Repression Of Long Non-Coding RNA-LET By Histone Deacetylase3Contributes To Hypoxia-Mediated Metastasis

Cancer is the most fatal factor in people’s health，millions of people die of cancereach year. Most cancer mortality often results from the high frequency of cancerrecurrence or metastasis after surgical resection. However, little is known about molecularmechanisms underlying recurrence or metastasis.The phenomenon make people moreconfuling is that the metastatic cancer is frequently refractory to the therapeutic approachesthat are effective to primary cancer.This is our project’s background.We must confirm thatthe aim of basal medical studies should be useful to solve the clinical problems.Therefore, identification of biomarkers that could accurately predict future metastasisand understanding the specific regulatory mechanisms underlying metastasis are criticalissues.We can provide valuable theoretical support for the early diagnosis of cancer or toimprove the surgical treatment. Recently, some studies have identified markers ofrecurrence or to predict metastasis, including protein coding genes and microRNAs(18-200nt). However, we still do not fully understand the mechanisms ofmetastasis.Therefore,finding the regulatory mechanism of cancer metastasis is veryvaluable for clinical research and cancer drugs treatment. At the same time,more and morestudies have shown that the exercise of functions in cancer metatasis in addition to codinggenes and proteins,RNA also plays important roles in cancer metatasis process.RNA is not only a messenger bridge between DNA and protein,other noncodingRNAs play different important roles in life processes. Long noncoding RNAs aretranscripts with no protein-coding capacity,the length＞200nt.Many of these transcriptswere once considered as transcriptional“noise”with no biologicaleffects.However,scientists have found lncRNAs have functions in normal lifeprocesses,simultaneously these lncRNAs contribute to the occurrence of diseases. So,theroles lncRNAs play in the occurrence and development of cancers arouse our great interest.Recently, long non-coding RNAs (lncRNAs) have been found to generally bederegulated in a variety of tumors. However, the key factors that control the expressionlevels of lncRNAs, and these lncRNAs involved precise molecular mechanisms are stillrarely known.In this study, our results indicated that an lncRNA (named lncRNA-LET) wasgenerally downregulated in hepatocellular carcinoma, colorectal cancer and lung squamouscell carcinoma.We confirm that lncRNA-LET is a noncoding RNA transcript about1945ntby5’ RACE and3’RACE. Lentiviral vectors encoding human lncRNA-LET gene were constructed.We find thatthe ability of metatasis of cancer cell is vigourly inhibited in cell lines stably expressinglncRNA-LET by cell transwell and cell invision experiment.The Orthotopic intra-hepaticmetastasis model shows that lncRNA-LET play an important role in inhibition of tumor’smetatasis in vivo.LncRNA-LET may be a anti-oncogene.A previous research has demonstrated that numerous lncRNAs are key constituents inthe p53-dependent transcriptional pathway. It also attracted strong interest that whetherlncRNAs expression can be controlled by epigenetic mechanisms, such as histonemodification.Hypoxia microenviroment is one of the key factors make tumor moremaglignant,hypoxia microenviroment can induce tumors metastatic. We further proved thatlncRNA-LET expression was controlled by hypoxia leaded histonedeacetylation(HDAC3).Many lncRNAs are involved in molecular regulation pathways through theirinteraction with proteins,we identified ILF3/nuclear factor90(NF90) as specificallyassociated with the sense (but not anti-sense) strand of lncRNA-LET by RNA-pulldownexperiment and RNA immunoprecipitation (RIP). More interesting, lncRNA-LETdownregulation in cancer tissues is a key step in the process of hypoxia induced cancer cellmigration by reducing nuclear factor90protein degradation.The relationship of hypoxia, lncRNA-LET and metastasis also obviously exist inclinic hepatocellular carcinoma sample. Hypoxia microenviroment in tumors upregulatesthe protein level of HDAC3which leads to silence lncRNA-LET expression.The resultincreases the stability of ILF3and upregulates the protein level of HIF1α，so that themetatasis ability of cancer cell was enhanced.Our study provides novel mechanistic insight into lncRNAs function in cancerprogression and contributes to better understanding of the important deregulated lncRNAsin hepatocellular carcinoma and other malignant tumors. We can provide valuabletheoretical support for the clinical studies of cancer metatasis in vivo or lncRNAs may beimportant targets for cancer medicine therapy.