The Hippo pathway plays critical roles in tissue development, regeneration, and immune homeostasis. The widespread pandemic of Coronavirus disease 2019 (COVID-19) caused by SARS-CoV-2 has resulted in a global healthcare crisis and strained health resources. How SARS-CoV-2 affects Hippo signaling in host cells has remained poorly understood. Here, we report that SARS-CoV-2 infection in patient lung cells and cardiomyocytes derived from human induced pluripotent stem cells (iPS-CMs) suppressed YAP target gene expression, as evidenced by RNA sequencing data. Furthermore, in a screening of nonstructural proteins from SARS-CoV-2, nonstructural protein 13 (NSP13) significantly inhibited YAP transcriptional activity independent of the YAP upstream suppressor kinase Lats1/2. Consistent with this, NSP13 suppressed active YAP (YAP5SA) in vivo, whereby NSP13 expression reverted the phenotype of YAP5SA transgenic mice. From a mechanistic standpoint, NSP13 helicase activity was shown to be required for its suppression of YAP. Furthermore, through the interaction of NSP13 with TEAD4, which is the most common YAP-interacting transcription factor in the nucleus, NSP13 recruited endogenous YAP suppressors such as CCT3 and TTF2 to inactivate the YAP/TEAD4 complex. These findings reveal the function and mechanism of the SARS-CoV-2 helicase NSP13 in host cells and partially explain the toxic effect of SARS-CoV-2 in particular host tissue with high YAP activity. less

Cells employ diverse strategies to repair double-strand breaks (DSBs), a dangerous form of DNA damage that threatens genome integrity. Eukaryotic nuclei consist of different chromatin environments, each displaying distinct molecular and biophysical properties that can significantly influence the DSB repair process. Specifically, DSBs arising in the compact and silenced heterochromatin domains have been found to move to the heterochromatin periphery in mouse and Drosophila to prevent aberrant recombination events. However, it is poorly understood how chromatin components, such as histone post-translational modifications, contribute to these DSB movements within heterochromatin. Using cultured cells and an in vivo single-DSB system in Drosophila, we identify that histone H3 lysine 9 acetylation (H3K9ac) is enriched at DSBs in heterochromatin but not euchromatin. We find that this enrichment is mediated by the histone acetyltransferase Gcn5, which rapidly localizes to heterochromatic DSBs. Moreover, we demonstrate that in the absence of Gcn5, heterochromatic DSBs display impaired recruitment of the SUMO E3 ligase Nse2/Qjt and fail to relocate to the heterochromatin periphery to complete repair. In summary, our results reveal a previously unidentified role for Gcn5 and H3K9ac in heterochromatin DSB repair and underscore the importance of differential chromatin responses at hetero- and eu-chromatic DSBs to promote safe repair. less

In Gaucher and Niemann-Pick C diseases, the glucosylceramide (GlcCer) depletion hypothesis states that depletion of non-lysosomal sphingolipid pools can lead to dysfunction in the secretory and lysosomal system. The hypothesis suggests: 1) lysosomal dysfunction can be separated from lysosomal storage, 2) Lysosomal/secretory dysfunction/vATPase activity is corrected by increasing non-lysosomal GlcCer pools, and 3) Changes in higher glycosphingolipid synthesis due to changes in Golgi pH and/or GlcCer non-vesicular transport. Evidence for this mechanism includes 1) Successful treatment of cells and animals by imino sugar inhibition of the non-lysosomal neutral pH GlcCer hydrolase GBA2, 2) Increasing ER/cytosol GlcCer increases in vATPase regulatory V0a1 subunit expression. Heterozygous mutations in GBA1, a lysosomal glucocerebrosidase (GCase), cause GCase misfolding and mislocalisation in the ER/cytoplasm which is linked to Parkinsons disease (GBA-PD). Unexpectedly, similar to previous results in storing fibroblasts, N370S and L444P fibroblasts revealed increased endolysosomal pH and size despite the absence of glucolipid storage. Induction of storage by reducing residual lysosomal GCase activity in the N370S/L444P fibroblasts by the addition conduritol B-epoxide had no further effect on lysosomal function. In contrast, the addition of a soluble GlcCer analogue (adaGlcCer) reverses increased endolysosomal pH and volume in N370S mutant fibroblasts. The results are consistent with ER/cytosolic glucolipid depletion in GBA-PD fibroblasts. We discuss the potential for toxic/ectopic GBA1 hydrolysis and disrupted vATPase activity may lead to defective dopamine packaging and synaptic vesicle endocytosis as a new hypothesis in GBA-PD. less

The loss of elasticity is a hallmark of systemic aging or genetic syndromes (e.g. cutis laxa, Williams-Beuren and supravalvular aortic stenosis) with direct consequences on tissue functions, and particularly deleterious when associated to the cardiovascular system. Tissue elasticity is mainly provided by large elastic fibers composed of supramolecular complexes of elastin and microfibrils. In arteries, the mature elastic fibers are located in the media compartment and form concentric elastic lamellar units together with the smooth muscle cells (SMCs). The main function of vascular elastic fibers is to allow extension and recoil of the vessel walls in response to the intraluminal pressure generated by the blood flow following cardiac systole. The synthesis of elastic fibers (elastogenesis) mainly occurs during the last third of fetal life with a peak in the perinatal period and then slowly decreases until the end of growth; as a result, elastic fiber repair is almost non-existent in adults. To date, no treatment exists to restore or repair deficient or degraded elastic fibers. A few pharmacological compounds have been proposed, but their efficacy/side effects balance remains very unfavorable. As an alternative strategy, we developed a synthetic elastic protein (SEP) inspired by the human tropoelastin, the elastin soluble precursor, to provide an elastic molecular prosthesis capable of integrating and reinforcing endogenous elastic fibers. The SEP was easily produced in E. coli and purified by inversed transition cycling method. The resulting 55 kDa protein recapitulates the main physicochemical properties of the tropoelastin as thermal responsiveness, intrinsically disordered structures, and spherical self-assembly. The cross-linked SEP displays linear elastic mechanical properties under uniaxial tension loads. Using a co-culture in vitro model of the endothelial barrier, our results show that SEP is able to cross the cohesive endothelial monolayer to reach underlying SMCs. Moreover, SEP is processed by SMCs through a lysyl oxidase-dependent mechanism to form fibrillar structures that colocalize with fibrillin-rich microfibrils. The SEP was further characterized in vivo through the zebrafish model. The results indicate a global innocuity on zebrafish embryos and an absence of neutrophil recruitment following injection into the yolk sac of zebrafish. Finally, intravenous injection of a fluorescent SEP highlights its deposition in the wall of tortuous vessels which persists for several days after injection of the larvae. Taken together, our results demonstrate for the first time the incorporation of a naked tropoelastin-bioinspired polypeptide in endogenous elastic fibrillar deposits from SMCs, and its recognition by the lysyl-oxidase enzymatic machinery. In absence of toxicity and proinflammatory signal combined to a long-lasting accumulation in vessels in vivo, the SEP fulfills the first prerequisites for the development of an original biotherapeutic compound addressing the repair of elastic fibers. less

The long noncoding RNA TERRA is transcribed from telomeres in virtually all eukaryotes with linear chromosomes. In humans, TERRA transcription is driven in part by promoters comprising CpG dinucleotide-rich repeats of 29 base pairs (29 bp repeats), believed to be present in half of the subtelomeres. Thus far, TERRA expression has been analyzed mainly using molecular biology-based approaches that only generate partial and somehow biased results. Here, we present a novel experimental pipeline to study human TERRA based on long read sequencing (TERRA ONTseq). By applying TERRA ONTseq to different cell lines, we show that the vast majority of human telomeres produce TERRA and that the cellular levels of TERRA transcripts varies according to their chromosomes of origin. Using TERRA ONTseq, we also identified regions containing TERRA transcription start sites (TSSs) in more than half of human subtelomeres. TERRA TSS regions are generally found immediately downstream of 29 bp repeat-related sequences, which appear to be more widespread than previously estimated. Finally, we isolated a novel TERRA promoter from the highly expressed subtelomere of the long arm of chromosome 7. With the development of TERRA ONTseq, we provide a refined picture of human TERRA biogenesis and expression and we equip the scientific community with an invaluable tool for future studies. less

Growth-dependent accumulation of the SBF transcription factor, composed of Swi4 and Swi6, occurs as cells approach the G1/S transition (Start) in budding yeast. Here we measure size-dependence of Swi4 protein copy number under different genetic contexts using the scanning number and brightness particle counting technique. Mutation of SBF binding sites in the SWI4 promoter or disruption of SBF activation resulted in ~33-50% decrease in the rate of Swi4 accumulation with cell size. Ectopic inducible expression of Swi4 in G1 phase cells increased production of Swi4 from the endogenous promoter and concomitantly upregulated transcription of the G1/S regulon. Despite the potential for Swi4 positive feedback, Swi4 accumulated linearly through G1 phase unless the Whi5 transcriptional repressor was inactivated. A threshold level of 190 Swi4 molecules titrating SBF binding sites in G1/S promoters predicted the effects of nutrients, ploidy, and G1/S regulatory mutations on cell size. These results reveal how transcription factor auto-production can contribute to a cell state transition. less

Cell cycle progression is regulated by the orderly balance between kinase and phosphatase activities. PP2A phosphatase holoenzymes containing the B55 family of regulatory B subunits (PP2A-B55) function as major CDK1-counteracting phosphatases during mitotic exit in mammals. However, the identification of the specific mitotic roles of these PP2A-B55 complexes has been hindered by the existence of multiple B55 isoforms. Here, through the generation of loss-of-function genetic mouse models for the two ubiquitous B55 isoforms (B55alpha and B55delta), we report that PP2A-B55 alpha/delta complexes display overlapping roles in controlling the dynamics of proper chromosome individualization and clustering during mitosis. In the absence of PP2A-B55alpha/delta activity, mitotic cells display increased chromosome individualization in the presence of enhanced phosphorylation and perichromosomal loading of Ki-67. These data provide experimental evidence for a new regulatory mechanism by which the balance between kinase and PP2A-B55 phosphatase activity controls the Ki-67-mediated spatial organization of the mass of chromosomes during mitosis. less

Mutations in the TANGO2 gene cause severe illness in humans, including life-threatening metabolic crises; however, the function of TANGO2 protein remains unknown. In a recent publication in Nature, Sun et al. proposed that TANGO2 helps transport haem within and between cells, from areas with high haem concentrations to those with lower concentrations. Caenorhabditis elegans has two versions of TANGO2 that Sun et al. called HRG-9 and HRG-10. They demonstrated that worms deficient in these proteins show increased survival upon exposure to a toxic haem analog, which Sun et al. interpreted as evidence of decreased haem uptake from intestinal cells into the rest of the organism. We repeated several experiments using the same C. elegans strain as Sun et al. and believe that their findings are better explained by reduced feeding behavior in these worms. We demonstrate that hrg-9 in particular is highly responsive to oxidative stress, independent of haem status. Our group also performed several experiments in yeast and zebrafish models of TANGO2 deficiency and was unable to replicate key findings from these models reported in the original study by Sun et al. Overall, we believe there is insufficient evidence to support haem transport as the primary function for TANGO2. less

Telomeres are the protective nucleoprotein structures at the end of linear eukaryotic chromosomes. Telomeres\' repetitive nature and length have traditionally challenged the precise assessment of the composition and length of individual human telomeres. Here, we present Telo-seq to resolve bulk, chromosome arm-specific and allele-specific human telomere lengths using Oxford Nanopore Technologies\' native long-read sequencing. Telo-seq resolves telomere shortening in five population doubling increments and reveals intrasample, chromosome arm-specific, allele-specific telomere length heterogeneity. Telo-seq can reliably discriminate between telomerase- and ALT-positive cancer cell lines. Thus, Telo-seq is a novel tool to study telomere biology during development, aging, and cancer at unprecedented resolution. less

Multispanning membrane proteins are inserted into the endoplasmic reticulum membrane by the ribosome-bound multipass translocon machinery. Based on cryo-electron tomography and extensive subtomogram analysis, we reveal the composition and arrangement of multipass translocon components in their native membrane environment. The intramembrane chaperone complex PAT and the translocon associated protein (TRAP) complex associate substoichiometrically with the multipass translocon in a translation-dependent manner. While PAT is preferentially recruited to active complexes, TRAP primarily associates with inactive translocons. The subtomogram average of the TRAP-multipass translocon reveals intermolecular contacts between the luminal domains of TRAP and an unknown subunit of the BOS complex. AlphaFold modeling suggests this protein is NOMO, bridging the luminal domains of nicalin and TRAP. Collectively, our results visualize the interplay of accessory factors associated with multipass membrane protein biogenesis under near-native conditions. less