Investigation of Long Non-Coding Rna on the Tumorigenesis in Human Colorectal Cancer

Recent studies have demonstrated that long noncoding RNAs (lncRNAs) are deregulated in cancer tissues and cells. Single nucleotide polymorphisms (SNPs) are significantly associated with carcinogenesis, however only about 3.3% SNPs occurs in the protein-coding sequences. Most SNPs locate in the sequences of non-coding genes, and several important lncRNAs in carcinogenesis exist SNPs, which have been linked to the abnormal expression of these lncRNAs. Generally, lncRNAs can regulate gene expression at many stages of transcription and post-transcription. It has been proposed that lncRNAs can repress transcription of adjacent gene through transcription interference. Several mechanisms about transcription interference have been demonstrated, including interfering with the binding of transcription factors and/or RNA polymerase II to the gene promoters as well as increasing nucleosome package in gene promoter, thereby blocking transcription in specific gene. Studies in miRNA host lncRNAs have found that these kinds of lncRNAs can not only generate miRNA but can also control its function via acting as a sponge for its own produced miRNA. In addition, miRNA host lncRNAs can act as other miRNA sponges and prevent these miRNAs from binding to their targets, therefore these lncRNAs function as a competing endogenous RNA (ceRNA). Whole transcriptome analysis using next generation sequencing (NGS), we have found 20 aberrant expression of lncRNAs in human colorectal cancer (CRC). The NR_033920 gene transcript a lncRNA (called lncRNA-920 in this project) that exists a SNP rs3803662 in its exon 4, and the rs3803662 has been known to be associated with the risk of breast cancer. Our preliminary results found that the expression of lncRNA-920 is downregulated in tumor tissues in comparison to the adjacent normal tissues of CRC patients. We also found that lncRNA-920 can inhibit its downstream TOX high mobility group box family member 3 (TOX3) gene expression, and also inhibit the cell migration. Moreover, we found that the rs3803662T has a higher inhibitory ability than the rs3803662C. High level of TOX3 has been linked to the tumor metastasis. Therefore, we hypothesize that lncRNA-920 can inhibit migration and metastasis in human CRC through inhibiting TOX3 gene expression by the mechanism of transcription interference. In addition, the inhibitory activity of lncRNA-920 is associated with the rs3803662. Interestingly, NR_132988 is a miRNA host lncRNA gene, which harbors the miR-3677 and miR-940 sequences in its intron 1 and exon 2, respectively. Our preliminary results found that the lncRNA-988 (transcript from NR_132988) can generate miR-940 and the miR-940 can inhibit the Nestin expression. Moreover, lncRNA-988 highly expresses in tumor tissues but the miR-940 expression is just contrary to the lncRNA-988. The high expression of Nestin has been linked to the growth and metastasis in human CRC. Therefore, we hypothesize that unknown inhibitor(s) is relatively high in tumor tissues to prevent lncRNA-988 from generating miR-940, therefore Nestin can’t be inhibited by miR-940, and the full length of linRNA-988 can act as sponge to absorb other miRNAs. Based on our recent findings and hypothesis, we would like to fully understand the molecular mechanisms of lncRNAs on the regulation of CRC growth and metastasis, and hope to achieve the following specific goals in three years. Year 1: to discovery and analyze the aberrant expression of lncRNAs in human CRC; Year 2: to investigate the molecular mechanisms of lncRNA-920 SNP rs3803662 on the regulation of tumor cell migration and invasion; Year 3: to investigate the molecular mechanisms of lncRNA-988 on the generation of miR-940 and regulation of other miRNAs’ activity.