Resistance to adverse environmental conditions, such as hypoxia, contributes to the reduced efficacy of anticancer therapies and tumor progression. Although deregulated expression of many long noncoding RNA (lncRNA) occurs in human cancers, the contribution of such RNA to tumor responses to hypoxia are unknown. RNA expression profiling identified several hypoxia-responsive lncRNAs, including the long intergenic noncoding RNA, regulator of reprogramming (linc-RoR), which is also increased in expression in malignant liver cancer cells. Linc-RoR expression was increased in hypoxic regions within tumor cell xenografts in vivo. Tumor cell viability during hypoxia was reduced by small interfering RNA (siRNA) to linc-RoR. Compared with controls, siRNA to linc-RoR decreased phosphorylation of p70S6K1 (RPS6KB1), PDK1 and HIF-1α protein expression and increased expression of the linc-RoR target microRNA-145 (miR-145). Linc-RoR was highly expressed in extracellular RNA released by hepatocellular cancer (HCC) cells during hypoxia. Incubation with extracellular vesicle preparations containing extracellular RNA increased linc-RoR, HIF-1α expression and cell survival in recipient cells. These studies show that linc-RoR is a hypoxia-responsive lncRNA that is functionally linked to hypoxia signaling in HCC through a miR-145-HIF-1α signaling module. Furthermore, this work identifies a mechanistic role for the extracellular transfer of linc-RoR in intercellular signaling to promote cell survival during hypoxic stress.
Keywords: Cell stress; Exosome; Extracellular vesicle; Gene expression; Hypoxia; Liver cancer; linc-RoR; microRNA.