LncRNA-536 and RNA-Binding Protein RBM25 Interactions in Pulmonary Artery Smooth Muscle Cells: Implications in Pulmonary Hypertension.

In this study, we define the mechanistic association between long noncoding RNA: ENST00000495536 (lnc-536) and transcription factor HOXB13 (homeobox B13) in mediating proproliferative smooth muscle phenotype associated with pulmonary hypertension. In vitro knockdown or knockin, along with RNA pull-down and immunoprecipitation studies, were used to evaluate the role of lnc-536 and HOXB13 in regulating pulmonary arterial smooth muscle cell (PASMCs) phenotype. The in vivo role was determined by injecting lnc-536 antisense oligos in pulmonary hypertensive rats. Increased levels of lnc-536 promote the proliferative phenotype of PASMCs by downregulating the expression of the tumor suppressor: HOXB13. Knockdown of lnc-536 and overexpression of HOXB13 in proliferative PASMCs resulted in increased expression of VGLL4 (vestigial-like family member 4), a negative regulator of Hippo and Wnt (Wingless-related integration site) signaling pathways, with a corresponding decrease in TEAD4 (TEA domain family member 1) expression. The lnc-536 pull-down assay and RNA-immunoprecipitation demonstrated the interactions of lnc-536 with RBP (RNA-binding protein): RBM25 (RNA-binding motif 25) and direct interactions of RBM25 with SFPQ (splicing factor proline/glutamine-rich), a transcriptional regulator that has a binding motif on HOXB13. The knockdown of RBM25 in the hyperproliferative PASMCs resulted in increased interactions of SFPQ and HOXB13 mRNA while attenuating PASMC proliferation. Furthermore, the increased levels of lnc-536 and decreased levels of HOXB13 were observed in PASMCs from idiopathic pulmonary hypertension patients but not in cells from familial pulmonary hypertension patients. We confirmed that lnc-536 contributes to the RBM25-mediated remodeling of the SFPQ-HOXB13 complex in the idiopathic PAH-PASMCs as well. Finally, in vivo inhibition of lnc-536 using GapmeRs (Gapmer antisense oligonucleotides) in Sugen-hypoxia and HIV-transgenic pulmonary hypertension rats prevented the increase in right ventricular systolic pressure, right ventricular hypertrophy/fibrosis, and pulmonary vascular remodeling with a parallel increase in HOXB13 expression in rat PASMCs. Lnc-536 acts as a decoy for RBM25, which in turn sequesters SFPQ, leading to a decrease in HOXB13 expression and hyperproliferation of smooth muscle cells by potentially regulating Wnt and Hippo signaling associated with PAH development.