Novel Differential Gene Expression in Human Cirrhosis Detected by Suppression Subtractive Hybridization

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Abstract
Pathogenic molecular pathways in cirrhotic liver diseases such as hepatitis C virus (HCV), autoimmune hepatitis (AIH) and primary biliary cirrhosis (PBC) are poorly characterized. Differentially expressed genes are often important in disease pathogenesis. Suppression subtractive hybridization (SSH) is a genome–wide approach that enriches for differentially expressed mRNA transcripts. We aimed to make novel observations of differential gene expression in cirrhosis using SSH combined with quantitative real–time reverse transcriptase polymerase chain reaction (RT–PCR). Liver transcriptomes in HCV cirrhosis, AIH cirrhosis, PBC, and nondiseased liver tissue were examined by SSH. Resulting complementary DNA (cDNA) clones were rescreened for differential expression by dot–blot hybridization and then sequenced. Selected gene expression was quantified by real–time RT–PCR. Following SSH, 694 clones were rescreened for differential gene expression, of which 145 were sequenced and found to derive from 89 different genes. Seven clones were homologous only with expressed sequence tag (EST) sequences encoding genes having no known function. Up–regulated expression of four genes was confirmed by real–time RT–PCR: transmembrane 4 superfamily member 3 (tetraspanin CO–029) in all forms of cirrhosis, hedgehog interacting protein (HIP) in AIH cirrhosis and chitinase 3–like–1 (HC gp–39 or ykl–40) and arginine–glutamic acid repeat (RERE) in HCV cirrhosis. RERE gene polymorphisms and splice variants were observed in all tissues examined. Tetraspanin CO–029 up–regulation was primarily localized to bile ductular cells. In conclusion, novel observations of differential gene expression in human cirrhosis were made using SSH as the primary discovery tool. In particular, further studies of the RERE gene and its products in HCV associated liver disease are warranted.