Mechanisms Of A-to-I RNA Editing Regulating Tumor-associated Genes

A-to-I RNA editing act as a central generator of transcriptome diversity regulation in higher eukaryotes. It is the most important post-transcriptional modification of transiting adenosine to inosine in dsRN A catalyzed by ADARs. Since inosine is recognized as guanosine by the base pairing machinery, A-to-I RNA editing exhibit " A-to-G" transition on the edited substrate. Thought A-to-I RNA editing at first to be found on coding regions of only a few genes, recent bioinformatic analyses on high-throughput sequencing revealed it is a widespread modification affecting mostly non-coding repetitive elements in thousands of genes. Editing sites occur in coding regions alter codon may result in amino acid substitutions and futher alter protein function. Editing in noncoding sequences was proposed to be involved in general functions such as RNA stabilization, splicing, miRNAs biogenesis and targeting.Recently, it has been a hot topic about the relationship between A-to-â…  RNA editing and carcinogenesis. Some researchs showed an imbalance in expression of ADAR enzymes with consequent editing dysregulation was a characteristic of human cancers. These alterations may be responsible for activating oncogenes or inactivating tumor-suppressors. We begin our work with the regulation of A-to-â…  RNA editing on tumor-associated genes, to explore the role of A-to-â…  RNA editing in carcinogenesis.Our work make thorough research to the A-to-â…  RNA editing on3'UTR of tumor suppressor gene ARHGAP26and coding region of oncogene GLI1. We detected editing sites on ARHGAP26and GLI1which predicted by bioinformatics, confirmed that this two editing events were widespread in human cells and with different editing levels in different tissues. We compared the A-to-â…  RNA editing event between normal and tumorous condition, found a general decrease in editing level of editing sites within ARHGAP263' UTR in brain, liver and breast tumors or cell lins compared to their corresponding normal controls, while there was also a decrease editing level of editing site on GUI1coding region in liver and breast tumors. We expect to explain downregulation of A-to-â…  RNA editing in tumors by studying the regulation mechanism of A-to-â…  RNA editing on this two type tumor-associated genes.We found ADAR1was the main editing enzyme which mediate the A-to-â…  RNA editing in ARHGAP263' UTR. The expression of ARHGAP26along with its editing level were downregulated when ADAR1was interfered. We further observed a positive correlation between the expression of ARHGAP26and A-to-â…  RNA editing level in various cell lines. These appearance indicate that A-to-â…  RNA editing can positively regulate the expression of ARHGAP26. With the prediction by bioinfomation tools, We find there highly possible exist a miR-30b*target region in ARHGAP263' UTR, and A-to-â…  RNA editing may destroy the combination of miRNA with its target. So we speculate that A-to-â…  RNA editing may positively regulate the expression of ARHGAP26through affecting miRNA targeting.We research the regulation mechanism of A-to-â…  RNA editing on oncogene GLI1with bioinformatics methods. We predict that the editing event in GLI1coding region may destroy exon splicing enhancer and affect the normal splicing of exon12while transition of arginine to glutamate may influence advanced structure and activity of GLI1protein.Based on the above results, we speculate that the A-to-â…  editing level downregulation in tumorigenesis lead to downregulate the expression of tumor suppressor gene ARHGAP26while promote the normal transcripts formation and restore protein activity of oncogene GLI1, all the efforts help to tumorigenesis. Our study focus on the editing event of tumor-associated genes, support the relationship between A-to-â…  RNA editing and tumorigenesis, and may provide new ideas to cancer diagnosis and therapy.