Multifunction Steroid Receptor Coactivator, E6-Associated Protein, Is Involved in Development of the Prostate Gland

Abstract

In this study we report that deletion of E6-associated protein (E6-AP) in mice results in a smaller prostate gland compared with that in normal wild-type animals. To investigate the mechanism(s) by which E6-AP affects prostate gland growth and development, we carried out both in vitro and in vivo experiments. In this study we show that E6-AP interacts with androgen receptor (AR) in a hormone-dependent manner and enhances the transactivation function of AR. Our in vivo data from E6-AP-null prostate glands show that the level of AR protein is elevated while the level of the AR target protein, probasin, is decreased. In contrast, the level of AR protein is decreased, and its target protein is increased in an E6-AP-overexpressing stable cell line, suggesting that E6-AP modulates both the protein level and the activity of AR. In addition, we show that the levels of phosphatidylinositol 3-kinase, total Akt, and phosphorylated Akt are decreased in E6-AP-null prostate, suggesting that E6-AP deletion down-regulates the signaling of the phosphatidylinositol 3-kinase-Akt pathway. We also show that RhoA negatively regulates AR function, and RhoA levels are increased in E6-AP-null prostate. Furthermore, expression levels of p53, Bax, active caspases, and apoptotic index are increased in E6-AP-null prostate. Collectively, our data suggest that E6-AP deletion attenuates the growth and development of the prostate gland by interfering with AR function as well as by stimulating p53-mediated apoptosis.

E6AP is required for replicative and oncogene-induced senescence in mouse embryo fibroblasts

“…It is the prototype of the subfamily of E3 ligases that covalently bind ubiquitin and are characterized by a C-terminal HECT (homologous to the E6AP C terminus) domain (for review see Scheffner et al, 1993;Talis et al, 1998;Ciechanover, 2006;and Beaudenon and Huibregtse, 2008). E6AP has also been reported to affect p53 levels in the absence of HPV-E6 (Jiang et al, 1998b andKhan et al, 2006). In this study we demonstrate a novel role for E6AP in the regulation of cellular senescence.…”

“…A role for E6AP in the degradation of p53 has been observed in HPV-infected cells (Scheffner et al, 1990), as well as in prostate and neuronal cells (Jiang et al, 1998b;Khan et al, 2006;Mishra and Jana, 2008). The reason for this opposing effect on p53 regulation is currently unclear.…”

“…E6AP is required for replicative and oncogene-induced senescence in MEFs Y Levav-Cohen et al (Khan et al, 2006) and neuronal cells (Jiang et al, 1998b andJana, 2008), it was important to examine the effect of E6AP deficiency on the expression levels of p53. For this purpose we compared the levels of p53 expression between WT and E6AP KO MEFs, where p53 KO MEFs were used as a control.…”

E6AP promotes the degradation of the PML tumor suppressor

“…To address this question, we measured the ability of E6AP to ubiquitinate PML in an in vitro ubiquitination assay. For a substrate 35 S-Met-labeled PML was translated in a rabbit reticulocyte lysate. E6AP and UbcH5b E2 were generated in baculovirus or Escherichia coli BL21 expression systems.…”

Calmodulin, a regulatory partner of the estrogen receptor alpha in breast cancer cells

“…This mechanism proceeds cyclically, grafting additional ubiquitin moieties to those already present in the target protein. E6AP has been identified as an E3 ubiquitin ligase implicated in ligand-induced elimination of steroid hormone receptors, (Khan et al, 2006;Nawaz et al, 1999b). Remarkably, CaM has been shown to attenuate the E6AP-mediated ubiquitination of ERα, as well as to decrease the capacity of E6AP to associate with the receptor, suggesting that it may protect the latter against proteasomal degradation .…”