SuPAR

suPAR, soluble urokinase-type plasminogen activator receptor, (NCBI Accession no. AAK31795) is the soluble form of uPAR. uPAR is a membrane bound receptor for uPA, otherwise known as urokinase. suPAR results from the cleavage and release of membrane-bound uPAR. suPAR concentration positively correlates to the activation level of the immune system and is present in plasma, urine, blood, serum, and cerebrospinal fluid.

Molecular characteristics
suPAR has a secondary structure of 17 anti parallel β-sheets with 3 short α-helices. There are three homologous domains of suPAR: DI, DII, and DIII. In the comparison of cDNA sequences, DI differs from DII and DIII in its primary and tertiary structure, causing its distinct ligand binding properties.

The GPI-anchor links uPAR to the cell membrane making it available for uPA binding. When uPA is bound to the receptor, there is cleavage between the GPI-anchor and DIII, forming suPAR. There are three different suPAR forms: suPAR I-III, suPAR II-III , and suPAR I. Of these three forms suPAR II-III is known to be a chemotactic agent for promoting the immune system.

Application
suPAR is a biomarker for activation of the inflammatory and immune systems. suPAR levels are positively correlated with pro-inflammatory biomarkers, such as tumor necrosis factor-α, leukocyte counts, and C-reactive protein. Elevated levels of suPAR are associated with increased risk of systemic inflammatory response syndrome (SIRS), cancer, cardiovascular disease, type 2 diabetes, infectious diseases, HIV, and mortality. suPARnostic is a prognostic test used to detect suPAR levels in blood plasma.