Hypoxia-induced autophagy contributes to radioresistance via c-Jun-mediated Beclin1 expression in lung cancer cells.

Abstract

Reduced radiosensitivity of lung cancer cells represents a pivotal obstacle in clinical oncology. The hypoxia-inducible factor (HIF)-1α plays a crucial role in radiosensitivity, but the detailed mechanisms remain elusive. A relationship has been suggested to exist between hypoxia and autophagy recently. In the current study, we studied the effect of hypoxia-induced autophagy on radioresistance in lung cancer cell lines. A549 and H1299 cells were cultured under normoxia or hypoxia, followed by irradiation at dosage ranging from 0 to 8 Gy. Clonogenic assay was performed to calculate surviving fraction. EGFP-LC3 plasmid was stably transfected into cells to monitor autophagic processes. Western blotting was used to evaluate the protein expression levels of HIF-1α, c-Jun, phosphorylated c-Jun, Beclin 1, LC3 and p62. The mRNA levels of Beclin 1 were detected by qRT-PCR. We found that under hypoxia, both A549 and H1299 cells were radio-resistant compared with normoxia. Hypoxia-induced elevated HIF-1α protein expression preferentially triggered autophagy, accompanied by LC3 induction, EGFP-LC3 puncta and p62 degradation. In the meantime, HIF-1α increased downstream c-Jun phosphorylation, which in turn upregulated Beclin 1 mRNA and protein expression. The upregulation of Beclin 1 expression, instead of HIF-1α, could be blocked by SP600125 (a specific inhibitor of c-Jun NH2-terminal kinase), followed by suppression of autophagy. Under hypoxia, combined treatment of irradiation and chloroquine (a potent autophagy inhibitor) significantly decreased the survival potential of lung cancer cells in vitro and in vivo. In conclusion, hypoxia-induced autophagy through evaluating Beclin1 expression may be considered as a target to reverse the radioresistance in cancer cells.

• Authors: Yan-Mei Zou, Guang-Yuan Hu, Xue-Qi Zhao, Tao Lu, Feng Zhu, Shi-Ying Yu, Hua Xiong
• Journal: Journal of Huazhong University of Science and Technology. Medical sciences = Hua zhong ke ji da xue xue bao. Yi xue Ying De wen ban = Huazhong keji daxue xuebao. Yixue Yingdewen ban (J Huazhong Univ Sci Technolog Med Sci) Vol. 34 Issue 5 Pg. 761-767 (Oct 2014) ISSN: 1672-0733 [Print] China
• PMID: 25318890 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Apoptosis Regulatory Proteins
• BECN1 protein, human
• Beclin-1
• HIF1A protein, human
• Hypoxia-Inducible Factor 1, alpha Subunit
• MAP1LC3A protein, human
• Membrane Proteins
• Microtubule-Associated Proteins
• Proto-Oncogene Proteins c-jun
• Green Fluorescent Proteins

Topics

• Animals
• Apoptosis Regulatory Proteins (genetics, metabolism)
• Autophagy
• Beclin-1
• Cell Hypoxia
• Cell Line, Tumor
• Cell Survival (genetics, radiation effects)
• Gene Expression Regulation, Neoplastic (radiation effects)
• Green Fluorescent Proteins (genetics, metabolism)
• Humans
• Hypoxia-Inducible Factor 1, alpha Subunit (metabolism)
• Immunoblotting
• Lung Neoplasms (genetics, metabolism, pathology)
• Membrane Proteins (genetics, metabolism)
• Mice, Nude
• Microscopy, Fluorescence
• Microtubule-Associated Proteins (genetics, metabolism)
• Phosphorylation
• Proto-Oncogene Proteins c-jun (metabolism)
• Radiation Tolerance (genetics)
• Reverse Transcriptase Polymerase Chain Reaction
• Transplantation, Heterologous
• Tumor Burden (genetics)