Exploiting the mitochondrial unfolded protein response for cancer therapy in mice and human cells
Markus D. Siegelin, Takehiko Dohi, Christopher M. Raskett, Gregory M. Orlowski, Christine M. Powers, Candace A. Gilbert, Alonzo H. Ross, Janet Plescia, Dario C. Altieri
Markus D. Siegelin, Takehiko Dohi, Christopher M. Raskett, Gregory M. Orlowski, Christine M. Powers, Candace A. Gilbert, Alonzo H. Ross, Janet Plescia, Dario C. Altieri
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Research Article Oncology

Exploiting the mitochondrial unfolded protein response for cancer therapy in mice and human cells

Abstract

Fine tuning of the protein folding environment in subcellular organelles, such as mitochondria, is important for adaptive homeostasis and may participate in human diseases, but the regulators of this process are still largely elusive. Here, we have shown that selective targeting of heat shock protein-90 (Hsp90) chaperones in mitochondria of human tumor cells triggered compensatory autophagy and an organelle unfolded protein response (UPR) centered on upregulation of CCAAT enhancer binding protein (C/EBP) transcription factors. In turn, this transcriptional UPR repressed NF-κB–dependent gene expression, enhanced tumor cell apoptosis initiated by death receptor ligation, and inhibited intracranial glioblastoma growth in mice without detectable toxicity. These data reveal what we believe to be a novel role of Hsp90 chaperones in the regulation of the protein-folding environment in mitochondria of tumor cells. Disabling this general adaptive pathway could potentially be used in treatment of genetically heterogeneous human tumors.

Authors

Markus D. Siegelin, Takehiko Dohi, Christopher M. Raskett, Gregory M. Orlowski, Christine M. Powers, Candace A. Gilbert, Alonzo H. Ross, Janet Plescia, Dario C. Altieri

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Figure 3

Mitochondrial Hsp90 regulates autophagy.

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Mitochondrial Hsp90 regulates autophagy. (A–C) LN229 cells were treated ...
(A–C) LN229 cells were treated with G-TPP and analyzed by EM (A and B) or immunoelectron microscopy with an antibody to COX-IV (C). Arrowheads, COX-IV–reactive material. Scale bars: 2 μm (A); 1 μm (B); 200 nm (C). (D) U87 cells were treated with G-TPP, harvested at the indicated time intervals, and analyzed by immunoblotting. The position of the unmodified (I) or lipidated (II) form of LC3 is indicated. (E) U251 cells were transfected with LC3-GFP, treated with vehicle or G-TPP, and analyzed after 16 hours by fluorescence microscopy (left). The percentage of cells with punctate GFP fluorescence was quantified (right). Mean ± SD of 4–6 independent microscopy fields. (F) U87 cells were incubated with inhibitors of phagosome formation, bafilomycin A (BF), or 3-methyladenine (3-MA) for 1 hour, treated with G-TPP, and analyzed after 16 hours by MTT. Mean ± SD of replicates. (G) L229 cells were transfected with control or atg5-directed siRNA and analyzed by immunoblotting. (H) siRNA-transfected LN229 cells as in G were analyzed for cell viability after 16 hours by MTT. Mean ± SD of replicates.