Effects of long noncoding RNA (linc-VLDLR) existing in extracellular vesicles on the occurrence and multidrug resistance of esophageal cancer cells.

OBJECTIVE: To investigate the relationship between the expression of linc-VLDLR in extracellular vesicles (EVs) and esophageal carcinomas development and drug resistance.

METHODS: The expression of linc-VLDLR and ABCG2 mRNA in 60 cases of esophageal carcinoma tissue, para-carcinoma tissue and the normal esophagus tissue were detected using Fluorescence quantitative reverse transcription polymerase chain reaction (qRT-PCR). Fifty percent inhibiting concentration (IC50) of adriamycin (ADM) to Eca109 cells was detected by MTT assay, after the treatment of different concentrations of adriamycin (ADM) on esophageal squamous cell carcinoma Eca109 cell line for 24 h. EVs were extracted from culture medium after the treatment of three concentrations of ADM (setting based on the IC50) on Eca109 cells for 24 h. Linc-VLDLR expression in EVs was detected by qRT-PCR. After the treatment of the extracted EVs on virgin Eca109 cells for 48 h, then intervening these cells for 24 h by different concentrations of ADM, the new values of IC50 were detected by MTT assay. Cell cycle, cell apoptosis and ABCG2 protein expression of these Eca109 cells were detected by flow cytometry (FCM). Linc-VLDLR and ABCG2 mRNA expression in these Eca109 cells were detected by qRT-PCR.

RESULTS: Expression of linc-VLDLR and ABCG2 mRNA in esophageal squamous cell carcinoma tissue were significantly higher than that in esophageal atypical hyperplasia and normal esophagus tissue, P < 0.01. After the treatment of ADM on Eca109 cells for 24 h, IC50 of Eca109 cells was detected as (0.44 ± 0.02) μg/mL, thus ADM concentrations of 0, 0.2, 0.4 and 0.8 μg/mL were selected to accomplish the following parts of this study. After four groups of Eca109 cells were treated by ADM in different concentrations separately, extracted EVs from the supernatant of all four groups, then labeling these four groups as EVs1, 2, 3 and 4. Linc-VLDLR expression in EVs4 was significantly higher than that in EVs1-3, P < 0.01. After the treatment of EVs1-4 on virgin Eca109 cells for 48 h, new values of IC50 of Eca109 to ADM were detected by MTT. It was found that the IC50 value of group EVs4 was significantly higher than that of other groups, P < 0.05. Flow cytometry results showed that the proliferation index of Eca109 cells in EVs4 was significantly higher than that in EVs1-3 and control groups, P < 0.01. Whereas, there was an obviously downward trend in the apoptosis rate of EVs4, compared to other three groups, P < 0.01. Linc-VLDLR and ABCG2 mRNA and protein expression level in Eca109 cells of EVs4 group were significantly higher than that of EVs1-3 and control groups, P < 0.05.

CONCLUSIONS: High expression of Linc-VLDLR and ABCG2 gene in esophageal cancer cells affected the formation of esophageal cancer drug resistance. EVs released by drug-resistant cells were proved that they could upregulate the expression of ABCG2 in esophageal cancer cells and thus regulate the drug resistance of esophageal cancer cells, which was related to the linc-VLDLR carried by EVs.