Human-antigen R (HuR) expression in hypertension: downregulation of the mRNA stabilizing protein HuR in genetic hypertension.

In aged spontaneously hypertensive rats (SHR), vasorelaxant responses to NO are attenuated compared with normotensive control rats (Wistar-Kyoto [WKY]) because of a decreased expression of the important NO receptor soluble guanylyl cyclase (sGC). Because the expression of sGC subunits alpha1 and beta1 is controlled at the post-transcriptional level by the mRNA-binding protein human-antigen R (HuR), we now assessed whether or not altered expression of HuR could account for downregulation of sGCalpha1 and sGCbeta1 in genetic hypertension. The expression of HuR (and sGCalpha1 and sGCbeta1) in aortas from aged SHR was significantly decreased at the mRNA and protein level compared with age-matched WKY rats, whereas expression of HuR was not different in prehypertensive young (2 months of age) SHR and age-matched WKY rats. The mRNA-binding activity of HuR in native aortic protein extracts from aged SHR was markedly reduced compared with normotensive WKY rats, as detected by RNA electrophoretic mobility shift analysis, using biotin-labeled adenine and uracil (AU)-rich element (ARE)-containing RNA probes from the 3'-untranslated region of sGCalpha1 and sGCbeta1. In contrast, ARE-binding activity was not different between prehypertensive young SHR and young WKY rats. In vitro RNA degradation assays using the same AU-rich sGC mRNA probes revealed an accelerated sGCalpha1 and sGCbeta1 mRNA decay in the presence of native protein extract from hypertensive SHR, which was less rapid with aortic protein from normotensive WKY rats. These findings suggest that in this animal model of genetic hypertension, the reduced expression of sGC subunits is mediated by downregulation of the sGC mRNA-stabilizing protein HuR.