TRIM8 Inhibits Breast Cancer Proliferation by Regulating Estrogen Signaling

Abstract Background: Breast cancer (BC) ranks first in female malignancies wordwide, 70% of which are estrogen receptor alpha (ERα) positive. Endocrine treatment, such as tamoxifen, is primary adjuvant therapy for patients with ER-positive BC, while some of them can develop acquired resistance during long-time treatment. Thus, further research on estrogen signaling is of significance to improve the prognosis of BC patients. Methods: In this study, we report that the E3 ubiquitin ligase TRIM8 acts as a novel regulator of ERα signaling. TRIM8 and ERα target genes expression levels were measured by RT-PCR, while protein expression levels were measured by western blot. CCK8 assay, clone formation, and EDU assay were used to measure cells proliferation. Wound healing assay was used to measure cells migration. Protein stability assay and protein ubiquitination analysis were used to detect ERα protein degradation. Co-immunoprecipitation assay was used to detect the interaction domain between TRIM8 and ERα. Results: TRIM8 is downregulated in BC and is associated with poor prognosis. The protein level of TRIM8 is negatively correlated with ERα. RNA-seq result revealed that estrogen signaling maybe a potential target of TRIM8. Knockdown of TRIM8 can significantly enhance BC cell proliferation and migration in vitro and in vivo. And this effect can be reversed by ERα depletion. Further mechanistic studies have shown that TRIM8 interacts with AF1 domain of ERα via its RING domain in the cytoplasm, and affects poly-ubiquitination of ERα protein. Conclusion: Our study reveals an interesting post-translational mechanism between ERα and TRIM8 in ER-positive BC, TRIM8 may be a potential therapeutic target for BC treatment.