T Study On Mechanisms Of H3K27me3 Involving In Multi-drug Resistance Of Small Cell Lung Cancer

BackgroundLung cancer,with approximately 1.8 million new cases.and more than 1 million related deaths each year,is the most common malignancy and has rapidly emerged as a primary cause of cancer-related death worldwide over the past several decades.Small cell lung cancer(SCLC)is the most aggressive type of lung cancer and accounts for approximately 15-18%of all lung cancer cases.The majority of SCLC patients are initially responsive to chemotherapy drugs,but they inevitably develop multidrug resistance within a year.Thus,a better understanding of the mechanisms underlying multidrug resistance is urgently needed for improving SCLC treatment.It has been indicated that the long non-coding RNA(lncRNA)HOX transcript antisense RNA(HOTAIR)serves as a powerful predictor of tumor progression and overall survival in patients.Our previous studies showed that HOTAIR modulated HOXA1 DNA methylation by reducing DNA methylase DNMT1 and DNMT3b expression in drugresistant small cell lung cancer(SCLC).Moreover,H3 lysine 27 trimethylation(H3K27me3)is catalyzed by enhancer of zeste homolog 2(EZH2)and plays a critical role in SCLC chemoresistance.Thus,the study aimed to explore whether H3K27me3 affects HOXA1 DNA methylation via the regulation of HOTAIR.MethodsThe levels of EZH2 and H3K27me3 were identified in SCLC tissues by immunohistochemical(IHC)staining and in SCLC multidrug-resistant cells by western blotting.Cell counting kit-8(CCK-8)and flow cytometry were used to detect and analyze the biological function of H3K27me3.We used lentiviruses to establish stable transfected cells to overexpress HOTAIR and siRNA to knockdown HOTAIR to deregulate HOTAIR expression.Then,we assessed the role of HOTAIR in the regulation of EZH2 and H3K27me3 in HOTAIR regulation and downregulation cells.Further,bisulfite sequencing PCR was conducted to detect the methylation levels of HOXA1 DNA.Finally,Western blotting was performed to examine the regulatory role of H3K27me3 in controlling HOTAIR expression in SCLC.ResultsIn the study,we initially found that EZH2 and H3K27me3 levels were markedly higher in SCLC tissues than in normal lung tissues.Furthermore,we found that EZH2 and H3K27me3 were upregulated in multidrug-resistant SCLC cells than sensitive SCLC cells.HOTAIR overexpression and knockdown showed that EZH2 and H3K27me3 were regulated by HOTAIR.HOTAIR affected HOXA1 DNA methylation through H3K27me3.Strikingly,we first found that H3K27me3 acted as a negative feedback regulator of HOTAIR in SCLC.ConclusionsOur study showed H3K27me3 played an important role in SCLC multidrug resistance.H3K27me3 affected HOXA1 DNA methylation via IncRNA-HOTAIR regulation in multidrug-resistant SCLC cells.Moreover,H3K27me3 modulated HOTAIR expression through a negative feedback mechanism.Thus,our study indicated that H3K27me3 may be a potential therapy target for SCLC chemoresistance.