CD13 is a protein found on the surface of various cells throughout the body. It plays a role in several biological processes, acting as a cell surface marker. Its presence on different cell types hints at its diverse functions within the body.
Understanding CD13
CD13 is also known as Aminopeptidase N (APN). This protein functions as an enzyme, which means it facilitates biochemical reactions in the body. Specifically, CD13 is a metalloprotease, an enzyme that uses a metal ion, typically zinc, to break down proteins. It acts by cleaving single amino acids from the N-terminus (the beginning) of various peptides.
The structure of CD13 is that of a type II transmembrane protein, meaning it spans the cell membrane with a short segment inside and a larger, active part extending outside. It has a molecular weight of approximately 150-160 kDa and typically forms a head-to-head homodimer, where two identical CD13 molecules link together.
Where CD13 is Found
CD13 is widely distributed throughout the body, found on many different cell types and tissues. It is commonly expressed on myeloid cells, which include immune cells such as monocytes, macrophages, and granulocytes. Endothelial cells, which line blood vessels, also express CD13, particularly when they are activated or involved in the formation of new blood vessels.
Epithelial cells in organs like the kidney and intestine also show CD13 expression. Fibroblasts, cells that contribute to connective tissue, are another cell type where CD13 is found.
Functions of CD13
CD13’s enzymatic activity, cleaving amino acids from the N-terminus of peptides, is significant in peptide metabolism. This influences the activity of various peptide hormones, cytokines, and chemokines by either activating or inactivating them. For example, it can process peptide hormones like angiotensin III and IV.
Beyond its enzymatic role, CD13 also participates in cell adhesion, which is how cells attach to each other and to their surrounding environment. It is involved in cell migration, the directed movement of cells, a process seen in wound healing and immune responses. CD13 also plays a role in signal transduction, transmitting signals from outside the cell to its interior, influencing cellular behavior.
CD13’s Role in Health and Disease
CD13 contributes to normal physiological processes and various disease states. In healthy individuals, it contributes to immune responses by influencing immune cell activity and regulating inflammatory mediators. It also participates in wound healing, facilitating cell migration and tissue remodeling.
CD13’s involvement in disease is notable in cancer. It plays a role in angiogenesis, the formation of new blood vessels that supply tumors, and is often highly expressed on tumor blood vessels. CD13 also contributes to tumor invasion and metastasis, which is the spread of cancer cells from the primary tumor to other parts of the body. Its increased expression or activity is associated with tumor progression in various cancers, including leukemia, breast, colon, lung, kidney, ovarian, pancreatic, and thyroid cancers. CD13 is being explored as a potential diagnostic marker and a target for therapeutic interventions in certain conditions.