Ectodomain shedding of the insulin‐like growth factor‐II/mannose 6‐phosphate receptor (IGF‐II/MPR)

TL;DRAbstract

The 300kDa IGF‐II/MPR is a multifunctional type I membrane glycoprotein that is required for the intracellular transport of lysosomal enzymes and the endocytosis of an increasing number of extracellular ligands. A soluble, truncated form of the IGF‐II/MPR has been identified in serum where it acts as a major IGF‐II carrier protein, modulating IGF‐II activity in a manner analogous to soluble IGF‐binding proteins. We have studied the shedding of the receptor in polarized human intestinal epithelial cells. Filter‐grown monolayers of Caco‐2 cells stably transfected with the bovine IGF‐II/MPR were incubated in serum‐free media for 48h. The medium and cell lysate were then assayed for IGF‐II/MPR by affinity chromatography and immunoblotting. Of the total receptor, 32% ± 11 was seen in the apical medium compared to only 10% ± 6 in the basolateral medium. To identify the class of protease involved, Caco‐2 cells were incubated with various protease inhibitors in serum‐free media for 18h and the

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