This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The overall goal of my research is to investigate the mechanisms by which developmental exposure to dioxin decreases cardiac beta-adrenergic receptor (beta-AR) signaling and induces dilated cardiomyopathy and heart failure in laboratory animals. We hypothesized that dioxin bound to its receptor, the aryl hydrocarbon receptor (AhR), along with its dimerization partner, ARNT, directly regulates beta-AR gene expression via putative dioxin response elements (DREs). DREs are particular sequences of DNA and exist in several genes. DREs bind to activated dioxin receptor and increase expression levels of the DRE-containing gene. We identified several putative DREs in the 5'- flanking regions of the human, rat, mouse, and chicken beta1-AR and beta2-AR genes and determined their functionality. Only one of the putative DREs, """"""""DRE 2"""""""" of the human beta2-AR promoter, binds with AhR and ARNT protein and shows modest increases in gene expression level following beta-naphthtoflavone (BNF) exposure. Furthermore, we observed no change in beta2-AR mRNA levels in a rat heart (H9c2) cell line exposed to ?NF, nor any change in beta1-AR and beta2-AR mRNA levels in hearts of chick embryos exposed to dioxin. This is unexpected but rather convincing data that the putative DREs of the beta1-AR and beta2-AR genes are not functional. Therefore, the dioxin-induced dysregulation of ?-AR receptor signaling must not result from direct interaction of the AhR and ARNT proteins altering beta-AR gene expression.
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