The Experimental Study Of MDIG Promoting Cisplatin Resistance Of Lung Adenocarcinoma By Regulating ABC Transporter Expression

Object: Cisplatin(DDP)is one of the most commonly used chemotherapeutic drugs for clinical NSCLC,although it is only 20~30% effective for patients with advanced non-surgical NSCLC.One of the reasons underlying this is the emergence of multidrug resistance(MDR).The mechanism of MDR formation in tumor cells is complex,the most important mechanism of drug resistance is the high expression of the ATP-binding cassette(ABC)transporter in the efflux pump on the tumor cell membrane,particularly high expression of P-glycoprotein(P-gp;ABCB1 gene-encoding),MDR-associated protein 1(MRP1;ABCC1 gene-encoding),and breast cancer resistance protein(BCRP;ABCG2 gene-encoding).Previous studies have revealed that the WNT/β-catenin pathway is an important signal transduction pathway regulating tumor cell DDP resistance.Following activation of the WNT signaling pathway,non-phosphorylated(activated)β-catenin is induced to enter the nucleus,promoting the expression of the downstream signaling molecules,ABCB1,ABCC1 and ABCG2,thereby promoting the occurrence of DDP resistance in tumor cells.Mineral dust-induced gene(MDIG)is a proto-oncogene associated with lung cancer that serves a key role in the biological processes of tumorigenesis.At present,the association between MDIG and DDP resistance in lung adenocarcinoma has yet to be fully elucidated.The aim of the present study was to investigate whether MDIG is involved in DDP resistance in lung adenocarcinoma,and the associated molecular mechanism.Methods: In this study,MDIG-silencing and MDIG-overexpressing A549 cells,and DDP-resistant A549/DDP cells,were initially constructed using lentiviral Vector,and reverse transcription-quantitative polymerase chain reaction(RT-qPCR)and western blotting experiments,respectively,were used to verify the silencing and overexpression effects of MDIG mRNA and protein.On this basis,RT-qPCR and western blotting experiments were used to detect the basic expression of MDIG in A549 and A549/DDP cells,and the effect of DDP on MDIG expression.The cell counting kit-8 cytotoxicity assay was used to examine the effects of the cytotoxicity of DDP on each group of cells.Subsequently,RT-qPCR and western blot experiments were used to detect the mRNA and protein expression levels of the efflux pump ATP-binding cassette(ABC)transporters(ABCB1,ABCC1,ABCG2).Results: The expression of a large number of green fluorescent proteins in A549 and A549/DDP cells was observed when MDIG silencing and overexpression constructed,sometimes RT-qPCR and Western blot analysis showed that the expression of MDIG mRNA and protein in MDIG-silenced group was lower than those in the control group,the expression of MDIG mRNA and protein in the overexpression group was higher than those in the control group.The results obtained revealed that the expression levels of MDIG mRNA and protein in A549/DDP cells were significantly higher compared with those in A549 cells,and that the protein expression level of MDIG increased in a dose-dependent manner with an increase in the DDP concentration;the IC50 value(value giving rise to half-maximal inhibition)of A549/DDP cells was significantly higher compared with that of A549 cells.The overexpression of MDIG in A549 and A549/DDP cells led to an increase in the IC50 value,whereas silencing of MDIG in the A549 and the A549/DDP cells,respectively,led to a clear reduction in the IC50 value.The basal expression levels of ABCB1,ABCC1 and ABCG2 mRNA and protein in A549/DDP cells were significantly higher compared with those in A549 cells,and the overexpression of MDIG in the A549 and A549/DDP cells markedly upregulated the mRNA and protein expression levels of the efflux pump transporters,ABCB1,ABCC1 and ABCG2,which were markedly decreased following MDIG silencing.Conclusion: These results demonstrated that the DDP resistance of lung adenocarcinoma may be associated with an upregulation of MDIG expression,and that the expression level of MDIG is positively correlated with the degree of DDP resistance.Furthermore,MDIG promotes the expression of ABC transporters in the extracellular drainage pump of tumor cells,which,in turn,leads to DDP resistance in lung adenocarcinoma.