The HCV ARFP/F/core+1 protein: Production and functional analysis of an unconventional viral product

Hepatitis C virus (HCV) is an enveloped positive‐strand RNA virus of the Flaviviridae family. It has a genome of about 9,600 nucleotides encoding a large polyprotein (about 3,000 amino acids) that is processed by cellular and viral proteases into at least 10 structural and nonstructural viral proteins. A novel HCV protein has also been identified by our laboratory and others. This protein—known as ARFP (alternative reading frame protein), F (for frameshift) or core+1 (to indicate the position) protein ‐ is synthesized by an open reading frame overlapping the core gene at nucleotide +1 (core+1 ORF). However, almost 10 years after its discovery, we still know little of the biological role of the ARFP/F/core+1 protein. Abolishing core+1 protein production has no affect on HCV replication in cell culture or uPA‐SCID mice, suggesting that core+1 protein is probably not important for the HCV reproductive cycle. However, the detection of specific anti‐core+1 antibodies and T‐cell responses in HCV‐infected patients, as reported by many independent laboratories, provides strong evidence that this protein is produced in vivo . Furthermore, analyses of the HCV sequences isolated from patients with hepatocellular carcinoma and in vitro studies have provided strong preliminary evidence to suggest that core+1 protein plays a role in advanced liver disease and liver cancer. The available in vitro data also suggest that certain core function proteins may depend on production of the core+1 protein. We describe here the discovery of the various forms of the core+1 protein and what is currently known about the mechanisms of their production and their biochemical and functional properties. We also provide a detailed summary of the results of patient‐based research. © 2009 IUBMB IUBMB Life, 61(7): 739–752, 2009