Antagonistic function of the RNA-binding protein HuR and miR-200b in post-transcriptional regulation of VEGF-A expression and angiogenesis

HuR, also known as Elavl1, is an RNA binding protein that regulates embryonic development, progenitor cell survival and cell stress responses. The role of HuR in angiogenesis is not known. Using a myeloid-specific HuR knockout mouse model (mϕ Elavl1 KO), we show that HuR expression in bone marrow-derived macrophages (BMDM) is needed to maintain the expression of genes enriched in ARE and U-rich elements in the 3 ′ -UTR. In addition, BMDM from mϕ Elavl1 KO also showed alterations in expression of several miRNAs. Interestingly, computational analysis suggested that miR-200b, which is up-regulated in mϕ Elavl1 KO BMDM, interacts with myeloid mRNAs very close to the HuR binding sites, suggesting competitive regulation of gene expression. One such mRNA encodes vascular endothelial growth factor (VEGF)-A, a major regulator of angiogenesis. Immunoprecipitation of RNA/ protein complexes and luciferase reporter assays indicate that HuR antagonizes the suppressive activity of miR-200b, downregulates miR-200b expression and promotes VEGF-A expression. Indeed, Vegf-a and other angiogenic regulatory transcripts were down-regulated in mϕ Elavl1 KO BMDM. Interestingly, tumor growth, angiogenesis, vascular sprouting, branching and permeability were significantly attenuated in mϕ Elavl1 KO mice, suggesting that HuR-regulated myeloid-derived factors modulate tumor angiogenesis in trans. Zebrafish embryos injected with an elavl1 morpholino oligomer (MO) or miR-200b mimic showed angiogenesis defects in the subintestinal vein (SIV) plexus, and elavl1 mRNA rescued the repressive effect of miR-200b. In addition, miR-200b and HuR MO suppressed the activity of a zVEGF 3 ′ -UTR luciferase reporter construct. Together, these studies reveal an evolutionarily-conserved post-transcriptional mechanism involving competitive interactions between HuR and miR-200b that controls angiogenesis.