Overexpression of lncRNA IGFBP4–1 reprograms energy metabolism to promote lung cancer progression

Reprogrammed energy metabolism as an emerging hallmark of cancer has recently drawn special attention since it facilitate cell growth and proliferation. Recently, long noncoding RNAs (lncRNAs) have been served as key regulators implicated in tumor development and progression by promoting proliferation, invasion and metastasis. However, the associations of lncRNAs with cellular energy metabolism in lung cancer (LC) need to be clarified. Here, we conducted bioinformatics analysis and found insulin-like growth factor binding protein 4–1 (IGFBP4–1) as a new candidate lncRNA located in the upstream region of IGFBP4 gene. The expression levels of lnc-IGFBP4–1, mRNA levels of IGFBP4 in 159 paired lung cancer samples and adjacent, histological normal tissues by qRT-PCR. Over-expression and RNA interference (RNAi) approaches were adopted to investigate the biological functions of lnc-IGFBP4–1. The intracellular ATP level was measured using the Cell Titer-Glo Luminescent Cell Viability Assay kit, and changes in metabolic enzymes were examined in cancer cells and normal pulmonary epithelial cells with qRT-PCR. Our results showed that lnc-IGFBP4–1 was significantly up-regulated in LC tissues compared with corresponding non-tumor tissues (P < 0.01), and its expression level was significantly correlated with TNM stage (P < 0.01) and lymph node metastasis (P < 0.05). Further investigation showed that overexpression of lnc-IGFBP4–1 significantly promoted LC cell proliferation in vitro and in vivo, while downregulation of endogenous lnc-IGFBP4–1 could inhibited cell proliferation and induce apoptosis. Moreover, we found lnc-IGFBP4–1 could influences ATP production levels and expression of enzymes including HK2, PDK1 and LDHA, in addition, decline in both ATP production and these enzymes in response to 2-DG and 2-DG-combined Rho123, respectively, was observed in lnc-IGFBP4–1-overespressing LC cells, indicative of an enhanced aerobic glycolysis rate. Finally, lnc-IGFBP4–1 was observed to negatively correlate with gene IGFBP4, and lower expression level of IGFPB4 was found after lnc-IGFBP4–1-overexpression was transfected into PC9 cells, higher expression level of IGFPB4 was also found after lnc-IGFBP4–1-downregulation was transfected into GLC-82 cells, which indicates that IGFBP4 may exert its targeting function regulated by lnc-IGFBP4–1. Taken together, these findings provide the first evidence that lnc-IGFBP4–1 is significantly up-regulated in LC tissues and plays a positive role in cell proliferation and metastasis through possible mechanism of reprogramming tumor cell energy metabolism, which suggests that lnc-IGFBP4–1 may be a promising biomarker in LC development and progression and as a potential therapeutic target for LC intervention.