PAX3 and alveolar rhabdomyosarcoma: We found that treatment of two ARMS cell lines with either a general or highly specific GSK3β inhibitor, which targets the kinase responsible for phosphorylating PAX3-FOXO1 at Ser201,16 resulted in titratable decreases in the phosphorylation of endogenous PAX3-FOXO1 at this site (Figure 1), which directly correlated to reductions in migration and invasion (Figures 2 and 3).