a-photodynamic-approach-to-study-function-intracellular-vesicle

A Photodynamic Approach to Study Function of Intracellular Vesicle Rupture

Intracellular vesicles (IVs) are formed through endocytosis of vesicles into cytoplasm. IV formation is involved in activating various signal pathways ...

Academia Sinica

Lysosomes are the major degradative compartments within cells, harbouring a wide variety of hydrolytic enzymes within their lumen. Release of lysosomal hydrolases from lysosomes into the cell cytoplasm results in cell death. Here we report that damaged lysosomes undergo autophagic turnover. Using a light-induced lysosome impairing scheme that can be controlled spatially and temporally within a cell, we show that damaged lysosomes are selectively ubiquitinated, recruit autophagic proteins and are eventually incorporated into autolysosomes for degradation. We propose that autophagic removal of lysosomes, which we term lysophagy, is a surveillance mechanism that alleviates cells from the adverse effects of lysosomal damage. We envision our method to induce lysosomal damage will enable detailed molecular studies of the lysophagy pathway in the future.

Spatiotemporally controlled induction of autophagy-mediated lysosome turnover.

Galectins are β-galactoside-binding animal lectins primarily found in the cytosol, while their carbohydrate ligands are mainly distributed in the extracellular space. Cytosolic galectins are anticipated to accumulate on damaged endocytic vesicles through binding to glycans initially displayed on the cell surface and subsequently located in the lumen of the vesicles, and this can be followed by cellular responses. To facilitate elucidation of the mechanism underlying this process, we adopted a model system involving induction of endocytic vesicle damage with light that targets the endocytosed amphiphilic photosensitizer disulfonated aluminum phthalocyanine. We demonstrate that the levels of galectins around damaged endosomes are dependent on the composition of carbohydrates recognized by the proteins. By super resolution imaging, galectin-3 and galectin-8 aggregates were found to be distributed in distinct microcompartments. Importantly, galectin accumulation is significantly affected when cell surface glycans are altered. Furthermore, accumulated galectins can direct autophagy adaptor proteins toward damaged endocytic vesicles, which are also significantly affected following alteration of cell surface glycans. We conclude that cytosolic galectins control cellular responses reflect dynamic modifications of cell surface glycans.

Intracellular galectins control cellular responses commensurate with cell surface carbohydrate composition.

Galectin-3 (GAL3) is a β-galactoside-binding lectin expressed in CD4 T cells infected with human immunodeficiency virus-1 (HIV-1). GAL3 promotes HIV-1 budding by associating with ALIX and Gag p6. GAL3 has been shown to localize in membrane lipid rafts in dendritic cells and positively regulate cell migration. HIV-1 spreads between T cells by forming supramolecular structures (virological synapses [VSs]), whose integrity depends on lipid rafts. Here, we addressed the potential role of GAL3 in cell-to-cell transmission of HIV-1 in CD4 T cells. GAL3 expressed in donor cells was more important for facilitating HIV-1 cell-to-cell transfer than GAL3 expressed in target cells. GAL3 was found to be co-transferred with Gag from HIV-1-positive donor to HIV-1-negative target T cells. HIV-1 infection induced translocation of GAL3 together with Gag to the cell-cell interfaces and colocalize with GM1, where GAL3 facilitated VS formation. GAL3 regulated the coordinated transfer of Gag and flotillin-1 into plasma membrane fractions. Finally, depletion of GAL3 reduced the cholesterol levels in membrane lipid rafts in CD4 T cells. These findings provide evidence that endogenous GAL3 stimulates lipid raft components and facilitates intercellular HIV-1 transfer among CD4 T cells, offering another pathway by which GAL3 regulates HIV-1 infection. These findings may inform the treatment of HIV-1 infection based on targeting GAL3 to modulate lipid rafts.

Yu-Hsien Hung

Inflammation Core Facility,
Institute of Biomedical Sciences,
Inflammation Core Facility, Institute of Biomedical Sciences

Academia Sinica

A Photodynamic Approach to Study Function of Intracellular Vesicle Rupture

Yu-Hsien Hung

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Inflammation Core Facility,Institute of Biomedical Sciences,Inflammation Core Facility, Institute of Biomedical Sciences

Academia Sinica

A Photodynamic Approach to Study Function of Intracellular Vesicle Rupture

Inflammation Core Facility,
Institute of Biomedical Sciences,
Inflammation Core Facility, Institute of Biomedical Sciences