Oncogenic Ras inhibits IRF1 to promote viral oncolysis

Area of Science:

• Virology
• Molecular Biology
• Cancer Research

Background:

• Oncolytic viruses selectively target cancer cells by exploiting molecular alterations absent in normal cells.
• Defects in type I interferon (IFN)-mediated antiviral responses, often linked to Ras transformation, are key to viral oncolysis.
• Previous work indicated Ras/MEK activation suppresses IFN-inducible genes, suggesting a role in cancer's impaired antiviral defense.

Purpose of the Study:

• To elucidate the mechanism by which Ras/MEK signaling downregulates IFN-induced gene transcription in cancer cells.
• To investigate the role of interferon regulatory factor 1 (IRF1) in this Ras/MEK-mediated transcriptional suppression.
• To determine the impact of IRF1 restoration on cancer cell susceptibility to oncolytic viruses.

Main Methods:

• Promoter deletion analysis of IFN-inducible genes (guanylate-binding protein 2 and Ifi47) to identify regulatory regions.
• MEK inhibition experiments in wild-type and IRF1-deficient mouse embryonic fibroblasts (MEFs).
• Assessment of IRF1 protein expression in RasV12-transformed cells and human cancer cells, with and without MEK inhibition.
• Evaluation of oncolytic vesicular stomatitis virus infection in human cancer cells with restored IRF1 expression.

Main Results:

• The IRF1 binding site was identified as the critical promoter region regulated by MEK.
• MEK inhibition restored IFN-inducible gene transcription in wild-type MEFs but not in IRF1(-/-) MEFs, confirming IRF1's role.
• RasV12 transformation reduced IRF1 protein levels, which were restored by MEK inhibition in both mouse and human cancer cells.
• Re-expression of IRF1 rendered human cancer cells resistant to oncolytic vesicular stomatitis virus infection.

Conclusions:

• Ras/MEK activation in cancer cells downregulates IFN-inducible gene transcription by suppressing IRF1 expression.
• This IRF1-mediated suppression enhances cancer cell susceptibility to oncolytic viral therapy.
• Targeting the Ras/MEK/IRF1 pathway may represent a strategy to improve oncolytic virotherapy efficacy.