Is the Serpin-Enzyme Complex Receptor an Orphan G-Protein Coupled Receptor?

Abstract

Alpha-1 antitrypsin (α1-AT) is a member of serine proteinase inhibitors, collectively known as serpins, that inactivate their target enzymes by forming a stabilized serpin-enzyme complex. α1-AT molecules interact with elastase, forming biologically active complexes. It was suggested that the formation of α1-AT-elastase complex would expose a domain from α1-AT molecule that is recognized by a specific cell receptor. Thus, a synthetic peptide, called 105Y, was made based on the sequence of the exposed domain. The peptide binds specifically to human hepatoma HepG2 cells, human monocytes, human neutrophils, and rat pheochromocytoma cells (PC12). This binding is blocked by α1-AT-elastase complex and other serpin-enzyme complexes, suggesting an existence of a specific cell surface receptor, termed SEC receptor, that recognizes serpin enzyme complexes. However, the identity of SEC receptor is still unknown. Thus, we decided to use the Deductive Reasoning Strategy approach to investigate if the SEC receptor belongs to G-protein-coupled receptor (GPCR) family. We measured responsiveness of HepG2 cells as well as human neuroblastoma SHSY5Y cells to 105Y peptide by quantifying their expression of an early response gene c-Fos using real time quantitative polymerase chain reaction (qPCR) and measured their expression of orphan GPCRs using polymerase chain reaction (PCR) followed by gel electrophoresis. Our results indicate that the cells were responding to 105Y peptide and express certain orphan GPCRs. Our goal is to evaluate the necessity of these oGPCRs in 105Y peptide signaling in order to determine the best candidate(s) for the 105Y receptor. These results would shed light on the identity of the SEC receptor for better understanding of the molecular biology and physiology of the serpin-enzyme complexes and their receptors. National Institute of Health. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.