GSK3B and embryonal rhabdomyosarcoma: Even though we observed titratable inhibition of PAX3-FOXO1 phosphorylation at Ser201, inhibition of GSK3β activity may affect unrelated pathways, as was previously demonstrated in myogenesis and embryonal rhabdomyosarcoma.23, 24 Further, inhibition of CK2, a ubiquitous and essential multifunctional enzyme, resulted in non-specific cell death (data not shown) preventing use of these small molecule inhibitors in these studies.