The Ubiquitin-Conjugating Enzyme UBCH7 Acts as a Coactivator for Steroid Hormone Receptors

Abstract

We investigated the role of the ubiquitin-conjugating enzyme UBCH7 in nuclear receptor transactivation. Using transient transfection assays, we demonstrated that UBCH7 modulates the transcriptional activity of progesterone receptor (PR) and glucocorticoid, androgen, and retinoic acid receptors in a hormone-dependent manner and that the ubiquitin conjugation activity of UBCH7 is required for its ability to potentiate transactivation by steroid hormone receptors (SHR). However, UBCH7 showed no significant effect on the transactivation functions of p53 and VP-16 activation domain. Depletion of endogenous UBCH7 protein by small interfering RNAs suggests that UBCH7 is required for the proper function of SHR. Furthermore, a chromatin immunoprecipitation assay demonstrated the hormone-dependent recruitment of UBCH7 onto estrogen receptor-and PR-responsive promoters. Additionally, we show that UBCH7 and E6-associated protein (E6-AP) synergistically enhance PR transactivation. We also demonstrate that UBCH7 interacts with steroid receptor coactivator 1 (SRC-1) and that UBCH7 coactivation function is dependent on SRC-1. Taken together, our results reveal the possible role of UBCH7 in steroid receptor transactivation and provide insights into the mechanism of action of UBCH7 in receptor function.Steroids, retinoids, thyroid hormones, and vitamin D control various biological processes, including growth, development, and homeostasis, via their cognate nuclear receptors, which are comprised of a superfamily of structurally related intracellular ligand-activated transcription factors (2, 57). In the absence of hormones, these receptors are transcriptionally inactive and often found in a large complex consisting of heat shock proteins (hsp90, hsp70, and hsp56) and other chaperone proteins. When bound to hormone, these receptors undergo a conformational change, dissociation from heat shock proteins, receptor dimerization, phosphorylation, DNA binding to the enhancer elements of target genes, interaction with coactivators, and subsequent recruitment of general transcription factors to form a preinitiation complex followed by induction of target gene transcription (4,36).

UbcH7 interacts with the glucocorticoid receptor and mediates receptor autoregulation

“…This interaction enhanced their transcriptional activities. Moreover, UbcH7 modulated nuclear receptor transactivation, including GR function, by interaction with the co-activator SRC-1 (Verma et al 2004). Independently, we identified UbcH7 as the physical interacting partner of the GR in a yeast two-hybrid screen.…”

“…This may reflect altered stability of the GR or its interactions with other proteins in the absence of authentic UbcH7 activity. For example, UbcH7 has been shown to interact with GR co-modulator proteins, and may be important for stabilizing the GR, or its interactions with UbcH7 (Verma et al 2004). By inhibiting the enzymatic activity of endogenous UbcH7 on these partner proteins, the dominant negative UbcH7 may stabilize interactions between the GR and the UbcH7.…”

“…explored the interactions between the GR and UbcH7, a direct interaction we identified in the yeast two-hybrid screen, and a functional interaction, which has been reported by other groups for the GR and other members of the nuclear receptor superfamily (Verma et al 2004). Co-immunoprecipitation experiments also identified interaction between GR and endogenous UbcH7, but only in cells transfected with the dominant negative UbcH7.…”

Estrogen Inhibits Transforming Growth Factor β Signaling by Promoting Smad2/3 Degradation

“…A ubiquitinconjugating enzyme (E2) also may be part of the coactivator complex (40). One report showed that an E2, UbcH7, interacts with SRC-1 to regulate the transcriptional activity of NRs (41). Such an interaction between ER␣ and an E2 may be necessary for Smad degradation.…”

Nuclear hormone receptor degradation and gene transcription: An update

“…Uba3-an ubiquitin-activating enzyme of the NEDD8 pathway, have all been reported to act as coactivators for NHRs (16, 20 -22). Our laboratory has recently demonstrated yet another ubiquitin-conjugating enzyme, UbcH7 which also acts as a coactivator and enhances the transcriptional activity of NHRs (17). Other examples of dual function proteins are the coactivator p300, which is known to possess intrinsic E3 ligase as well as HAT activities and the general transcription factor TAFII250, which has an intrinsic ubiquitin-conjugating activity (23,24).…”