YAP1 and Ewing sarcoma: However, high levels of the PP1 subunit PP1c [220], epigenetic promoter silencing of the upstream negative YAP regulatory proteins RASSF2 and RASSF1A [221,222] and, as a consequence, expression from a cryptic downstream promoter of an oncogenic RASSF1 variant, RASSF1C, containing an alternative exon 1 were observed in Ewing sarcoma.