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Serine 220 phosphorylation of the M erkel cell polyomavirus large T antigen crucially supports growth of Merkel cell carcinoma cells
Author(s) -
Schrama David,
Hesbacher Sonja,
Angermeyer Sabrina,
Schlosser Andreas,
Haferkamp Sebastian,
Aue Annemarie,
Adam Christian,
Weber Alexandra,
Schmidt Marc,
Houben Roland
Publication year - 2015
Publication title -
international journal of cancer
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.475
H-Index - 234
eISSN - 1097-0215
pISSN - 0020-7136
DOI - 10.1002/ijc.29862
Subject(s) - merkel cell polyomavirus , phosphorylation , serine , merkel cell carcinoma , biology , cell growth , microbiology and biotechnology , retinoblastoma protein , phosphoserine , immunoprecipitation , cancer research , cell , cell cycle , biochemistry , carcinoma , gene , genetics
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.