BCR/ABL recruits p53 tumor suppressor protein to induce drug resistance

Tumors expressing the ABL oncoproteins (BCR/ABL, TEL/ABL, v-ABL) can avoid apoptosis triggered by DNA damaging agents. The tumor suppressor protein p53 is an important activator of apoptosis in normal cells; conversely its functional loss may cause drug resistance. The ABL oncoprotein-p53 paradigm represents the relationship between an oncogenic tyrosine kinase and a tumor suppressor gene. Here we show that BCR/ABL oncoproteins employ p53 to induce resistance to DNA damage in myeloid leukemia cells. Cells transformed by the ABL oncoproteins displayed accumulation of p53 upon DNA damage. In contrast, only a modest increase of p53 expression followed by activation of caspase-3 were detected in normal cells expressing endogenous c-ABL. Phosphatidylinositol-3 kinase-like protein kinases (ATR and also ATM) -dependent phosphorylation of p53-Ser15 residue was associated with the accumulation of p53, and stimulation of p21 ^Waf-1 and GADD45, resulting in G₂/M delay in BCR/ABL cells after genotoxic treatment. Inhibition of p53 by siRNA or by the temperature-sensitive mutation reduced G₂/M accumulation and drug resistance of BCR/ABL cells. In conclusion, accumulation of the p53 protein contributed to prolonged G₂/M checkpoint activation and drug resistance in myeloid cells expressing the BCR/ABL oncoproteins.