(665c) Dissecting the Role of a Tumor Suppressor Protein in Enabling Highly-Efficient Reprogramming

Reprogramming is the transformation of a cell from one lineage to another by the forced overexpression of lineage-specifying factors. Regardless of the initial or final cell type, the tumor suppressor protein p53 serves as a barrier to reprograming. p53 maintains genomic integrity in response to DNA damage, earning it the moniker of “guardian of the genome.” Active p53 induces cell cycle arrest and apoptosis, which limit reprogramming yields. A wide variety of methods to inhibit p53 have been employed to enhance reprogramming efficiency, including RNA interference, gene knockout, chemical inhibition, and “dominant negative” mutants of p53. We find that not all methods produce equal results. We find that inclusion of mutant p53 in the reprograming cocktail produces the greatest yield increase, inducing up to a 100-fold increase in induced motor neurons from fibroblasts. Curiously, this p53 mutant enables rapidly proliferating cells to accumulate wild-type p53. Combining this mutant with RNA interference to knockdown expression of wild-type p53 reduces this accumulation and reduces reprograming efficiency, indicating an indispensable role for wild-type p53 in highly-efficient reprogramming that our mutant p53 cannot fulfill. How then does wild-type p53 both limit and promote reprogramming? By combining mathematical modeling with targeted mutations of the p53 protein, we are defining the specific protein-protein and protein-DNA interactions that allow p53 to promote high efficiency reprogramming. Together, our data suggest a dual role for p53 in cell-fate transitions that functions as a band-pass filter to restrict transitions. Understanding how p53 promotes cellular plasticity may help to identify processes that promote reprogramming and that can be enhanced without oncogenic mutants. Our observations also implicate a role for p53 in oncogenic transitions and may help to identify specific interactions that could be interrupted to limit cancerous transformations.