The lysosomal enzyme receptor protein (LERP) is not essential, but is implicated in lysosomal function in Drosophila melanogaster.

Medina Hasanagic,Eline Van Meel,Rajeev Aurora,Stuart Kornfeld,Joel C Eissenberg,Shan Luan

doi:10.1242/bio.013334

Medina Hasanagic, Eline Van Meel + Show 4 more

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https://doi.org/10.1242/bio.013334

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Abstract

ABSTRACTThe lysosomal enzyme receptor protein (LERP) of Drosophila melanogaster is the ortholog of the mammalian cation-independent mannose 6-phosphate (Man 6-P) receptor, which mediates trafficking of newly synthesized lysosomal acid hydrolases to lysosomes. However, flies lack the enzymes necessary to make the Man 6-P mark, and the amino acids implicated in Man 6-P binding by the mammalian receptor are not conserved in LERP. Thus, the function of LERP in sorting of lysosomal enzymes to lysosomes in Drosophila is unclear. Here, we analyze the consequence of LERP depletion in S2 cells and intact flies. RNAi-mediated knockdown of LERP in S2 cells had little or no effect on the cellular content or secretion of several lysosomal hydrolases. We generated a novel Lerp null mutation, LerpF6, which abolishes LERP protein expression. Lerp mutants have normal viability and fertility and display no overt phenotypes other than reduced body weight. Lerp mutant flies exhibit a 30–40% decrease in the level of several lysosomal hydrolases, and are hypersensitive to dietary chloroquine and starvation, consistent with impaired lysosome function. Loss of LERP also enhances an eye phenotype associated with defective autophagy. Our findings implicate Lerp in lysosome function and autophagy.

Highlights

In mammalian cells, the two mannose 6-phosphate (Man 6-P) receptors (MPRs), cation-independent (CI) and cation-dependent (CD) MPRs, function to transport newly synthesized lysosomal acid hydrolases from the trans-Golgi network (TGN) to the endosomal/ lysosomal system (Ghosh et al, 2003)
Depletion of lysosomal enzyme receptor protein (LERP) in Drosophila melanogaster S2 cells To explore the possibility that LERP functions as a sorting receptor for lysosomal enzymes at the TGN, the consequence of LERP depletion was first studied in Drosophila S2 cells using RNAi-mediated knockdown
To further test the role of Lerp in autophagy, we examined the interaction of LerpF6 with the autophagy-associated gene Blue cheese (Bchs)

Summary

Introduction

The two mannose 6-phosphate (Man 6-P) receptors (MPRs), cation-independent (CI) and cation-dependent (CD) MPRs, function to transport newly synthesized lysosomal acid hydrolases from the trans-Golgi network (TGN) to the endosomal/ lysosomal system (Ghosh et al, 2003) These receptors bind the acid hydrolases via Man 6-P tags that are added to the hydrolases in the cis-Golgi and simultaneously bind adaptor proteins, GGAs and AP-1, for their incorporation into clathrin-coated vesicles at the trans-Golgi interface. These features are consistent with LERP functioning as a receptor involved in transporting cargo from the TGN to its destination In support of this concept, Dennes et al expressed LERP in MPRdeficient mouse fibroblasts and reported that it partially rescues the missorting of several lysosomal acid hydrolases (Dennes et al, 2005). Kowalewski-Nimmerfall et al reported that RNAi knockdown of LERP in S2 cells had only a small effect on the retention of the lysosomal enzyme cathepsin L and no effect on lysosomal CREG (cellular repressor of EIA-stimulated genes retention), leading them to suggest that LERP is not a universal sorting receptor for lysosomal proteins in flies (KowalewskiNimmerfall et al, 2014)

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