Tumor necrosis factor-α-induced protein 8 (TNFAIP8) is a stress-response gene that has been associated with cancer, but no studies have differentiated among or defined the regulation or function of any of its several recently described expression variants. We found that TNFAIP8 variant 2 (v2) is overexpressed in multiple human cancers, whereas other variants are commonly downregulated in cancer (v1) or minimally expressed in cancer or normal tissue (v3-v6). Silencing v2 in cancer cells induces p53-independent inhibition of DNA synthesis, widespread binding of p53, and induction of target genes and p53-dependent cell cycle arrest and DNA damage sensitization. Cell cycle arrest induced by v2 silencing requires p53-dependent induction of p21. In response to the chemotherapeutic agent doxorubicin, p53 regulates v2 through binding to an intragenic enhancer, together indicating that p53 and v2 engage in complex reciprocal regulation. We propose that TNFAIP8 v2 promotes human cancer by broadly repressing p53 function, in essence offsetting p53-dependent tumor suppression. Cell Death and Differentiation (2017) 24, 181-191; doi:10.1038/cdd.2016 published online 11 November 2016 Tumor necrosis factor-α-induced protein 8 (TNFAIP8) is the founding member of a recently described family of environmental stress response genes that are induced by TNFα. TNFAIP8 has been shown to promote or inhibit apoptosis, depending on cell type and context. 1,2 Although little is known about TNFAIP8, it has recently been found to be overexpressed in a wide range of human cancers. Some studies have suggested protumor functions for TNFAIP8, including enhancement of cell survival, proliferation, and metastasis [3][4][5][6][7][8][9] and resistance to cancer chemotherapeutics in mice.
4,10Nonetheless, nothing is known about how TNFAIP8 influences responses to DNA damage in cancer cells. Moreover, several transcript variants from the TNFAIP8 gene were recently registered in the NCBI reference sequence database, but no study to date has differentiated among them or defined the factors that govern their expression.The tumor suppressor p53 is a transcription factor that regulates many biological processes through its target gene network. Some of the well-characterized p53 target genes including p21/CDKN1A, growth arrest and DNA damageinducible 45a (GADD45A) and Bcl-2-like protein 4 (BAX) together promote senescence, cell cycle arrest, and apoptosis, all of which may contribute to the tumor suppressing functions of p53.
11,12Additional noncanonical tumorsuppressive pathways from p53 have recently been identified. [13][14][15] Improved characterization of the p53 DNAbinding sequence with modern sequencing techniques has led to the identification of a rapidly expanding list of p53 target genes. [16][17][18] Continued identification of these genes and characterization of their mechanisms of regulation and function will be critical to a full understanding of p53 and for full realization of opportunities to intervene upon p53 in cancer.Here, we identify ...