Identification of novel regulatory GRE-binding elements in the porcine IP3R1 gene promoter and their transcriptional activation under glucocorticoid stimulation.

Inositol 1,4,5-trisphosphate receptor 1 (IP3R1) is a type of ligand-gated calcium channel that is expressed predominantly in mammalian skeletal muscle, where it acts as a key regulator of calcium homeostasis. In meat, calcium disequilibrium is accompanied by the deterioration of meat quality. Here we show that serum cortisol concentration was higher and the IP3R1 gene expression level increased markedly in pigs exposed to high stress. In porcine primary muscle cells, dexamethasone (DEX, a synthetic glucocorticoid) increased the protein levels of porcine IP3R1 and GRα, and cell apoptosis, and the specific GRα inhibitor RU486 attenuated these effects. DEX also increased the expression of IP3R1 at both the gene and protein levels, and this expression was attenuated by RU486, siRNA against GRα, and the transcriptional inhibitor actinomycin D. DEX significantly reduced cell viability and increased the intracellular calcium concentration, and these effects were attenuated by siRNA against GRα. Bioinformatics analyses predicted a potential glucocorticoid response element (GRE) located in the region -326 to -309 upstream of the IP3R1 promoter and highly conserved in pigs and other mammalian species. Promoter analysis showed that this region containing the GRE was critical for transcriptional activity of porcine IP3R1 under DEX stimulation. This was confirmed by deletion and site-mutation methods. EMSA and ChIP assays showed that this potential GRE bound specifically to GRα and this complex activated the transcription of the IP3R1 gene. Taken together, these data suggest that DEX-mediated induction of IP3R1 influences porcine muscle cells through the transcriptional activation of a mechanism involving interactions between GRα and a GRE present in the proximal IP3R1 promoter. This process can lead to an imbalance in intracellular calcium concentration, which may subsequently activate the apoptosis signal and decrease cell activity, and cause deterioration of meat quality.