Distinct Regulation of EZH2 and its Repressive H3K27me3 Mark in Polyomavirus-Positive and -Negative Merkel Cell Carcinoma

Marie-Alice Durand, Aurélie Drouin, Alice Mouchard, Laurine Durand, Clara Esnault, Patricia Berthon, Anne Tallet, Yannick Le Corre, Ewa Hainaut-Wierzbicka, Astrid Blom, Philippe Saiag, Nathalie Beneton, Guido Bens, Charlee Nardin, François Aubin, Monica Dinulescu, Christine Collin, Gaelle Fromont-Hankard, Bernard Cribier, Sara Laurent-Roussel, Kristof Cokelaere, Roland Houben, David Schrama, Paul Peixoto, Eric Hervouet, Kamel Bachiri, Diala Kantar, Etienne Coyaud, Serge Guyétant, Mahtab Samimi, Antoine Touzé, Thibault Kervarrec,

J Invest Dermatol

https://doi.org/10.1016/j.jid.2023.02.038

Abstract

Merkel cell carcinoma (MCC) is an aggressive skin cancer for which Merkel cell polyomavirus integration and expression of viral oncogenes small T and Large T have been identified as major oncogenic determinants. Recently, a component of the PRC2 complex, the histone methyltransferase enhancer of zeste homolog 2 (EZH2) that induces H3K27 trimethylation as a repressive mark has been proposed as a potential therapeutic target in MCC. Because divergent results have been reported for the levels of EZH2 and trimethylation of lysine 27 on histone 3, we analyzed these factors in a large MCC cohort to identify the molecular determinants of EZH2 activity in MCC and to establish MCC cell lines’ sensitivity to EZH2 inhibitors. Immunohistochemical expression of EZH2 was observed in 92% of MCC tumors (156 of 170), with higher expression levels in virus-positive than virus-negative tumors (P = 0.026). For the latter, we showed overexpression of EZHIP, a negative regulator of the PRC2 complex. In vitro, ectopic expression of the large T antigen in fibroblasts led to the induction of EZH2 expression, whereas the knockdown of T antigens in MCC cell lines resulted in decreased EZH2 expression. EZH2 inhibition led to selective cytotoxicity on virus-positive MCC cell lines. This study highlights the distinct mechanisms of EZH2 induction between virus-negative and -positive MCC.