1
|
Yao W, Feng Y, Zhang Y, Yang H, Yi C. The molecular mechanisms regulating the assembly of the autophagy initiation complex. Bioessays 2024; 46:e2300243. [PMID: 38593284 DOI: 10.1002/bies.202300243] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2023] [Revised: 03/23/2024] [Accepted: 03/25/2024] [Indexed: 04/11/2024]
Abstract
The autophagy initiation complex is brought about via a highly ordered and stepwise assembly process. Two crucial signaling molecules, mTORC1 and AMPK, orchestrate this assembly by phosphorylating/dephosphorylating autophagy-related proteins. Activation of Atg1 followed by recruitment of both Atg9 vesicles and the PI3K complex I to the PAS (phagophore assembly site) are particularly crucial steps in its formation. Ypt1, a small Rab GTPase in yeast cells, also plays an essential role in the formation of the autophagy initiation complex through multiple regulatory pathways. In this review, our primary focus is to discuss how signaling molecules initiate the assembly of the autophagy initiation complex, and highlight the significant roles of Ypt1 in this process. We end by addressing issues that need future clarification.
Collapse
Affiliation(s)
- Weijing Yao
- Department of Biochemistry, and Department of Hepatobiliary and Pancreatic Surgery of the First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, China
| | - Yuyao Feng
- Department of Vascular Surgery, Peking Union Medical College Hospital, Chinese Academy of Medical Science, Beijing, China
| | - Yi Zhang
- Department of Biochemistry, and Department of Hepatobiliary and Pancreatic Surgery of the First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, China
| | - Huan Yang
- Department of Biochemistry, and Department of Hepatobiliary and Pancreatic Surgery of the First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, China
| | - Cong Yi
- Department of Biochemistry, and Department of Hepatobiliary and Pancreatic Surgery of the First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, China
| |
Collapse
|
2
|
Newer Methods Drive Recent Insights into Rab GTPase Biology: An Overview. Methods Mol Biol 2021. [PMID: 34453706 DOI: 10.1007/978-1-0716-1346-7_1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/18/2023]
Abstract
The conserved Ypt/Rab GTPases regulate all major intracellular protein traffic pathways, including secretion, endocytosis and autophagy. These GTPases undergo distinct changes in conformation between their GTP- and GDP-bound forms and cycle between the cytoplasm and membranes with the aid of their upstream regulators. When activated on the membrane in the GTP-bound form, they recruit their downstream effectors, which include components of vesicular transport. Progress in the past 5 years regarding mechanisms of Rab action, functions, and the effects of disruption of these functions on the well-being of cells and organisms has been propelled by advances in methodologies in molecular and cellular biology. Here, we highlight methods used recently to analyze regulation, localization, interactions, and function of Rab GTPases and their roles in human disease. We discuss contributions of these methods to new insights into Rabs, as well as their future use in addressing open questions in the field of Rab biology.
Collapse
|
3
|
Lipatova Z, Segev N. Ypt/Rab GTPases and their TRAPP GEFs at the Golgi. FEBS Lett 2019; 593:2488-2500. [PMID: 31400292 PMCID: PMC6989042 DOI: 10.1002/1873-3468.13574] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2019] [Revised: 08/07/2019] [Accepted: 08/08/2019] [Indexed: 11/06/2022]
Abstract
The conserved Ypt/Rab GTPases regulate the different steps of all intracellular trafficking pathways. Ypt/Rabs are activated by their specific nucleotide exchangers termed GEFs, and when GTP bound, they recruit their downstream effectors, which mediate vesicular transport substeps. In the yeast exocytic pathway, Ypt1 and Ypt31/32 regulate traffic through the Golgi and the conserved modular TRAPP complex acts a GEF for both Ypt1 and Ypt31/32. However, the precise localization and function of these Ypts have been under debate, as is the identity of their corresponding GEFs. We have established that Ypt1 and Ypt31 reside on the two sides of the Golgi, early and late, respectively, and regulate Golgi cisternal progression. We and others have shown that whereas a single TRAPP complex, TRAPP II, activates Ypt31, three TRAPP complexes can activate Ypt1: TRAPPs I, III, and IV. We propose that TRAPP I and II activate Ypt1 and Ypt31, respectively, at the Golgi, whereas TRAPP III and IV activate Ypt1 in autophagy. Resolving these issues is important because both Rabs and TRAPPs are implicated in multiple human diseases, ranging from cancer to neurodegenerative diseases.
Collapse
Affiliation(s)
- Zhanna Lipatova
- Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago, IL, USA
| | - Nava Segev
- Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago, IL, USA
| |
Collapse
|
4
|
Thomas LL, Joiner AMN, Fromme JC. The TRAPPIII complex activates the GTPase Ypt1 (Rab1) in the secretory pathway. J Cell Biol 2017; 217:283-298. [PMID: 29109089 PMCID: PMC5748984 DOI: 10.1083/jcb.201705214] [Citation(s) in RCA: 47] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2017] [Revised: 09/01/2017] [Accepted: 10/03/2017] [Indexed: 12/30/2022] Open
Abstract
The TRAPP complexes are nucleotide exchange factors that activate Rab GTPases, and four different versions of TRAPP have been reported. Thomas et al. show that only two versions of TRAPP are detectable in normal cells and demonstrate that the TRAPPIII complex regulates Golgi trafficking in addition to its established role in autophagy. Rab GTPases serve as molecular switches to regulate eukaryotic membrane trafficking pathways. The transport protein particle (TRAPP) complexes activate Rab GTPases by catalyzing GDP/GTP nucleotide exchange. In mammalian cells, there are two distinct TRAPP complexes, yet in budding yeast, four distinct TRAPP complexes have been reported. The apparent differences between the compositions of yeast and mammalian TRAPP complexes have prevented a clear understanding of the specific functions of TRAPP complexes in all cell types. In this study, we demonstrate that akin to mammalian cells, wild-type yeast possess only two TRAPP complexes, TRAPPII and TRAPPIII. We find that TRAPPIII plays a major role in regulating Rab activation and trafficking at the Golgi in addition to its established role in autophagy. These disparate pathways share a common regulatory GTPase Ypt1 (Rab1) that is activated by TRAPPIII. Our findings lead to a simple yet comprehensive model for TRAPPIII function in both normal and starved eukaryotic cells.
Collapse
Affiliation(s)
- Laura L Thomas
- Department of Molecular Biology and Genetics, Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY
| | - Aaron M N Joiner
- Department of Molecular Biology and Genetics, Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY
| | - J Christopher Fromme
- Department of Molecular Biology and Genetics, Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY
| |
Collapse
|
5
|
Yan S, Huda N, Khambu B, Yin XM. Relevance of autophagy to fatty liver diseases and potential therapeutic applications. Amino Acids 2017; 49:1965-1979. [PMID: 28478585 DOI: 10.1007/s00726-017-2429-y] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2017] [Accepted: 04/21/2017] [Indexed: 12/19/2022]
Abstract
Autophagy is an evolutionarily conserved lysosome-mediated cellular degradation program. Accumulating evidence shows that autophagy is important to the maintenance of liver homeostasis. Autophagy involves recycling of cellular nutrients recycling as well as quality control of subcellular organelles. Autophagy deficiency in the liver causes various liver pathologies. Fatty liver disease (FLD) is characterized by the accumulation of lipids in hepatocytes and the dysfunction in energy metabolism. Autophagy is negatively affected by the pathogenesis of FLD and the activation of autophagy could ameliorate steatosis, which suggests a potential therapeutic approach to FLD. In this review, we will discuss autophagy and its relevance to liver diseases, especially FLD. In addition, we will discuss recent findings on potential therapeutic applications of autophagy modulators for FLD.
Collapse
Affiliation(s)
- Shengmin Yan
- Department of Pathology and Laboratory Medicine, Indiana University School of Medicine, Indianapolis, IN, 46202, USA
| | - Nazmul Huda
- Department of Pathology and Laboratory Medicine, Indiana University School of Medicine, Indianapolis, IN, 46202, USA
| | - Bilon Khambu
- Department of Pathology and Laboratory Medicine, Indiana University School of Medicine, Indianapolis, IN, 46202, USA
| | - Xiao-Ming Yin
- Department of Pathology and Laboratory Medicine, Indiana University School of Medicine, Indianapolis, IN, 46202, USA.
| |
Collapse
|
6
|
Kim JJ, Lipatova Z, Majumdar U, Segev N. Regulation of Golgi Cisternal Progression by Ypt/Rab GTPases. Dev Cell 2016; 36:440-52. [PMID: 26906739 DOI: 10.1016/j.devcel.2016.01.016] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2015] [Revised: 12/29/2015] [Accepted: 01/22/2016] [Indexed: 10/22/2022]
Abstract
Current models entail that transport through the Golgi-the main sorting compartment of the cell-occurs via cisternal progression/maturation and that Ypt/Rab GTPases regulate this process. However, there is very limited evidence that cisternal progression is regulated, and no evidence for involvement of Ypt/Rab GTPases in such a regulation. Moreover, controversy about the placement of two of the founding members of the Ypt/Rab family, Ypt1 and Ypt31, to specific Golgi cisternae interferes with addressing this question in yeast, where cisternal progression has been extensively studied. Here, we establish the localization of Ypt1 and Ypt31 to opposite faces of the Golgi: early and late, respectively. Moreover, we show that they partially overlap on a transitional compartment. Finally, we determine that changes in Ypt1 and Ypt31 activity affect Golgi cisternal progression, early-to-transitional and transitional-to-late, respectively. These results show that Ypt/Rab GTPases regulate two separate steps of Golgi cisternal progression.
Collapse
Affiliation(s)
- Jane J Kim
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL 60607, USA
| | - Zhanna Lipatova
- Department of Biochemistry and Molecular Genetics, College of Medicine, University of Illinois at Chicago, Molecular Biology Research Building, 900 South Ashland Avenue, Chicago, IL 60607, USA
| | - Uddalak Majumdar
- Department of Biochemistry and Molecular Genetics, College of Medicine, University of Illinois at Chicago, Molecular Biology Research Building, 900 South Ashland Avenue, Chicago, IL 60607, USA
| | - Nava Segev
- Department of Biochemistry and Molecular Genetics, College of Medicine, University of Illinois at Chicago, Molecular Biology Research Building, 900 South Ashland Avenue, Chicago, IL 60607, USA.
| |
Collapse
|
7
|
Lipatova Z, Segev N. A Role for Macro-ER-Phagy in ER Quality Control. PLoS Genet 2015; 11:e1005390. [PMID: 26181331 PMCID: PMC4504476 DOI: 10.1371/journal.pgen.1005390] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2015] [Accepted: 06/23/2015] [Indexed: 11/18/2022] Open
Abstract
The endoplasmic-reticulum quality-control (ERQC) system shuttles misfolded proteins for degradation by the proteasome through the well-defined ER-associated degradation (ERAD) pathway. In contrast, very little is known about the role of autophagy in ERQC. Macro-autophagy, a collection of pathways that deliver proteins through autophagosomes (APs) for degradation in the lysosome (vacuole in yeast), is mediated by autophagy-specific proteins, Atgs, and regulated by Ypt/Rab GTPases. Until recently, the term ER-phagy was used to describe degradation of ER membrane and proteins in the lysosome under stress: either ER stress induced by drugs or whole-cell stress induced by starvation. These two types of stresses induce micro-ER-phagy, which does not use autophagic organelles and machinery, and non-selective autophagy. Here, we characterize the macro-ER-phagy pathway and uncover its role in ERQC. This pathway delivers 20-50% of certain ER-resident membrane proteins to the vacuole and is further induced to >90% by overexpression of a single integral-membrane protein. Even though such overexpression in cells defective in macro-ER-phagy induces the unfolded-protein response (UPR), UPR is not needed for macro-ER-phagy. We show that macro-ER-phagy is dependent on Atgs and Ypt GTPases and its cargo passes through APs. Moreover, for the first time the role of Atg9, the only integral-membrane core Atg, is uncoupled from that of other core Atgs. Finally, three sequential steps of this pathway are delineated: Atg9-dependent exit from the ER en route to autophagy, Ypt1- and core Atgs-mediated pre-autophagsomal-structure organization, and Ypt51-mediated delivery of APs to the vacuole.
Collapse
Affiliation(s)
- Zhanna Lipatova
- Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago, Chicago, Illinois, United States of America
| | - Nava Segev
- Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago, Chicago, Illinois, United States of America
- * E-mail:
| |
Collapse
|
8
|
Lipatova Z, Hain AU, Nazarko VY, Segev N. Ypt/Rab GTPases: principles learned from yeast. Crit Rev Biochem Mol Biol 2015; 50:203-11. [PMID: 25702751 DOI: 10.3109/10409238.2015.1014023] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Ypt/Rab GTPases are key regulators of all membrane trafficking events in eukaryotic cells. They act as molecular switches that attach to membranes via lipid tails to recruit their multiple downstream effectors, which mediate vesicular transport. Originally discovered in yeast as Ypts, they were later shown to be conserved from yeast to humans, where Rabs are relevant to a wide array of diseases. Major principles learned from our past studies in yeast are currently accepted in the Ypt/Rab field including: (i) Ypt/Rabs are not transport-step specific, but are rather compartment specific, (ii) stimulation by nucleotide exchangers, GEFs, is critical to their function, whereas GTP hydrolysis plays a role in their cycling between membranes and the cytoplasm for multiple rounds of action, (iii) they mediate diverse functions ranging from vesicle formation to vesicle fusion and (iv) they act in GTPase cascades to regulate intracellular trafficking pathways. Our recent studies on Ypt1 and Ypt31/Ypt32 and their modular GEF complex TRAPP raise three exciting novel paradigms for Ypt/Rab function: (a) coordination of vesicular transport substeps, (b) integration of individual transport steps into pathways and (c) coordination of different transport pathways. In addition to its amenability to genetic analysis, yeast provides a superior model system for future studies on the role of Ypt/Rabs in traffic coordination due to the smaller proteome that results in a simpler traffic grid. We propose that different types of coordination are important also in human cells for fine-tuning of intracellular trafficking, and that coordination defects could result in disease.
Collapse
Affiliation(s)
- Zhanna Lipatova
- a Department of Biochemistry and Molecular Genetics , University of Illinois at Chicago , Chicago , IL , USA
| | | | | | | |
Collapse
|