Exploring The Mechanism Of Retinoic Acid Receptor A On Drug Sensitivity And Aerobic Glycolysis In Cholangiocarcinoma

Due to its unique anatomical location and physiological characteristics,Cholangiocarcinoma(CCA)lacks early diagnosis and effective treatment.Besides,CCA cells are drug-resistant.It is urgent to explore specific targets for the diagnosis and treatment of CCA.Retinoic acid receptor α(RARα),as a nuclear receptor,plays an important role in a variety of biological processes such as cell development,differentiation and tumor formation.Our previous study found its oncogenic roles in Colorectal Cancer,Gastric Carcinoma and Esophagus Cancer.And the expressions and functions of RARa homologous protein RARβ and RARy in CCA have been reported.However,the roles of RARα in CCA have not been elucidated.Hence,in this study,we selected RARα as the research object to explore its functions in CCA.Here,we found that the expression of RARa was significantly increased in CCA cell lines and clinical tissues.The high expression of RARa in tumor tissues was correlated with the degree of pathologic differentiation,tumor size and clinical stage.In vitro,RARα promoted cell proliferation and aerobic glycolysis,and drug resistance of CCA cells.In vivo,the growths of xenograft tumors were inhibited and drug sensitivities of tumors were significantly enhanced after RARa knockdown.These data demonstrated the oncogenic function of RARa in CCA.Proteomic analysis showed that 138 proteins were significantly up-regulated and 40 proteins were significantly downregulated in RARa knockdown cells.The functions of these differentially expressed proteins were concentrated in carbohydrate metabolism pathway,cisplatin resistance pathway,ABC transporter family and so on.Screening of these proteins revealed that drug-resistant protein ABCC2 and mitochondrial oxidative phosphorylation protein ANT1 mediated the regulation of RARa on drug sensitivity and aerobic glycolysis of CCA cells.The expressions of RARa and ABCC2 were significantly increased in cisplatin resistant CCA cells.Further mechanism studies showed that RARα,as a transcription factor,promoted transcription of ABCC2 and inhibited transcription of ANT1 by binding to retinoic acid response elements DR1,DR2,DR5 and IRO.RARαbound to HDAC1 in cells,and the transcriptional inhibition of ANT1 was related to the recruitment of HDAC1 by RARα.Furthermore,hypoxic microenvironment and inflammatory microenvironment promoted the expression of RARa in CCA cells,and IL-6 induced the expression of RARα protein by activating STAT3.In this study,a combination of experiments and proteomic analysis revealed the oncogenic function of RARa in CCA.RARa promoted cell proliferation and aerobic glycolysis,and reduced the sensitivity to chemotherapy drugs.These functions were mediated by two target genes,ABCC2 and ANT1.RARa acted as a transcription factor to directly regulate the transcription of these two genes.These findings lay a foundation for the study of the molecular mechanism of CCA progression.