Merkel cell polyomavirus oncoproteins induce microRNAs that suppress multiple autophagy genes

Area of Science:

• Virology and Cancer Biology
• Molecular mechanisms of viral oncogenesis
• Autophagy regulation in disease

Background:

• Merkel cell polyomavirus (MCPyV) T-antigens are implicated in Merkel cell carcinoma (MCC) pathogenesis.
• Viral evasion of host autophagy is crucial for immune suppression and cancer development.
• The precise mechanisms by which MCPyV T-antigens drive tumorigenesis remain incompletely understood.

Purpose of the Study:

• To investigate how MCPyV T-antigens modulate host autophagy.
• To elucidate the role of autophagy suppression in MCPyV-mediated tumorigenesis and MCC.
• To identify potential therapeutic targets for MCC based on autophagy modulation.

Main Methods:

• Analysis of MCPyV T-antigen-induced microRNA (miRNA) expression.
• Assessment of autophagy-related gene (ATG7, SQSTM1/p62, BECN1) expression in MCC tumors.
• Functional studies involving ectopic expression of MCPyV T-antigens and treatment with autophagy modulators (Torin-1, autophagy inhibitor) and pan-caspase inhibitor.

Main Results:

• MCPyV T-antigens induce miR-375, miR-30a-3p, and miR-30a-5p, targeting key autophagy genes ATG7, SQSTM1 (p62), and BECN1.
• Low ATG7 and p62 expression correlate with MCPyV-positive MCC tumors.
• MCPyV small T-antigen and truncated large T-antigen suppress autophagy, while wild-type large T-antigen does not; Torin-1 treatment induces cell death, partially dependent on autophagy but not caspases.

Conclusions:

• MCPyV oncoproteins suppress host autophagy, contributing to immune evasion and tumorigenesis.
• Autophagy suppression by MCPyV T-antigens protects cancer cells from cell death, highlighting its role in MCC development.
• Targeting autophagy evasion presents a potential therapeutic strategy for Merkel cell carcinoma.