Identifying and Characterizing Interplay between Hepatitis B Virus X Protein and Smc5/6

• Main Authors: Christine M. Livingston, Dhivya Ramakrishnan, Michel Strubin, Simon P. Fletcher, Rudolf K. Beran
• Format: Article
• Language: English
• Published: MDPI AG 2017-04-01
• Series: Viruses
• Subjects: HBx; HBV; DDB1; Smc5/6; cccDNA
• Online Access: http://www.mdpi.com/1999-4915/9/4/69

Hepatitis B X protein (HBx) plays an essential role in the hepatitis B virus (HBV) replication cycle, but the function of HBx has been elusive until recently. It was recently shown that transcription from the HBV genome (covalently-closed circular DNA, cccDNA) is inhibited by the structural maintenance of chromosome 5/6 complex (Smc5/6), and that a key function of HBx is to redirect the DNA-damage binding protein 1 (DDB1) E3 ubiquitin ligase to target this complex for degradation. By doing so, HBx alleviates transcriptional repression by Smc5/6 and stimulates HBV gene expression. In this review, we discuss in detail how the interplay between HBx and Smc5/6 was identified and characterized. We also discuss what is known regarding the repression of cccDNA transcription by Smc5/6, the timing of HBx expression, and the potential role of HBx in promoting hepatocellular carcinoma (HCC).