Absence of p53 enhances growth defects and etoposide sensitivity of human cells lacking the bloom syndrome helicase BLM

The Bloom syndrome helicase BLM and the tumor-suppressor protein p53 play important roles in preserving genome integrity. Here, we knock out the genes for BLM and p53 in a human pre-B-cell line, Nalm-6. We show that p53 plays an important role in cell proliferation, but not apoptosis, when BLM is absent. Intriguingly, despite the apoptotic function of p53, BLM(-/-)TP53(-/-) cells were more sensitive than either single mutant to etoposide, an anticancer agent that poisons DNA topoisomerase II. Our results suggest a direct, BLM-independent role for p53 in etoposide-induced, topoisomerase II-mediated DNA damage in human cells.