Transcriptional reprogramming by oncogenic mutations of TP53 in breast cancer cell lines.

Understanding the regulatory basis of the transcriptional program in tumor cells has a great promise for therapeutic interventions. Somatic mutations in the tumor suppressor TP53 gene are prominent and found in over 50% of human cancers cases. Hotspots mutations at the DNA binding domain of the P53 transcription factor (amino acid R248Q, R273H, R248W) or at loci that can lead to structural deformation (structural mutations (amino acid R249S and R175H)), impair the protein capacity to interact with its cognate binding sites or with other proteins. To understand how such mutations affect the carcinogenic transcription program we introduced them to MCF10A cells. Next to identify genes which are miss-regulated by these mutations, we performed microarray analysis and uncovered 50-300 differentially expressed genes (compare to TP53 knock-out). In order to understand the mechanistic basis of these transcriptional alterations, we investigated the changes in the accessibility of regulatory sites by ATAC-seq. We found that one structural mutation, R249S, showed the highest variation in chromatin accessibility (355 unique peaks). Interestingly, these loci are proximal to variably expressed genes, suggesting their regulatory relevance. Furthermore, we have identified possible regulatory factors governing these changes in chromatin accessibility. We are currently investigating the role of these factors in the transcriptional reprogramming of the R249S p53 mutant.