How post-translational modifications influence the biological activity of chemokines

Chemokines are important proteins involved in the regulation of directed leukocyte migration during inflammation and the homeostatic homing of immune cells. In addition, they play a role in angiogenesis, hematopoiesis, organogenesis, tumor growth and metastasis. Therefore, the chemokine/chemokine receptor network is highly complex and needs to be tightly controlled. An important mechanism of fine-tuning chemokine activity and reducing its apparent redundancy is post-translational modification (PTM) of chemokines and their receptors. Under inflammatory conditions, enzymes such as matrix metalloproteinases (MMPs), plasmin, CD13, CD26, and peptidylarginine deiminases (PADs) and protein-modifying agents, such as peroxynitrite, are upregulated and released and may provoke truncation, degradation, nitration or citrullination of chemokines. Most modified chemokines show altered biological activity. This review reports how PTMs influence the biological functions of chemokines, with special attention for the impact beyond chemotaxis.