Regulation of PPARγ expression in luminal muscle invasive bladder cancer

Peroxisome proliferator-activated receptor gamma (PPARγ) is a ligand-dependent transcription factor belonging to the type II nuclear receptor family. PPARγ overexpression and activation are important hallmarks of the luminal subtype of muscle invasive bladder cancer (MIBC), where PPARγ has been ascribed an oncogenic role and has been associated with immune exclusion. There is therefore an important need to better understand the mechanisms that regulate PPARγ. A high throughput genome-wide CRISPR knock-out screen in a luminal MIBC cell line was performed to identify endogenous regulators of PPARγ expression. Using CRISPR knock-in technology, the cells were engineered to express GFP and PPARγ proportionally. The top candidates were then individually validated by RNAi and CRISPR gene knockout for their ability to alter PPARγ mRNA and protein levels. The screen highlighted 47 potential regulators of PPARγ expression with a false discovery rate below 1%. These can be grouped in functional clusters of transcription factors and chromatin remodeling enzymes currently known for orchestrating cellular oxidative stress response, detoxification from xenobiotic chemicals or general gene transcription regulation. In this study we developed a powerful screening tool for the characterization of novel factors involved in the expression of key bladder cancer players. In particular, our results revealed the intricated regulatory mechanisms of PPARγ expression exploited by luminal MIBC, thus highlighting the importance of fine-tuning of this nuclear receptor in the biology of the disease.