Expression profile and functional interrogation of G protein-coupled receptors in endometrial cancer

Abstract

Endometrial cancer (EC) is the sixth most diagnosed cancer in women and unlike most other cancers the incidence of this disease is rising; women are being diagnosed at an earlier age; and mortality is increasing, highlighting an urgent need for novel therapies. Tumours are multicellular units working in concert to achieve the hallmarks of cancer, communicating through autocrine and paracrine factors. G protein-coupled receptors (GPCRs) are the largest family of cell surface receptors that are involved in transducing extracellular signals into intracellular cascades, ultimately altering the trajectory of the cell. Gonadotrophin hormone receptors are prototypical GPCRs, that demonstrate multi-dimensional signalling capacity, and play key roles in reproduction, however, have also been reported to promote EC cell growth. Newer concepts in GPCR biology such as oligomerisation and endomembrane signalling have highlighted greater complexity in signalling and how GPCRs achieve diverse functional effects through the same receptor. Therefore, this thesis sought to identify GPCRs highly expressed in EC, through mining RNA sequencing databases; delineate gonadotrophin hormone receptor signalling and functional consequences in EC cells; and probe the regulation of the gonadotrophin receptor, follicle-stimulating hormone receptor (FSHR), through oligomerisation and endomembrane signalling. This thesis found 16 overexpressed GPCR genes in EC using differential expression analysis of matched normal and tumour samples. FSHR was found to preferentially activate non-classical Gαi/o signalling in Ishikawa EC cells, and induce lipid droplet accumulation via Gαi/o and β-arrestins, highlighting a novel function for β-arrestins in FSHR action. Using super-resolution imaging technique, PD-PALM, FSHR heterologously expressed in HEK293 cells was visualised on the plasma membrane and was demonstrated to exist as monomers and higher-order oligomers. Interestingly, FSHR complexes were altered after ligand stimulation and density-dependent effects were found. Together, this thesis has demonstrated that through system bias, the function and regulation of GPCRs are altered.