FIGURE 5.

CUL4A is responsible for the EGFR inhibition-mediated PCNA polyubiquitylation. Upper panel, MDA-MB-468 cells were treated with and without the EGFR inhibitor AG1478 (8 μm) for 18 h in the presence of the proteasome inhibitor MG132 (5 μm). Cell lysates were then immunoprecipitated (IP) with an anti-PCNA antibody (Santa Cruz Biotechnology). The blot was then probed with an anti-ubiquitin (Ub) antibody. The numbers indicate the intensity of the ubiquitylated ladder normalized by the intensity of total PCNA. Lower panel, the input levels of PCNA, phospho-EGFR (Y1068), total EGFR, and tubulin are shown. WB, Western blotting.