Reversal of viral and epigenetic HLA class I repression in Merkel cell carcinoma

Area of Science:

• Oncology
• Immunology
• Virology

Background:

• Cancers employ immune evasion strategies, including downregulating HLA class I antigen presentation.
• Merkel cell carcinoma (MCC), an aggressive skin cancer, is characterized by low HLA class I expression and is often linked to Merkel cell polyomavirus (MCPyV).

Purpose of the Study:

• To identify key regulators responsible for HLA class I loss in MCC.
• To explore potential therapeutic targets for restoring HLA class I expression in MCC.

Main Methods:

• Characterization of 11 patient-derived MCC cell lines.
• Genome-scale, parallel, gain- and loss-of-function screens in an MCPyV-positive MCC cell line.
• Investigation of protein interactions and pharmacologic targeting.

Main Results:

• Transcriptional suppression of HLA class I antigen presentation genes was observed in MCC.
• MYCL and the non-canonical Polycomb repressive complex 1.1 (PRC1.1) were identified as critical repressors of HLA class I.
• A physical interaction between MYCL and the MCPyV small T antigen suggests viral mediation of HLA-I suppression.
• USP7, a PRC1.1 component, was identified as a target capable of restoring HLA class I expression.

Conclusions:

• MYCL and PRC1.1 are key drivers of HLA class I loss in Merkel cell carcinoma.
• Viral proteins may contribute to immune evasion by suppressing HLA class I presentation.
• Targeting USP7 offers a promising therapeutic strategy to enhance anti-tumor immunity in MCC.