Modulation of mannose receptor activity by proteolysis

Abstract

Macrophages express a receptor on the cell surface that functions to clear glycoproteins from the extracellular milieu. The activity of this receptor is sensitive to treatment with trypsin. In inflammatory situations, macrophages are activated and exposed to increased levels of extracellular proteases. Under these conditions, mannose receptor activity on the macrophages is diminished. We therefore decided to study the effects of trypsin treatment on the structure and activity of cell-associated and purified receptor that might contribute to the activation-associated receptor down-regulation. Trypsin treatment (1 microgram/ml for 3 h) resulted in the production of a 140 kDa, trypsin-resistant fragment from both intact cells and isolated receptor. This fragment was no longer able to bind ligand. The remaining 35 kDa fragment apparently is further degraded into smaller fragments, since no evidence of this domain was found on Coomassie Blue-stained gels. The 140 kDa fragment retained immunoreactivity and contained at least a portion of the iodinated tyrosine residues following surface labelling with Na125I. Neither calcium nor ligand protected the receptor from proteolysis. In addition, prior treatment with oxidants did not increase the susceptibility of the receptor to trypsin digestion. We conclude from these results that the macrophage mannose receptor is clipped by the serine protease trypsin at the cell surface, resulting in the release and further degradation of the binding domain, and the production of a membrane-associated 140 kDa fragment. This trypsin-mediated down-regulation of receptor activity might be important in controlling glycoprotein clearance during inflammation.

Characterization of a rat alveolar macrophage cell line that expresses a functional mannose receptor

“…The MR is a member of the C-type lectin family [3] and has been purified from a variety of sources [4][5][6]. The MR is a single polypeptide of 175 kDa molecular mass with eight carbohydrate recognition domains that cooperate to mediate binding of mannose-containing ligands [7,8].…”

Isolation and characterization of the mannose receptor from human liver potentially involved in the plasma clearance of tissue-type plasminogen activator

“…Although the isolation procedures yielded several protein bands after the first affinity chromatography of the crude liver extract on the t-PA Sepharose column, a second similar purification step showed only two bands, the 175,000 band and a minor band at 140,000, possibly derived from the 175,000 band by proteolytic degradation. This 140,000 fragment could indeed be generated by trypsin digestion of the intact protein, as suggested by Shepherd et al (58). The other proteins, which were eluted from the t-PA column, could not rebind in a second purification procedure.…”

Macrophages from Patients with Cirrhotic Ascites Showed Function Alteration of Host Defense Receptor

“…5 MR internalizes rapidly in the presence of reactive oxygen intermediates released in RB and MR also internalizes in the presence of other inflammatory mediators like trypsin and antigenic products. 11,14,34,35 In such an environment clearance of products from inflammatory milieu by host defense receptors is reduced. 14 This study showed a significantly lower MR specific uptake in patients' PMv than that in controls (P = 0.023).…”

“…11,12,[34][35][36][37] Unfortunately we were unable to perform these techniques. However, in order to back-up the initial results we obtained from fluorescence technique we opted for PCR analysis.…”