Aminopeptidase N is a widely expressed, membrane-bound proteolytic enzyme that breaks down peptides during digestion, cleaves cell surface antigens during antigen presentation, and acts as a receptor for human viruses, including several coronaviruses. This multifunctional protein is implicated in the regulation of many biological processes, including angiogenesis, cell proliferation, cell migration, inflammation and immune response . APN was originally identified as the cell surface antigen CD13, which is expressed in myeloid lineage hematopoietic cells and myeloid leukemia. Identified substrates of aminopeptidase N include the angiotensin I-III peptide hormones, the opioid peptide met-enkephalin, and cytokines MCP-1 and MIP-1 . Abnormal APN protein expression is seen in various forms of cancer, with high APN expression associated with poor survival in colon cancer and non-small cell lung cancer and silenced APN expression related to poor prognosis in prostate cancer .