Fbxo22-mediated KDM4B degradation determines selective estrogen receptor modulator activity in breast cancer
Yoshikazu Johmura, … , Tomohiko Ohta, Makoto Nakanishi
Yoshikazu Johmura, … , Tomohiko Ohta, Makoto Nakanishi
Published December 3, 2018; First published November 12, 2018
Citation Information: J Clin Invest. 2018;128(12):5603-5619. https://doi.org/10.1172/JCI121679.
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Research Article Endocrinology

Fbxo22-mediated KDM4B degradation determines selective estrogen receptor modulator activity in breast cancer

Abstract

The agonistic/antagonistic biocharacter of selective estrogen receptor modulators (SERMs) can have therapeutic advantages, particularly in the case of premenopausal breast cancers. Although the contradictory effects of these modulators have been studied in terms of crosstalk between the estrogen receptor α (ER) and coactivator dynamics and growth factor signaling, the molecular basis of these mechanisms is still obscure. We identify a series of regulatory mechanisms controlling cofactor dynamics on ER and SERM function, whose activities require F-box protein 22 (Fbxo22). Skp1, Cullin1, F-box–containing complex (SCFFbxo22) ubiquitylated lysine demethylase 4B (KDM4B) complexed with tamoxifen-bound (TAM-bound) ER, whose degradation released steroid receptor coactivator (SRC) from ER. Depletion of Fbxo22 resulted in ER-dependent transcriptional activation via transactivation function 1 (AF1) function, even in the presence of SERMs. In living cells, TAM released SRC and KDM4B from ER in a Fbxo22-dependent manner. SRC release by TAM required Fbxo22 on almost all ER-SRC–bound enhancers and promoters. TAM failed to prevent the growth of Fbxo22-depleted, ER-positive breast cancers both in vitro and in vivo. Clinically, a low level of Fbxo22 in tumor tissues predicted a poorer outcome in ER-positive/human epidermal growth factor receptor type 2–negative (HER2-negative) breast cancers with high hazard ratios, independently of other markers such as Ki-67 and node status. We propose that the level of Fbxo22 in tumor tissues defines a new subclass of ER-positive breast cancers for which SCFFbxo22-mediated KDM4B degradation in patients can be a therapeutic target for the next generation of SERMs.

Authors

Yoshikazu Johmura, Ichiro Maeda, Narumi Suzuki, Wenwen Wu, Atsushi Goda, Mariko Morita, Kiyoshi Yamaguchi, Mizuki Yamamoto, Satoi Nagasawa, Yasuyuki Kojima, Koichiro Tsugawa, Natsuko Inoue, Yasuo Miyoshi, Tomo Osako, Futoshi Akiyama, Reo Maruyama, Jun-ichiro Inoue, Yoichi Furukawa, Tomohiko Ohta, Makoto Nakanishi

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Figure 1

Proteasome-dependent protein degradation is required for the antagonistic activity of TAM.

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Proteasome-dependent protein degradation is required for the antagonisti...
(A) Experimental outline (top). MCF7 cells starved of E2 for 72 hours were cultured in medium containing E2 (10 nM) for 6 hours and then incubated in medium containing 4-OHT (100 nM) with or without MG132 (10 μg/ml). Total RNA from the treated cells collected at the indicated time points was subjected to qRT-PCR analysis using the indicated primers. Data are presented as the mean ± SD of 3 independent experiments. ****P < 0.001 and ***P < 0.005, by 2-tailed Student’s t test. (B) Nuclear extracts (NEs) of cells treated as in A were collected at 12 hours and immunoprecipitated using the indicated antibodies and then subjected to immunoblotting. (C) MCF7 cells starved of E2 for 72 hours were cultured with medium containing E2 (10 nM) for 18 hours (E2), or for 6 hours with or without MG132 (10 μg/ml) and then starved of E2 (E2-dep) for 12 hours. Total RNA from the treated cells was subjected to qRT-PCR analysis using the indicated primers. Data are presented as the mean ± SD of 3 independent experiments. *P < 0.05, by 2-tailed Student’s t test. (D) Nuclear extracts of cells treated as described in C were immunoprecipitated using the indicated antibodies and subjected to immunoblotting. (E) MCF7 cells expressing the indicated doxycycline-inducible shRNAs (Dox-shRNA-MCF7 cells) were starved of E2 in the presence of doxycycline (1 μg/ml) for 72 hours and then treated with E2 (10 nM) for 6 hours. Nuclear extracts were immunoprecipitated using the indicated antibodies and subjected to immunoblotting.