Differential expression of p53, p21waf1/cip1 and hdm2 dependent on DNA damage in Bloom's syndrome fibroblasts.

The Bloom's syndrome gene, BLM, encodes a protein which bears homology to the RecQ helicases. It is believed to be involved in DNA replication and has been implicated in the maintenance of genomic stability. To investigate whether BLM was involved in cellular responses to DNA damage Bloom's syndrome fibroblasts were treated with either UV or ionizing radiation and the levels of p53 and two of its down stream effectors, p21waf1/cip1 and hdm2, were determined by western blot analysis. Following 20 J/m2 UVC-radiation we observed that the maximal accumulation of p21waf1/cip1 and hdm2 proteins preceded that of p53 in both a normal diploid fibroblast cell strain (GM0038) and in two Bloom's syndrome cell strains. Furthermore, the Bloom's syndrome cells demonstrated a delayed and prolonged accumulation of all three proteins and a delayed recovery of the protein levels back to pre-damage levels compared with the normal cell strain. Conversely, normal and Bloom's syndrome cell response following 2.5 Gy of ionizing radiation was quite similar for p21waf1/cip1 and hdm2, but differed significantly for p53. Maximum accumulation of p53 occurred within 2 h of damage and preceded that of p21waf1/cip1 and hdm2. These results suggest that the BLM protein may play a role in the detection of certain types of DNA damage and in the cellular response to that damage.