Abstract
Background: The roles of many long noncoding RNAs (lncRNAs) in breast cancer (BC) are unclear, and the medications that affect them have attracted less attention. Objectives: This study aimed to identify lncRNAs that have the highest association with poor prognosis in BC. Moreover, the relationship between the expression of identified lncRNA and conventional chemotherapy agents was investigated. Methods: The cancer genome atlas data were used to identify lncRNA with the most significant impact on BC survival. The relation of identified lncRNA levels with different subtypes of BC and mutation was assessed. PharmacoGX data and the GEO database were used to evaluate the association of identified lncRNA levels with drug sensitivity and find appropriate medications to reduce its expression, respectively. To assess the effect of the identified drug on the level of lncRNA expression, MCF7, and MDA-MB-468 cell lines were used, and the expression level of target genes was assessed by quantitative reverse transcription polymerase chain reaction. Results: The expression level of lncRNA MIR4435-2HG was most associated with the poor survival of BC patients, and its expression level can be related to TP53 mutation and estrogen and progesterone receptors. Increased expression of MIR4435-2HG was observed in cancer samples, and MIR4435-2HG level was correlated with metastasis pathway genes. Drug sensitivity to epirubicin, irinotecan, and lestaurtinib correlated with MIR4435-2HG levels. Furthermore, GEO data showed that the expression level of MIR4435-2HG could decrease under estrogen receptor (ER) activity. Finally, in vitro, results showed that MIR4435-2HG expression declined in response to estradiol as an ER-activating ligand in the MCF7 cell line. Conclusions: The expression of MIR4435-2HG can be a powerful biomarker for poor prognosis in BC. The data also suggested that this lncRNA may play an oncogenic role in metastatic pathways, and ER activity could regulate its expression.