Association of positive EBAG9 immunoreactivity with unfavorable prognosis in breast cancer patients treated with tamoxifen

EBAG9-deficient mice display decreased bone mineral density with suppressed autophagy

Estrogen receptor-binding fragment associated antigen 9 (EBAG9) exerts tumor-promoting effects by inducing immune escape. We focused on the physiological functions of EBAG9 by investigating the bone phenotypes of Ebag9-knockout mice. Female Ebag9-knockout mice have fragile bones with lower bone mineral density (BMD) compared with wild-type mice. Histomorphometric analyses demonstrated that lower BMD was mainly caused by decreased bone formation. Serum bone turnover markers showed that enhanced bone resorption also contributed to this phenotype. We revealed that EBAG9 promoted autophagy in both osteoblastic and osteoclastic lineages. In addition, the knockdown of Tm9sf1, a gene encoding a protein that functionally interacts with EBAG9, suppressed autophagy and osteoblastic differentiation of the murine preosteoblastic cell line MC3T3-E1. Finally, overexpression of TM9SF1 rescued the suppression of autophagy caused by the silencing of Ebag9. These results suggest that EBAG9 plays a physiological role in bone maintenance by promoting autophagy together with its interactor TM9SF1.

Molecular markers associated with the outcome of tamoxifen treatment in estrogen receptor-positive breast cancer patients: scoping review and in silico analysis

Tamoxifen (TMX) is used as adjuvant therapy for estrogen receptor-positive (ER+) breast cancer cases due to its affinity and inhibitory effects. However, about 30% of cases show drug resistance, resulting in recurrence and metastasis, the leading causes of death. A literature review can help to elucidate the main cellular processes involved in TMX resistance. A scoping review was performed to find clinical studies investigating the association of expression of molecular markers profiles with long-term outcomes in ER+ patients treated with TMX. In silico analysis was performed to assess the interrelationship among the selected markers, evaluating the joint involvement with the biological processes. Forty-five studies were selected according to the inclusion and exclusion criteria. After clustering and gene ontology analysis, 23 molecular markers were significantly associated, forming three clusters of strong correlation with cell cycle regulation, signal transduction of proliferative stimuli, and hormone response involved in morphogenesis and differentiation of mammary gland. Also, it was found that overexpression of markers in selected clusters is a significant indicator of poor overall survival. The proposed review offered a better understanding of independent data from the literature, revealing an integrative network of markers involved in cellular processes that could modulate the response of TMX. Analysis of these mechanisms and their molecular components could improve the effectiveness of TMX.

Identification of novel prognosis-related genes associated with cancer using integrative network analysis

Prognosis identifies the seriousness and the chances of survival of a cancer patient. However, it remains a challenge to identify the key cancer genes in prognostic studies. In this study, we collected 2064 genes that were related to prognostic studies by using gene expression measurements curated from published literatures. Among them, 1820 genes were associated with copy number variations (CNVs). The further functional enrichment on 889 genes with frequent copy number gains (CNGs) revealed that these genes were significantly associated with cancer pathways including regulation of cell cycle, cell differentiation and mitogen-activated protein kinase (MAPK) cascade. We further conducted integrative analyses of CNV and their target genes expression using the data from matched tumour samples of The Cancer Genome Atlas (TCGA). Ultimately, 95 key prognosis-related genes were extracted, with concordant CNG events and increased up-regulation in at least 300 tumour samples. These genes, and the number of samples in which they were found, included: ACTL6A (399), ATP6V1C1 (425), EBAG9 (412), FADD (308), MTDH (377), and SENP5 (304). This study provides the first observation of CNV in prognosis-related genes across pan-cancer. The systematic concordance between CNG and up-regulation of gene expression in these novel prognosis-related genes may indicate their prognostic significance.

Extracellular vesicle-mediated EBAG9 transfer from cancer cells to tumor microenvironment promotes immune escape and tumor progression

The antitumor immune response is a critical defense system that eliminates malignant cells. The failure of the system results in immune escape and proceeds to tumor growth. We have previously showed that estrogen receptor-binding fragment-associated antigen 9 (EBAG9) is a relevant cancer biomarker and facilities immune escape of cancers from the immune surveillance. EBAG9 in cancer cells suppresses T-cell infiltration into tumor in vivo, whereas that in host immune cells functions as a limiter for T-cell cytotoxicity. Considering that EBAG9 plays immune suppressive roles in both tumor and microenvironment, we here questioned whether EBAG9 is a transferable protein from cancer to surrounding T cells and affects antitumor immune response. In this study, we showed that spontaneous development of prostate cancer was repressed in a model of Ebag9 knockout mice crossed with transgenic adenocarcinoma of the mouse prostate (TRAMP) mice. We identified TM9SF1 as a collaborative EBAG9 interactor, which regulates epithelial-mesenchymal transition (EMT) in cancer cells. Notably, extracellular vesicles (EVs) from EBAG9-overexpressing prostate cancer cells have a potential to facilitate immune escape of tumors by inhibiting T-cell cytotoxicity and modulating immune-related gene expression in T cells. Furthermore, we showed that a neutralizing antibody for EBAG9 could rescue the EV-mediated immune suppression by recovering T-cell cytotoxicity. In addition to its autocrine functions in cancer cells, EBAG9 could behave as a new class of immune checkpoint that suppresses tumor immunity in a secretory manner. We propose that EBAG9-targeting cancer treatment could be alternative therapeutic options for advanced diseases, particularly for those with EBAG9 overexpression.

miR-378a-3p modulates tamoxifen sensitivity in breast cancer MCF-7 cells through targeting GOLT1A

Breast cancer is a hormone-dependent cancer and usually treated with endocrine therapy using aromatase inhibitors or anti-estrogens such as tamoxifen. A majority of breast cancer, however, will often fail to respond to endocrine therapy. In the present study, we explored miRNAs associated with endocrine therapy resistance in breast cancer. High-throughput miRNA sequencing was performed using RNAs prepared from breast cancer MCF-7 cells and their derivative clones as endocrine therapy resistant cell models, including tamoxifen-resistant (TamR) and long-term estrogen-deprived (LTED) MCF-7 cells. Notably, miR-21 was the most abundantly expressed miRNA in MCF-7 cells and overexpressed in TamR and LTED cells. We found that miR-378a-3p expression was downregulated in TamR and LTED cells as well as in clinical breast cancer tissues. Additionally, lower expression levels of miR-378a-3p were associated with poor prognosis for tamoxifen-treated patients with breast cancer. GOLT1A was selected as one of the miR-378a-3p candidate target genes by in silico analysis. GOLT1A was overexpressed in breast cancer specimens and GOLT1A-specific siRNAs inhibited the growth of TamR cells. Low GOLT1A levels were correlated with better survival in patients with breast cancer. These results suggest that miR-378a-3p-dependent GOLT1A expression contributes to the mechanisms underlying breast cancer endocrine resistance.

EBAG9 modulates host immune defense against tumor formation and metastasis by regulating cytotoxic activity of T lymphocytes

Estrogen receptor-binding fragment-associated antigen 9 (EBAG9) is a primary estrogen-responsive gene that we previously identified in MCF-7 breast cancer cells using the CpG genomic binding-site cloning technique. The expression of EBAG9 protein is often upregulated in malignant tumors, suggesting that this protein is involved in cancer pathophysiology. In the present study, we investigated the role of EBAG9 in host defense against implanted tumors in Ebag9-knockout (Ebag9KO) mice. MB-49 mouse bladder cancer cells were subcutaneously implanted into Ebag9KO and control mice. We found that tumor formation and metastasis to the lung by MB-49 cells were substantially reduced in Ebag9KO mice compared with control mice. The infiltration of CD8⁺, CD3⁺ and CD4⁺ T cells into the generated tumors was enhanced in Ebag9KO mice compared with controls. Notably, CD8⁺ T cells isolated from tumors in Ebag9KO mice exhibited substantial upregulation of immunity- and chemoattraction-related genes, including interleukin-10 receptor, interferon gamma, granzyme A, granzyme B and chemokine (C-X-C motif) receptor 3 compared with CD8⁺ T cells from tumors in control mice. The CD8⁺ T cells isolated from tumors in Ebag9KO mice also exhibited enhanced degranulation and increased cytolytic activity. Furthermore, the adoptive transfer of CD8⁺ T cells isolated from tumors in Ebag9KO host could repress tumor growth by MB-49 cells implanted in wild-type host. These results suggest that EBAG9 modulates tumor growth and metastasis by negatively regulating the adaptive immune response in host defense. EBAG9 could be a potential target for tumor immunotherapy.