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J Ovarian Res. 2015 Aug 4;8:52. doi: 10.1186/s13048-015-0182-y.

Beclin-1 expression is retained in high-grade serous ovarian cancer yet is not essential for autophagy induction in vitro.

Correa RJ1,2, Valdes YR3, Shepherd TG4,5,6,7, DiMattia GE8,9,10,11,12.

Author information

1
Translational Ovarian Cancer Research Program, London Regional Cancer Program, London, Ontario, Canada. rcorrea2016@meds.uwo.ca.
2
Department of Biochemistry, Schulich School of Medicine & Dentistry, The University of Western Ontario, London, Ontario, Canada. rcorrea2016@meds.uwo.ca.
3
Translational Ovarian Cancer Research Program, London Regional Cancer Program, London, Ontario, Canada. yudithramos@yahoo.es.
4
Translational Ovarian Cancer Research Program, London Regional Cancer Program, London, Ontario, Canada. tshephe6@uwo.ca.
5
Department of Obstetrics & Gynaecology, Schulich School of Medicine & Dentistry, The University of Western Ontario, London, Ontario, Canada. tshephe6@uwo.ca.
6
Department of Oncology, Schulich School of Medicine & Dentistry, The University of Western Ontario, London, Ontario, Canada. tshephe6@uwo.ca.
7
Department of Anatomy & Cell Biology, Schulich School of Medicine & Dentistry, The University of Western Ontario, London, Ontario, Canada. tshephe6@uwo.ca.
8
Translational Ovarian Cancer Research Program, London Regional Cancer Program, London, Ontario, Canada. dimattia@uwo.ca.
9
Department of Biochemistry, Schulich School of Medicine & Dentistry, The University of Western Ontario, London, Ontario, Canada. dimattia@uwo.ca.
10
Department of Obstetrics & Gynaecology, Schulich School of Medicine & Dentistry, The University of Western Ontario, London, Ontario, Canada. dimattia@uwo.ca.
11
Department of Oncology, Schulich School of Medicine & Dentistry, The University of Western Ontario, London, Ontario, Canada. dimattia@uwo.ca.
12
London Regional Cancer Program, 790 Commissioners Road East, Room A4-919A, London, Ontario, Canada, N6A 4 L6. dimattia@uwo.ca.

Abstract

BACKGROUND:

Autophagy is a conserved cellular self-digestion mechanism that can either suppress or promote cancer in a context-dependent manner. In ovarian cancer, prevalent mono-allelic deletion of BECN1 (a canonical autophagy-inducer) suggests that autophagy is impaired to promote carcinogenesis and that Beclin-1 is a haploinsufficient tumor suppressor. Nonetheless, autophagy is known to be readily inducible in ovarian cancer cells. We sought to clarify whether Beclin-1 expression is in fact disrupted in ovarian cancer and whether this impacts autophagy regulation.

METHODS:

BECN1 expression levels were assessed using The Cancer Genome Atlas (TCGA) datasets from 398 ovarian high-grade serous cystadenocarcinomas (HGSC) and protein immunoblot data from HGSC samples obtained at our institution. Knockdown of BECN1 and other autophagy-related gene expression was achieved using siRNA in established human ovarian cancer cell lines (CaOV3, OVCAR8, SKOV3, and HeyA8) and a novel early-passage, ascites-derived cell line (iOvCa147-E2). LC3 immunoblot, autophagic flux assays, transmission electron microscopy and fluorescence microscopy were used to assess autophagy.

RESULTS:

We observed prevalent mono-allelic BECN1 gene deletion (76%) in TCGA tumors, yet demonstrate for the first time that Beclin-1 protein expression remains relatively unaltered in these and additional samples generated at our institution. Surprisingly, efficient siRNA-mediated Beclin-1 knockdown did not attenuate autophagy induction, whereas knockdown of other autophagy-related genes blocked the process. Beclin-1 knockdown instead decreased cell viability without inducing apoptosis.

CONCLUSIONS:

Taken together, these data demonstrate that despite its sustained expression, Beclin-1 is dispensable for autophagy induction in ovarian tumor cells in vitro, yet may be retained to promote cell viability by a mechanism independent of autophagy or apoptosis regulation. Overall, this work makes novel observations about tumor expression of Beclin-1 and challenges the accepted understanding of its role in regulating autophagy in ovarian cancer.

PMID:
26239434
PMCID:
PMC4524172
DOI:
10.1186/s13048-015-0182-y
[Indexed for MEDLINE]
Free PMC Article

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