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.
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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
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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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Li, Ww., Li, J. & Bao, Jk. Microautophagy: lesser-known self-eating. Cell. Mol. Life Sci. 69, 1125–1136 (2012). https://doi.org/10.1007/s00018-011-0865-5
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DOI: https://doi.org/10.1007/s00018-011-0865-5