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AMPK regulates metabolism and survival in response to ionizing radiation
Vanessa E Zannella1, Dan Cojocari, Susan Hilgendorf
1Ontario Cancer Institute and Campbell Family Institute for Cancer Research, University Health Network, Canada.
Background And Purpose:
AMPK is a metabolic sensor and an upstream inhibitor of mTOR activity. AMPK is phosphorylated by ionizing radiation (IR) in an ATM dependent manner, but the cellular consequences of this phosphorylation event have remained unclear. The objective of this study was to assess whether AMPK plays a functional role in regulating cellular responses to IR.
Methods:
The importance of AMPK expression for radiation responses was investigated using both MEFs (mouse embryo fibroblasts) double knockout for AMPK α1/α2 subunits and human colorectal carcinoma cells (HCT 116) with AMPK α1/α2 shRNA mediated knockdown.
Results:
We demonstrate here that IR results in phosphorylation of both AMPK and its substrate, ACC. IR moderately stimulated mTOR activity, and this was substantially exacerbated in the absence of AMPK. AMPK was required for IR induced expression of the mTOR inhibitor REDD1, indicating that AMPK restrains mTOR activity through multiple mechanisms. Likewise, cellular metabolism was deregulated following irradiation in the absence of AMPK, as evidenced by a substantial increase in oxygen consumption rates and lactate production. AMPK deficient cells showed impairment of the G1/S cell cycle checkpoint, and were unable to support long-term proliferation during starvation following radiation. Lastly, we show that AMPK proficiency is important for clonogenic survival after radiation during starvation.
Conclusions:
These data reveal novel functional roles for AMPK in regulating mTOR signaling, cell cycle, survival and metabolic responses to IR.
Insights
AMPK (AMP-activated protein kinase) is crucial for cellular responses to ionizing radiation (IR). Its absence impairs mTOR regulation, cell cycle control, and survival, highlighting its role in managing radiation damage.
Area of Science:
- Cellular Biology
- Radiation Oncology
- Metabolism
Background:
- AMPK acts as a metabolic sensor and inhibits mTOR.
- Ionizing radiation (IR) phosphorylates AMPK in an ATM-dependent manner.
- The functional impact of IR-induced AMPK phosphorylation was previously unknown.
Purpose of the Study:
- To determine if AMPK plays a functional role in cellular responses to IR.
- To investigate the consequences of AMPK deficiency on radiation response.
Main Methods:
- Utilized mouse embryo fibroblasts (MEFs) lacking AMPK α1/α2 subunits.
- Employed human colorectal carcinoma cells (HCT 116) with AMPK α1/α2 shRNA knockdown.
Main Results:
- IR phosphorylates AMPK and ACC; AMPK deficiency exacerbates IR-induced mTOR activity.
- AMPK is essential for REDD1 expression, restraining mTOR signaling.
- AMPK absence deregulates cellular metabolism (increased oxygen consumption, lactate production).
- AMPK deficiency impairs G1/S cell cycle checkpoint and long-term proliferation post-IR.
- AMPK proficiency is vital for clonogenic survival after IR during starvation.
Conclusions:
- AMPK has novel functional roles in regulating mTOR signaling after IR.
- AMPK is critical for cell cycle progression and survival post-IR.
- AMPK plays a key role in metabolic adaptation to IR.
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