Introduction and questions: 

In the rat heart an alternative renin transcript [exon(1A-9)] is expressed, which is characterized by the absence of exon 1 in exchange for a short 80 bp sequence (exon1A) from intron 1 of the renin gene. Its expression is up regulated after myocardial infarction and the encoded cytosolic renin acts cardio-protective under ischemia related conditions. Therefore we hypothesized that 1) an alternative promoter exists in intron 1 of the renin gene and 2) the promoter activity is regulated by ischemia related condition such as glucose depletion, hypoxia or oxidative stress.

Material and Methods: 

To clarify these hypotheses we cultured H9c2 cardiomyoblasts under ischemia relevant condition like glucose depletion, hypoxia or 100 mM H₂O₂ for 6 h and 20 h. Then the expression levels of the transcripts for cytosolic exon(1A-9)renin and secretory exon(1–9)renin were determined by TaqMan analysis and related to the Ywhaz expression. Further, promoter analysis was performed time dependently by the dual luciferase assay using different deletion fragments integrated within the pGL4.10 vector.

Results: 

After 6 h as well as 20 h glucose depletion we found a significant increase of exon(1A-9)renin mRNA from basal 0,5± 0,02x10^-3 to 1,8±0,5x10^-3 and 1,2±0,6x10^-3. Hypoxia enhanced exon(1A-9)renin expression significantly to 1,3±0,3x10^-3 and 2,1±0,1x10^-3. 100 mM H₂O₂ also increased exon(1A-9)renin expression. Expression of exon(1–9)renin could not be observed. Promoter analysis revealed a minimal promoter activity around 180 bp downstream of the transcription point. We also found an ubiquitary inhibitory element around -757 bp and a strong glucose-responsible enhancer element in the region around -546 bp. Glucose depletion increased promoter activity 6 times.

Conclusion: 

The data verify the existence of an unknown promoter for the transcription of the alternative exon(1A-9)renin. The promoter activity is further stimulated under ischemia related conditions.