Autophagy: From structure to metabolism to therapeutic regulation

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Citation for this paper:

Jardon, M. A., Rothe, K., Bortnik, S., Vezenkov, L., Jiang, X., Young, R. N…Gorski, S. M. (2013). Autophagy: From structure to metabolism to therapeutic regulation.

Autophagy, 9(12), 2180-2182. https://doi.org/10.4161/auto.26378

UVicSPACE: Research & Learning Repository

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Autophagy: From structure to metabolism to therapeutic regulation

Mario A Jardon, Katharina Rothe, Svetlana Bortnik, Lubomir Vezenkov, Xiaoyan Jiang, Robert N Young…Sharon M Gorski

2013

Xiaoyan Jiang, Robert N Young…Sharon M Gorski. This article is an open access

article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license. http://creativecommons.org/licenses/by/3.0/

This article was originally published at: https://doi.org/10.4161/auto.26378

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Autophagy

ISSN: 1554-8627 (Print) 1554-8635 (Online) Journal homepage: https://www.tandfonline.com/loi/kaup20

Autophagy

From structure to metabolism to therapeutic regulation

Mario A Jardon, Katharina Rothe, Svetlana Bortnik, Lubomir Vezenkov,

Xiaoyan Jiang, Robert N Young, Julian J Lum & Sharon M Gorski

To cite this article: Mario A Jardon, Katharina Rothe, Svetlana Bortnik, Lubomir Vezenkov, Xiaoyan Jiang, Robert N Young, Julian J Lum & Sharon M Gorski (2013) Autophagy, Autophagy, 9:12, 2180-2182, DOI: 10.4161/auto.26378

To link to this article: https://doi.org/10.4161/auto.26378

Published online: 30 Sep 2013.

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2180 Autophagy Volume 9 issue 12

Metabolic Implications of Dysregulated Selective Autophagy

Different forms of autophagy have been described includ-ing macroautophagy, microautophagy, and chaperone-mediated autophagy (CMA), each delivering cargo to the lysosome by dis-tinct mechanisms. Dr Ana Maria Cuervo investigates CMA in the context of disease, including cancer. The abundance of the LAMP2A (lysosomal-associated membrane protein 2) isoform in lysosomes directly correlates with CMA activity. Dr Cuervo’s studies on cancer cell lines and tumor tissues revealed that the communication between macroautophagy and CMA is dereg-ulated in cancer and that tumor cells display relatively higher levels of CMA than normal cells. Knockdown of LAMP2A

enhances apoptosis and cell death in tumors, while proliferation and metastatic properties of these cells are decreased. In addi-tion, CMA inhibition in established tumors by inducible knock-down of LAMP2A can result in tumor shrinkage and limits xenograft tumor growth. The difference between normal and cancer cells seems to be the result of shifts in cellular energetic balance, including increased glycolysis, and lower TP53 protein levels, correlating with higher LAMP2A expression. Inhibition of LAMP2A in cancer cells can restore TP53 expression levels to those comparable with normal cells. Another approach under investigation in Dr Cuervo’s laboratory is evaluating the possible use of RAR (retinoic acid receptor) agonists to inhibit CMA, as a potential therapy for cancer. Her studies exemplify the important links between metabolism and its regulation by different forms of autophagy.

Metabolic Implications of Altered Macroautophagy

Dr Jayanta Debnath showed that upregulation of glycoly-sis and of the pentose phosphate pathway are key features of autophagic cells with oncogenic RAS mutations. High glycoly-sis and lactate production levels are maintained under hypoxic conditions due to the ATG-dependent increase of cell surface glucose transporters and glucose uptake. Dr Debnath is also investigating the underlying mechanisms of anti-malarials cur-rently used as autophagy inhibitors in clinical trials to improve cancer therapies. Chloroquine and hydroxychloroquine (HCQ) are two such autophagy inhibitors, but a complete understand-ing of their mode of action is still lackunderstand-ing. Dr Debnath’s studies in KRAS mutant non-small cell lung carcinoma showed that chloroquine does not promote significant levels of apoptosis despite its ability to inhibit autophagic flux. Similar effects are observed upon RNAi-mediated knockdown of ATG7 and ATG12, further supporting the idea that autophagy inhibi-tion does not promote apoptosis in KRAS mutant lung cancer cells. Investigations with another FDA-approved antimalar-ial drug, quinacrine, revealed that quinacrine-mediated cell death is TP53-dependent and acts via inhibition of the pen-tose phosphate pathway. These studies highlight interconnec-tions between glucose metabolism and autophagy that could be potentially exploited in tumor cells.

*Correspondence to: Sharon M Gorski; Email: sgorski@bcgsc.ca Submitted: 08/19/2013; Revised: 08/30/2013; Accepted: 09/04/2013 http://dx.doi.org/10.4161/auto.26378

Autophagy

From structure to metabolism to therapeutic regulation

Mario A Jardon,1,2_{Katharina Rothe,}3,4_{Svetlana Bortnik,}1,5_{Lubomir Vezenkov,}6_{Xiaoyan Jiang,}3,4_{Robert n Young,}6

Julian J Lum,7,8_{and Sharon M gorski}1,2,5,_*

1_{genome Sciences Centre; BC Cancer Agency; Vancouver, BC CA;}2_{Department of Molecular Biology and Biochemistry; Simon Fraser University; Burnaby, BC CA;} 3_{terry Fox Laboratory; BC Cancer Agency; Vancouver, BC CA;}4_{Department of Medical genetics; University of British Columbia; Vancouver, BC CA;} 5_{interdisciplinary oncology program; University of British Columbia; Vancouver, BC Canada;}6_{Department of Chemistry; Simon Fraser University; Burnaby, BC CA;}

7_{Deeley Research Centre; BC Cancer Agency; Victoria, BC CA;}8_{Department of Biochemistry and Microbiology; University of Victoria; Victoria, BC CA}

Keywords: macroautophagy, chaperone-mediated autophagy, metabolism, glycolysis, cancer, drug resistance

Multidisciplinary approaches are increasingly being used to elucidate the role of autophagy in health and disease and to harness it for therapeutic purposes. the broad range of topics included in the program of the Vancouver Autophagy Sympo-sium (VAS) 2013 illustrated this multidisciplinarity: structural biology of Atg proteins, mechanisms of selective autophagy, in silico drug design targeting Atg proteins, strategies for drug screening, autophagy-metabolism interplay, and thera-peutic approaches to modulate autophagy. VAS 2013 took place at the British Columbia Cancer Research Centre, and was hosted by the CiHR team in investigating Autophagy pro-teins as Molecular targets for Cancer treatment. the program was designed as a day of research exchanges, featuring two invited keynote speakers, internationally recognized for their groundbreaking contributions in autophagy, Dr Ana Maria Cuervo (Albert einstein College of Medicine, Bronx, nY) and Dr Jayanta Debnath (University of California, San Francisco). By bringing together international and local experts in cell biol-ogy, drug discovery, and clinical translation, the symposium facilitated rich interdisciplinary discussions focused on mul-tiple forms of autophagy and their regulation and modulation in the context of cancer.

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Meeting RepoRt Meeting RepoRt

The Potential of Targeting Autophagy in Cancer

Accumulating evidence suggests that the role of autophagy in tumor progression and chemotherapy resistance is context-dependent (e.g., cancer subtype, stage, grade, treatment used), making it difficult to generalize the approach of autophagy inhibition to all patients. A number of short talks and poster presentations addressed this problem by investigating the role of autophagy in chemo-resistance and the effects of autophagy inhibition in specific cancer models, including triple-negative (TNBC) and ERBB2/HER2-positive breast cancers, prostate cancer (PC), and chronic myeloid leukemia. Katharina Rothe from Dr Jiang’s laboratory reported elevated expression lev-els of some autophagy genes, such as ATG4 family members,

ATG5 and BECN1 in primary CD34+_{chronic myeloid}

leuke-mia cells compared with normal cells from healthy donors, and that this may represent an inherent clinically pertinent feature that influences a patient’s response to therapy and could thus potentially be useful as a potential predictive biomarker to aid in the decision making process of patients’ treatment options in the future. Drs Sherry Weppler and Marcel Bally showed that resistance of ERBB2-overexpressing breast cancer cells to lapa-tinib, a catalytic MTOR inhibitor, can be effectively reversed by treating cells with a combination of lapatinib and an autophagy inhibitor (HCQ), which may be a feasible treatment strategy for relapsed or metastatic ERBB2-positive breast cancer. Drs Svetlana Bortnik and Suganthi Chittaranjan demonstrated that anthracycline-resistant TNBC cells have higher autophagy levels than anthracycline-sensitive cells, and that autophagy inhibition with HCQ sensitizes TNBC tumors to, and enhances efficacy of, chemotherapy in animal models. Drs Fan Zhang and Martin Gleave showed that CLU (clusterin), a stress-activated molecular chaperone protein, confers treatment resistance in PC by regu-lating stress-induced autophagy activation. Anti-CLU treatment attenuates stress-induced autophagy and improves chemotherapy effects in PC; co-targeting CLU and autophagy amplifies proteo-toxic stress to delay castrate-resistant PC progression. All of these studies are consistent with a role for autophagy in chemother-apy-resistance, and support autophagy inhibition as a promising avenue to improve the efficacy of chemotherapy and counteract chemo-resistance.

Autophagy Protein Interactions:

Structure, Function, and a New Class of Inhibitors

Junyan Shi from Dr Honglin Luo’s research group showed that coxsackievirus B3 (CVB3) infection results in lower SQSTM1/p62 protein levels, due to cleavage by the viral pro-tease 2Apro. This impairment of SQSTM1 function decreases autophagy and disables the ability of SQSTM1 to activate the NFKB pathway, contributing to viral pathogenesis. In response to an immune challenge with an OVA-antigen expressing influ-enza virus strain, Dr Katrin Schlie from Dr Julian Lum’s labora-tory showed that autophagy is required for the subsequent host CD8+_{T cell response. Dr Ivan Nabi showed that AMFR/gp78}

(autocrine motility factor receptor, E3 ubiquitin protein ligase)

mediates mitophagy through interaction with MFN1 (mitofusin 1), but not MFN2. Leon Chew from Dr Calvin Yip’s labora-tory presented the structural characterization of the autophagy regulatory complex Atg17-Atg31-Atg29 in S. cerevisiae, by

single-particle electron microscopy, showing that the complex is dimeric. This dimerization is mediated by Atg17, which generates a central scaffold, but requires the presence of Atg31 and Atg29 to adopt the single functional conformation that leads to auto-phagosome formation.

Dr Robert Young’s group has concentrated its efforts on inhi-bition of the ATG4B enzyme for selectively blocking the auto-phagy process. ATG4B is a key proteolytic enzyme involved in the processing of pro-LC3 to LC3-I and the subsequent release of LC3-II from autophagosomes. Dr Lubomir Vezenkov presented the development of high-throughput screening for ATG4B enzy-matic activity based on a small latent fluorophore substrate of the enzyme. This methodology is being used to screen a 200,000-com-pound synthetic library in collaboration with the Centre for Drug Research and Development, and has led to the identification of compounds with inhibitory potencies in the low micromolar range which are currently being tested in vitro and optimized for in vivo studies. In a related study, Adrienne Kyle from Dr Sharon Gorski’s research group presented the characterization of a lead ATG4B inhibitor compound that was discovered via an in silico screening approach by Drs Jianghong An and Steven Jones. Four potential small-molecule binding sites on ATG4B were identified using the PocketFinder program, and a computational screen was performed against the NCI and Chembridge small molecule databases. This screening identified a compound able to inhibit ATG4B activity in a cell-free system and that inhibited autophagy flux in three breast cancer cell lines. Consistent with previous results in the group with RNAi-mediated knockdown of ATG4B, preliminary data suggest that the compound also leads to decreased growth of breast cancer cells.

Conclusions

Autophagy, whether macro-, micro-, or chaperone-medi-ated, is increasingly recognized as a mediator of numerous cell functions. While most studies to date have focused on macro-autophagy, it is clear that we also need to consider the contribu-tions of CMA, and likely microautophagy, to health and disease. The relationship between autophagy and metabolic pathways warrants further investigation, particularly the link between auto-phagy regulation and altered metabolism in cancer. Likewise, the metabolic consequences of modulating autophagy should also be better understood to design more efficient therapeutic strate-gies. A greater understanding in this area may provide insights into treatment resistance and/or reveal vulnerabilities that may be exploited for treating cancers. As exemplified in VAS 2013, insights derived from structural biology, genomics, metabolo-mics, and drug development are contributing novel resources to understand and control autophagy. And, in this regard, several new strategies for targeting autophagy in cancer are forthcom-ing, promising to expand the potential for clinical translation of autophagy modulation.

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2182 Autophagy Volume 9 issue 12

Disclosure of Potential Conflicts of Interest

No potential conflicts of interest were disclosed.

Acknowledgments

The authors wish to thank all the members of the CIHR Team in Investigating Autophagy Proteins as Molecular Targets for Cancer Treatment for valuable input and discussions. In par-ticular, we thank Dr Stephanie McInnis for her efforts in coordi-nating many aspects of the symposium. We also acknowledge our

funding sources: the CIHR Team in Investigating Autophagy (GPG-102167), Simon Fraser University through support from the Vice-President Academic Conference Fund, the BC Cancer Foundation and the Centre for Drug Research and Development (CDRD). This meeting was also made possible through financial support by Merck (Merck Better Care, Healthy Communities Funding Program). We express our appreciation for all the speakers and poster presenters who participated in this exciting symposium.