Merkel cell polyomavirus tumor antigen (MCPyV T antigen)

Merkel cell polyomavirus tumor antigens are oncoproteins produced by cells infected with MCPyV. The most clinically relevant antigens are the large T antigen (LT), small tumor antigen (ST), and, less commonly, the middle T antigen (MT). LT and ST antigens are necessary for Merkel cell carcinoma cell survival and proliferation, exerting their oncogenic effects by inactivating key cellular tumor suppressors like pRB and p53, promoting DNA replication, cell cycle progression, and inhibiting apoptosis. ST antigen uniquely promotes cell transformation through interactions with protein degradation machinery (especially the SCF/FBW7 pathway), facilitating the accumulation of oncogenic factors (such as c-Myc and cyclin E) and enhancing genomic instability. LT and ST are used both as diagnostic biomarkers (by immunohistochemistry or serology) and as emerging therapeutic targets, especially in immune-based strategies. No receptor or enzyme activity is directly attributed to these antigens—they act as viral oncoproteins.

Other names

MCPyV antigenMerkel cell polyomavirus T antigenMCPyV LT (large T antigen)MCPyV ST (small tumor antigen)MCV antigenPolyomavirus Merkel cell antigenMCPyV middle T antigen

Interference with tumor suppressor pathways (e.g., RB and p53 inhibition by LT antigen); Stabilization of cellular oncoproteins (e.g., c-Myc, cyclin E by ST antigen); Inhibition of ubiquitin ligase complexes (such as SCF and FBW7) to drive protein stabilization and transformation; Activation of cell signaling pathways (e.g., Src family kinases by middle T antigen)