cAMP responsiveness of the bovine calpastatin gene promoter

Previous studies have shown that transcription of the gene encoding bovine calpastatin, an inhibitor of the calcium-activated cysteine protease calpain, is upregulated following activation of cAMP-dependent signaling pathways. In this study, deletion and site-directed mutagenesis experiments were performed to identify cis elements conferring cAMP responsiveness. Heterologous promoter assays demonstrated that all cAMP-responsive cis elements were located within -102 nucleotides (nt) of transcription initiation. Deletion of an element (GTCA) at nt +13 that is identical to half of the palindromic cAMP-responsive element (TGACGTCA) identified in other cAMP-responsive gene promoters had no effect on the response of the calpastatin promoter to dibutyryl-cAMP, although a 67% reduction in basal promoter activity was observed. In contrast, two point mutations in a cis element at nt -76 (GTCA to aTCt) abolished cAMP responsiveness. These results demonstrate that the calpastatin promoter sequence between nt -1653 and +130 contains a single cAMP-responsive element (GTCA) located at nt -76, and suggest a direct molecular pathway by which activation of cAMP signaling could lead to increased calpastatin gene transcription and reduction in calpain-mediated proteolysis.