Advertisement

Molecular Medicine

, Volume 9, Issue 3–4, pp 65–76 | Cite as

The Molecular Mechanism of Autophagy

  • Chao-Wen Wang
  • Daniel J. Klionsky
In Overview

Abstract

Autophagy is a conserved trafficking pathway that is highly regulated by environmental conditions. During autophagy, portions of cytoplasm are sequestered into a double-membrane autophagosome and delivered to a degradative organelle, the vacuole in yeast and the lysosome in mammalian cells, for breakdown and recycling. Autophagy is induced under starvation conditions and in mammalian cells is also invoked in response to specific hormones. In yeast, under nutrient-rich conditions, a constitutive biosynthetic pathway, termed the cytoplasm to vacuole targeting (Cvt) pathway, utilizes most of the same molecular machinery and topologically similar vesicles for the delivery of the resident hydrolase aminopeptidase I to the vacuole. Both autophagy and the Cvt pathway have been extensively studied and comprehensively reviewed in the past few years. In this review, we focus on the yeast system, which has provided most of the insight into the molecular mechanism of autophagy and the Cvt pathway, and highlight the most recent additions to our current knowledge of both pathways.

Notes

Acknowledgments

The work was supported by National Institutes of Health Public Health Service Grant GM53396 (to DJK) and the Lewis E and Elaine Prince Wehmeyer Trust (to C-WW).

References

  1. 1.
    Reggiori F, Klionsky DJ. (2002) Autophagy in the eukaryotic cell. Eukaryot. Cell 1:11–21.CrossRefGoogle Scholar
  2. 2.
    Kim J, Klionsky DJ. (2000) Autophagy, cytoplasm-to-vacuole targeting pathway, and pexophagy in yeast and mammalian cells. Annu. Rev. Biochem. 69:303–42.CrossRefGoogle Scholar
  3. 3.
    Tuttle DL, Dunn Jr WA. (1995) Divergent modes of autophagy in the methylotrophic yeast Pichia pastoris. J. Cell Sci. 108:25–35.PubMedGoogle Scholar
  4. 4.
    Bursch W. (2001) The autophagosomal-lysosomal compartment in programmed cell death. Cell Death Differ. 8:569–81.CrossRefGoogle Scholar
  5. 5.
    Xue L, Fletcher GC, Tolkovsky AM. (1999) Autophagy is activated by apoptotic signalling in sympathetic neurons: an alternative mechanism of death execution. Mol. Cell. Neurosci. 14:180–98.CrossRefGoogle Scholar
  6. 6.
    Klionsky DJ, Emr SD. (2000) Autophagy as a regulated pathway of cellular degradation. Science 290:1717–21.CrossRefGoogle Scholar
  7. 7.
    Liang XH et al. (1999) Induction of autophagy and inhibition of tumorigenesis by beclin 1. Nature 402:672–6.CrossRefGoogle Scholar
  8. 8.
    Kihara A, Kabeya Y, Ohsumi Y, Yoshimori T. (2001) Beclin-phosphatidylinositol 3-kinase complex functions at the trans-Golgi network. EMBO Rep. 2:330–5.CrossRefGoogle Scholar
  9. 9.
    Beck T, Hall MN. (1999) The TOR signalling pathway controls nuclear localization of nutrient-regulated transcription factors. Nature 402:689–92.CrossRefGoogle Scholar
  10. 10.
    Noda T, Ohsumi Y. (1998) Tor, a phosphatidylinositol kinase homologue, controls autophagy in yeast. J. Biol. Chem. 273:3963–6.CrossRefGoogle Scholar
  11. 11.
    Hutchins MU, Klionsky DJ. (2001) Vacuolar localization of oligomeric α-mannosi-dase requires the cytoplasm to vacuole targeting and autophagy pathway components in Saccharomyces cerevisiae. J. Biol. Chem. 276:20491–8.CrossRefGoogle Scholar
  12. 12.
    Scott SV, Guan J, Hutchins MU, Kim J, Klionsky DJ. (2001) Cvt19 is a receptor for the cytoplasm-to-vacuole targeting pathway. Mol. Cell. 7:1131–41.CrossRefGoogle Scholar
  13. 13.
    Shintani T, Huang W-P, Stromhaug PE, Klionsky DJ. (2002) Mechanism of cargo selection in the cytoplasm to vacuole targeting pathway. Dev. Cell. 3:825–37.CrossRefGoogle Scholar
  14. 14.
    Suzuki K, Kamada Y, Ohsumi Y. (2002) Studies of cargo delivery to the vacuole mediated by autophagosomes in Saccharomyces cerevisiae. Dev. Cell. 3:815–24.CrossRefGoogle Scholar
  15. 15.
    Kim J et al. (2001) Cvt9/Gsa9 functions in sequestering selective cytosolic cargo destined for the vacuole. J. Cell Biol. 153:381–96.CrossRefGoogle Scholar
  16. 16.
    Kim J, Huang W-P, Stromhaug PE, Klionsky DJ. (2002) Convergence of multiple autophagy and cytoplasm to vacuole targeting components to a perivacuolar membrane compartment prior to de novo vesicle formation. J. Biol. Chem. 277:763–73.CrossRefGoogle Scholar
  17. 17.
    Suzuki K, Kirisako T, Kamada Y, Mizushima N, Noda T, Ohsumi Y. (2001) The pre-autophagosomal structure organized by concerted functions of APG genes is essential for autophagosome formation. EMBO J. 20:5971–81.CrossRefGoogle Scholar
  18. 18.
    Kihara A, Noda T, Ishihara N, Ohsumi Y. (2001) Two distinct Vps34 phosphatidylinositol 3-kinase complexes function in autophagy and carboxypeptidase Y sorting in Saccharomyces cerevisiae. J. Cell Biol. 152:519–30.CrossRefGoogle Scholar
  19. 19.
    Nice DC, Sato TK, Stromhaug PE, Emr SD, Klionsky DJ. (2002) Cooperative binding of the cytoplasm to vacuole targeting pathway proteins, Cvt13 and Cvt20, to phosphatidylinositol 3-phosphate at the pre-autophagosomal structure is required for selective autophagy. J. Biol. Chem. 277:30198–207.CrossRefGoogle Scholar
  20. 20.
    Wurmser AE, Emr SD. (2002) Novel PtdIns(3)P-binding protein Etf1 functions as an effector of the Vps34 PtdIns 3-kinase in autophagy. J. Cell Biol. 158:761–72.CrossRefGoogle Scholar
  21. 21.
    Ohsumi Y. (2001) Molecular dissection of autophagy: 2 ubiquitin-like systems. Nat. Rev. Mol. Cell. Biol. 2:211–6.CrossRefGoogle Scholar
  22. 22.
    Kuma A, Mizushima N, Ishihara N, Ohsumi Y. (2002) Formation of the approximately 350-kDa Apg12-Apg5-Apg16 multimeric complex, mediated by Apg16 oligomerization, is essential for autophagy in yeast. J. Biol. Chem. 277:18619–25.CrossRefGoogle Scholar
  23. 23.
    Mizushima N et al. (2001) Dissection of autophagosome formation using Apg5-deficient mouse embryonic stem cells. J. Cell Biol. 152:657–68.CrossRefGoogle Scholar
  24. 24.
    Yung HW, Xue L, Tolkovsky AM. (2002) Apoptosis-specific protein (ASP 45 kDa) is distinct from human Apg5, the homologue of the yeast autophagic gene apg5. FEBS Lett. 531:168–72.CrossRefGoogle Scholar
  25. 25.
    Lang T, Schaeffeler E, Bernreuther D, Bredschneider M, Wolf DH, Thumm M. (1998) Aut2p and Aut7p, 2 novel microtubule-associated proteins are essential for delivery of autophagic vesicles to the vacuole. EMBO J. 17:3597–607.CrossRefGoogle Scholar
  26. 26.
    Ichimura Y et al. (2000) A ubiquitin-like system mediates protein lipidation. Nature 408:488–92.CrossRefGoogle Scholar
  27. 27.
    Kirisako T et al. (2000) The reversible modification regulates the membrane-binding state of Apg8/Aut7 essential for autophagy and the cytoplasm to vacuole targeting pathway. J. Cell Biol. 151:263–76.CrossRefGoogle Scholar
  28. 28.
    Kim J, Huang W-P, Klionsky DJ. (2001) Membrane recruitment of Aut7p in the autophagy and cytoplasm to vacuole targeting pathways requires Aut1p, Aut2p, and the autophagy conjugation complex. J. Cell Biol. 152:51–64.CrossRefGoogle Scholar
  29. 29.
    Huang W-P, Scott SV, Kim J, Klionsky DJ. (2000) The itinerary of a vesicle component, Aut7p/Cvt5p, terminates in the yeast vacuole via the autophagy/Cvt pathways. J. Biol. Chem. 275:5845–51.CrossRefGoogle Scholar
  30. 30.
    Abeliovich H, Zhang C, Dunn WA, Jr, Shokat KM, Klionsky DJ. (2003) Chemical genetic analysis of Apg1 reveals a non-kinase role in the induction of autophagy. Mol. Biol. Cell 14:477–90.CrossRefGoogle Scholar
  31. 31.
    Kabeya Y et al. (2000) LC3, a mammalian homologue of yeast Apg8p, is localized in autophagosome membranes after processing. EMBO J. 19:5720–8.CrossRefGoogle Scholar
  32. 32.
    Tanida I, Tanida-Miyake E, Komatsu M, Ueno T, Kominami E. (2002) Human Apg3p/Aut1p homologue is an authentic E2 enzyme for multiple substrates, GATE-16, GABARAP, and MAP-LC3, and facilitates the conjugation of hApg12p to hApg5p. J. Biol. Chem. 277:13739–44.CrossRefGoogle Scholar
  33. 33.
    Matsuura A, Tsukada M, Wada Y, Ohsumi Y. (1997) Apg1p, a novel protein kinase required for the autophagic process in Saccharomyces cerevisiae. Gene 192:245–50.CrossRefGoogle Scholar
  34. 34.
    Kamada Y et al. (2000) Tor-mediated induction of autophagy via an Apg1 protein kinase complex. J. Cell Biol. 150:1507–13.CrossRefGoogle Scholar
  35. 35.
    Scott SV et al. (2000) Apg13p and Vac8p are part of a complex of phosphoproteins that are required for cytoplasm to vacuole targeting. J. Biol. Chem. 275:25840–9.CrossRefGoogle Scholar
  36. 36.
    Gavin AC et al. (2002) Functional organization of the yeast proteome by systematic analysis of protein complexes. Nature 415:141–7.CrossRefGoogle Scholar
  37. 37.
    Okazaki N et al. (2000) Interaction of the Unc-51-like kinase and microtubule-associated protein light chain 3 related proteins in the brain: possible role of vesicular transport in axonal elongation. Brain Res. Mol. Brain Res. 85:1–12.CrossRefGoogle Scholar
  38. 38.
    Shintani T, Suzuki K, Kamada Y, Noda T, Ohsumi Y. (2001) Apg2p functions in autophagosome formation on the perivacuolar structure. J. Biol. Chem. 276: 30452–60.CrossRefGoogle Scholar
  39. 39.
    Wang C-W et al. (2001) Apg2 is a novel protein required for the cytoplasm to vacuole targeting, autophagy, and pexophagy pathways. J. Biol. Chem. 276: 30442–51.CrossRefGoogle Scholar
  40. 40.
    Noda T et al. (2000) Apg9p/Cvt7p is an integral membrane protein required for transport vesicle formation in the Cvt and autophagy pathways. J. Cell Biol. 148:465–80.CrossRefGoogle Scholar
  41. 41.
    Ishihara N et al. (2001) Autophagosome requires specific early Sec proteins for its formation and NSF/SNARE for vacuolar fusion. Mol. Biol. Cell 12:3690–702.CrossRefGoogle Scholar
  42. 42.
    Reggiori F, Wang C-W, Stromhaug PE, Shintani T, Klionsky DJ. (2003) Vps51 is part of the yeast Vps fifty-three tethering complex essential for retrograde traffic from the early endosome and Cvt vesicle completion. J. Biol. Chem. 278:5009–20.CrossRefGoogle Scholar
  43. 43.
    Darsow T, Rieder SE, Emr SD. (1997) A multispecificity syntaxin homologue, Vam3p, essential for autophagic and biosynthetic protein transport to the vacuole. J. Cell Biol. 138:517–29.CrossRefGoogle Scholar
  44. 44.
    Fischer von Mollard G, Stevens TH. (1999) The Saccharomyces cerevisiae v-SNARE Vti1p is required for multiple membrane transport pathways to the vacuole. Mol. Biol. Cell 10:1719–32.CrossRefGoogle Scholar
  45. 45.
    Sato TK, Darsow T, Emr SD. (1998) Vam7p, a SNAP-25-like molecule, and Vam3p, a syntaxin homolog, function together in yeast vacuolar protein trafficking. Mol. Cell. Biol. 18:5308–19.CrossRefGoogle Scholar
  46. 46.
    Kim J, Dalton VM, Eggerton KP, Scott SV, Klionsky DJ. (1999) Apg7p/Cvt2p is required for the cytoplasm-to-vacuole targeting, macroautophagy, and peroxisome degradation pathways. Mol. Biol. Cell 10:1337–51.CrossRefGoogle Scholar
  47. 47.
    Wang C-W, Stromhaug PE, Shima J, Klionsky DJ. (2002) The Ccz1-Mon1 protein complex is required for the late step of multiple vacuole delivery pathways. J. Biol. Chem. 277:47917–27.CrossRefGoogle Scholar
  48. 48.
    Sato TK, Rehling P, Peterson MR, Emr SD. (2000) Class C Vps protein complex regulates vacuolar SNARE pairing and is required for vesicle docking/fusion. Mol. Cell 6:661–71.CrossRefGoogle Scholar
  49. 49.
    Rieder SE, Emr SD. (1997) A novel RING finger protein complex essential for a late step in protein transport to the yeast vacuole. Mol. Biol. Cell 8:2307–27.CrossRefGoogle Scholar
  50. 50.
    Wurmser AE, Sato TK, Emr SD. (2000) New component of the vacuolar class C-Vps complex couples nucleotide exchange on the Ypt7 GTPase to SNARE-dependent docking and fusion. J. Cell. Biol. 151:551–62.CrossRefGoogle Scholar
  51. 51.
    Takeshige K, Baba M, Tsuboi S, Noda T, Ohsumi Y. (1992) Autophagy in yeast demonstrated with proteinase-deficient mutants and conditions for its induction. J. Cell Biol. 119:301–11.CrossRefGoogle Scholar
  52. 52.
    Epple UD, Suriapranata I, Eskelinen EL, Thumm M. (2001) Aut5/Cvt17p, a putative lipase essential for disintegration of autophagic bodies inside the vacuole. J. Bacteriol. 183:5942–55.CrossRefGoogle Scholar
  53. 53.
    Suriapranata I et al. (2000) The breakdown of autophagic vesicles inside the vacuole depends on Aut4p. J. Cell Sci. 113:4025–33.PubMedGoogle Scholar
  54. 54.
    Teter SA et al. (2001) Degradation of lipid vesicles in the yeast vacuole requires function of Cvt17, a putative lipase. J. Biol. Chem. 276:2083–7.CrossRefGoogle Scholar
  55. 55.
    Stromhaug PE, Klionsky DJ. (2001) Approaching the molecular mechanism of autophagy. Traffic 2:524–31.CrossRefGoogle Scholar
  56. 56.
    Khalfan WA, Klionsky DJ. (2002) Molecular machinery required for autophagy and the cytoplasm to vacuole targeting (Cvt) pathway in S. cerevisiae. Curr. Opin. Cell Biol. 14:468–75.CrossRefGoogle Scholar

Copyright information

© Feinstein Institute for Medical Research 2003

Authors and Affiliations

  1. 1.Department of Molecular, Cellular and Developmental Biology, Department of Biological Chemistry, and the Life Sciences InstituteUniversity of MichiganAnn ArborUSA

Personalised recommendations