(A) H1299 cells were transfected with Myc-β-catenin, CK1α and MDMX mutants. Phosphorylation of β-catenin S45 was determined by western blot. Co-expression of MDMX blocked the increase of pS45 level. MDMXSG (W200S/W201G) and MDMX-1-300 were defective for CK1α binding. 