Cell-intrinsic tumorigenic functions of PPARγ in bladder urothelial carcinoma

Abstract

The role of peroxisome proliferator-activated receptor gamma (PPARγ) has been well characterized in the developmental process of adipogenesis, yet its aberrant expression patterns and functions in cancer subtypes are less understood. While PPARγ has been recently demonstrated to play non-cell-autonomous roles in promoting bladder urothelial carcinoma (UC) progression, underlying mechanisms of the cell-intrinsic oncogenic activity remain unknown. Here, we report robust expression and nuclear accumulation of PPARγ in 47% of UC patient samples, exceeding mRNA expression patterns published by The Cancer Genome Atlas. In vitro assays revealed for the first time that treatment of UC cells with PPARγ inverse agonist or PPARG knockout by CRISPR-Cas9 reduces proliferation, migration, and invasion of multiple established UC cell lines, most strongly in those characterized by PPARG genomic amplification or activating mutations of RXRA, the obligate heterodimer of PPARγ. Through genome-wide approaches including ChIP- and RNA-seq, we define a novel set of PPARγ-regulated genes in UC, including Sonic Hedgehog (SHH). Similar to PPARγ, genetic inhibition of SHH reduces -proliferation and motility. Finally, we demonstrate the PPARγ dependency of UC tumors in vivo by genetic and pharmacological PPARγ inhibition in subcutaneous xenografts. Collectively, our data indicate that PPARγ promotes UC progression in a subset of patients, at least in part, through cell-autonomous mechanisms linked to SHH signaling. Implications: Genome wide analysis of DNA binding sites for oncogenic factor PPARγ revealed SHH as a novel downstream target involved in UC progression, providing important insight into the tumorigenic nature and molecular mechanism of PPARγ signaling in UC.