Maho Hamasaki

University of Michigan, Ann Arbor, MI, United States

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Publications (16)137.49 Total impact

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    ABSTRACT: Diverse causes, including pathogenic invasion or the uptake of mineral crystals such as silica and monosodium urate (MSU), threaten cells with lysosomal rupture, which can lead to oxidative stress, inflammation, and apoptosis or necrosis. Here, we demonstrate that lysosomes are selectively sequestered by autophagy, when damaged by MSU, silica, or the lysosomotropic reagent L-Leucyl-L-leucine methyl ester (LLOMe). Autophagic machinery is recruited only on damaged lysosomes, which are then engulfed by autophagosomes. In an autophagy-dependent manner, low pH and degradation capacity of damaged lysosomes are recovered. Under conditions of lysosomal damage, loss of autophagy causes inhibition of lysosomal biogenesis in vitro and deterioration of acute kidney injury in vivo. Thus, we propose that sequestration of damaged lysosomes by autophagy is indispensable for cellular and tissue homeostasis.
    The EMBO Journal 08/2013; · 9.82 Impact Factor
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    ABSTRACT: When cells are starved, are invaded by foreign bodies such as bacteria, and contain damaged organelles or aggregated proteins, double-membrane organelles called autophagosomes are formed within the cytoplasm to surround, isolate and deliver these materials to lysosomes for degradation. This pathway, called 'autophagy', is conserved from yeast to mammalian cells. Unlike other organelles, the autophagosome forms de novo, thus raising unique questions regarding its membrane biogenesis. Here we highlight a number of recent findings related to autophagosome formation and possible involvement of autophagy-specific vesicles originating from other organelles, but with particular attention on the formation sites and the relationship of the autophagosome to other organelles.
    Current opinion in cell biology 04/2013; · 14.15 Impact Factor
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    ABSTRACT: Autophagy is a tightly regulated intracellular bulk degradation/recycling system that has fundamental roles in cellular homeostasis. Autophagy is initiated by isolation membranes, which form and elongate as they engulf portions of the cytoplasm and organelles. Eventually isolation membranes close to form double membrane-bound autophagosomes and fuse with lysosomes to degrade their contents. The physiological role of autophagy has been determined since its discovery, but the origin of autophagosomal membranes has remained unclear. At present, there is much controversy about the organelle from which the membranes originate-the endoplasmic reticulum (ER), mitochondria and plasma membrane. Here we show that autophagosomes form at the ER-mitochondria contact site in mammalian cells. Imaging data reveal that the pre-autophagosome/autophagosome marker ATG14 (also known as ATG14L) relocalizes to the ER-mitochondria contact site after starvation, and the autophagosome-formation marker ATG5 also localizes at the site until formation is complete. Subcellular fractionation showed that ATG14 co-fractionates in the mitochondria-associated ER membrane fraction under starvation conditions. Disruption of the ER-mitochondria contact site prevents the formation of ATG14 puncta. The ER-resident SNARE protein syntaxin 17 (STX17) binds ATG14 and recruits it to the ER-mitochondria contact site. These results provide new insight into organelle biogenesis by demonstrating that the ER-mitochondria contact site is important in autophagosome formation.
    Nature 03/2013; · 38.60 Impact Factor
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    ABSTRACT: ABSTRACT Lipomannan (LM) and lipoarabinomannan (LAM) are mycobacterial glycolipids containing a long mannose polymer. While they are implicated in immune modulations, the significance of LM and LAM as structural components of the mycobacterial cell wall remains unknown. We have previously reported that a branch-forming mannosyltransferase plays a critical role in controlling the sizes of LM and LAM and that deletion or overexpression of this enzyme results in gross changes in LM/LAM structures. Here, we show that such changes in LM/LAM structures have a significant impact on the cell wall integrity of mycobacteria. In Mycobacterium smegmatis, structural defects in LM and LAM resulted in loss of acid-fast staining, increased sensitivity to β-lactam antibiotics, and faster killing by THP-1 macrophages. Furthermore, equivalent Mycobacterium tuberculosis mutants became more sensitive to β-lactams, and one mutant showed attenuated virulence in mice. Our results revealed previously unknown structural roles for LM and LAM and further demonstrated that they are important for the pathogenesis of tuberculosis. IMPORTANCE Tuberculosis (TB) is a global burden, affecting millions of people worldwide. Mycobacterium tuberculosis is a causative agent of TB, and understanding the biology of M. tuberculosis is essential for tackling this devastating disease. The cell wall of M. tuberculosis is highly impermeable and plays a protective role in establishing infection. Among the cell wall components, LM and LAM are major glycolipids found in all Mycobacterium species, show various immunomodulatory activities, and have been thought to play roles in TB pathogenesis. However, the roles of LM and LAM as integral parts of the cell wall structure have not been elucidated. Here we show that LM and LAM play critical roles in the integrity of mycobacterial cell wall and the pathogenesis of TB. These findings will now allow us to seek the possibility that the LM/LAM biosynthetic pathway is a chemotherapeutic target.
    mBio 01/2013; 4(1). · 5.62 Impact Factor
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    ABSTRACT: In 2008 we published the first set of guidelines for standardizing research in autophagy. Since then, research on this topic has continued to accelerate, and many new scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Accordingly, it is important to update these guidelines for monitoring autophagy in different organisms. Various reviews have described the range of assays that have been used for this purpose. Nevertheless, there continues to be confusion regarding acceptable methods to measure autophagy, especially in multicellular eukaryotes. A key point that needs to be emphasized is that there is a difference between measurements that monitor the numbers or volume of autophagic elements (e.g., autophagosomes or autolysosomes) at any stage of the autophagic process versus those that measure flux through the autophagy pathway (i.e., the complete process);5,6 thus, a block in macroautophagy that results in autophagosome accumulation needs to be differentiated from stimuli that result in increased autophagic activity, defined as increased autophagy induction coupled with increased delivery to, and degradation within, lysosomes (in most higher eukaryotes and some protists such as Dictyostelium) or the vacuole (in plants and fungi). In other words, it is especially important that investigators new to the field understand that the appearance of more autophagosomes does not necessarily equate with more autophagy. In fact, in many cases, autophagosomes accumulate because of a block in trafficking to lysosomes without a concomitant change in autophagosome biogenesis, whereas an increase in autolysosomes may reflect a reduction in degradative activity. Here, we present a set of guidelines for the selection and interpretation of methods for use by investigators who aim to examine macroautophagy and related processes, as well as for reviewers who need to provide realistic and reasonable critiques of papers that are focused on these processes. These guidelines are not meant to be a formulaic set of rules, because the appropriate assays depend in part on the question being asked and the system being used. In addition, we emphasize that no individual assay is guaranteed to be the most appropriate one in every situation, and we strongly recommend the use of multiple assays to monitor autophagy. In these guidelines, we consider these various methods of assessing autophagy and what information can, or cannot, be obtained from them. Finally, by discussing the merits and limits of particular autophagy assays, we hope to encourage technical innovation in the field.
    Autophagy 04/2012; 8(4). · 12.04 Impact Factor
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    ABSTRACT: In 2008 we published the first set of guidelines for standardizing research in autophagy. Since then, research on this topic has continued to accelerate, and many new scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Accordingly, it is important to update these guidelines for monitoring autophagy in different organisms. Various reviews have described the range of assays that have been used for this purpose. Nevertheless, there continues to be confusion regarding acceptable methods to measure autophagy, especially in multicellular eukaryotes. A key point that needs to be emphasized is that there is a difference between measurements that monitor the numbers or volume of autophagic elements (e.g., autophagosomes or autolysosomes) at any stage of the autophagic process vs. those that measure flux through the autophagy pathway (i.e., the complete process); thus, a block in macroautophagy that results in autophagosome accumulation needs to be differentiated from stimuli that result in increased autophagic activity, defined as increased autophagy induction coupled with increased delivery to, and degradation within, lysosomes (in most higher eukaryotes and some protists such as Dictyostelium) or the vacuole (in plants and fungi). In other words, it is especially important that investigators new to the field understand that the appearance of more autophagosomes does not necessarily equate with more autophagy. In fact, in many cases, autophagosomes accumulate because of a block in trafficking to lysosomes without a concomitant change in autophagosome biogenesis, whereas an increase in autolysosomes may reflect a reduction in degradative activity. Here, we present a set of guidelines for the selection and interpretation of methods for use by investigators who aim to examine macroautophagy and related processes, as well as for reviewers who need to provide realistic and reasonable critiques of papers that are focused on these processes. These guidelines are not meant to be a formulaic set of rules, because the appropriate assays depend in part on the question being asked and the system being used. In addition, we emphasize that no individual assay is guaranteed to be the most appropriate one in every situation, and we strongly recommend the use of multiple assays to monitor autophagy. In these guidelines, we consider these various methods of assessing autophagy and what information can, or cannot, be obtained from them. Finally, by discussing the merits and limits of particular autophagy assays, we hope to encourage technical innovation in the field.
    Autophagy 04/2012; 8(4):445-544. · 12.04 Impact Factor
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    [Show abstract] [Hide abstract]
    ABSTRACT: In 2008 we published the first set of guidelines for standardizing research in autophagy. Since then, research on this topic has continued to accelerate, and many new scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Accordingly, it is important to update these guidelines for monitoring autophagy in different organisms. Various reviews have described the range of assays that have been used for this purpose. Nevertheless, there continues to be confusion regarding acceptable methods to measure autophagy, especially in multicellular eukaryotes. A key point that needs to be emphasized is that there is a difference between measurements that monitor the numbers or volume of autophagic elements (e.g., autophagosomes or autolysosomes) at any stage of the autophagic process vs. those that measure flux through the autophagy pathway (i.e., the complete process); thus, a block in macroautophagy that results in autophagosome accumulation needs to be differentiated from stimuli that result in increased autophagic activity, defined as increased autophagy induction coupled with increased delivery to, and degradation within, lysosomes (in most higher eukaryotes and some protists such as Dictyostelium) or the vacuole (in plants and fungi). In other words, it is especially important that investigators new to the field understand that the appearance of more autophagosomes does not necessarily equate with more autophagy. In fact, in many cases, autophagosomes accumulate because of a block in trafficking to lysosomes without a concomitant change in autophagosome biogenesis, whereas an increase in autolysosomes may reflect a reduction in degradative activity. Here, we present a set of guidelines for the selection and interpretation of methods for use by investigators who aim to examine macroautophagy and related processes, as well as for reviewers who need to provide realistic and reasonable critiques of papers that are focused on these processes. These guidelines are not meant to be a formulaic set of rules, because the appropriate assays depend in part on the question being asked and the system being used. In addition, we emphasize that no individual assay is guaranteed to be the most appropriate one in every situation, and we strongly recommend the use of multiple assays to monitor autophagy. In these guidelines, we consider these various methods of assessing autophagy and what information can, or cannot, be obtained from them. Finally, by discussing the merits and limits of particular autophagy assays, we hope to encourage technical innovation in the field.
    Autophagy 04/2012; 8(4):445. · 12.04 Impact Factor
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    Autophagy 04/2012; 8(4):1-100. · 12.04 Impact Factor
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    ABSTRACT: The vaccinia virus (VACV) precursor membrane, the crescent, consists of an open membrane sheet and is formed by rupture of a cellular compartment. Here, we asked whether A17, a viral membrane protein, plays a role in membrane rupture. Without A17 synthesis, crescents are not formed, and instead, tubular and vesicular membranes accumulate (Rodriguez et al. in J Virol 69:4640-4648, 1). We used electron tomography (ET) to analyze whether the viral membranes lacking A17 consist of open membrane sheets. Tubular, vesicular and so far not described onion-shaped membranes, which consisted of open membrane sheets, were seen. Thus, the data show that membrane rupture occurs independently of the A17 protein.
    Archives of Virology 05/2011; 156(9):1647-53. · 2.03 Impact Factor
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    ABSTRACT: Autophagy is a catabolic process that delivers cytoplasmic material to the lysosome for degradation. The mechanisms regulating autophagosome formation and size remain unclear. Here, we show that autophagosome formation was triggered by the overexpression of a dominant-negative inactive mutant of Myotubularin-related phosphatase 3 (MTMR3). Mutant MTMR3 partially localized to autophagosomes, and PtdIns3P and two autophagy-related PtdIns3P-binding proteins, GFP-DFCP1 and GFP-WIPI-1alpha (WIPI49/Atg18), accumulated at sites of autophagosome formation. Knock-down of MTMR3 increased autophagosome formation, and overexpression of wild-type MTMR3 led to significantly smaller nascent autophagosomes and a net reduction in autophagic activity. These results indicate that autophagy initiation depends on the balance between PI 3-kinase and PI 3-phosphatase activity. Local levels of PtdIns3P at the site of autophagosome formation determine autophagy initiation and the size of the autophagosome membrane structure.
    Traffic 04/2010; 11(4):468-78. · 4.65 Impact Factor
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    Maho Hamasaki, Tamotsu Yoshimori
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    ABSTRACT: Autophagosomes (APs) are unique organelles that enwrap cytoplasmic components when necessary. APs then fuse with lysosomes and enclosed materials are degraded. Although approximately 30 autophagy-related genes (ATG) required for AP formation have been identified, fundamental questions on the membrane source or dynamics during the formation remain unresolved. Here, we present a comprehensive overview of the putative membrane sources identified to date.
    FEBS letters 02/2010; 584(7):1296-301. · 3.54 Impact Factor
  • Maho Hamasaki, Yoshinori Ohsumi
    Tanpakushitsu kakusan koso. Protein, nucleic acid, enzyme 09/2006; 51(10 Suppl):1469-73.
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    ABSTRACT: Autophagy is a survival mechanism necessary for eukaryotic cells to overcome nutritionally challenged environments. When autophagy is triggered, cells degrade nonselectively engulfed cytosolic proteins and free ribosomes that are evenly distributed throughout the cytoplasm. The resulting pool of free amino acids is used to sustain processes crucial for survival. Here we characterize an autophagic degradation of the endoplasmic reticulum (ER) under starvation conditions in addition to cytosolic protein degradation. Golgi membrane protein was not engulfed by the autophagosome under the same conditions, indicating that the uptake of ER by autophagosome was the specific event. Although the ER exists in a network structure that is mutually connected and resides predominantly around the nucleus and beneath the plasma membrane, most of autophagosome engulfed ER. The extent of the ER uptake by autophagy was nearly identical to that of the soluble cytosolic proteins. This phenomenon was explained by the appearance of fragmented ER membrane structures in almost all autophagosomes. Furthermore, ER dynamism is required for this process: ER uptake by autophagosomes occurs in an actin-dependent manner.
    Traffic 02/2005; 6(1):56-65. · 4.65 Impact Factor
  • Maho Hamasaki, Takeshi Noda, Yoshinori Ohsumi
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    ABSTRACT: Autophagy is a starvation response in eukaryotes by which the cell delivers cytoplasmic components to the vacuole for degradation, and is mediated by a double membrane structure called the autophagosome. We have previously proposed that the specific combination of COPII like components, including Sec24p, is required for autophagy (Ishihara, N. et al. (2001) Mol. Biol. Cell, 12: 3690-3702). The autophagic defect in sec24 deleted mutant cells was, however, suppressed upon the recovery of its secretory flow by the overexpression of its homologue, Sfb2p. We have also reported that the autophagic defect is not observed in sec13 and sec31 mutants, a phenomenon that can be explained by the fact that starvation stress suppresses the secretory defect of these mutants. These observations indicate that the active flow in the early secretory pathway plays an important role in autophagy; that is, autophagy proceeds in the presence, but not in the absence of the early secretory flow. Both autophagy and its closely related cytoplasm to vacuole-targeting (Cvt) pathway occur through a pre-autophagosomal structure (PAS), and since the PAS and the functional Cvt pathway exist in all sec mutants, the early secretory pathway must be involved specifically in autophagy, subsequent to PAS formation.
    Cell Structure and Function 03/2003; 28(1):49-54. · 1.65 Impact Factor
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    ABSTRACT: Double membrane structure, autophagosome, is formed de novo in the process of autophagy in the yeast Saccharomyces cerevisiae, and many Apg proteins participate in this process. To further understand autophagy, we analyzed the involvement of factors engaged in the secretory pathway. First, we showed that Sec18p (N-ethylmaleimide-sensitive fusion protein, NSF) and Vti1p (soluble N-ethylmaleimide-sensitive fusion protein attachment protein, SNARE), and soluble N-ethylmaleimide-sensitive fusion protein receptor are required for fusion of the autophagosome to the vacuole but are not involved in autophagosome formation. Second, Sec12p was shown to be essential for autophagy but not for the cytoplasm to vacuole-targeting (Cvt) (pathway, which shares mostly the same machinery with autophagy. Subcellular fractionation and electron microscopic analyses showed that Cvt vesicles, but not autophagosomes, can be formed in sec12 cells. Three other coatmer protein (COPII) mutants, sec16, sec23, and sec24, were also defective in autophagy. The blockage of autophagy in these mutants was not dependent on transport from endoplasmic reticulum-to-Golgi, because mutations in two other COPII genes, SEC13 and SEC31, did not affect autophagy. These results demonstrate the requirement for subgroup of COPII proteins in autophagy. This evidence demonstrating the involvement of Sec proteins in the mechanism of autophagosome formation is crucial for understanding membrane flow during the process.
    Molecular Biology of the Cell 12/2001; 12(11):3690-702. · 4.60 Impact Factor

Publication Stats

868 Citations
137.49 Total Impact Points

Institutions

  • 2012
    • University of Michigan
      • Life Sciences Institute
      Ann Arbor, MI, United States
  • 2011
    • Osaka University
      • Department of Cellular Regulation
      Suika, Ōsaka, Japan
  • 2003–2005
    • National Institute for Basic Biology
      Okazaki, Aichi, Japan