Caveolin-1 associates with TRAF2 to form a complex that is recruited to tumor necrosis factor receptors

Tumor necrosis factor (TNF) receptor-associated factor (TRAF) 2 is an intra cellular adapter protein, which, upon TNF stimulation, is directly recruite d to the intracellular region of TNF receptor 2 (TNFR2) or indirectly, via TRADD, to the intracellular region of TNF receptor 1 (TNFR1). In cultured h uman umbilical vein endothelial cells, endogenous TRAF2 colocalizes with th e membrane-organizing protein caveolin-1 at regions of enrichment subjacent to the plasma membrane as detected by confocal fluorescence microscopy. Bo th endogenous and transfected TRAF2 protein coimmunoprecipitate with caveol in-1 in the absence of ligand. Upon TNF treatment, the TRAF2-caveolin-1 com plex transiently associates with TRADD, and upon overexpression of TNFR2, t he TRAF2-caveolin-1 complex stably associates with and causes redistributio n of this receptor as detected by confocal fluorescence microscopy, In huma n embryonic kidney 293 cells, which have minimal endogenous expression of c aveolin-1, cotransfection of TRAF2 and caveolin-1 results in spontaneous as sociation of these proteins which can further associate with and redistribu te transfected TNFR2 molecules. The association of caveolin-1 with TNFR2 de pends upon TRAF2. Cotransfection of caveolin-1 protein increases TRAF2 prot ein expression levels in HEK 293 cells, which correlates with enhancement o f TNF and TRAF2 signaling, measured as transcription of a NF-kappaB promote r-reporter gene, although the caveolin-enhanced response to TNF is attenuat ed at higher caveolin levels. These findings suggest that intracellular dis tribution of activated TNF receptors may be regulated by caveolin-1 via its interaction with TRAF2.