| 【Background】The development of multidrug resistance(MDR) in gastric cancer cells is not only themost primary reason for failed chemotherapy, but also an important cause for relapse andmetastasis of gastric cancer(GC). Therefore, it s a vital direction in cancer research toclarify the underlying mechanism of MDR in GC and to search for the drug targets forreversing MDR. MicroRNA(miRNA), a recently discovered class of intrinsic noncodingsmall RNA, could regulate kinds of biological processes via binding to its complementarysequences within the3-untranslated region(3-UTR) of target mRNA, leading to eitherdegradation of target mRNA or inhibition of the protein translation process. Recently, ithas been showed that miRNAs are widely involved in lots of pathophysiological processesin eukaryotes, such as cancer cell proliferation, metastasis, MDR and so on. Let-7f, amember of miRNA let-7family, is usually downregulated in the tumor and known astumor suppressor. Our previous study has already demonstrated that upregulation of let-7fcould suppress GC cell invasion and migration by directly inhibiting metastasis-relatedgene MYH9. A good number of studies show that there is a close relationship betweentumor metastasis and MDR. To our knowledge, it has been not reported about study of let-7f in modulating MDR of gastric cancer before. Therefore, we predict that let-7f mightplay important role in regulating MDR of gastric cancer and this will be discussed nextstep.【Aims】To investigate the regulatory role and the underlying molecular mechanism of let-7f inMDR of gastric cancer.【Methods】1. Quantitative real-time PCR (qRT-PCR) was performed to detect the differentialexpression levels of let-7f between drug-resistant SGC7901/ADR and its parentalcells SGC7901.2. let-7f mimic was transfected into SGC7901/ADR cells to up-regulate its expressionlevel by cell transfection.3. Drug sensitivity to anticancer drugs was tested in SGC7901, SGC7901/ADR and theSGC7901/ADR cells transfected with let-7f mimic by MTT assay.4. Releasing index was detected in the SGC7901/ADR cells transfected with let-7fmimic by ADR accumulation and retention test.5. Cell apoptosis was analyzed in the SGC7901/ADR cells transfected with let-7f mimicby flow cytometry.6. The protein expression levels of P-gp, Bcl-2and Caspase-3were assayed by Westernblot.【Results】1. qRT-PCR analysis demonstrated that the relative expression level of let-7f indrug-resistant SGC7901/ADR was significantly lower than that in its parental cellsSGC7901(p<0.05).2. The expression level of let-7f in the SGC7901/ADR cells transfected with let-7fmimic was significantly upregulated (p<0.05).3. The half inhibition concentration (IC50) of ADR to SGC7901and SGC7901/ADRcells were (0.95±0.08) g/L and (5.40±0.28) g/L, respectively, in MTT assay.Overexpression of let-7f sensitized drug-resistant SGC7901/ADR to ADR and5-FU. 4. In ADR accumulation and retention test, releasing index in the SGC7901/ADR cellstransfected with let-7f mimic was significantly decreased (p<0.05).5. The rate of apoptosis in the SGC7901/ADR transfected with let-7f mimic wassignificantly increased (p<0.05) using the flow cytometry.6. In the SGC7901/ADR transfected with let-7f mimic, protein levels of P-gp andcleaved Caspase-3were significantly decreased (p<0.05) and no visible differencewas observed in Bcl-2protein level, compared with those in let-7f negative control(NC)-transfected cells.【Conclusions】The expression level of let-7f in drug-resistant SGC7901/ADR and its parental cellsSGC7901was significantly different. It is certified that upregulation of let-7f can enhancethe sensitivity of drug-resistant SGC7901/ADR to anticancer drugs. Let-7f might regulateMDR of gastric cancer through decreasing drug efflux to anticancer drugs and inducingapoptosis, thereby enhancing sensitivity of drug-resistant cells to anticancer drugs andreversing MDR of gastric cancer. In summary, let-7f plays a regulatory role in MDR ofgastric cancer, and this will lay the theoretical foundations for finding novel therapeutictargets of tumors. |
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