Delineation of Sequences Essential for Specific Promoter Activation During Pressure Overloaded Hypertrophy or Factor-Induced Hypertrophy

Earlier studies from our laboratory have demonstrated the appearance of a high M_r (182-kDa) phosphoprotein during early stages of development of cardiac hypertrophy in the sera of animals subjected to aortic constriction. Furthermore, it has been reported that the injection of purified 182-kDa protein into normal animals led to the development of hypertrophy, and the injection of polyclonal antibodies into the aorta constricted animals completely, abolished the development of hypertrophy, and downregulated the expression of the -Myosin heavy chain (MHC) gene. To identify the cis-acting regulatory element(s), which controls induction of the -MHC gene in acute pressureoverloaded cardiac hypertrophy induced by the 182-kDa protein, the -MHC promoter fragments of various lengths linked to the chloramphenicol acetyl transferase (CAT) reporter were injected into the left ventricular apex of adult rats, which underwent aortic constriction/182-kDa protein injection or were sham-operated. Activation of the -MHC gene by the 182-kDa protein was studied by a chimeric gene constructed by fusion of the 5′ regulatory regions of the -MHC gene to bacterial CAT, demonstrating that at least 431 bp of the -MHC promoter (+103 toβ328) with one E-box motif, along with upstream regulatory sequences such as the TATA box, N-Fe, C-rich, and M-CAT elements are required for -MHC gene expression in vivo during cardiac hypertrophy induced by the 182-kDa protein.