ABSTRACT
Resistance to epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs), such as gefitinib, has greatly affected clinical outcomes in non-small cell lung cancer (NSCLC) patients. The long noncoding RNAs (lncRNAs) are known to regulate tumorigenesis and cancer progression, but their contributions to NSCLC gefitinib resistance remain poorly understood. In this study, by analyzing the differentially expressed lncRNAs in gefitinib-resistant cells and gefitinib-sensitive cells in the National Institute of Health GEO dataset, we found that lncRNA CASC9 expression was upregulated, and this was also verified in resistant tissues. Gain and loss of function studies showed that CASC9 inhibition restored gefitinib sensitivity both in vitro and in vivo, whereas CASC9 overexpression promoted gefitinib resistance. Mechanistically, CASC9 repressed the tumor suppressor DUSP1 by recruiting histone methyltransferase EZH2, thereby increasing the resistance to gefitinib. Furthermore, ectopic expression of DUSP1 increased gefitinib sensitivity by inactivating the ERK pathway. Our results highlight the essential role of CASC9 in gefitinib resistance, suggesting that the CASC9/EZH2/DUSP1 axis might be a novel target for overcoming EGFR-TKI resistance in NSCLC.
Subject(s)
Antineoplastic Agents/therapeutic use , Carcinoma, Non-Small-Cell Lung/genetics , Dual Specificity Phosphatase 1/genetics , Gefitinib/therapeutic use , Lung Neoplasms/genetics , RNA, Long Noncoding/genetics , Animals , Antineoplastic Agents/pharmacology , Carcinoma, Non-Small-Cell Lung/metabolism , Carcinoma, Non-Small-Cell Lung/pathology , Cell Line, Tumor , Down-Regulation , Dual Specificity Phosphatase 1/metabolism , Epigenetic Repression , Gefitinib/pharmacology , Humans , Lung Neoplasms/metabolism , Lung Neoplasms/pathology , Male , Mice , Mice, Nude , RNA, Long Noncoding/metabolism , TransfectionABSTRACT
The number of documented long noncoding RNAs (lncRNAs) has dramatically increased, and their biological functions and underlying mechanisms in pathological processes, especially cancer, remain to be elucidated. Actin filament-associated protein 1 antisense RNA 1 (AFAP1-AS1) is a 6810-nt lncRNA located on chromosome 4p16.1 that was first reported to be upregulated in esophageal adenocarcinoma tissues and cell lines. Here we reported that AFAP1-AS1, recruiting and binding to lysine-specific demethylase 1 (LSD1), was generally overexpressed in human non-small-cell lung cancer (NSCLC) tissues using quantitative real-time PCR. Higher AFAP1-AS1 expression was significantly correlated with larger tumor size (P = .008), lymph node metastasis (P = .025), higher TNM stage (P = .024), and worse overall survival in NSCLC patients. In vitro experiments revealed that AFAP1-AS1 downregulation inhibited cell migration and induced apoptosis; AFAP1-AS1 knockdown also hindered tumorigenesis in vivo. Moreover, mechanistic investigations including RNA immunoprecipitation and ChIP assays validated that AFAP1-AS1 repressed HMG box-containing protein 1 (HBP1) expression by recruiting LSD1 to the HBP1 promoter regions in PC-9 and H1975 cells. Furthermore, HBP1 functions as a tumor suppressor, and its ectopic expression hindered cell proliferation. Rescue assays determined that the oncogenic effect of AFAP1-AS1 is partially dependent on the epigenetic silencing of HBP1. In conclusion, our results indicate that AFAP1-AS1 is carcinogenic and that the AFAP1-AS1/LSD1/HBP1 axis could constitute a new therapeutic direction for NSCLC.
