HBV preS2 transactivates FOXP3 expression in malignant hepatocytes

Area of Science:

• Hepatocellular Carcinoma (HCC) Research
• Molecular Biology
• Virology

Background:

• Increased expression of forkhead box protein 3 (FOXP3) observed in hepatocellular carcinoma (HCC) cells.
• Mechanisms underlying FOXP3 upregulation in HCC remain largely unknown.
• Hepatitis B virus (HBV) preS2 protein previously shown to transactivate hTERT in malignant hepatocytes.

Purpose of the Study:

• To investigate the role of HBV preS2 protein in regulating FOXP3 expression within HCC.
• To elucidate the molecular mechanisms by which preS2 influences FOXP3 levels in HCC.

Main Methods:

• Detection of FOXP3 expression via RT-PCR, Western blot, and immunohistochemistry.
• Utilized cotransfection and siRNA knockdown in HCC cell lines to assess preS2 effects on FOXP3.
• Employed luciferase reporter and Electrophoretic Mobility Shift Assay (EMSA) to explore preS2-mediated FOXP3 transcriptional regulation.

Main Results:

• Significant increase in FOXP3 expression in malignant hepatocytes of HCC patients, particularly in HBsAg-positive cases (P = 0.002).
• Overexpression of preS2 enhanced FOXP3 expression in HCC cell lines; preS2 knockdown reduced FOXP3 levels.
• preS2 dose-dependently transactivated the FOXP3 promoter, with an identified AP-1 binding site (-465 to -445 bp) crucial for this activation.

Conclusions:

• Demonstrated for the first time that the HBV preS2 oncoprotein directly transactivates FOXP3 transcription in HCC cells.
• Identified a specific mechanism involving preS2-mediated activation of the FOXP3 promoter via an AP-1 binding site.