A cellular complex of BACE1 and {gamma}-secretase sequentially generates A{beta} from its full-length precursor
We describe a hitherto unrecognized multiprotease complex containing active β- and -secretases. BACE1 coimmunoprecipitated and cofractionated with -secretase in cultured cells and in mouse and human brain. An endogenous high molecular weight (HMW) complex (~5 MD) containing β- and -secretases and holo-APP was catalytically active in vitro and generated a full array of Aβ peptides, with physiological Aβ42/40 ratios. The isolated complex responded properly to -secretase modulators. Alzheimer’s-causing mutations in presenilin altered the Aβ42/40 peptide ratio generated by the HMW β/-secreta...
Source: Journal of Cell Biology - February 4, 2019 Category: Cytology Authors: Liu, L., Ding, L., Rovere, M., Wolfe, M. S., Selkoe, D. J. Tags: Protein Homeostasis, Biochemistry, Neuroscience Articles Source Type: research
Detyrosinated microtubules spatially constrain lysosomes facilitating lysosome-autophagosome fusion
Microtubule post-translational modifications impart functional diversity to microtubules by affecting their dynamics, organization, and interaction with proteins. Using super-resolution microscopy, we show that only a small subpopulation of microtubules are detyrosinated in epithelial cells, while acetylated and tyrosinated microtubules comprise the majority of all microtubules. Surprisingly, lysosomes are enriched by approximately threefold on detyrosinated microtubules. Further, their motility on detyrosinated microtubules is impaired, showing shorter runs and more frequent and longer pauses. Lysosome enrichment is media...
Source: Journal of Cell Biology - February 4, 2019 Category: Cytology Authors: Mohan, N., Sorokina, E. M., Verdeny, I. V., Alvarez, A. S., Lakadamyali, M. Tags: Cytoskeleton, Trafficking, Biophysics Articles Source Type: research
Retromer has a selective function in cargo sorting via endosome transport carriers
Retromer is a peripheral membrane protein complex that coordinates multiple vesicular trafficking events within the endolysosomal system. Here, we demonstrate that retromer is required for the maintenance of normal lysosomal morphology and function. The knockout of retromer subunit Vps35 causes an ultrastructural alteration in lysosomal structure and aberrant lysosome function, leading to impaired autophagy. At the whole-cell level, knockout of retromer Vps35 subunit reduces lysosomal proteolytic capacity as a consequence of the improper processing of lysosomal hydrolases, which is dependent on the trafficking of the catio...
Source: Journal of Cell Biology - February 4, 2019 Category: Cytology Authors: Cui, Y., Carosi, J. M., Yang, Z., Ariotti, N., Kerr, M. C., Parton, R. G., Sargeant, T. J., Teasdale, R. D. Tags: Organelles, Trafficking Articles Source Type: research
ROMO1 is a constituent of the human presequence translocase required for YME1L protease import
The mitochondrial presequence translocation machinery (TIM23 complex) is conserved between the yeast Saccharomyces cerevisiae and humans; however, functional characterization has been mainly performed in yeast. Here, we define the constituents of the human TIM23 complex using mass spectrometry and identified ROMO1 as a new translocase constituent with an exceptionally short half-life. Analyses of a ROMO1 knockout cell line revealed aberrant inner membrane structure and altered processing of the GTPase OPA1. We show that in the absence of ROMO1, mitochondria lose the inner membrane YME1L protease, which participates in OPA1...
Source: Journal of Cell Biology - February 4, 2019 Category: Cytology Authors: Richter, F., Dennerlein, S., Nikolov, M., Jans, D. C., Naumenko, N., Aich, A., MacVicar, T., Linden, A., Jakobs, S., Urlaub, H., Langer, T., Rehling, P. Tags: Organelles, Protein Homeostasis, Biochemistry Articles Source Type: research
The lysine catabolite saccharopine impairs development by disrupting mitochondrial homeostasis
Amino acid catabolism is frequently executed in mitochondria; however, it is largely unknown how aberrant amino acid metabolism affects mitochondria. Here we report the requirement for mitochondrial saccharopine degradation in mitochondrial homeostasis and animal development. In Caenorhbditis elegans, mutations in the saccharopine dehydrogenase (SDH) domain of the bi-functional enzyme α-aminoadipic semialdehyde synthase AASS-1 greatly elevate the lysine catabolic intermediate saccharopine, which causes mitochondrial damage by disrupting mitochondrial dynamics, leading to reduced adult animal growth. In mice, failure ...
Source: Journal of Cell Biology - February 4, 2019 Category: Cytology Authors: Zhou, J., Wang, X., Wang, M., Chang, Y., Zhang, F., Ban, Z., Tang, R., Gan, Q., Wu, S., Guo, Y., Zhang, Q., Wang, F., Zhao, L., Jing, Y., Qian, W., Wang, G., Guo, W., Yang, C. Tags: Disease, Organelles, Development Articles Source Type: research
Developmental regulation of an organelle tether coordinates mitochondrial remodeling in meiosis
Cellular differentiation involves remodeling cellular architecture to transform one cell type to another. By investigating mitochondrial dynamics during meiotic differentiation in budding yeast, we sought to understand how organelle morphogenesis is developmentally controlled in a system where regulators of differentiation and organelle architecture are known, but the interface between them remains unexplored. We analyzed the regulation of mitochondrial detachment from the cell cortex, a known meiotic alteration to mitochondrial morphology. We found that mitochondrial detachment is enabled by the programmed destruction of ...
Source: Journal of Cell Biology - February 4, 2019 Category: Cytology Authors: Sawyer, E. M., Joshi, P. R., Jorgensen, V., Yunus, J., Berchowitz, L. E., Ünal, E. Tags: Organelles, Cell Cycle and Division, Genetics Articles Source Type: research
ENSA and ARPP19 differentially control cell cycle progression and development
Greatwall (GWL) is an essential kinase that indirectly controls PP2A-B55, the phosphatase counterbalancing cyclin B/CDK1 activity during mitosis. In Xenopus laevis egg extracts, GWL-mediated phosphorylation of overexpressed ARPP19 and ENSA turns them into potent PP2A-B55 inhibitors. It has been shown that the GWL/ENSA/PP2A-B55 axis contributes to the control of DNA replication, but little is known about the role of ARPP19 in cell division. By using conditional knockout mouse models, we investigated the specific roles of ARPP19 and ENSA in cell division. We found that Arpp19, but not Ensa, is essential for mouse embryogenes...
Source: Journal of Cell Biology - February 4, 2019 Category: Cytology Authors: Hached, K., Goguet, P., Charrasse, S., Vigneron, S., Sacristan, M. P., Lorca, T., Castro, A. Tags: Cell Cycle and Division, Development Articles Source Type: research
The Drosophila Ninein homologue Bsg25D cooperates with Ensconsin in myonuclear positioning
Skeletal muscle consists of multinucleated cells in which the myonuclei are evenly spaced throughout the cell. In Drosophila, this pattern is established in embryonic myotubes, where myonuclei move via microtubules (MTs) and the MT-associated protein Ensconsin (Ens)/MAP7, to achieve their distribution. Ens regulates multiple aspects of MT biology, but little is known about how Ens itself is regulated. We find that Ens physically interacts and colocalizes with Bsg25D, the Drosophila homologue of the centrosomal protein Ninein. Bsg25D loss enhances myonuclear positioning defects in embryos sensitized by partial Ens loss. Bsg...
Source: Journal of Cell Biology - February 4, 2019 Category: Cytology Authors: Rosen, J. N., Azevedo, M., Soffar, D. B., Boyko, V. P., Brendel, M. B., Schulman, V. K., Baylies, M. K. Tags: Organelles, Development, Genetics Articles Source Type: research
Autophagic degradation of lamins facilitates the nuclear egress of herpes simplex virus type 1
Dendritic cells (DCs) are crucial for the induction of potent antiviral immune responses. In contrast to immature DCs (iDCs), mature DCs (mDCs) are not permissive for infection with herpes simplex virus type 1 (HSV-1). Here, we demonstrate that HSV-1 infection of iDCs and mDCs induces autophagy, which promotes the degradation of lamin A/C, B1, and B2 in iDCs only. This in turn facilitates the nuclear egress of progeny viral capsids and thus the formation of new infectious particles. In contrast, lamin protein levels remain stable in HSV-1–infected mDCs due to an inefficient autophagic flux. Elevated protein levels of...
Source: Journal of Cell Biology - February 4, 2019 Category: Cytology Authors: Turan, A., Grosche, L., Krawczyk, A., Mühl-Zürbes, P., Drassner, C., Düthorn, A., Kummer, M., Hasenberg, M., Voortmann, S., Jastrow, H., Dörrie, J., Schaft, N., Kraner, M., Döhner, K., Sodeik, B., Steinkasserer, A., Tags: Cell Death and Autophagy, Immunology Articles Source Type: research
Dual regulation of lin28a by Myc is necessary during zebrafish retina regeneration
Cellular reprogramming leading to induction of Muller glia–derived progenitor cells (MGPCs) with stem cell characteristics is essential for zebrafish retina regeneration. Although several regeneration-specific genes are characterized, the significance of MGPC-associated Mycb induction remains unknown. Here, we show that early expression of Mycb induces expression of genes like ascl1a, a known activator of lin28a in MGPCs. Notably, mycb is simultaneously activated by Ascl1a and repressed by Insm1a in regenerating retina. Here, we unravel a dual role of Mycb in lin28a expression, both as an activator through Ascl1a in ...
Source: Journal of Cell Biology - February 4, 2019 Category: Cytology Authors: Mitra, S., Sharma, P., Kaur, S., Khursheed, M. A., Gupta, S., Chaudhary, M., Kurup, A. J., Ramachandran, R. Tags: Stem Cells, Chromatin or Epigenetics, Development Articles Source Type: research
Drosophila kinesin-8 stabilizes the kinetochore-microtubule interaction
Kinesin-8 is required for proper chromosome alignment in a variety of animal and yeast cell types. However, it is unclear how this motor protein family controls chromosome alignment, as multiple biochemical activities, including inconsistent ones between studies, have been identified. Here, we find that Drosophila kinesin-8 (Klp67A) possesses both microtubule (MT) plus end–stabilizing and –destabilizing activity, in addition to kinesin-8's commonly observed MT plus end–directed motility and tubulin-binding activity in vitro. We further show that Klp67A is required for stable kinetochore–MT attachmen...
Source: Journal of Cell Biology - February 4, 2019 Category: Cytology Authors: Edzuka, T., Goshima, G. Tags: Cytoskeleton, Cell Cycle and Division Articles Source Type: research
Electron cryotomography analysis of Dam1C/DASH at the kinetochore-spindle interface in situ
In dividing cells, depolymerizing spindle microtubules move chromosomes by pulling at their kinetochores. While kinetochore subcomplexes have been studied extensively in vitro, little is known about their in vivo structure and interactions with microtubules or their response to spindle damage. Here we combine electron cryotomography of serial cryosections with genetic and pharmacological perturbation to study the yeast chromosome segregation machinery in vivo. Each kinetochore microtubule has one (rarely, two) Dam1C/DASH outer kinetochore assemblies. Dam1C/DASH contacts the microtubule walls and does so with its flexible "...
Source: Journal of Cell Biology - February 4, 2019 Category: Cytology Authors: Ng, C. T., Deng, L., Chen, C., Lim, H. H., Shi, J., Surana, U., Gan, L. Tags: Cell Cycle and Division, Structural Biology Articles Source Type: research
Time-resolved ultrastructure of the cortical actin cytoskeleton in dynamic membrane blebs
Membrane blebbing accompanies various cellular processes, including cytokinesis, apoptosis, and cell migration, especially invasive migration of cancer cells. Blebs are extruded by intracellular pressure and are initially cytoskeleton-free, but they subsequently assemble the cytoskeleton, which can drive bleb retraction. Despite increasing appreciation of physiological significance of blebbing, the molecular and, especially, structural mechanisms controlling bleb dynamics are incompletely understood. We induced membrane blebbing in human HT1080 fibrosarcoma cells by inhibiting the Arp2/3 complex. Using correlative platinum...
Source: Journal of Cell Biology - February 4, 2019 Category: Cytology Authors: Chikina, A. S., Svitkina, T. M., Alexandrova, A. Y. Tags: Cytoskeleton, Migration, Motility, Cancer Reports Source Type: research
Visualization of long-lived proteins reveals age mosaicism within nuclei of postmitotic cells
Many adult tissues contain postmitotic cells as old as the host organism. The only organelle that does not turn over in these cells is the nucleus, and its maintenance represents a formidable challenge, as it harbors regulatory proteins that persist throughout adulthood. Here we developed strategies to visualize two classes of such long-lived proteins, histones and nucleoporins, to understand the function of protein longevity in nuclear maintenance. Genome-wide mapping of histones revealed specific enrichment of long-lived variants at silent gene loci. Interestingly, nuclear pores are maintained by piecemeal replacement of...
Source: Journal of Cell Biology - February 4, 2019 Category: Cytology Authors: Toyama, B. H., Arrojo e Drigo, R., Lev-Ram, V., Ramachandra, R., Deerinck, T. J., Lechene, C., Ellisman, M. H., Hetzer, M. W. Tags: Protein Homeostasis, Development Reports Source Type: research
Mitotic regulators TPX2 and Aurora A protect DNA forks during replication stress by counteracting 53BP1 function
In this study, we identify the TPX2/Aurora A heterodimer, nominally considered a mitotic kinase complex, as a novel binding partner of 53BP1. We find that TPX2/Aurora A plays a previously unrecognized role in DNA damage repair and replication fork stability by counteracting 53BP1 function. Loss of TPX2 or Aurora A compromises DNA end resection, BRCA1 and Rad51 recruitment, and homologous recombination. Furthermore, loss of TPX2 or Aurora A causes deprotection of stalled replication forks upon replication stress induction. This fork protection pathway counteracts MRE11 nuclease activity but functions in parallel to BRCA1. S...
Source: Journal of Cell Biology - February 4, 2019 Category: Cytology Authors: Byrum, A. K., Carvajal-Maldonado, D., Mudge, M. C., Valle-Garcia, D., Majid, M. C., Patel, R., Sowa, M. E., Gygi, S. P., Harper, J. W., Shi, Y., Vindigni, A., Mosammaparast, N. Tags: DNA Biology Reports Source Type: research
