TRUSS, TNF-R1, and TRPC Ion Channels Synergistically Reverse Endoplasmic Reticulum Ca2+ Storage Reduction in Response to m1 Muscarinic Acetylcholine Receptor Signaling

Although most signaling responses initiated by tumor necrosis factor-alpha (TNF-alpha) occur in a Ca2+-independent fashion, TNF-alpha receptor signaling augments Ca2+ entry induced by G alpha(q/11) G-protein coupled receptors (GPCRs) in endothelial cells and increases transendothelial permeability. The signaling events involved in GPCR-induced Ca2+ influx have been characterized and involve storeoperated Ca2+ entry facilitated by the Ca2+ permeable ion channel, transient receptor potential canonical 4 (TRPC4). Little is known about the mechanisms by which TNF-alpha receptor signaling augments GPCR-induced Ca2+ entry. TNF-alpha Receptor Ubiquitous Signaling and Scaffolding protein (TRUSS) is a tumor necrosis factor receptor-1 (TNF-R1)-associated protein whose gene name is TRPC4-associated protein (TRPC4AP). The goal of our study was to test the hypothesis that TRUSS serves to link TNF-R1 and GPCR-signaling pathways at the level of TRPC4 by: (i) determining if TRUSS and TNF-R1 interact with TRPC4, and (ii) investigating the role of TRUSS, TNF-R1, and TRPC4 in GPCR-induced Ca2+ signaling. Here, we show that TRUSS and TNF-R1 interact with a sub-family of TRPC channels (TRPC1, 4, and 5). In addition, we show that TRUSS and TNF-R1 function together with TRPC4 to elevate endoplasmic reticulum Ca2+ filling in the context of reduced endoplasmic reticulum Ca2+ storage initiated by G-protein coupled m1 muscarinic acetylcholine receptor (m1AchR) signaling. Together, these findings suggest that TNF-R1, TRUSS, and TRPC4 augment Ca2+ loading of endoplasmic reticulum Ca2+ stores in the context of m1AchR stimulation and provide new insights into the mechanisms that connect TNF-R1 to GPCR-induced Ca2+ signaling. J. Cell. Physiol. 225: 444-453, 2010. (C) 2010 Wiley-Liss, Inc.