The Role Of MiRNA In Cancer Energy Metabolic Reprogramming And Autophagy

Metabolic reprogramming and autophagy are immediate areas of cancer research focus and play vital roles in tumorigenesis,metastasis and drug resistance.Metabolic reprogramming means that tumor cells modify their energy sources from oxidative phosphorylation to glycolysis and synthesize macromolecules at sufficient rates to meet the demands of malignant proliferation.This switch provides a survival advantage for tumor cells.Autophagy is a lysosome-dependent catabolic process that delivers cytoplasmic materials,including organelles and proteins,to lysosomes for degradation and recycle the macromolecular substances to maintain cell stability and metabolic balance.Autophagy often contributes to cancer cell survival under various stresses,such as hypoxia,chemoradiotherapy and nutrient deficiency.The protective function of autophagy also contributes to the chemoresistance in various types of tumors,making cancer treatment more difficult.However,at present,the regulatory mechanisms of tumor metabolic reprogramming and autophagy are not clear.miRNA(microRNA)are small(～22 nucleotides)non-coding RNA molecules that regulate gene expression at the post-transcriptional level and play important roles in a wide variety of physiological and pathological cellular processes.Many miRNAs express abnormally in cancer progression,thereby affecting tumor development.Recent studies have reported that miRNAs play important roles in tumor metabolism and autophagy,however,as a key molecule in cellular regulatory network,the mechanisms of tumor metabolic reprogramming and autophagy regulation by miRNAs have not yet been systematically reported.In this thesis,we study the miRNA function in energy metabolic reprogramming and autophagy of tumor.Our study was composed of two parts.In the first part,we researched the role of HIF-1α-induced miR-23a～27a～24 cluster on colorectal cancer metabolic reprogramming.Firstly,we found that three miRNAs in miR-23a-27a-24 cluster,miR-23a,miR-27a and miR-24,were most upregulated miRNAs in CRC under hypoxia.Chromatin Immunoprecipitation(ChIP)and luciferase assays confirmed that the miR～23a～27a～24 cluster were upregulated by HIF-1α via the specific HIF-1α binding motifs.Gene pathway analyses,gain-and loss-of-function assays and a global glucose metabolism array confirmed that HIF-1α-induced miR-23a～27a～24 cluster serve as global regulators of glucose metabolic reprogramming via modulating metabolic related AMPK,PI3K-Akt and insulin signaling pathway,and targeting cancer metabolic pathway genes associated with TCA cycle.In addition,in vitro,in vivo and clinical samples assays conformed that miR-24/VHL/HIF-1α in CRC form a double-negative feedback loop,in which HIF-1αinduced miR-24 expression,which in turn silenced VHL,an inhibitor of HIF-1α,leading to higher HIF-1α activity.This positive feedback loop would facilitate tumor cell survival and progression via promoting tumor cells to the ’high HIF-1α/miR-24 but low VHL’ state.Our findings reveal that the miR-23a～27a～24 cluster is critical regulator switching CRC metabolism from oxidative phosphorylation to aerobic glycolysis,and controlling their expression can suppress colorectal cancer progression.In the second part,we studied the role of miR-26 family in autophagy and cancer chemosensitivity.HCC shows high chemoresistance,and autophagy is an important factor promoting tumor drug resistance.Firstly,we found that chemotherapeutic drug induced autophagy but decreased the level of miR-26a/b in HCC cells.Activating autophagy using rapamycin can directly downregulate the level of miR-26a/b in HCC cells.In turn,restoring the expression of miR-26a/b inhibited autophagy induced by chemotherapeutic drug and promoted apoptosis in HCC cells.Further mechanistic study,luciferase assays and clinical patient samples identified that miR-26a and miR-26b target ULK1,a critical initiator of autophagy,at post-transcriptional level.Gain-and loss-of-function assay confirmed that miR-26a/b inhibited autophagic flux at the initial stage,promoted cell apoptosis and enhanced the chemosensitivity of HCC cells.Using xenograft models in nude mice,we confirmed that miR-26a/b,via inhibiting autophagy,promoted apoptosis and sensitized hepatomas to Dox treatment in vivo.Our findings demonstrate for the first time that miR-26a/b can promote apoptosis and sensitize HCC to chemotherapy via suppressing the expression of autophagy initiator ULK1,and provide the reduction of miR-26a/b in HCC as a novel mechanism of tumor chemoresistance.