Expression of Beclin Family Proteins Is Associated with Tumor Progression in Oral Cancer.
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.
Department of Pathology, Chang Gung Memorial Hospital Chiayi Branch, Chiayi, Taiwan; Graduate Institute of Clinical Medical Sciences, College of Medicine, Chang Gung University, Taoyuan, Taiwan.
Jing-Lan
JL
Liu
Department of Pathology, Chang Gung Memorial Hospital Chiayi Branch, Chiayi, Taiwan.
Fen-Fen
FF
Chen
Department of Medical Research and Development, Chang Gung Memorial Hospital Chiayi Branch, Chiayi, Taiwan.
Shun-Fu
SF
Chang
Department of Biochemical Science and Technology, National Chiayi University, Chiayi, Taiwan.
Cheng-Nan
CN
Chen
Division of Pulmonary and Critical Care Medicine, Department of Medicine, Chang Gung Memorial Hospital Chiayi Branch, Chiayi, Taiwan.
Jrhau
J
Lung
Department of Oral and Maxillofacial Surgery, St. Martin De Porres Hospital, Chiayi, Taiwan.
Cheng-Hsing
CH
Lo
Department of Oral and Maxillofacial Surgery, St. Martin De Porres Hospital, Chiayi, Taiwan.
Fang-Hui
FH
Lee
Department of Otolaryngology, St. Martin De Porres Hospital, Chiayi, Taiwan.
Ying-Chou
YC
Lu
Graduate Institute of Clinical Medical Sciences, College of Medicine, Chang Gung University, Taoyuan, Taiwan.
Chien-Hui
CH
Hung
D000368:Aged; D000369:Aged, 80 and over; D051017:Apoptosis Regulatory Proteins / Q000096:biosynthesis* / Q000235:genetics; D001343:Autophagy / Q000235:genetics*; D000071186:Beclin-1; D045744:Cell Line, Tumor; D018450:Disease Progression; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000096:biosynthesis* / Q000235:genetics; D053208:Kaplan-Meier Estimate; D008297:Male; D008565:Membrane Proteins / Q000096:biosynthesis* / Q000235:genetics; D008875:Middle Aged; D009062:Mouth Neoplasms / Q000235:genetics* / Q000473:pathology; D011379:Prognosis
D051017:Apoptosis Regulatory Proteins; C491997:BECN1 protein, human; C584110:BECN2 protein, human; D000071186:Beclin-1; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins