Circular RNA Profiling Identifies as a -Derived Regulator of Endothelial Proliferation and Stress Responses.

BACKGROUND

The gene encodes the BMPR-II (bone morphogenetic protein receptor type-II) and is a known regulator of endothelial proliferation, apoptosis, and translational stress responses. While these effects are generally attributed to the actions of BMPR-II protein, we used circular RNA profiling to identify and as new -derived functional RNAs.

METHODS

Circular RNAs were profiled by ultradeep RNA sequencing of human pulmonary artery endothelial cells. Novel -derived circular RNAs were assessed for their effects on endothelial proliferation, apoptosis, and translational stress responses in human pulmonary artery endothelial cells and endothelial cells from patients with pulmonary arterial hypertension with heterozygous loss-of-function mutations. to linear mRNA ratios were quantified in cultured lymphocytes from patients with pulmonary arterial hypertension with mutations versus unaffected mutation carriers.

RESULTS

Depletion of enhanced human pulmonary artery endothelial cell apoptosis, whereas silencing increased proliferation. Enhanced proliferation with depletion was eliminated by cosilencing of with either linear mRNA or the stress granule protein, Caprin-1, indicating a potential interdependence of transcripts in the regulation of endothelial function. Patients with pulmonary arterial hypertension with mutations exhibited increased to linear mRNA ratios, alongside impaired stress responses in patient endothelial cells that were deficient in linear transcripts but not . depletion enhanced stress responses in human pulmonary artery endothelial cells and rescued stress granule formation in patient endothelial cells, independent of BMPR-II protein levels. Assessment of translational regulation by polysome profiling did not identify any impact of linear or circular transcript loss on global protein synthesis or stress-induced eIF2α (eukaryotic initiation factor 2α) phosphorylation but did identify the enhanced translational efficiency of select nuclear-encoded mitochondrial ribosome proteins with depletion, offering a link between mitochondrial function and the -deficient endothelial phenotype.

CONCLUSIONS

The identification of and as novel -derived gene products reveals interdependent roles for coding and noncoding transcripts as regulators of endothelial function.