Exosome-mediated transfer of lncRNA PART1 induces gefitinib resistance in esophageal squamous cell carcinoma via functioning as a competing endogenous RNA.

BACKGROUND: Currently, resistance to tyrosine kinase inhibitors, such as gefitinib, has become a major obstacle in improving the clinical outcome of patients with metastatic and advanced-stage esophageal squamous cell carcinoma (ESCC). While cell behavior can be modulated by long non-coding RNAs (lncRNAs), the roles of lncRNAs within extracellular vesicles (exosomes) are largely unknown. Therefore, we investigated the involvement and regulatory functions of potential lncRNAs enclosed in exosomes during formation of chemoresistance in human ESCC.

METHODS: Gefitinib-resistant cell lines were established by continuously grafting TE1 and KYSE-450 cells into gefitinib-containing culture medium. LncRNA microarray assay followed by RT-qPCR were used to verify the differential expression of lncRNA Prostate Androgen-Regulated Transcript 1 (PART1) between gefitinib resistant and parental cell lines. RNA fluorescence in situ hybridization (FISH) was used to investigate whether extracellular PART1 could be incorporated into exosomes and transmitted to recipient cells. Subsequently, a series of in vitro assays and a xenograft tumor model were used to observe the functions of lncRNA PART1 in ESCC cells. A signal transduction reporter array, bioinformatics analysis, western blotting, and immunofluorescence were carried out to verify the regulation of PART1 and its downstream Bcl-2 signaling pathway.

RESULTS: lncRNA PART1 was upregulated in gefitinib-resistant cells when compared to parental ESCC cells. It was found that STAT1 can bind to the promoter region of lncRNA PART1, resulting in its activation. Knockdown of lncRNA PART1 potently promoted the gefitinib-induced cell death, while elevated PART1 promoted gefitinib resistance by competitively binding to miR-129 to facilitate Bcl-2 expression in ESCC cells. In addition, extracellular PART1 could be incorporated into exosomes and transmitted to sensitive cells, thus disseminating gefitinib resistance. Clinically, high levels of serum lncRNA PART1 in exosome were associated with poor response to gefitinib treatment in ESCC patients.

CONCLUSIONS: LncRNA PART1 promotes gefitinib resistance by regulating miR-129/Bcl-2 pathway, and may serve as a therapeutic target for ESCC patients.