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Background: Small cell lung cancer (SCLC), the most malignant of all the lung cancer subtypes, is characterized by drug resistance. This study sought to explore the key genes and pathways associated with the chemoresistance of SCLC. Methods: The drug sensitivity of chemosensitive and chemoresistance SCLC cell lines was measured by Cell Counting Kit-8 assays. The total RNA from chemosensitive cell line H69 and chemoresistance cell line H69AR cells was extracted and subjected to messenger RNA (mRNA) and long non-coding RNA (lncRNA) microarray analyses. The differentially expressed genes (DEGs) and the differentially expressed lncRNAs (DELs) were screened out with a threshold of a |log fold change | ≥1 and an adjusted P value <0.05. A protein-protein interaction network was constructed, and hub genes were screened out. A lncRNA-mRNA co-expression network was also constructed. Gene Ontology and Kyoto Encyclopedia of Genes, Genomes enrichment analyses and Cis-regulatory element analyses were conducted on the DEGs and the top 10 upregulated DEL-co-expressed DEGs. The expression of the key genes was further analyzed in the GSE149507 data set and validated in H69/H69AR and H446/H446DDP cells by quantitative polymerase chain reaction assays. Results: The microarray results showed that a total of 609 mRNAs and 394 lncRNAs were differentially expressed in the chemoresistant SCLC cells. The mammalian target of rapamycin (mTOR) signaling pathway was enriched among the DEGs, the top 10 upregulated DEL-co-expressed DEGs, and the NCRNA00173-co-expressed DEGs, which included IGF1, INS, WNT6, WNT11, WNT2B, and SESN2. IGF1, WNT2B, and SESN2 were downregulated, and WNT11 was upregulated in the SCLC tumor tissues in the GSE149507 data set. Further, IGF1, WNT6, WNT11, and WNT2B were lowlier expressed and SESN2 and NCRNA00173 were more highly expressed in the chemoresistant cells than sensitive cells. Conclusions: The top 10 upregulated DELs containing NCRNA00173 may be involved in the regulation of drug resistance in SCLC. These DELs may regulate the genes related to the mTOR signaling pathway. These genes may also be biomarkers and potential targets for the treatment of SCLC.
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Targeted therapy involving the activation of death receptors DR4 and/or DR5 by its ligand, TRAIL, can selectively induce apoptosis in certain tumor cells. In order to profile the dynamic activation or trimerization of TRAIL-DR4 in live cells in real-time, the development of an apoptosis reporter cell line is essential. Fluorescence resonance energy transfer (FRET) technology via a FRET pair, cyan fluorescence protein (CFP) and yellow fluorescence protein (YFP), was used in this study. DR4-CFP and DR4-YFP were stably expressed in human lung cancer PC9 cells. Flow cytometer sorting and limited dilution coupled with fluorescence microscopy were used to select a monoclonal reporter cell line with high and compatible expression levels of DR4-CFP and DR4-YFP. FRET experiments were conducted and FRET efficiencies were monitored according to the Siegel's YFP photobleaching FRET protocol. Upon TRAIL induction a significant increase in FRET efficiencies from 5% to 9% demonstrated the ability of the DR4-CFP/YFP reporter cell line in monitoring the dynamic activation of TRAIL pathways. 3D reconstructed confocal images of DR4-CFP/YFP reporter cells exhibited a colocalized expression of DR4-CFP and DR4-YFP mainly on cell membranes. FRET results obtained during this study complements the use of epi-fluorescence microscopy for FRET analysis. The real-time FRET analysis allows the dynamic profiling of the activation of TRAIL pathways by using the time-lapse fluorescence microscopy. Therefore, DR4-CFP/YFP PC9 reporter cells along with FRET technology can be used as a tool for anti-cancer drug screening to identify compounds that are capable of activating TRAIL pathways.