TRIM3 Facilitates Estrogen Signaling and Modulates Breast Cancer Cell Progression

Abstract Background: Breast cancer ranks NO.1 in women cancer incidence worldwide, while 70% of breast cancers are estrogen receptor (ER) alpha positive. Compared with ER alpha negative breast cancer, which is more aggressive and shorter prognosis, ER alpha positive breast cancer could be well-controlled by endocrine therapy. Most of ER alpha positive breast cancer patients could benefit from selective ER alpha modulators, such as tamoxifen. However, approximately half of them will eventually develop endocrine resistance, making it an important clinical issue in breast cancer therapy. Thus, decoding the turnover of estrogen signaling, including the control of ER alpha expression and stability, are critical to the improvement of breast cancer therapeutics. Methods: TRIM3 and ER alpha protein expression levels were measured by western blot, while the ER alpha target genes were measured by real-time PCR. MTT assay was used to measure cell viability. RNA sequencing was analyzed by Ingenuity Pathway Analysis. Identification of ER alpha signaling was accomplished with luciferase assays, real-time RT-PCR and Western blotting. Protein stability assay and ubiquitin assay was used to detect ER alpha protein degradation. The ubiquitin-based Immuno-precipitation based assays were used to detect the specific ubiquitination manner happened on ER alpha. Results: In our current study, we identified TRIM3 as an E3 ligase, which promotes ER alpha signaling and breast cancer progression. TRIM3 depletion inhibits breast cancer cell proliferation and invasion, while the unbiased RNA sequencing data indicates that TRIM3 is required for the activation of estrogen signaling in whole genomic scale. Molecular studies show that TRIM3 associates with ER alpha and promotes ER alpha mono-ubiquitination. Conclusion: our study provides a novel post-translational mechanism in estrogen signaling. Modulation of TRIM3 expression or its function could be an interesting approach for breast cancer treatment.