Abstract
BACKGROUND: Melanoma differentiation-associated gene 7 (Mda-7) encodes IL-24, which can induce apoptosis in cancer cells. A novel gene therapy approach to treat deadly brain tumors, recombinant mda-7 adenovirus (Ad/mda-7) efficiently kills glioma cells. In this study, we investigated the factors affecting cell survival and apoptosis and autophagy mechanisms that destroy glioma cells by Ad/IL-24. METHODS: Human glioblastoma U87 cell line was exposed to a multiplicity of infections of Ad/IL-24. Antitumor activities of Ad/IL-24 were assessed by cell proliferation (MTT) and lactate dehydrogenase (LDH) release analysis. Using flow cytometry, cell cycle arrest and apoptosis were investigated. Using the ELISA method, the tumor necrosis factor (TNF-α) level was determined as an apoptosis-promoting factor and Survivin level as an anti-apoptotic factor. The expression levels of TNF-related apoptosis inducing ligand(TRAIL) and P38 MAPK genes were assessed by the Reverse transcription-quantitative polymerase chain reaction(RT‑qPCR) method. The expression levels of caspase-3 and protein light chain 3-II (LC3-II) proteins were analyzed by flow cytometry as intervening factors in the processes of apoptosis and autophagy in the cell death signaling pathway, respectively. RESULTS: The present findings demonstrated that transduction of IL-24 inhibited cell proliferation and induced cell cycle arrest and cell apoptosis in glioblastoma. Compared with cells of the control groups, Ad/IL24-infected U87 cells exhibited significantly increased elevated caspase-3, and TNF-α levels, while the survivin expression was decreased. TRAIL was shown to be upregulated in tumor cells after Ad/IL-24 infection and studies of the apoptotic cascade regulators indicate that Ad/IL-24 could further enhance the activation of apoptosis through the TNF family of death receptors. In the current study, we demonstrate that P38 MAPK is significantly activated by IL-24 expression. In addition, the overexpression of mda-7/IL-24 in GBM cells induced autophagy, which was triggered by the upregulation of LC3-II. CONCLUSIONS: Our study demonstrates the antitumor effect of IL-24 on glioblastoma and may be a promising therapeutic approach for GBM cancer gene therapy.