Expression of endothelial-leukocyte adhesion molecule is dramatically induced by inflammatory cytokines. This increased expression occurs at the transcriptional level and requires activation of the nuclear factor-kappaB (NF-kB) system. Recent studies indicate that the p65 component of NF-kB, like many signal dependent transcriptional activators, interacts with the transcriptional co-activator CREB-binding protein (CBP). In this continuing project, we will investigate whether CBP is part of a novel level of nuclear regulation linking diverse signaling systems in endothelial cells and test the hypothesis that competition for limiting amounts of CBP facilitates the activation of some signal dependent genes at the expense of others. In the renewal period we propose to determine if this regulatory system is relevant to the process of endothelial activation during inflammatory responses.
In Specific Aim #1, the antagonistic interactions between p65 and other signal-dependent transcription factors occur because for limiting amounts of the common transcriptional co-activator, CBP. These studies will examine the levels of CBP expression in quiescent and cytokine-activated cultured endothelial cells, determine if levels of the co-activator limit NF-kappaB dependent gene expression, and will explore the molecular basis of the antagonistic interaction.
In Specific Aim #2, the pathophysiologic consequences of CBP over- expression in endothelial cells will be examined in a transgenic model of endothelial activation. In this defined genetic context, we will determine if CBP over expression increases induction of NF-kappaB dependent genes and diminishes the negative regulatory effects of the activated nuclear receptors on the induction of kappaB-dependent genes. Like the induction process, decreased expression of the endothelial adhesion molecules following cytokine exposure is an active process that occurs at the transcriptional level. This level of negative regulation my be key in preventing inappropriate or prolonged expression of some adhesion molecule genes.
In Specific Aim #3, the mechanisms responsible for the post-induction transcriptional repression of E-selectin will continue to be investigated. These studies will determine the role of the dual specificity phosphatases in limiting the expression of this adhesion molecule gene using tools developed in this project, as well as unique cellular and animal reagents developed by collaborators. Collectively, the findings from these studies should provide insights into two new endothelial regulatory systems: first, they should indicate if CBP serves an integration function for interactions between p65 and other classes of CBP dependent transcription factors during cytokine-induced gene expression; and second, they should define the mechanisms which tightly control the post-induction transcriptional repression of the E- selectin gene.
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