Abstract
Tumor necrosis factor-alpha (TNF-alpha), a proinflammatory cytokine, has been implicated as a central mediator in multiple homeostatic and pathologic processes. Signaling cascades downstream of its cellular cognate receptors, as well as the resultant transcriptional responses have received intense interest in regards to how such signals impact cellular physiology. Notably, TNF-alpha was shown to potentiate neuronal Ca(2+) signaling by enhancing type-1 inositol 1,4,5-trisphosphate receptor (IP(3)R) steady-state mRNA levels. In the present study, we sought to determine the promoter region ultimately responsive to TNF-alpha exposure. We report that a sequence encompassing a specificity protein 1 (SP-1) binding site is necessary for TNF-alpha regulation. Electrophoretic mobility shift analysis demonstrated specific binding to this sequence, while site-directed mutagenesis of this site abrogated both JNK-mediated regulation as well as transcription factor binding. Expression of a dominant-negative SP-1 eliminated both the enhanced promoter activity and the elevated IP(3)R-mediated Ca(2+) signals observed with TNF-alpha exposure. Overall, these data delineate a key pathway by which TNF-alpha in a neuronal environment modulates IP(3)R expression and intracellular Ca(2+) homeostasis.
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