Implication of Ref-1 in the repression of renin gene transcription by intracellular calcium.

OBJECTIVE: The production of renin, which catalyzes the rate-limiting step of the renin-angiotensin system, is tightly regulated by intracellular second messengers. Among them, an increase of intracellular calcium represses renin gene expression. This inhibition of gene expression by intracellular calcium is exceptional, and the molecular mechanism supporting this phenomenon has not yet been identified. As the renin gene is negatively regulated by calcium in the same way as the parathormone (PTH) gene, we hypothesized that a similar molecular transcriptional mechanism could be involved.
RESULTS: Analysis of the human renin proximal promoter led to the identification of a negative calcium response element (nCaRE), which is identical to the region of the PTH promoter and is involved in its repression by calcium. Transfection experiments in renin-expressing chorio-decidual cells demonstrated the transcriptional functionality of the human renin promoter nCaRE. In addition, mutation of nCaRE suppressed the sensitivity of the renin promoter to the increase in intracellular calcium. Gel shift assays demonstrated that Redox factor 1, a multifunctional protein involved in the repair of damaged DNA and the redox activation of AP-1 transcriptional factors, binds specifically to nCaRE. Immunostaining showed that this factor is translocated from the cytoplasm to the nucleus in response to an increase in the intracellular calcium concentration.
CONCLUSION: Thus, the repression of renin expression by intracellular calcium may be mediated by the calcium-induced translocation of Ref-1 to the nucleus, where it binds to the renin promoter nCaRE, to repress the transcription of the renin gene.