A novel LncRNA HITT forms a regulatory loop with HIF-1α to modulate angiogenesis and tumor growth

Increasing evidence has indicated that long noncoding RNAs (lncRNAs) play important roles in human diseases, including cancer; however, only a few of them have been experimentally validated and functionally annotated. Here, we identify a novel lncRNA that we term HITT (HIF-1 alpha inhibitor at translation level). HITT is commonly decreased in multiple human cancers. Decreased HITT is associated with advanced stages of colon cancer. Restoration of the expression of HITT in cancer cells inhibits angiogenesis and tumor growth in vivo in an HIF-1 alpha-dependent manner. Further study reveals that HITT inhibits HIF-1 alpha expression, mainly by interfering with its translation. Mechanically, HITT titrates away YB-1 from the 5 '-UTR of HIF-1 alpha mRNA via a high-stringency YB-1-binding motif. The reverse correlation between HITT and HIF-1 alpha expression is further validated in human colon cancer tissues. Moreover, HITT is one of the most altered lncRNAs upon the hypoxic switch and HITT downregulation is required for hypoxia-induced HIF-1 alpha expression. We further demonstrate that HITT and HIF-1 alpha form an autoregulatory feedback loop where HIF-1 alpha destabilizes HITT by inducing MiR-205, which directly targets HITT for degradation. Together, these results expand our understanding of the cancer-associated functions of lncRNAs, highlighting the HITT-HIF-1 alpha axis as constituting an additional layer of regulation of angiogenesis and tumor growth, with potential implications for therapeutic targeting.