RNA binding protein ELAVL1-mediated USP33 stabilizes HIF1A to promote pathological proliferation, migration and angiogenesis of RECs.

Background: Dysfunction of retinal vascularization plays pathogenic roles in retinopathy of prematurity (ROP). Hypoxia-inducible factor 1 alpha (HIF1A) is activated by hypoxia and contributes to ROP progression. Herein, we clarified the mechanism underlying HIF1A activation in human retinal vascular endothelial cells (HRECs) under hypoxia.

Methods: Protein expression was assayed by immunoblot analysis. Cell migration, microtubule formation, invasion, proliferation, and viability were detected by wound-healing, tube formation, transwell, EdU, and CCK-8 assays, respectively. Bioinformatics was used to predict the deubiquitinase-HIF1A interactions and RNA binding proteins (RBPs) bound to USP33. The impact of USP33 on HIF1A deubiquitination was validated by immunoprecipitation (IP) assay. RNA stability analysis was performed with actinomycin D (Act D) treatment. The ELAVL1/USP33 interaction was assessed by RNA immunoprecipitation experiment.

Results: In hypoxia-exposed HRECs, HIF1A and USP33 protein levels were upregulated. Deficiency of HIF1A or USP33 suppressed cell migration, proliferation and microtubule formation of hypoxia-exposed HRECs. Mechanistically, USP33 deficiency led to an elevation in HIF1A ubiquitination and degradation. USP33 deficiency reduced HIF1A protein levels to suppress the proliferation and microtubule formation of hypoxia-induced HRECs. Moreover, the RBP ELAVL1 stabilized USP33 mRNA to increase USP33 protein levels. ELAVL1 decrease repressed the proliferation and microtubule formation of hypoxia-induced HRECs by reducing USP33.

Conclusion: Our study identifies a novel ELAVL1/USP33/HIF1A regulatory cascade with the ability to affect hypoxia-induced pathological proliferation, angiogenesis, and migration in HRECs.