Macroautophagy is a complex multistep process for lysosome-mediated degradation of intracellular components. Its main functions are to maintain cellular homeostasis by removing damaged organelles and to promote cell survival under stress conditions by recycling cell nutrients. Plectin is an important cytolinker protein which regulates the organization of cytoskeleton in mammalian cells. The involvement of plectin in macroautophagy is still poorly understood. Using plasmid ptfLC3, encoding reporter protein LC3 (a marker of autophagic compartments), and fluorescence microscopy we evaluated multiple parameters of macroautophagy in plectin-expressing and plectin-null astrocytes. We show that in astrocytes plectin is involved in autophagic compartment positioning, autolysosome size regulation, basal autophagy fine-tuning and triggering efficient autophagic response in stimulated conditions such as starvation and viral infections. Autophagy is often manipulated by viruses from different families to facilitate their replication and survival in host cells. Immunocytochemical detection of infected cells in astrocyte cell culture revealed that neurotropic flaviviruses, associated with severe neurological complications in humans, infect human and mouse astrocytes. We found that infection of astrocytes, neuroglial cells performing numerous homeostatic and metabolic processes in the brain, with selected neurotropic flaviviruses induces autophagy, without affecting late autophagy events or the size of autophagic compartments. We suggest that the mechanism of action involves flavivirus-induced reorganization of host cell cytoskeleton, as tick-borne encephalitis virus (TBEV) triggered vast changes in plectin, vimentin and microtubule networks, as well as the increase in the amount of actin in infected astrocytes. In conclusion, virus-triggered autophagic response in astrocytes, infected by neurotropic flaviviruses, depends on plectin and is most likely connected to massive reorganization of vimentin filaments and/or microtubules.
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