Recently, targeting cancer stem cells (CSCs) metabolism is becoming a promising therapeutic approach to improve cancer treatment outcomes. However, knowledge of the metabolic state of CSCs in small cell lung cancer is still lacking. In this study, we found that CSCs had significantly lower oxygen consumption rate and extracellular acidification rate than non-stem cancer cells. Meanwhile, this subpopulation of cells consumed less glucose, produced less lactate and maintained lower ATP levels. We also revealed that CSCs could produce more ATP through mitochondrial substrate-level phosphorylation during respiratory inhibition compared with non-stem cancer cells. Furthermore, they were more sensitive to suppression of oxidative phosphorylation. Therefore, oligomycin (inhibitor of oxidative phosphorylation) could severely impair sphere-forming and tumor-initiating abilities of CSCs. Our work suggests that CSCs represent metabolically inactive tumor subpopulations which sustain in a state showing low metabolic activity. However, mitochondrial substrate-level phosphorylation of CSCs may be more active than that of non-stem cancer cells. Moreover, CSCs showed preferential use of oxidative phosphorylation over glycolysis to meet their energy demand. These results extend our understanding of CSCs metabolism, potentially providing novel treatment strategies targeting metabolic pathways in small cell lung cancer.
Cancer growth is driven by cancer stem-like cells within a tumor, called cancer stem cells (CSCs). Since miRNAs can regulate cell-fate decisions, we compared miRNA expression in stem-like cells and differentiated cells from small cell lung cancer (SCLC) cell lines to develop further understanding of the molecular mechanisms involved in the pathogenesis of SCLC. First, SCLC stem-like cells were enriched by isolating sphere-forming cells using a defined serum-free medium. Further, microRNA microarrays were used to measure the expression of 1212 miRNAs in sphere-forming cells and parental cells. We found 86 miRNAs that were differentially expressed, including 48 upregulated miRNAs and 38 downregulated miRNAs between sphere-forming cells and parental cells. Among them, five downregulated miRNAs (let-7, miR-20, 21, 27a and 30b) and one upregulated miRNA (miR-149*) were selected for validation in 3 sets of SCLC cell lines by qRT-RCR. The qRT-PCR analysis confirmed that all six miRNAs were indeed differentially expressed. However, only miR-27a was consistently downregulated in sphere-forming cells of all 3 cell lines. Antagonizing miR-27a by inhibitor in parental cells enhanced proliferation, self renewal, and the proportion of undifferentiated cells in vitro. The candidate miRNA and some miRNAs with same seed sequence are predicted to have several target genes related to apoptosis, cell proliferation and cell cycle. Our results suggest that downregulation of miR-27a enhanced the stem-like properties of SCLC cells in vitro and may be critical to maintaining a stem cell function in SCLC.
PurposeCancer stem cells (CSCs) are a small population of cancer cells located within a tumor that are highly tumorigenic, capable of tumor initiation, and resistant to cancer therapies. We identified the potential genes involved in regulating stemness properties and investigated the mechanisms in small-cell lung cancer (SCLC).Materials and methodsWhole transcriptome sequencing technology was used to screen the potential genes involved in regulating stemness properties from SCLC-SCs (uPAR+) and differentiated cells (uPAR-) in the H446 cell line. The selected genes were validated by quantitative reverse transcription PCR and ELISAs. The effect of IL-8 on stemness of sphere-forming cells was determined through tumor sphere formation, wound healing migration, and in vivo tumorigenesis assays.ResultsIn our study, uPAR+ and uPAR- cells showed different gene expression profiles. IL-8 was upregulated in SCLC sphere-forming cells. Blocking IL-8 expression with siRNA led to loss of stemness, including the self-renewal capability, migration, expression of stemness-related genes, and in vivo tumorigenicity, in sphere-forming cells. Consistently, exogenously added IL-8 enhanced stemness properties in parental cells.ConclusionIL-8 was upregulated in SCLC sphere-forming cells, and critical for the acquisition and/or maintenance of the stemness features in the SCLC cell line H446. Our results suggest that blocking IL-8 signaling may provide a novel therapeutic approach for targeting SCLC-SCs and improve treatment and outcomes in SCLC.
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