Angiotensin II Induces Renal Plasminogen Activator Inhibitor-1 and Cyclooxygenase-2 Expression Post-Transcriptionally via Activation of the mRNA-Stabilizing Factor Human-Antigen R

Abstract

Angiotensin (Ang) II-induced fibrosis of the kidney is characterized by the enhanced expression of profibrotic and proinflammatory genes, including the serine protease inhibitor plasminogen activator inhibitor-1 (PAI-1) and cyclooxygenase-2 (COX-2). In addition to transcriptional regulation, both genes are subject to post-transcriptional control by AU-rich destabilizing elements that reside within the 3' untranslated region of the mRNA. We demonstrated that the continuous infusion of AngII in rats induced fibrosis concomitant with a significant increase in glomerular PAI-1 and COX-2 expression levels. Using RNA pull-down assays and electromobility shift assays, we demonstrated the increased binding of the ubiquitous RNA-binding protein human-antigen R (HuR) to the mRNAs of both PAI-1 and COX-2 in the cytoplasmic fractions of renal homogenates from AngII-treated rats. Actinomycin D experiments in rat mesangial cells revealed that AngII stabilizes both mRNAs via HuR as proven by small interfering RNA. Mechanistically, AngII promotes an increase in nucleo-cytoplasmic HuR shuttling, which was blocked by the PKC inhibitor rottlerin and the type-I AngII (AT(1)) receptor antagonist valsartan but was unaffected by both AT(2) receptor antagonists PD123319 and CGP42112. Co-immunoprecipitation revealed that AngII treatment caused an increase in nuclear PKC-delta concomitant with binding to nuclear HuR both in vitro and in vivo. The post-transcriptional regulation of PAI-1 and COX-2 by PKC-delta-dependent HuR shuttling may contribute to the pathogenesis of hypertensive nephrosclerosis triggered by AngII.