Controlled Tau Cleavage in Cells Reveals Abnormal Localizations of Tau Fragments

International audienceIn several forms of dementia, such as Alzheimer's disease, the cytoskeleton-associated protein tau undergoes proteolysis, giving rise to fragments that have a toxic impact on neuronal homeostasis. How these fragments interact with cellular structures, in particular with the cytoskeleton, is currently incompletely understood. Here, we developed a method, derived from a Tobacco Etch Virus (TEV) protease system, to induce controlled cleavage of tau at specific sites. Five tau proteins containing specific TEV recognition sites corresponding to pathological proteolytic sites were engineered, and tagged with GFP at one end and mCherry at the other. After a controlled cleavage to produce GFP-N-terminal and C-terminal-mCherry fragments, we followed the fate of tau fragments in cells. Our results showed that whole engineered tau proteins associate with the cytoskeleton similarly to the non-modified tau, whereas tau fragments adopted different localizations with respect to the actin and microtubule cytoskeletons. These distinct localizations were confirmed by expressing each separate fragment in cells. Some cleavages-in particular cleavages at amino-acid positions 124 or 256-displayed a certain level of cellular toxicity, with an unusual relocalization of the N-terminal fragments to the nucleus. Based on the data presented here, inducible cleavage of tau by the TEV protease appears to be a valuable tool to reproduce tau fragmentation in cells and study the resulting consequences on cell physiology

The mitotic role of Adenomatous Polyposis Coli requires its bilateral interaction with tubulin and microtubules

International audienceAdenomatous polyposis coli (APC) is a scaffold protein with tumour suppressor properties. Mutations causing the loss of its C-terminal domain (APC-C), which bears cytoskeleton-regulating sequences, correlate with colorectal cancer. The cellular roles of APC in mitosis are widely studied, but the molecular mechanisms of its interaction with the cytoskeleton are poorly understood. Here, we investigated how APC-C regulates microtubule properties, and found that it promotes both microtubule growth and shrinkage. Strikingly, APC-C accumulates at shrinking microtubule extremities, a common characteristic of depolymerases. Cryo-electron microscopy revealed that APC-C adopts an extended conformation along the protofilament crest and showed the presence of ring-like tubulin oligomers around the microtubule wall, which required the presence of two APC-C sub-domains. A mutant of APC-C that was incapable of decorating microtubules with ring-like tubulin oligomers exhibited a reduced effect on microtubule dynamics. Finally, whereas native APC-C rescued defective chromosome alignment in metaphase cells silenced for APC, the ring-incompetent mutant failed to correct mitotic defects. Thus, the bilateral interaction of APC-C with tubulin and microtubules likely contributes to its mitotic functions

Tau antagonizes end-binding protein tracking at microtubule ends through a phosphorylation- dependent mechanism

International audienceProper regulation of microtubule dynamics is essential for cell functions and involves various microtubule-associated proteins (MAPs). Among them, end-binding proteins (EBs) accumulate at microtubule plus ends, whereas structural MAPs bind along the microtu-bule lattice. Recent data indicate that the structural MAP tau modulates EB subcellular local-ization in neurons. However, the molecular determinants of EB/tau interaction remain unknown , as is the effect of this interplay on microtubule dynamics. Here we investigate the mechanisms governing EB/tau interaction in cell-free systems and cellular models. We find that tau inhibits EB tracking at microtubule ends. Tau and EBs form a complex via the C-terminal region of EBs and the microtubule-binding sites of tau. These two domains are required for the inhibitory activity of tau on EB localization to microtubule ends. Moreover, the phos-phomimetic mutation S262E within tau microtubule-binding sites impairs EB/tau interaction and prevents the inhibitory effect of tau on EB comets. We further show that microtubule dynamic parameters vary, depending on the combined activities of EBs and tau proteins. Overall our results demonstrate that tau directly antagonizes EB function through a phos-phorylation-dependent mechanism. This study highlights a novel role for tau in EB regulation, which might be impaired in neurodegenerative disorders

Successful treatment of JAK1 associated inflammatory disease

International audienceBackground: Gain of function (GOF) variants of JAK1 drive a rare immune dysregulation syndrome associated with atopic dermatitis, allergy and eosinophilia.Objectives: To describe the clinical and immunological characteristics associated with a new GOF variant of JAK1 and report the therapeutic efficacy of JAK inhibition.Methods: We identified a family affected by JAK1 associated autoinflammatory disease and performed clinical assessment and immunological monitoring on 9 patients. JAK1 signalling was studied by flow and mass cytometry in patients' cells at basal state, or after immune stimulation. A molecular disease signature in the blood was studied at the transcriptomic level. Patients were treated with one of two JAK inhibitors; either baricitinib or upadacitinib. Clinical, cellular, and molecular response were evaluated over a 2-year period.Results: Affected individuals displayed a syndromic disease with prominent allergy including atopic dermatitis, ichthyosis, arthralgia, chronic diarrhoea, disseminated calcifying fibrous tumours and elevated whole blood histamine levels. A variant of JAK1 localized in the pseudokinase domain was identified in all 9 affected tested patients. Hyper-phosphorylation of STAT3 was found in 5 out of 6 patients tested. Treatment of patients' cells with baricitinib controlled most of the atypical hyper-phosphorylation of STAT3. Administration of baricitinib to patients led to rapid improvement of the disease in all adults and was associated with reduction of systemic inflammation.Conclusions: Patients with this new JAK1 GOF pathogenic variant displayed very high levels of blood histamine and showed a variable combination of atopy with articular and gastrointestinal manifestations as well as calcifying fibrous tumours. The disease, that appears to be linked to STAT3 hyper-activation, was well controlled under treatment by JAK inhibitors in adult patients

DOCK11 deficiency in patients with X-linked actinopathy and autoimmunity

International audienceDedicator of cytokinesis (DOCK) proteins play a central role in actin cytoskeleton regulation. This is highlighted by the DOCK2 and DOCK8 deficiencies leading to actinopathies and immune deficiencies. DOCK8 and DOCK11 activate CDC42, a RHO-GTPase involved in actin cytoskeleton dynamics, among many cellular functions. The role of DOCK11 in human immune disease has been long suspected but has never been described so far. We studied eight male patients, from seven unrelated families, with hemizygous DOCK11 missense variants leading to reduced DOCK11 expression. The patients were presenting with early-onset autoimmunity, including cytopenia, systemic lupus erythematosus, skin, and digestive manifestations. Patients’ platelets exhibited abnormal ultrastructural morphology and spreading as well as impaired CDC42 activity. In vitro activated T cells and B lymphoblastoid cell lines (B-LCL) of patients exhibited aberrant protrusions and abnormal migration speed in confined channels concomitant with altered actin polymerization during migration. A DOCK11 knock-down recapitulated these abnormal cellular phenotypes in monocytes-derived dendritic cells (MDDC) and primary activated T cells from healthy controls. Lastly, in line with the patients’ autoimmune manifestations, we also observed abnormal regulatory T cells (Tregs) phenotype with profoundly reduced FOXP3 and IKZF2 expression. Moreover, we found a reduced T cell proliferation and an impaired STAT5B phosphorylation upon IL2 stimulation of the patients’ lymphocytes. In conclusion, DOCK11 deficiency is a new X-linked immune-related actinopathy leading to impaired CDC42 activity and STAT5 activation, and associated with abnormal actin cytoskeleton remodeling as well as Tregs phenotype culminating in immune dysregulation and severe early-onset autoimmunity