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Cellular and Molecular Life Sciences

, Volume 69, Issue 7, pp 1125–1136 | Cite as

Microautophagy: lesser-known self-eating

  • Wen-wen Li
  • Jian Li
  • Jin-ku Bao
Review

Abstract

Microautophagy, the non-selective lysosomal degradative process, involves direct engulfment of cytoplasmic cargo at a boundary membrane by autophagic tubes, which mediate both invagination and vesicle scission into the lumen. With its constitutive characteristics, microautophagy of soluble substrates can be induced by nitrogen starvation or rapamycin via regulatory signaling complex pathways. The maintenance of organellar size, membrane homeostasis, and cell survival under nitrogen restriction are the main functions of microautophagy. In addition, microautophagy is coordinated with and complements macroautophagy, chaperone-mediated autophagy, and other self-eating pathways. Three forms of selective microautophagy, including micropexophagy, piecemeal microautophagy of the nucleus, and micromitophagy, share common ground with microautophagy to some degree. As the accumulation of experimental data, the precise mechanisms that govern microautophagy are becoming more appreciated. Here, we review the microautophagic molecular machinery, its physiological functions, and relevance to human diseases, especially in diseases involving multivesicular bodies and multivesicular lysosomes.

Keywords

Autophagy Microautophagy Autophagic tube Selective autophagy Lysosomophagy 

Abbreviations

Alp

Alkaline phosphatase

Apg/Atg/ATG/Aut

Autophagy-related gene

CMA

Chaperone-mediated autophagy

Cpy

Carboxypeptidase Y

CVT

Cytoplasm-to-vacuole targeting

EGO

Exit from rapamycin-induced growth arrest

ESCRT

Endosomal sorting complex required for transport

hsc70

Heat shock cognate 70

MIPA

Micropexophagic membrane apparatus

MPT

Mitochondrial permeability transition

MVB

Multivesicular body

NV

Nucleus–vacuole

PAS

Pre-autophagosomal structure

PCD

Programmed cell death

PE

Phosphatidylethanolamine

PMN

Piecemeal microautophagy of the nucleus

PVS

Peri-vacuolar dot-like structures

ROS

Reactive oxygen species

SNARE

Soluble NSF attachment protein receptors

TOR

Target of rapamycin

Ublc

Ubiquitin-like conjugation

VSM

Vacuolar sequestering membrane

VTC

Vacuolar transporter chaperone

Notes

Acknowledgments

We thank Dr. Bo Liu for providing constructive suggestions, Yi Wang, Zi-yue Li, Jun-jie Liu and Qian Liu for critically reading the manuscript, and Chi Yang, Hao-yu Hu for technical assistance. This work was supported in part by grants from the National Natural Science Foundation of China (No. 30970643, No. 81173093 and No. J1103518), and National Key Technologies R&D Program of 11th 5-year plan.

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© Springer Basel AG 2011

Authors and Affiliations

  1. 1.School of Life Sciences and State Key Laboratory of Oral DiseasesSichuan UniversityChengduChina
  2. 2.Molecular and Cellular Biology Program, Department of Biological SciencesOhio UniversityAthensUSA

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