Differential expression of p53, p21(waf1/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 t he RecQ helicases, It is believed to be involved in DNA replication and has been implicated in the maintenance of genomic stability, To investigate wh ether BLM was involved in cellular responses to DNA damage Bloom's syndrome fibroblasts were treated with either UV or ionizing radiation and the leve ls of p53 and two of its down stream effecters, p21(waf1/cip1) and hdm2, we re determined by western blot analysis. Following 20 J/m(2) UVC-radiation w e observed that the maximal accumulation of p21(waf1/cip1). and hdm2 protei ns preceded that of p53 in both a normal diploid fibroblast cell strain (GM 0038) and in two Bloom's syndrome cell strains, Furthermore, the Bloom's sy ndrome cells demonstrated a delayed and prolonged accumulation of all three proteins and a delayed recovery of the protein levels back to pre-damage l evels compared with the normal cell strain. Conversely, normal and Bloom's syndrome cell response following 2.5 Gy of ionizing radiation was quite sim ilar for p21(waf1/cip1) and hdm2, but differed significantly for p53, Maxim um accumulation of p53 occurred within 2 h of damage and preceded that of p 21(waf1/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.