The von Hippel-Lindau protein pVHL suppresses renal tumorigenesis in part by promoting degradation of hypoxia-inducible HIF-alpha transcription factors1, and additional mechanisms have been proposed2. pVHL also stabilizes plant homeodomain (PHD) protein Jade-1, which is a candidate renal tumor suppressor that may correlate with renal cancer risk3-5. We show here that Jade-1 binds the oncoprotein β-catenin in Wnt-responsive fashion. Moreover, Jade-1 destabilizes wild-type β-catenin, but not a cancer-causing form of β-catenin. While β-TrCP ubiquitinates only phosphorylated β-catenin6, Jade-1 ubiquitinates both phosphorylated and non-phosphorylated β-catenin and therefore regulates canonical Wnt signaling in both Wnt-off and Wnt-on phases. Thus, the different characteristics of β-TrCP and Jade-1 may ensure optimal Wnt pathway regulation. Furthermore, pVHL down-regulates β-catenin in a Jade-1-dependent manner and inhibits Wnt signaling, supporting a role for Jade-1 and Wnt signaling in renal tumorigenesis. The pVHL tumor suppressor and the Wnt tumorigenesis pathway are therefore directly linked through Jade-1.

Regulation of global chromatin acetylation is important for chromatin remodeling. A small family of Jade proteins includes Jade-1L, Jade-2, and Jade-3, each bearing two mid-molecule tandem plant homology domain (PHD) zinc fingers. We previously demonstrated that the short isoform of Jade-1L protein, Jade-1, is associated with endogenous histone acetyltransferase (HAT) activity. It has been found that Jade-1L/2/3 proteins co-purify with a novel HAT complex, consisting of HBO1, ING4/5, and Eaf6. We investigated a role for Jade-1/1L in the HBO1 complex. When overexpressed individually, neither Jade-1/1L nor HBO1 affected histone acetylation. However, co-expression of Jade-1/1L and HBO1 increased acetylation of the bulk of endogenous histone H4 in epithelial cells in a synergistic manner, suggesting that Jade1/1L positively regulates HBO1 HAT activity. Conversely, small interfering RNA-mediated depletion of endogenous Jade resulted in reduced levels of H4 acetylation. Moreover, HBO1-mediated H4 acetylation activity was enhanced severalfold by the presence of Jade-1/1L in vitro. The removal of PHD fingers affected neither binding nor mutual Jade-1-HBO1 stabilization but completely abrogated the synergistic Jade-1/ 1L-and HBO1-mediated histone H4 acetylation in live cells and in vitro with reconstituted oligonucleosome substrates. Therefore, PHDs are necessary for Jade-1/1L-induced acetylation of nucleosomal histones by HBO1. In contrast to Jade-1/1L, the PHD zinc finger protein ING4/5 failed to synergize with HBO1 to promote histone acetylation. The physical interaction of ING4/5 with HBO1 occurred in the presence of Jade-1L or Jade-3 but not with the Jade-1 short isoform. In summary, this study demonstrates that Jade-1/1L are crucial co-factors for HBO1-mediated histone H4 acetylation.Gene for apoptosis and differentiation-1, Jade-1 (PHF17), has been identified as a protein interacting with the von Hippel Lindau gene product by a yeast two-hybrid approach (1). The 509-amino acid Jade-1 protein contains one canonical Cys 4 HisCis 3 plant homology domain (PHD) 2 followed by a noncanonical extended PHD domain, which are zinc-binding motifs. Most PHD family proteins are localized to the cell nucleus and are associated with chromatin, chromatin-modifying enzymes, and transcription factors (2, 3). We recently reported that endogenous Jade-1 is localized to the cell nucleus and that ectopically expressed Jade-1 possesses intrinsic transcriptional activity (4). Most importantly, we demonstrated that Jade-1 can promote endogenous histone H4 acetylation by associating with a histone H4-specific endogenous HAT. Interestingly, the histone H4-specific HAT, TIP60, interacted with Jade-1 physically and functionally in vitro and in live cells.Gene data base analysis revealed two other Jade-1 homologs, Jade-2 (PHF15) and Jade-3 (PHF16). Jade-3 has been previously identified by screening genes induced by steroid hormones in breast cancer cells (5). Jade-1 mRNA gives rise to two protein products, the full-length Jade-1L consisting of ...

Medical therapies are lacking for advanced renal cancer, so there is a great need to understand its pathogenesis. Most renal cancers have defects in the von Hippel-Lindau tumor suppressor pVHL. The mechanism by which pVHL protein functions in renal tumor suppression remains unclear. Jade-1 is a short-lived, kidney-enriched transcription factor that is stabilized by direct interaction with pVHL. Loss of Jade-1 stabilization by pVHL correlates with renal cancer risk, making the relationship between Jade-1 and renal cancer compelling. We report that Jade-1 expression was barely detectable in all tested renal cancer cell lines, regardless of VHL status. Strikingly, proteasome inhibitor treatment increased endogenous Jade-1 expression up to 10-fold. Jade-1 inhibited renal cancer cell growth, colony formation, and tumor formation in nude mice. Intriguingly, Jade-1 also affected the pattern of cell growth in monolayer culture and 3D culture. Jade-1 increased apoptosis by 40 -50% and decreased levels of antiapoptotic Bcl-2. Antisense Jade-1-expressing cells confirmed these results. Therefore, Jade-1 may suppress renal cancer cell growth in part by increasing apoptosis. Jade-1 may represent a proapoptotic barrier to proliferation that must be overcome generally in renal cancer, perhaps initially by pVHL inactivation and subsequently by increased proteasomal activity. Therefore, Jade-1 may be a renal tumor suppressor.pVHL ͉ renal cancer ͉ von Hippel-Lindau ͉ proteasome