The Oncogenic MicroRNA Hsa-miR-155-5p Targets the Transcription Factor ELK3 and Links It to the Hypoxia Response

Abstract

The molecular response to hypoxia is a critical cellular process implicated in cancer, and a target for drug development. The activity of the major player, HIF1α, is regulated at different levels by various factors, including the transcription factor ELK3. The molecular mechanisms of this intimate connection remain largely unknown. Whilst investigating global ELK3-chromatin interactions, we uncovered an unexpected connection that involves the microRNA hsa-miR-155-5p, a hypoxia-inducible oncomir that targets HIF1α. One of the ELK3 chromatin binding sites, detected by Chromatin Immuno-Precipitation Sequencing (ChIP-seq) of normal Human Umbilical Vein Endothelial Cells (HUVEC), is located at the transcription start site of the MIR155HG genes that expresses hsa-miR-155-5p. We confirmed that ELK3 binds to this promoter by ChIP and quantitative polymerase chain reaction (QPCR). We showed that ELK3 and hsa-miR-155-5p form a double-negative regulatory loop, in that ELK3 depletion induced hsa-miR-155-5p expression and hsa-miR-155-5p expression decreased ELK3 expression at the RNA level through a conserved target sequence in its 3′-UTR. We further showed that the activities of hsa-miR-155-5p and ELK3 are functionally linked. Pathway analysis indicates that both factors are implicated in related processes, including cancer and angiogenesis. Hsa-miR-155-5p expression and ELK3 depletion have similar effects on expression of known ELK3 target genes, and on in-vitro angiogenesis and wound closure. Bioinformatic analysis of cancer RNA-seq data shows that hsa-miR-155-5p and ELK3 expression are significantly anti-correlated, as would be expected from hsa-miR-155-5p targeting ELK3 RNA. Finally, hypoxia (0% oxygen) down-regulates ELK3 mRNA in a microRNA and hsa-miR-155-5p dependent manner. These results tie ELK3 into the hypoxia response pathway through an oncogenic microRNA and into a circuit implicated in the dynamics of the hypoxic response. This crosstalk could be important for the development of new treatments for a range of pathologies.

Single and Compound Knock-outs of MicroRNA (miRNA)-155 and Its Angiogenic Gene Target CCN1 in Mice Alter Vascular and Neovascular Growth in the Retina via Resident Microglia

“…The important role of miR-155 in retinal vessel growth and morphogenesis was further evidenced in our study by the formation of denser and largely anastomosed retinal vessels following exogenous intravitreal injection of miR-155 mimic. miR-155 has been found to be expressed in endothelial cells and was shown to regulate hypoxia by targeting the ELK3 gene (48,49). Herein, we identified and characterized a direct link between miR-155 and CCN1, an angiogenic factor largely produced by vascular cells, whereby miR-155 can directly repress expression of CCN1 and impede its function as an angiogenic factor orchestrating normal vessel growth and patterning.…”

MicroRNAs in the Host Response to Viral Infections of Veterinary Importance

“…In addition to the above mentioned in vivo models, there are several examples of in vitro trials that have unraveled multiple roles of cellular miRNAs in different scenarios of infections with animal viral diseases of veterinary importance. One prominent example can be seen in the oncogenic miR-155 ( 155 ). miR-155 was initially identified as a gene that was activated by promoter insertion at a common retroviral integration locus in B-cell lymphomas called B-cell integration cluster ( BIC ) ( 156 ).…”

MicroRNAs and PIWI-interacting RNAs in oncology

“…In addition, high levels of miR-155 are present in solid tumors, such as breast, prostate, gastric, colon and lung cancers ( 27 , 28 ). miR-155 is also involved in the regulation of multiple targets involved in different cancer phenotypes, such as TP53INP1 in apoptosis ( 29 ), VHL in angiogenesis ( 30 ), and ELK3 in hypoxia ( 31 ).…”