Although mitogen-activated protein kinase (MAPK) was shown to be activated by CD99 silencing in Ewing sarcoma (Rocchi et al., 2010), GDF6 silencing still induced p21 when the MAPK pathway was suppressed by a MEK inhibitor, PD98059 (Figure S4C). The gene discussed is WNK2; the disease is Ewing sarcoma.