Pituitary Tumor Transforming Gene Causes Aneuploidy and p53-dependent and p53-independent Apoptosis*

The pituitary tumor transforming gene, PTTG, is abundantly expressed in several neoplasms. We recently showed that PTTG overexpression is associated with apoptosis and therefore have now studied the role of p53 in this process. In MCF-7 breast cancer cells that express wild type p53, PTTG overexpression caused apoptosis. p53 was translocated to the nuclei in cells expressing PTTG. Overexpression of p53, along with PTTG, augmented apoptosis, whereas expression of the human papillomavirus E6 protein inhibited PTTG-induced apoptosis. In MG-63 osteosarcoma cells that are deficient in p53, PTTG caused cell cycle arrest and subsequent apoptosis that was inhibited by caspase inhibitors. A proteasome inhibitor augmented PTTG expression in stable PTTG transfectants, suggesting that down-regulated PTTG expression is required for cell survival. Finally, MG-63 cells expressing PTTG showed signs of aneuploidy including the presence of micronuclei and multiple nuclei. These results indicate that PTTG overexpression causes p53-dependent and p53-independent apoptosis. In the absence of p53, PTTG causes aneuploidy. These results may provide a mechanism for PTTG-induced tumorigenesis whereby PTTG mediates aneuploidy and subsequent cell transformation.