Molecular and Functional Heterogeneity of Cancer Associated Fibroblasts in High Grade Serous Ovarian Cancer

Cancer-associated fibroblasts (CAFs) have been shown to play a role in promotion of cancer cell proliferation and invasion, and mediation of chemotherapy resistance in several cancer types. The work described in this thesis explores the role of CAFs in high-grade serous ovarian cancer (HGSOC) and their heterogeneity at the intra-tumoral and inter-tumoral levels. I demonstrate that CAFs derived from primary tumors by outgrowth in culture mediate cancer cell invasion and chemotherapy resistance. Following a high-throughput flow cytometry screen of a large panel of cell surface-specific antibodies, I have identified CD49e to be uniquely expressed on the surface of CAFs in HGSOC. I further validated and characterized CD49e+ fibroblasts through transcriptional profiling and discovered that patients stratify into two groups based on their CAF gene expression profiles. One group of patients has predominantly CD49e+Fibroblast Activation Protein (FAP)-Hi CAFs in the stroma, while the other group of patients has predominantly CD49e+FAP-Lo CAFs. The molecular signature of CD49e+FAP-Hi CAFs resembles the classical CAF phenotype in its expression of alpha-smooth muscle actin (αSMA), collagens, and growth factors. However, the CD49e+FAP-Lo subset is distinct and possesses a novel preadipocyte-like signature. The CD49e+FAP-Lo phenotype has remained largely unnoticed as it is generally outcompeted in vitro by CD49e+FAP-Hi cells when grown under classical CAF culture conditions. Subsequently, I functionally characterized the properties of each of these subsets in the context of cancer using in vitro and in vivo assays. I showed that FAP-Hi CAFs better promote cancer invasion, growth, metastasis, and chemoresistance than their FAP-Lo counterparts. Moreover, I identified transcription factor TCF21 as a candidate master regulator of the functional disparities between FAP-Hi and FAP-Lo fibroblasts. Through RNA-Seq profiling, I generated a gene signature that is unique to each subtype of CAFs. I applied the gene signature to the existing Cancer Genome Atlas (TCGA) database and showed that infiltrating fibroblasts heavily contribute to the molecular classification of HGSOC patients and their survival outcomes. Finally, I demonstrated that FAP-Hi and FAP-Lo stromal phenotypes are present in pancreatic, bladder, and esophageal carcinomas.Ph.D