Fig. 3. Phosphorylation of Chk1, Chk2 and p53 in HGPS and RD cells. Western blotting was performed as described in Materials and Methods. The phosphorylation status of p53 was determined with p53 Ser-15 phosphorylation-specific antibody. The total p53 was probed as the loading control to ensure that the same amounts of p53 were loaded for BJ, RD and HGPS cells. In the right panel, ß-actin was probed to ensure that similar amounts of proteins were loaded for the three cell lines.