Transcriptional trans-activating function of hepatitis B virus

Area of Science:

• Virology
• Molecular Biology
• Genetics

Background:

• Hepatitis B virus (HBV) infection is a significant global health concern.
• Understanding how HBV interacts with host cellular machinery is crucial for developing antiviral strategies.

Purpose of the Study:

• To investigate the ability of hepatitis B virus (HBV) to stimulate cellular gene expression.
• To identify the specific HBV DNA region responsible for trans-activation of cellular genes.

Main Methods:

• Construction of a transient-expression system using a plasmid with the bacterial chloramphenicol acetyltransferase (cat) gene under the control of the human beta-interferon gene promoter.
• Cotransfection of Vero cells with the test plasmid and HBV DNA fragments.
• Analysis of CAT gene expression to determine trans-activation activity.

Main Results:

• A 2.7-kilobase BglII DNA fragment of HBV stimulated the expression of the cat gene in Vero cells.
• This trans-activation was specific to HBV DNA, with no significant effect observed from other viral promoter/enhancer elements.
• Subcloning identified a 944-base-pair EcoRV-BglII fragment containing the HBV X gene and its promoter as responsible for the trans-activating function.
• Mutations within the X gene, including promoter removal or frameshift, abolished trans-activating activity.

Conclusions:

• The X gene product of Hepatitis B virus possesses trans-activating function.
• This function is dependent on the X gene's promoter and intact coding sequence.
• The HBV X antigen may play a role in Hepatitis B virus infections by modulating the expression of host cellular genes.