Enhanced tumor suppression by a p14ARF/p53 bicistronic adenovirus through increased p53 protein translation and stability

The p53 tumor suppressor controls a cell cycle arrest and apoptosis pathway that is central to tumor Suppression and often disrupted in cancer. The accumulation and activity of p53 are positively controlled by the p14 ADP p14ARF ribosylation factor (AR) tumor suppressor, and full restoration of the pathway in cancer cells may require that both p53 and p14ARF be supplied. To address this issue, we have constructed a bicistronic adenoviral vector encoding the two proteins (Adp14/p53) and compared its tumor suppressor activity with that of a single gene vector for p53 (Adp53). We find that tumor cells treated with Adp14/p53 undergo a much sharper decrease in viability with increasing multiplicities of infection than do cells treated with Adp53, even when cells express endogenous p14ARF. Adp14/p53 is also more effective than is a combination of single gene vectors for p14 and p53. The sharper decrease in cell viability after treatment of cells with Adp14/p53 correlates with an increased rate of p53 protein synthesis and a decreased rate of p53 protein turnover, leading to increased steady-state levels of p53 protein and increased levels of p53 downstream targets mdm2, p21waf1, and bax. Adp14/p53 treatment leads to an elevated bax:bcl2 ratio and induction of apoptosis in vitro and in vivo, coupled with a failure of the tumor cells to induce neovascularization in vivo. The results indicate that endogenous p14ARF expression may be insufficient to ensure efficient accumulation of ectopic p53 after gene transfer and demonstrate that for tumor suppression, bicistronic coexpression of p14ARF and p53 is superior to p53 alone. The results show that in this setting, p14ARF promotes p53 accumulation by increasing p53 protein synthesis, in addition to its well-characterized ability to oppose mdm2-mediated degradation of p53.