Lysosomes are the primary catabolic compartments of eukaryotic cells. They degrade extracellular material that has been internalized by endocytosis and intracellular components that have been sequestered by autophagy. In addition, specialized cells contain lysosome-related organelles that store and secrete proteins for cell-type-specific functions. The functioning of a healthy cell is dependent on the proper targeting of newly synthesized lysosomal proteins. Accumulating evidence suggests that there are multiple lysosomal delivery pathways that together allow the regulated and sequential deposition of lysosomal components. The importance of lysosomal trafficking pathways is emphasized by recent findings that reveal new roles for lysosomal membrane proteins in cellular physiology and in an increasing number of diseases that are characterized by defects in lysosome biogenesis.

Lysosome biogenesis and lysosomal membrane proteins: trafficking meets function

Furin catalyses a simple biochemical reaction--the proteolytic maturation of proprotein substrates in the secretory pathway. But the simplicity of this reaction belies furin's broad and important roles in homeostasis, as well as in diseases ranging from Alzheimer's disease and cancer to anthrax and Ebola fever. This review summarizes various features of furin--its structural and enzymatic properties, intracellular localization, trafficking, substrates, and roles in vivo.

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Furin at the cutting edge: from protein traffic to embryogenesis and disease.

The two mannose 6-phosphate (M6P) receptors were identified because of their ability to bind M6P-containing soluble acid hydrolases in the Golgi and transport them to the endosomal-lysosomal system. During the past decade, we have started to understand the structural features of these receptors that allow them to do this job, and how the receptors themselves are sorted as they pass through various membrane-bound compartments. But trafficking of acid hydrolases is only part of the story. Evidence is emerging that one of the receptors can regulate cell growth and motility, and that it functions as a tumour suppressor.

https://ressources.unisciel.fr/biocell/chap9/res/07_17_Mannose6P_Receptor_Review_Ghosh-Kornfeld.pdf

Mannose 6-phosphate receptors: new twists in the tale

Organelles in the endocytic pathway are composed of a mosaic of structural and functional regions. These regions consist, at least in part, of specialized protein-lipid domains within the plane of the membrane, or of protein complexes associated with specific membrane lipids. Whereas some of these molecular assemblies can be found in more than one compartment, a given combination seems to be unique to each compartment, indicating that membrane organization might be modular.

The endocytic pathway: a mosaic of domains

Sorting of lysosomal proteins.

The heterotetrameric AP-1 complex is involved in the formation of clathrin-coated vesicles at the trans-Golgi network (TGN) and interacts with sorting signals in the cytoplasmic tails of cargo molecules. Targeted disruption of the mouse µ1A-adaptin gene causes embryonic lethality at day 13.5. In cells deficient in µ1A-adaptin the remaining AP-1 adaptins do not bind to the TGN. Polarized epithelial cells are the only cells of µ1A-adaptin-deficient embryos that show γ-adaptin binding to membranes, indicating the formation of an epithelial specific AP-1B complex and demonstrating the absence of additional µ1A homologs. Mannose 6-phosphate receptors are cargo molecules that exit the TGN via AP-1–clathrin-coated vesicles. The steady-state distribution of the mannose 6-phosphate receptors MPR46 and MPR300 in µ1A-deficient cells is shifted to endosomes at the expense of the TGN. MPR46 fails to recycle back from the endosome to the TGN, indicating that AP-1 is required for retrograde endosome to TGN transport of the receptor.

μ1A‐adaptin‐deficient mice: lethality, loss of AP‐1 binding and rerouting of mannose 6‐phosphate receptors

Zebrafish larvae show a clear and distinct pattern of swimming in response to light and dark conditions, following the development of a swim bladder at 4 days post fertilization. This swimming behavior is increasingly employed in the screening of neuroactive drugs. The recent emergence of high-throughput techniques for the automatic tracking of zebrafish larvae has further allowed an objective and efficient way of finding subtle behavioral changes that could go unnoticed during manual observations. This review highlights the use of zebrafish larvae as a high-throughput behavioral model for the screening of neuroactive compounds. We describe, in brief, the behavior repertoire of zebrafish larvae. Then, we focus on the utilization of light-dark locomotion test in identifying and screening of neuroactive compounds.

https://www.mdpi.com/2227-9059/7/1/23/pdf

Zebrafish Larvae as a Behavioral Model in Neuropharmacology.

Early embryonic death of mice deficient in gamma-adaptin.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1016/S0014-5793%2803%2900709-9

Overexpression of cytosolic sialidase Neu2 induces myoblast differentiation in C2C12 cells

Ferroptosis is a programmed form of iron-dependent cell death caused by lipid hydroperoxide accumulation, which can be prevented by glutathione peroxidase 4 (GPx4) activity. Here we investigated the effects of ferroptosis inducers called erastin and RSL3, which act by glutathione depletion and GPx4 inactivation, respectively, on muscle-derived cell lines of embryonal and alveolar rhabdomyosarcoma (RMS), and mouse normal skeletal C2C12 myoblasts. Myogenic lines were exposed to stepwise increasing concentrations of ferroptosis inducers either alone or in combination with iron supplementation, iron chelating agents (bathophenanthrolinedisulfonic acid, BPS), antioxidant molecules (glutathione, N-acetylcysteine), lipid peroxidation inhibitors (ferrostatin-1), and chemotherapeutic agents (doxorubicin and actinomycin D). Drug susceptibility was quantified by measuring cell viability, proliferation and differentiation via neutral red assay, crystal violet assay and Giemsa staining, respectively. The detection of lipid hydroperoxide and protein levels was performed by immunofluorescence and Western blot analysis, respectively. Erastin and RSL3 increased lipid hydroperoxide levels preferentially in the embryonal U57810 and myoblast C2C12 lines, leading to ferroptosis that was accentuated by iron supplementation or prevented by co-treatment with BPS, glutathione, N-acetylcysteine and ferrostatin-1. The inhibition of extracellular regulated kinases (ERK) pathway prevented ferroptosis in U57810 and C2C12 cells, whereas its increased activation in the embryonal RD cells mediated by caveolin-1 (Cav-1) overexpression led to augmented ferroptosis susceptibility. Finally, we observed the combination of erastin or RSL3 with chemotherapeutic doxorubicin and actinomycin D agents to be effective in increasing cell death in all RMS lines. Erastin and RSL3 trigger ferroptosis in highly proliferating myogenic lines through a ERK pathway-dependent fashion.

Daniela Zizioli

Papers

μ1A‐adaptin‐deficient mice: lethality, loss of AP‐1 binding and rerouting of mannose 6‐phosphate receptors

Zebrafish Larvae as a Behavioral Model in Neuropharmacology.

Early embryonic death of mice deficient in gamma-adaptin.

Overexpression of cytosolic sialidase Neu2 induces myoblast differentiation in C2C12 cells

Cell growth potential drives ferroptosis susceptibility in rhabdomyosarcoma and myoblast cell lines