Replication of Brucella abortus and Brucella melitensis in fibroblasts does not require Atg5-dependent macroautophagy.

Background: Several intracellular bacterial pathogens have evolved subtle strategies to subvert vesicular trafficking pathways of their host cells to avoid killing and to replicate inside the cells. Brucellae are Gram-negative facultative intracellular bacteria that are responsible for brucellosis, a worldwide extended chronic zoonosis. Following invasion, Brucella abortus is found in a vacuole that interacts first with various endosomal compartments and then with endoplasmic reticulum sub-compartments.

Different molecular mechanisms involved in spontaneous and oxidative stress-induced mitochondrial fragmentation in tripeptidyl peptidase-1 (TPP-1)-deficient fibroblasts.

NCLs (neuronal ceroid lipofuscinoses) form a group of eight inherited autosomal recessive diseases characterized by the intralysosomal accumulation of autofluorescent pigments, called ceroids. Recent data suggest that the pathogenesis of NCL is associated with the appearance of fragmented mitochondria with altered functions. However, even if an impairement in the autophagic pathway has often been evoked, the molecular mechanisms leading to mitochondrial fragmentation in response to a lysosomal dysfunction are still poorly understood.

Lipids and lysosomes.

Lysosomes are cytoplasmic organelles delimited by a single membrane and filled with a variety of hydrolytic enzymes active at acidic pH and collectively capable to degrade the vast majority of macromolecules entering lysosomes via endocytosis, phagocytosis or autophagy. In this review, we describe the lipid composition and the dynamic properties of lysosomal membrane, the main delivery pathways of lipids to lysosomes and their catabolism inside lysosomes. Then, we present the consequences of a lipid accumulation as seen in various lysosomal storage diseases on lysosomal functions.

Up-regulation of cathepsin B expression and enhanced secretion in mitochondrial DNA-depleted osteosarcoma cells.

Background Information: mtDNA (mitochondrial DNA) mutations that impair oxidative phosphorylation can contribute to carcinogenesis through the increased production of reactive oxygen species and through the release of proteins involved in cell motility and invasion. On the other hand, many human cancers are associated with both the up-regulation and the increased secretion of several proteases and heparanase. In the present study, we tried to determine whether the depletion in mtDNA could modulate the expression and/or the secretion of some lysosomal hydrolases in the 143B osteosarcoma cells, as these mtDNA-depleted cells are characterized by a higher degree of invasiveness than the parental cells.

A dileucine signal situated in the C-terminal tail of the lysosomal membrane protein p40 is responsible for its targeting to lysosomes.

Transport of newly synthesized lysosomal membrane proteins from the TGN (trans-Golgi network) to the lysosomes is due to the presence of specific signals in their cytoplasmic domains that are recognized by cytosolic adaptors. p40, a hypothetical transporter of 372 amino acids localized in the lysosomal membrane, contains four putative lysosomal sorting motifs in its sequence: three of the YXXphi-type (Y(6)QLF, Y(106)VAL, Y(333)NGL) and one of the [D/E]XXXL[L/I]-type (EQERL(360)L(361)). To test the role of these motifs in the biosynthetic transport of p40, we replaced the most critical residues of these consensus sequences, the tyrosine residue or the leucine-leucine pair, by alanine or alanine-valine respectively.

Intracellular localization of p40, a protein identified in a preparation of lysosomal membranes.

Unlike lysosomal soluble proteins, few lysosomal membrane proteins have been identified. Rat liver lysosomes were purified by centrifugation on a Nycodenz density gradient. The most hydrophobic proteins were extracted from the lysosome membrane preparation and were identified by MS.

Endolysosomal transport of newly-synthesized cathepsin D in a sucrose model of lysosomal storage.

Newly-synthesized soluble lysosomal enzymes are transported from the trans-Golgi network to lysosomes by a mannose 6-phosphate receptor-mediated pathway. Lysosomal storage of indigestible material has been reported to perturb the biosynthesis and the fate of lysosomal hydrolases. In this study, we have focused our attention on the last steps in the transport of newly-synthesized cathepsin D to lysosomes in sucrose-treated WI-38 fibroblasts.

Role of two dileucine-like motifs in insulin receptor anchoring to microvilli.

In the absence of ligand, the insulin receptor is maintained on microvilli on the cell surface. A dileucine motif (LL(986-987)) is necessary but not sufficient for this anchoring, which also required the presence of additional sequence(s) downstream of position 1000. The aim of the present study was to identify this (these) additional sequence(s).