Etoposide Induces ATM-Dependent Mitochondrial Biogenesis through AMPK Activation

Abstract

BackgroundDNA damage such as double-stranded DNA breaks (DSBs) has been reported to stimulate mitochondrial biogenesis. However, the underlying mechanism is poorly understood. The major player in response to DSBs is ATM (ataxia telangiectasia mutated). Upon sensing DSBs, ATM is activated through autophosphorylation and phosphorylates a number of substrates for DNA repair, cell cycle regulation and apoptosis. ATM has been reported to phosphorylate the α subunit of AMP-activated protein kinase (AMPK), which senses AMP/ATP ratio in cells, and can be activated by upstream kinases. Here we provide evidence for a novel role of ATM in mitochondrial biogenesis through AMPK activation in response to etoposide-induced DNA damage.Methodology/Principal FindingsThree pairs of human ATM+ and ATM- cells were employed. Cells treated with etoposide exhibited an ATM-dependent increase in mitochondrial mass as measured by 10-N-Nonyl-Acridine Orange and MitoTracker Green FM staining, as well as an increase in mitochondrial DNA content. In addition, the expression of several known mitochondrial biogenesis regulators such as the major mitochondrial transcription factor NRF-1, PGC-1α and TFAM was also elevated in response to etoposide treatment as monitored by RT-PCR. Three pieces of evidence suggest that etoposide-induced mitochondrial biogenesis is due to ATM-dependent activation of AMPK. First, etoposide induced ATM-dependent phosphorylation of AMPK α subunit at Thr172, indicative of AMPK activation. Second, inhibition of AMPK blocked etoposide-induced mitochondrial biogenesis. Third, activation of AMPK by AICAR (an AMP analogue) stimulated mitochondrial biogenesis in an ATM-dependent manner, suggesting that ATM may be an upstream kinase of AMPK in the mitochondrial biogenesis pathway.Conclusions/SignificanceThese results suggest that activation of ATM by etoposide can lead to mitochondrial biogenesis through AMPK activation. We propose that ATM-dependent mitochondrial biogenesis may play a role in DNA damage response and ROS regulation, and that defect in ATM-dependent mitochondrial biogenesis could contribute to the manifestations of A-T disease.

ATM signals to TSC2 in the cytoplasm to regulate mTORC1 in response to ROS

“…This contrasts with the earlier finding that in HeLa cells (which lack LKB1), AMPK could be activated by etoposide in an ATM-dependent manner to regulate mitochondrial biogenesis (36). Of interest mechanistically, however, this study required prolonged treatment with etoposide, again suggesting that multiple pathways exist to regulate AMPK and mTORC1 dependent on the type of cellular damage and perhaps in a cell-type dependent manner.…”

Nicotinamide-induced Mitophagy

“…In these studies, treatment with either resveratrol (44) or SRT1720 (45) activated PGC-1␣ and thereby induced mitochondrial biogenesis, which in turn results in an increased aerobic capacity of primary cultured cells or mice. If both mitochondrial autophagy and biogenesis occur simultaneously in a cell, these seemingly contradictory effects of SIRT1 would play an important role in mitochondrial quality maintenance, because mitochondrial biogenesis coupled with active mitophagy would repopulate functional mitochondria, resulting in the restoration of a healthy population of mitochondria (46). However, in our study, no activator, at any concentration, increased the MMP (Fig.…”

Inhibition of Hsp90 via 17-DMAG induces apoptosis in a p53-dependent manner to prevent medulloblastoma

“…Therefore, it will be interesting to determine if Stat3 function contributes to a p53-dependent enhancement of 17-DMAG-induced cell death in Atm deficient cells. Cells lacking Atm also display a reduced ability to induce AMP kinase in response to several stimuli (35) and the inhibition of AMPK in combination with cisplatin-induced DNA damage leads to hyperinduction of p53 (36). It is unclear if this scenario could account for the increased sensitivity to 17-DMAG in Atm Ϫ/Ϫ cells but it will be interesting to investigate this possibility in the future.…”