Role of SUMOylation in Full Antiestrogenicity

Abstract

The selective estrogen receptor downregulator (SERD) fulvestrant can be used as second-line treatment for patients relapsing after treatment with tamoxifen, a selective estrogen receptor modulator (SERM). Unlike tamoxifen, SERDs are devoid of partial agonist activity. While the full antiestrogenicity of SERDs may result in part from their capacity to downregulate levels of estrogen receptor alpha (ER␣) through proteasome-mediated degradation, SERDs are also fully antiestrogenic in the absence of increased receptor turnover in HepG2 cells. Here we report that SERDs induce the rapid and strong SUMOylation of ER␣ in ER␣-positive and -negative cell lines, including HepG2 cells. Four sites of SUMOylation were identified by mass spectrometry analysis. In derivatives of the SERD ICI164,384, SUMOylation was dependent on the length of the side chain and correlated with full antiestrogenicity. Preventing SUMOylation by the overexpression of a SUMO-specific protease (SENP) deSUMOylase partially derepressed transcription in the presence of full antiestrogens in HepG2 cells without a corresponding increase in activity in the presence of agonists or of the SERM tamoxifen. Mutations increasing transcriptional activity in the presence of full antiestrogens reduced SUMOylation levels and suppressed stimulation by SENP1. Our results indicate that ER␣ SUMOylation contributes to full antiestrogenicity in the absence of accelerated receptor turnover. E strogens, mainly 17␤-estradiol (E2), play a crucial role in normal breast development but also contribute to mammary tumorigenesis. Antiestrogens (AEs) used for breast cancer treatment and prevention, such as tamoxifen (Tam), raloxifene (Ral), or fulvestrant (9, 17, 52, 63), block the proliferative effects of estrogens on breast epithelial and carcinoma cells by competing for estrogen receptors (ERs) (ER␣ and ER␤). Similar to other nuclear receptors, ERs activate gene transcription by binding to specific DNA sites and recruiting transcriptional coactivators in a liganddependent manner (13,40,41,70,85).AEs prevent ER activation through the induction of an altered conformation of the receptor ligand binding domain (LBD) that suppresses the recruitment of coactivators (8,66,79) and/or increases the recruitment of corepressors (23,34,45,61,77,83,94). However, selective ER modulators (SERMs) (which include Tam and Ral) have partial agonist activity in a tissue-and gene-specific manner. For example, both have estrogenic effects on bone mass (6), and Tam has estrogenic effects on the uterus (2,5,21,88,90), while Ral does not cause uterine hypertrophy (6). Tam and, to a lesser extent, Ral also have partial agonist activity in breast cancer cells in a gene-specific manner (22). The tissue-specific recruitment of coactivators and corepressors is thought to underlie selective partial agonist activity, and alterations in the expression patterns or activity of ER cofactors in breast cancer cells could contribute to the development of resistance to AE-based therapy (23,37,38,45,77,81,82).Other AEs,...

RETRACTED ARTICLE: Regulation of estrogen receptor signaling in breast carcinogenesis and breast cancer therapy

“…Proteomics also identified K299 in the hinge region and K472 in the steroid-binding domain to be sumoylated. The selective estrogen receptor downregulator fulvestrant induces rapid and strong sumoylation of ERα at K171, K180, K299, and K472 residue [151]. These results indicate that ERα sumoylation contributes to full antiestrogenicity in the absence of accelerated receptor turnover.…”

Antiestrogens: structure-activity relationships and use in breast cancer treatment

“…2007, Kocanova et al . 2010, Hilmi et al . 2012), decreased steady-state levels of ERα were observed to variable extents in the presence of endoxifen (a tamoxifen metabolite), raloxifene and bazedoxifene.…”

“…Further, although the steady-state levels of transfected ERα were not decreased but rather increased in the presence of ICI 182,780 in HepG2 cells, ICI 182,780 still acted as an inverse agonist in these cells, whereas tamoxifen had partial agonist activity (Lupien et al . 2007, Hilmi et al . 2012).…”

“…2A); however, combined mutagenesis of these sites did not abolish the SUMOylation of ERα in the presence of ICI 182,780 (Hilmi et al . 2012), suggesting that other sites remain to be discovered.…”

The estrogen receptor antagonist ICI 182,780 can act both as an agonist and an inverse agonist when estrogen receptor α AF-2 is modified

“…Involvement of the F-domain in the antagonist-dependent LBD dimerization occurred not only with the AF-2-mutated ERα but also with WT ERα (28). A portion of the antagonistic effect of ICI on WT ERα results from the stimulation of ERα proteolysis (28)(29)(30), and it was recently reported that ICI induces SUMOylation of human ERα protein and that the mutations of H12 reduced SUMOylation in the presence of ICI (31). These results suggest that the prevention of ICI-dependent proteolysis maintains the dimer formation of AF-2-mutated ERα and that this increases ERE binding and transcription activation.…”