Induction of Apoptotic Genes by a p73-Phosphatase and Tensin Homolog (p73-PTEN) Protein Complex in Response to Genotoxic Stress

Abstract The p53 family member, p73, has been characterized as a tumor suppressor and functions in a similar manner as p53 to induce cellular death. The phosphatase and tensin homolog (PTEN) can function as a dual specificity lipid/protein phosphatase. However, recent data have described multiple roles for nuclear PTEN independent of its lipid phosphatase activity. PTEN can directly or indirectly activate p53 to promote apoptosis. We examined whether PTEN would interact and regulate p73 independent of p53. Co-localization in the nucleus and complex formation of p73/PTEN were observed after DNA damage. Furthermore, we also demonstrate that p73α/PTEN proteins directly bind one another. Both overexpressed and endogenous p73-PTEN interactions were determined to be the strongest in the nuclear fraction after DNA damage, which suggested formation of a transcriptional complex. We employed chromatin immunoprecipitation (ChIP) and found that p73 and PTEN were associated with the PUMA promoter after genotoxic stress in TP53-null cells. We found that another p73 target, BAX, had an increased expression in the presence of p73 and PTEN. In addition, in virus-transduced cell lines stably expressing p73, PTEN, or both p73/PTEN, we found that the p73/PTEN cells were more sensitive to genotoxic stress and cellular death as measured by increased poly(ADP-ribose) polymerase cleavage and PUMA/Bax induction. Conversely, knockdown of PTEN dramatically reduced Bax and PUMA levels. Thus, a p73-PTEN protein complex is engaged to induce apoptosis independent of p53 in response to DNA damage.