Charting the impact of supraphysiologic MDM2 on gene regulatory circuits in sarcoma

Amplification of the ubiquitin ligase MDM2 is a common mechanism of P53 inactivation across human tumors. Here we investigated the impact of supraphysiologic MDM2 expression on chromatin topology, gene expression and cellular phenotypes in liposarcoma tumors and models. We identified three independent gene regulatory circuits that predominate in aggressive, dedifferentiated tumors. RUNX and AP-1 family transcription factors bind a shared set of enhancers associated with mesenchymal lineage genes that underlie the developmental state of these tumors. P53 and MDM2 co-occupy enhancers and promoters associated with P53 pathways. When highly expressed, MDM2 also binds an additional set of P53-independent promoters that engage in multi-way physical interactions and regulate genes involved in cell division, RNA splicing, translation and stress responses. We find that liposarcoma cells with low to moderate MDM2 levels are sensitive to P53 inhibitors and their combination with pro-apoptotic agents, but that cells with very high-level MDM2 amplification and expression resist treatment. Hence, heterogeneity of MDM2 expression between and within tumors may compromise therapeutic regimens. In conclusion, we distinguished P53-dependent and P53-independent circuits in MDM2 copy number amplified tumors whose interplay has implications for targeted therapy. Samples from liposarcoma. ChIP-Seq and RNA-Seq data was extracted from Non Treated (NT) cells, or cells treated with HDM201. NOTE FROM SUBMITTER: The tumor data is still pending IRB. The raw data will be submitted to the dbGAP