Expression of Beclin Family Proteins Is Associated with Tumor Progression in Oral Cancer

PLoS One. 2015 Oct 27;10(10):e0141308. doi: 10.1371/journal.pone.0141308. eCollection 2015.

Abstract

Background: Beclin 1 and Beclin 2 are autophagy-related proteins that show similar amino acid sequences and domain structures. Beclin 1 established the first connection between autophagy and cancer. However, the role of Beclin 2 in cancer is unclear. The aims of this study were to analyze Beclin 1 and Beclin 2 expressions in oral cancer tissues and in cell lines, and to evaluate their possible roles in cancer progression.

Methods: We investigated Beclin 1 and Beclin 2 expressions by immunohistochemistry in 195 cases of oral cancer. The prognostic roles of Beclin 1 and Beclin 2 were analyzed statistically. In vitro, overexpression and knockdown of Beclin proteins were performed on an oral cancer cell line, SAS. The immunofluorescence and autophagy flux assays confirmed that Beclin proteins were involved in autophagy. The impacts of Beclin 1 and Beclin 2 on autophagy and tumor growth were evaluated by conversion of LC3-I to LC3-II and by clonogenic assays, respectively.

Results: Oral cancer tissues exhibited aberrant expressions of Beclin 1 and Beclin 2. The cytoplasmic Beclin 1 and Beclin 2 expressions were unrelated in oral cancer tissues. In survival analyses, high cytoplasmic Beclin 1 expression was associated with low disease specific survival, and negative nuclear Beclin 1 expression was associated with high recurrent free survival. Patients with either high or low cytoplasmic Beclin 2 expression had significantly lower overall survival and disease specific survival rates than those with moderate expression. In oral cancer cells, overexpression of either Beclin 1 or Beclin 2 led to autophagy activation and increased clonogenic survival; knockdown of Beclin 2 impaired autophagy and increased clonogenic survival.

Conclusions: Our results indicated that distinct patterns of Beclin 1 and Beclin 2 were associated with aggressive clinical outcomes. Beclin 1 overexpression, as well as Beclin 2 overexpression and depletion, contributed to tumor growth. These findings suggest Beclin proteins are associated with tumorigenesis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Aged, 80 and over
  • Apoptosis Regulatory Proteins / biosynthesis*
  • Apoptosis Regulatory Proteins / genetics
  • Autophagy / genetics*
  • Beclin-1
  • Cell Line, Tumor
  • Disease Progression
  • Female
  • Gene Expression Regulation, Neoplastic
  • Humans
  • Intracellular Signaling Peptides and Proteins / biosynthesis*
  • Intracellular Signaling Peptides and Proteins / genetics
  • Kaplan-Meier Estimate
  • Male
  • Membrane Proteins / biosynthesis*
  • Membrane Proteins / genetics
  • Middle Aged
  • Mouth Neoplasms / genetics*
  • Mouth Neoplasms / pathology
  • Prognosis

Substances

  • Apoptosis Regulatory Proteins
  • BECN1 protein, human
  • BECN2 protein, human
  • Beclin-1
  • Intracellular Signaling Peptides and Proteins
  • Membrane Proteins

Grant support

This work was supported by grants from the Ministry of Science and Technology of Taiwan (MOST 103-2320-B-182A-018-, NMRPG6D0071) (MOST 104-2320-B-182A-012-, NMRPG6E0041), Chang Gung Memorial Hospital Chiayi Branch (CMRPG6E0071), and Chang Gung Medical Research Center (CMRPD6C0013). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.