FIG. 4.

CK1α binding to MDMX is required for p53 regulation. (a) p53 activation of BP100-luciferase reporter was detected after transient transfection into MDMX/p53 double-null 41.4 cells. The inhibitory effects of MDMX mutants and stimulation by CK1α were determined by cotransfection. (b) Binding efficiency between MDMX mutants and p53 was determined by transient cotransfection of H1299 cells with MDMX, p53, and CK1α expression plasmids, followed by MDMX IP/p53 Western blotting (WB). Whole-cell extracts (WCE) were analyzed to confirm similar levels of p53 expression. (c) MDMX-C306S zinc finger point mutant was not regulated by CK1α in a luciferase reporter assay similar to the results shown in panel a. (d) MDMX-C306S mutant did not bind CK1α after cotransfection into H1299 cells.