55840

EAF2

BM040|TRAITS|U19;ELL associated factor 2;EAF2;ELL associated factor 2

ELL-associated factor 2|testosterone-regulated apoptosis inducer and tumor suppressor protein

3q13.33

protein-coding

Androgens control prostate homeostasis and regulate androgen response genes. Here, we report the identification and characterization of U19, a novel testosterone-regulated apoptosis inducer with tumor suppressive activity. U19 is an evolutionarily conserved protein expressed in many human tissues, with the most abundant expression in the prostate, bone marrow, kidney, and lymph nodes. Overexpression of U19 in 12 surveyed cell lines induced apoptosis, and new protein synthesis is required for apoptosis induction. expression of U19 in xenograft prostate tumors markedly induced apoptosis and inhibited tumor growth in vivo. Consistent with its tumor-suppressive role, U19 down-regulation was observed in all of the surveyed prostate cancer cell lines and in 19 of 23 clinical human prostate tumor specimens. Loss of heterozygosity analysis revealed U19 allelic loss in 19 of the 23 specimens. Furthermore, two of the specimens had homozygous U19 deletions, and one specimen had hypermethylated U19 promoter, indicating that U19 can be inactivated genetically or epigenetically. These observations suggest that U19 is growth inhibitory and tumor suppressive and that the disruption of androgen-dependent growth inhibition via U19 down-regulation is commonly associated with prostate cancer progression.

Von Hippel-Lindau (VHL) disease results from the inactivation of the VHL gene and is characterized by highly vascular tumors. A consequence of VHL loss is the stabilization of hypoxia-inducible factor (HIF) alpha subunits and increased expression of HIF target genes, which include pro-angiogenic growth factors such as vascular endothelial growth factor (VEGF). In mice, homozygous deletion of VHL is embryonic lethal due to vascular abnormalities in the placenta; and, VHL(+/-) mice develop proliferative vascular lesions in several major organs, most prominently the liver. Loss of ELL-associated factor (EAF2) in murine models has also been shown to induce increased vascular density in the liver as well as the prostate. Previously, EAF2 was determined to be a binding partner of VHL and loss of EAF2 induced a reduction in pVHL levels and an increase in hypoxia induced factor 1alpha (HIF1alpha) levels in vitro. Here we characterized the cooperative effects of VHL- and EAF2-deficiency on angiogenesis in the liver and prostate of male mice. VHL deficiency consistently increased the incidence of hepatic vascular lesions across three mouse strains. These vascular lesions where characterized by an increase in microvessel density, and staining intensity of VHL target proteins HIF1alpha and VEGF. EAF2(-/-)VHL(+/-) mice had increased incidence of proliferative hepatic vascular lesions (4/4) compared to VHL(+/-) (10/18) and EAF2(-/-) (0/5) mice. Prostates of EAF2(-/-)VHL(+/-) mice also displayed an increase in microvessel density, as well as stromal inflammation and prostatic intraepithelial neoplasia. These results suggest that cooperation of VHL and EAF2 may be critical for angiogenic regulation of the liver and prostate, and concurrent loss of these two tumor suppressors may result in a pro-angiogenic phenotype.

Eaf factors play a crucial role in tumor suppression and embryogenesis. To investigate the potential mechanism of Eaf activity, we performed loss- and gain-of-function assays in zebrafish using morpholino and mRNA injections, respectively. We found that eaf1 and eaf2 inhibit Wnt/beta-catenin signaling, thereby modulating mesodermal and neural patterning in the embryo. Moreover, ectopic expression of eaf1 and eaf2 in embryos and cultured cells blocked beta-catenin reporter activity. By immunoprecipitation, we also observed that Eaf1 and Eaf2 bound to the Armadillo repeat region and C-terminus of beta-catenin, as well as to other beta-catenin transcription complex proteins, such as c-Jun, Tcf and Axin, suggesting the formation of a novel complex. In addition, the N-terminus of Eaf1 and Eaf2 bound to beta-catenin and exhibited dominant-negative activity, whereas the C-terminus appeared to either harbor a suppression domain or to recruit a repressor. Both the N- and C-terminus must be intact for Eaf1 and Eaf2 suppressive activity. Lastly, we demonstrate a conservation of biological activities for Eaf family proteins across species. In summary, our evidence points to a novel role for Eaf1 and Eaf2 in inhibiting canonical Wnt/beta-catenin signaling, which might form the mechanistic basis for Eaf1 and Eaf2 tumor suppressor activity.