Interferon regulatory factor 1 (IRF-1) and IRF-2 regulate PD-L1 expression in hepatocellular carcinoma (HCC) cells

Area of Science:

• Immunology
• Oncology
• Molecular Biology

Background:

• Immune checkpoint blockade (ICB) therapy, particularly anti-PD-L1/PD-1, shows limited efficacy in hepatocellular carcinoma (HCC).
• Understanding the regulatory mechanisms of PD-L1 expression is crucial for enhancing ICB response rates in HCC.

Purpose of the Study:

• To investigate the roles of transcription factors IRF-1 and IRF-2 in regulating PD-L1 expression in HCC.
• To elucidate the signaling pathways involved in PD-L1 modulation within the HCC tumor microenvironment.

Main Methods:

• Analysis of IRF-1, IRF-2, and PD-L1 mRNA expression in human HCC tumors and adjacent noncancerous tissue.
• In vitro studies using mouse and human HCC cell lines treated with interferon-gamma (IFN-γ).
• Co-culture experiments with murine HCC cells and activated T cells.
• Reporter assays and site-directed mutagenesis to identify functional elements in the PD-L1 promoter.

Main Results:

• IRF-1 and PD-L1 mRNA expression were significantly lower in HCC tumors compared to normal liver tissue.
• IRF-1, IRF-2, and PD-L1 mRNA expression levels positively correlated within HCC tumors.
• IFN-γ upregulated PD-L1 expression via IRF-1 induction in HCC cells.
• IRF-1 and IRF-2 were found to bind to specific response elements (IRE1/IRE2) in the PD-L1 promoter, with IRF-2 negatively regulating PD-L1 expression.

Conclusions:

• IRF-1 plays a complex role in HCC, acting to upregulate PD-L1 in inflammatory conditions, contrary to its typical tumor suppressor function.
• IRF-1 antagonizes IRF-2 binding to the PD-L1 promoter, offering new insights into PD-L1 regulation.
• These findings provide a novel understanding of PD-L1 regulation in HCC, potentially leading to improved strategies for ICB therapy.