MIR193BHG: a novel hypoxia-inducible long noncoding RNA involved in the fine-tuning of cholesterol metabolism

Abstract

The human genome generates a vast number of functionally and structurally diverse noncoding transcripts, incorporated into complex networks which modulate the activity of classic pathways. Long noncoding RNAs (lncRNA) have been shown to exhibit diverse regulatory roles in various physiological and pathological processes. Hypoxia, a key feature of the tumor microenvironment, triggers adaptive responses in cancer cells that involve hundreds of genes. While the coding component of hypoxia signaling has been extensively studied, much less information is available regarding its noncoding arm. My doctoral work identified and functionally characterized a novel hypoxia-inducible lncRNAs encoded from the miR193b-host gene (MIR193BHG) locus, on chromosome 16. In the pursuit of understanding how MIR193BHG responds to hypoxia, we discovered a more complex transcriptional control of MIR193BHG by hypoxia. Ectopic expression of MIR193BHG in breast cancer cell lines in vitro and in xenografts significantly represses cell invasion, as well as the metastasis to lung and liver. Conversely, inhibition of MIR193BHG promotes cancer cell invasiveness and metastasis. RNAseq followed by pathway analysis revealed that MIR193BHG is a negative modulator of cholesterol biosynthesis pathway. MIR193BHG exerts a highly coordinated effect on the expression of cholesterol biosynthetic genes which leads to a measurable impact on the total cellular cholesterol content. The role of MIR193BHG in cholesterol metabolism also provided a mechanistic explanation for the sex maturation associated SNPs located in vicinity of this gene locus. Our work also provided preliminary insights into the functional mechanism of MIR193BHG by showing that its modulation of genes in cholesterol synthesis is predominantly at transcriptional level. Overall, my dissertation project identified a non-canonical hypoxia-inducible lncRNA, MIR193BHG, which modulates breast cancer invasion and metastasis via finetuning of cholesterol synthesis.