytokines and in vivo by LPS administration but CRE-dependent reporter activity was decreased by cytokine stimulation. A c-jun N-terminal kinase (JNK) inhibitor reversed the cytokine-induced increase in CRE binding and increased CRE-dependent reporter activity. Supershift assays indicated that cyclic AMP response element binding protein (CREB) and c-Jun proteins were included in the CRE binding complex. CREB induced and c-Jun suppressed reporter activity using a CRE-dependent construct transfected into cultured primary hepatocytes. In conclusion, these data demonstrate that proinflammatory cytokines regulate CRE binding and activity in cultured hepatocytes and suggest that sepsis-induced changes in CRE binding may participate in the cellular response to inflammation.