Title: Transcriptional targets and functional activities of thep53 gene family
Description: The p53 family is comprised of three members--p53, p63, and p73--each having important and distinct biological functions. p53 is a major tumor suppressor, p63 is required for epithelial morphogenesis, while p73 affects neurogenesis, inflammation, sensory, and other processes. How these three highly homologous transcription factors play such disparate physiological roles remains an unresolved question. Furthermore, while considerable information is available for genes regulated by p53, few in vivo targets are known for p63 and p73. We used chromatin immunoprecipitation and tiled microarrays to generate an unbiased, global map of p63 DNA binding sites. Over 5800 targets were identified, which are enriched for genes in cell adhesion, proliferation, death, and signaling pathways. We coupled this analysis with expression profiling of p63-depleted cells, and revealed a significant but complex relationship between p63 binding targets and p63-responsive genes. Moreover, many p63 binding regions are evolutionarily conserved and/or associated with sequence motifs for other transcription factors. Together, these data support the biological relevance of p63 binding sites identified in this study.

A similar analysis of p73 DNA binding sites in the same cells showed a striking overlap with p63 and evidence of co-occupancy by these two factors. In another cell type tested, the overlap is still high but differences in binding affinity are observed. Together, these data indicate that p73 binding in vivo is highly similar to that of p63, but target selection can be subject to cell type-specificity and relative expression levels. An intriguing feature of the p53 family is the presence of multiple isoforms resulting from distinct promoters and alternative splicing. Using a mouse model for TAp63-deficiency, we addressed an important controversy in the field, demonstrating that ΔNp63, rather than TAp63, controls epithelial morphogenesis. We also uncovered a novel function for TAp63 in the DNA damage response in oocytes. TAp63's genome-protective role in the female germ line is similar to that of p53 in somatic cells, underscoring a conserved relationship between genotoxic stimuli and activation of the p53 family. This dissertation contributes to a comprehensive view of transcriptional regulation and DNA binding by the p53 family, and addresses isoform-specific functions in vivo. We anticipate that these data will help us understand the individual and interactive functions of the p53 family, and provide important insights into signaling pathways in cancer and development.