Journal
AUTOPHAGY
Volume 11, Issue 2, Pages 332-343Publisher
TAYLOR & FRANCIS INC
DOI: 10.1080/15548627.2015.1023047
Keywords
autophagy; alternative autophagy; Keima; mitochondria; mitogen-activated protein kinase; mitophagy
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Funding
- Ministry of Education, Culture, Sports, Science and Technology (MEXT) program Promotion of Environmental Improvement for Independence of Young Researchers under the Special Coordination Funds for Promoting Science and Technology
- Japan Society for the Promotion of Science KAKENHI Grant [23689032, 25560414, 23790371]
- MEXT KAKENHI Grant [25117714]
- Uehara Memorial Foundation
- Tokyo Biochemical Research Foundation
- Suzuken Memorial Foundation
- Grants-in-Aid for Scientific Research [23790371, 25117714, 23689032, 13J04836, 25560414, 25253041] Funding Source: KAKEN
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In cultured cells, not many mitochondria are degraded by mitophagy induced by physiological cellular stress. We observed mitophagy in HeLa cells using a method that relies on the pH-sensitive fluorescent protein Keima. With this approach, we found that mitophagy was barely induced by carbonyl cyanide m-chlorophenyl hydrazone treatment, which is widely used as an inducer of PARK2/Parkin-related mitophagy, whereas a small but modest amount of mitochondria were degraded by mitophagy under conditions of starvation or hypoxia. Mitophagy induced by starvation or hypoxia was marginally suppressed by knockdown of ATG7 and ATG12, or MAP1LC3B, which are essential for conventional macroautophagy. In addition, mitophagy was efficiently induced in Atg5 knockout mouse embryonic fibroblasts. However, knockdown of RAB9A and RAB9B, which are essential for alternative autophagy, but not conventional macroautophagy, severely suppressed mitophagy. Finally, we found that the MAPKs MAPK1/ERK2 and MAPK14/p38 were required for mitophagy. Based on these findings, we conclude that mitophagy in mammalian cells predominantly occurs through an alternative autophagy pathway, requiring the MAPK1 and MAPK14 signaling pathways.
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