Re-expression of DIRAS3 and P53 induces apoptosis and impaired autophagy in head and neck squamous cell carcinoma

Background:p53 and DIRAS3 are tumor suppressors that are frequently silenced in tumors.In this study,we sought to determine whether the concurrent re-expression of p53 and DIRAS3 could effectively induce head and neck squamous cell carcinoma(HNSCC)cell death.Methods:CAL-27 and SCC-25 cells were treated with Ad-DIRAS3 and rAd-p53 to induce re-expression of DIRAS3 and p53 respectively.The effects of DIRAS3 and p53 re-expression on the growth and apoptosis of HNSCC cells were examined by TUNEL assay,flow cytometric analysis and MTT.The effects of DIRAS3 and p53 re-expression on Akt phosphorylation,oncogene expression,and the interaction of 4 E-BP1 with eIF4 E were determined by real-time PCR,Western blotting and immunoprecipitation analysis.The ability of DIRAS3 and p53 re-expression to induce autophagy was evaluated by transmission electron microscopy,LC3 fluorescence microscopy and Western blotting.The effects of DIRAS3 and p53 re-expression on HNSCC growth were evaluated by using an orthotopic xenograft mouse model.Results:TUNEL assay and flow cytometric analysis showed that the concurrent re-expression of DIRAS3 and p53 significantly induced apoptosis(P<0.001).MTT and flow cytometric analysis revealed that DIRAS3 and p53 reexpression significantly inhibited proliferation and induced cell cycle arrest(P<0.001).Mechanistically,the concurrent re-expression of DIRAS3 and p53 down-regulated signal transducer and activation of transcription 3(STAT3)and upregulated p21WAF1/CIP1 and Bax(P<0.001).DIRAS3 and p53 re-expression also inhibited Akt phosphorylation,increased the interaction of eIF4 E with 4 E-BP1,and reduced the expression of c-Myc,cyclin D1,vascular endothelial growth factor(VEGF),fibroblast growth factor(FGF),epidermal growth factor receptor(EGFR)and Bcl-2(P<0.001).Moreover,the concurrent re-expression of DIRAS3 and p53 increased the percentage of cells with GFP-LC3 puncta compared with that in cells treated with control adenovirus(50.00%±4.55%vs.4.67%±1.25%,P<0.001).LC3 fluorescence microscopy and Western blotting further showed that DIRAS3 and p53 re-expression significantly promoted autophagic activity but also inhibited autophagic flux,resulting in overall impaired autophagy.Finally,the concurrent re-expression of DIRAS3 and p53 significantly decreased the tumor volume compared with the control group in a HNSCC xenograft mouse model[(3.12±0.75)mm^(3) vs.(189.02±17.54)mm^(3),P<0.001].Conclusions:The concurrent re-expression of DIRAS3 and p53 is a more effective approach to HNSCC treatment than current treatment strategies.