Endocytosis provides a major alternative pathway for lysosomal biogenesis in kidney proximal tubular cells

Item Type:	Article
Title:	Endocytosis provides a major alternative pathway for lysosomal biogenesis in kidney proximal tubular cells
Creators Name:	Nielsen, R. and Courtoy, P.J. and Jacobsen, C. and Dom, G. and Lima, W.R. and Jadot, M. and Willnow, T.E. and Devuyst, O. and Christensen, E.I.
Abstract:	Recruitment of acid hydrolases to lysosomes generally occurs by intracellular sorting based on recognition of a common mannose 6-phosphate signal in the transGolgi network and selective transport to late endosomes/lysosomes. Here we provide evidence for an alternative, efficient secretion-recapture pathway mediated by megalin and exemplified by cathepsin B in kidney proximal convoluted tubules (PCT). We found that in mouse kidneys with defective megalin expression [megalin knockout (KO)] or apical PCT trafficking (ClC-5 KO), the (pro)cathepsin B mRNA level was essentially preserved, but the protein content was greatly decreased and the enzyme was excreted in the urine as mannose 6-phosphate-devoid species. In polarized PCT-derived cells, purified cathepsin B was avidly and selectively taken up at the apical membrane, and uptake was abolished by the megalin competitor, receptor-associated protein. Direct interaction of cathepsin B with megalin was demonstrated by surface plasmon resonance. Procathepsin B was detected in normal mouse serum. Purified cathepsin B injected into mice was efficiently taken up by kidneys ( approximately 10% of injection) and targeted to lysosomes where it remained active, as shown by autoradiography and subcellular fractionation. A single cathepsin B injection into cathepsin B KO mice could reconstitute full lysosomal enzyme activity in the kidneys. These findings demonstrate a pathway whereby circulating lysosomal enzymes are continuously filtered in glomeruli, reabsorbed by megalin-mediated endocytosis, and transferred into lysosomes to exert their function, providing a major source of enzymes to PCT. These results also extend the significance of megalin in PCT and have several physiopathological and clinical implications
Keywords:	Lysosomes, Mannose 6-phosphate, Megalin, Cathepsin B, Animals, Mice
Source:	Proceedings of the National Academy of Sciences of the United States of America
ISSN:	0027-8424
Publisher:	National Academy of Sciences
Volume:	104
Number:	13
Page Range:	5407-5412
Date:	27 March 2007
Official Publication:	https://doi.org/10.1073/pnas.0700330104
PubMed:	View item in PubMed

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