Tumor necrosis factor receptor (TNFR) signaling mediates cell death and inflammation and is implicated in cancer. TNFR-associated death domain (TRADD) is a cytoplasmic adaptor protein required for cell death and pro-inflammatory signaling. Using a mouse model for skin carcinoma to investigate tumor formation in Tradd-deficient (Tradd–/–) mice, Chio et al. discovered that Tradd–/– mice developed tumors faster than did wild-type mice. In response to constitutively active Ras, some primary cell types increase expression of the gene encoding the nuclear protein p19Arf, which stabilizes the tumor suppressor and transcription factor p53, thus leading to cellular senescence and preventing transformation. Compared to wild-type murine embryonic fibroblasts (MEFs), Tradd–/– MEFs, transduced with constitutively active HRasV12, exhibited decreased growth arrest, reduced p19Arf protein abundance (but not the abundance of its transcript), and reduced accumulation of p53. The stability of p19Arf is controlled by ubiquitylation. TRADD overexpression, in HEK293 cells in which the proteasome was inhibited, reduced the amount of ubiquitylated (Ub)–p19Arf. TRADD mutated in its putative nuclear export signal, which accumulated in the nucleus, even further reduced the amount of Ub-p19Arf in cells in which the proteasome was inhibited. Similarly, TRADD lacking a nuclear localization sequence did not reduce Ub-p19Arf. Immunoprecipitation of p19Arf with its E3 ubiquitin ligase, ULF, in the presence and absence of overexpressed TRADD, indicated that TRADD diminished the interaction between p19Arf and ULF. ULF also coimmunoprecipitated with TRADD, and they colocalized in the nucleus. Thus, TRADD may function as a tumor suppressor by sequestration of ULF away from p19Arf in the nucleus, allowing the accumulation of p19Arf to promote senescence.
I. I. C. Chio, M. Sasaki, D. Ghazarian, J. Moreno, S. Done, T. Ueda, S. Inoue, Y.-L. Chang, N. J. Chen, T. W. Mak, TRADD contributes to tumour suppression by regulating ULF-dependent p19Arf ubiquitylation. Nat. Cell Biol. 14, 625–633 (2012). [PubMed]