Serine 220 phosphorylation of the Merkel cell polyomavirus large T antigen crucially supports growth of Merkel cell carcinoma cells.

Abstract

Merkel cell polyomavirus (MCPyV) is regarded as a major causal factor for Merkel cell carcinoma (MCC). Indeed, tumor cell growth of MCPyV-positive MCC cells is dependent on the expression of a truncated viral Large T antigen (LT) with an intact retinoblastoma protein (RB)-binding site. Here we determined the phosphorylation pattern of a truncated MCPyV-LT characteristically for MCC by mass spectrometry revealing MCPyV-LT as multi-phospho-protein phosphorylated at several serine and threonine residues. Remarkably, disruption of most of these phosphorylation sites did not affect its ability to rescue knockdown of endogenous T antigens in MCC cells indicating that phosphorylation of the respective amino acids is not essential for the growth promoting function of MCPyV-LT. However, alteration of serine 220 to alanine completely abolished the ability of MCPyV-LT to support proliferation of MCC cells. Conversely, mimicking the phosphorylated state by mutation of serine 220 to glutamic acid resulted in a fully functional LT. Moreover, MCPyV-LT(S220A) demonstrated reduced binding to RB in co-immunoprecipitation experiments as well as weaker induction of RB target genes in MCC cells. In conclusion, we provide evidence that phosphorylation of serine 220 is required for efficient RB inactivation in MCC and may therefore be a potential target for future therapeutic approaches.

• Authors: David Schrama, Sonja Hesbacher, Sabrina Angermeyer, Andreas Schlosser, Sebastian Haferkamp, Annemarie Aue, Christian Adam, Alexandra Weber, Marc Schmidt, Roland Houben
• Journal: International journal of cancer (Int J Cancer) Vol. 138 Issue 5 Pg. 1153-62 (Mar 01 2016) ISSN: 1097-0215 [Electronic] United States
• PMID: 26383606 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: © 2015 UICC.

Chemical References

• Antigens, Polyomavirus Transforming
• Retinoblastoma Protein
• Serine

Topics

• Active Transport, Cell Nucleus
• Amino Acid Sequence
• Antigens, Polyomavirus Transforming (metabolism)
• Carcinoma, Merkel Cell (pathology)
• Cell Cycle
• Cell Line, Tumor
• Humans
• Merkel cell polyomavirus (immunology)
• Molecular Sequence Data
• Phosphorylation
• Retinoblastoma Protein (metabolism)
• Serine
• Skin Neoplasms (pathology)