Stem cell reprogramming during oncogenesis and development

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Project Summary: Tissue stem cells are critical for the replenishment of dying cells and for wound-repair. Previous studies have demonstrated that many cancers can arise from the dysfunction of stem cells, either through accumulation of mutations, or more recently, aberrancies in the epigenetic landscape. Sox9, a transcription factor, plays an important role in the development and maintenance of many stem cell compartments. In the skin, Sox9 is essential for hair follicle stem cells, while epidermal stem cells are characterized by lack of Sox9 expression. Interestingly, basal cell carcinomas (BCC) overexpress Sox9, yet have been demonstrated to arise from epidermal and not hair follicle stem cells. Moreover, Sox9 is critical for BCC as genetic loss of Sox9 completely abolishes tumor formation in vivo. The mechanisms by which ectopic Sox9 contributes to tumor formation for BCC and other cancers remain to be elucidated. However, in HFs, Sox9 binds and regulates the key open chromatin domains (super-enhancers) that choreograph stem cell genes, and my preliminary studies indicate that ectopic expression of Sox9 in the adult epidermis shifts the chromatin landscape by activating previously silenced genes that may be important for BCC transformation. Therefore, I hypothesize that Sox9 elicits a fate switch in Epidermal stem cells by directly binding and remodeling chromatin at key enhancers. Utilizing a newly developed transgenic mouse that expresses an inducible Sox9 in the epidermal stem cells, I will map and annotate the chromatin and transcriptional changes that occur after induction of Sox9 to pinpoint deviations from Sox9-negative epidermal and Sox9+ hair follicle stem cells. Exploiting a combination of nucleosome binding experiments, immunoprecipitations and mass spectrometry, I will determine whether Sox9 can directly recognize and remodel heterochromatin, or whether it achieves this through the interactions of other proteins. Finally, using a powerful in utero lentiviral approach developed in the Fuchs lab, I will functionally test the results of candidates identified using CRISPR/CAS in the context of tumor formation and progression. My studies will directly further our knowledge regarding Sox9 mediated chromatin remodeling and subsequent activation of oncogenic and stem cell transcriptional pathways. Identifying the key Sox9 target genes as well as the proteins involved in epidermal to BCC reprogramming will lead to the development of novel therapeutics used to “reset” the tumor epigenetic landscape into a non-malignant form.