Showing papers by "Eeva-Liisa Eskelinen published in 2023"

Upregulation of the ESCRT pathway and multivesicular bodies accelerates degradation of proteins associated with neurodegeneration.

Abstract: Many neurodegenerative diseases, including Huntington's disease (HD) and Alzheimer's disease (AD), occur due to an accumulation of aggregation-prone proteins, which results in neuronal death. Studies in animal and cell models show that reducing the levels of these proteins mitigates disease phenotypes. We previously reported a small molecule, NCT-504, which reduces cellular levels of mutant huntingtin (mHTT) in patient fibroblasts as well as mouse striatal and cortical neurons from an HdhQ111 mutant mouse. Here, we show that NCT-504 has a broader potential, and in addition reduces levels of Tau, a protein associated with Alzheimer's disease, as well as other tauopathies. We find that in untreated cells, Tau and mHTT are degraded via autophagy. Notably, treatment with NCT-504 diverts these proteins to multivesicular bodies (MVB) and the ESCRT pathway. Specifically, NCT-504 causes a proliferation of endolysosomal organelles including MVB, and an enhanced association of mHTT and Tau with endosomes and MVB. Importantly, depletion of proteins that act late in the ESCRT pathway blocked NCT-504 dependent degradation of Tau. Moreover, NCT-504-mediated degradation of Tau occurred in cells where Atg7 is depleted, which indicates that this pathway is independent of canonical autophagy. Together, these studies reveal that upregulation of traffic through an ESCRT-dependent MVB pathway may provide a therapeutic approach for neurodegenerative diseases.

A TRAFFIC themed series ‐ Host membrane trafficking subversion by pathogens

Abstract: Pathogens requiring to invade host's intracellular compartment, e.g. viruses, parasites, bacteria, have evolved multiple ways to manipulate their host cells in order to expand in non-permissive environments. They often exploit membrane trafficking pathways at multiple steps of their infection cycle such as entering the cell, escaping degradation pathways and immune response, building a replicative niche and sustaining replication (from an energy standpoint) and lastly, exiting the host cells. The pathogen's evolutive processes are very efficient for them to avoid clearance by host cells. Further, intracellular pathogens also provide the cell biology community with efficient tools to study intracellular trafficking. For instance, the VSV-G TsO45 protein is thermosensitive and accumulates in the Endoplasmic Reticulum (ER) at a non-permissive temperature. Shifting cells to the permissive temperature results in folding and trafficking through the secretory pathway. VSV-G-ts045 has been used to thoroughly gain insight into the dynamics and mechanisms of secretory trafficking. On the same line, bacterial toxins have been used to artificially alter protein secretion to better understand the underlying mechanisms (and actors) involved. For instance, mycolactone (produced from Mycobacterium ulcerans) blocks the translocation channel Sec61 and was used to study protein entry in the ER and the structure of the translocon. The metalloprotease activity of botulinum and tetanus neurotoxins was used to show that SNAREs control vesicle fusion and neurotransmitter secretion from neuronal synapses. Recent studies on how intracellular pathogens exploit membrane trafficking have led to the discovery of new important mechanisms in cell biology, such as the characterization of non-canonical ubiquitination mechanisms., Thus, studying how pathogens target host cell membrane trafficking pathways is not only important for characterization of host-pathogen interactions, or the development of new therapeutics, but also for exploring fundamental mechanisms of cell biology. The three articles of this special issue provide examples of the plans put in place by different viruses to hijack strategic molecular machineries of the host cells such as molecular motors, phosphoinositide signalling or regulatory mechanisms of RNA synthesis. Fulvio Reggiori and colleagues review the literature highlighting the ability of some human viruses (including rabies virus, adenovirus, herpes simplex virus, human immunodeficiency virus, influenza A virus and papillomavirus) to exploit dynein and kinesin-driven centripetal and centrifugal movements along microtubules to promote cell invasion and replication or virus assembly and egression from the host cells, respectively. This ability is mainly due to the property of some viral components to directly bind the molecular motors, but also, in selected cases, to trigger signalling cascades that boost the motor activity. Stephen Rawlinson, Gregory Moseley and colleagues identify a property shared by different negative sense RNA viruses, in the ability to interact with Treacle, a protein involved in the nucleolar DNA-Damage-Response. By subverting Treacle function these viruses are thus able to impact on and repress ribosomal RNA synthesis. Jacob McPhail and John Burke provide a survey on the existing data demonstrating the articulate strategy some viruses put in place to subvert a key signalling lipid, that is the phosphoinositide PtdIns4P. Hepatitis C virus “uses” its ns5 protein to bind PtdIns-4-kinase IIIα and attract it to the viral replication organelle (RO) where PtdIns4P generated by the kinase recruits a lipid transfer protein that feeds the growing RO. Entero and kobuchi viruses instead hijack another key generator of PtdIns4P, the PtdIns-4-kinase IIIβ to feed their RO. They do it, not by directly binding the kinase, but by interacting with its key regulators such as ACBD3 and GBF1. The authors also highlight how some inhibitors, initially identified as anti-viral agents, were then found to indeed target the PtdIns-4-kinases required for viral replication.

Mammalian ATG8 proteins maintain autophagosomal membrane integrity through ESCRTs

Abstract: The canonical autophagy pathway in mammalian cells sequesters diverse cytoplasmic cargo within the double membrane autophagosomes that eventually convert into degradative compartments via fusion with endolysosomal intermediates. Here, we report that autophagosomal membranes show permeability in cells lacking principal ATG8 proteins (mATG8s) and are unable to mature into autolysosomes. Using a combination of methods including a novel in vitro assay to measure membrane sealing, we uncovered a previously unappreciated function of mATG8s to maintain autophagosomal membranes in a sealed state. The mATG8 proteins GABARAP and LC3A bind to key ESCRT‐I components contributing, along with other ESCRTs, to the integrity and imperviousness of autophagic membranes. Autophagic organelles in cells lacking mATG8s are permeant, are arrested as amphisomes, and do not progress to functional autolysosomes. Thus, autophagosomal organelles need to be maintained in a sealed state in order to become lytic autolysosomes.