Tumor necrosis factor (TNF) signaling via the receptors TNFRI and TNFR2 contributes to both cell death and protection after stroke or other brain trauma. We must understand how these different signaling pathways work if we are to develop ways to minimize tissue damage after stroke or other trauma. TNFRI causes cell death by a well-understood apoptosis pathway that activates a caspase cascade and is inhibited by caspase inhibitors such as zVAD.fink. However, TNF can also kill cells by a mechanism that cannot be inhibited by zVAD.fink, and which may also contribute to TNF-induced tissue damage. The molecular mechanism by which this pathway kills cells is unknown. We recently made the surprising discovery that TRADD, an adaptor protein that mediates downstream signaling through TNFR1 binding at the cell membrane, is not solely a cytoplasmic protein. Rather, TRADD shuttles into and out of the nucleus via active nuclear import and export. Furthermore, an isolated domain from TRADD is localized exclusively in the nucleus where it induces apoptosis via a mechanism that is not inhibited by zVAD.fmk. We therefore hypothesize: nuclear signaling from TRADD contributes to the resistant cell death that is caused by TNF. Here, we propose to test this hypothesis with the following specific aims. 1) To determine the role of TRADD nuclear import and export in inducing cell death. 2) To determine how TRADD induces cell death from the nucleus. Our studies relate to the purpose of the R21 mechanism for NS-00-01 I in the following ways. Our experiments will provide the first information regarding the significance and mechanism of action of this unexpected nuclear activity of TRADD and. establish the concept that nuclear shuttling of a receptor interacting protein activates a novel apostolic pathway. The work proposed here should also form a strong basis for future projects to determine how these activities contribute to the tissue damage that is caused by stroke or other brain trauma. This information may lead to improved strategies for therapeutic manipulation of TNF signaling pathways in damaged brain tissues.
| Morgan, Michael; Thorburn, Jacqueline; Pandolfi, Pier Paolo et al. (2002) Nuclear and cytoplasmic shuttling of TRADD induces apoptosis via different mechanisms. J Cell Biol 157:975-84 |
