Molecular Signatures of G-Protein Coupled Receptors in Pancreatic Cancer using Super-Resolution Microscopy

Emerging data indicate that G protein-coupled receptors (GPCRs) play important roles in the pathogenesis of cancers. Many GPCRs are constitutively overexpressed in various cancers, and their aberrant signaling is implicated in different stages of tumorigenesis and metastasis. For GPCRs to mediate signaling, one proposed mechanism involves formation of GPCR homo- and hetero-oligomers. However, certain details of the process remain unknown. To address this, we combine pointillistic super-resolution methods and pair-correlation analysis to quantitatively characterize GPCR oligomerization domains both with single molecule sensitivity and at nanometer scale precision. With this approach, we systematically investigated healthy/cancerous cells and multicellular tumor spheroids - a 3D tumor model. Our data suggests that overexpression of mu and kappa opioid receptors induces formation of dense oligomers with both short- and long-distance organization (also supported by fluorescence correlation spectroscopy measurements). Additionally, endogenous oligomers of various sizes are evident in pancreatic cancer cells; these include opioid receptors, somatostatin receptor 2, chemokine C-X-C motif receptor 4, and chemokine C-C motif receptor 5. Importantly, the results suggest that somatostatin receptor 2 associates with mu opioid receptor (i.e. forms hetero-oligomers) in pancreatic cancer cells and multicellular tumor spheroids. In the future, successful application of this innovative approach can be used as a tool for quantitative screening of GPCRs and drug discovery. Ultimately, this strategy may produce novel markers and therapeutic targets for pancreatic cancer.