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Homeobox genes are critical in tumor development. An isoform protein of DLX4 called BP1 is expressed in 80% of invasive ductal breast carcinomas. BP1 overexpression is implicated in an aggressive phenotype and poor prognosis. BP1 upregulation is associated with estrogen receptor negativity so those tumors do not respond to antiestrogens. Breast cancer is the second leading cause of death in women. BP1 could serve as both a novel prognostic biomarker for breast cancer and a therapeutic target. In this review, we address the role of BP1 protein in tumorigenesis of breast cancer and four other malignancies. A number of functions of BP1 in cancer are also discussed. Female breast cancer represents 14.6% of all new cancer cases in the USA according to the National Cancer Institute [1]. An estimated 252,710 new cases of invasive breast cancer are expected to be diagnosed in women in the USA in 2017. It is also estimated that 30% of newly diagnosed cancers in women will be breast cancers [2].Breast cancer is a hormone-dependent cancer, and estrogen (17β-estradiol) plays a critical role in the initiation and the progression of this disease [3]. Estrogen, produced by the ovaries, affects the growth and function of mammary glands by binding to the estrogen receptors (ERs) α and β. Through dimerization of the receptor, translocation to the nucleus and interaction with estrogen response elements in the promoter region of targeted genes, gene expression leads to multiple biological outcomes [4]. 70% of invasive breast cancers are ER positive (ER + ), making antiestrogens essential in treating these patients [5]. Targeting the ER or its pathway using tamoxifen (a selective ER modulator) or fulvestrant (an ER downregulator) have been successful therapeutic strategies [6]. However, drug resistance remains a major challenge in treating breast cancer. The main pathway leading to resistance involves loss of ER expression or selection of an ER-negative population of cells. Moreover, these ER-negative breast cancers have a higher histologic grade and a higher proliferative rate and are associated with poorer prognosis. This highlights the key importance of finding alternative targets to treat these patients and identifying a new biomarker for breast cancer prognosis.BP1 protein, an isoform of DLX4, belongs to the homeobox gene family which includes regulatory genes implicated in early development and cell differentiation that are frequently dysregulated in cancer [7]. Therefore, targeting BP1 may provide a new avenue for breast cancer management. The first related paper was published in 1998, when the authors mapped this new homeobox gene to chromosome 17q21 and characterized its role in repression of the β-globin gene [8]. During the last 20 years, several studies have been carried out to measure BP1 levels in breast cancer and other carcinomas, with the primary aim of confirming its diagnostic and prognostic value as a biomarker. We are writing this review to consolidate and update all of the available information on BP1. Homeobox...

Obesity increases the risk of cancer death among postmenopausal women with estrogen receptor-positive (ER+) breast cancer, but the direct evidence for the mechanisms is lacking. The purpose of this study is to demonstrate direct evidence for the mechanisms mediating this epidemiologic phenomenon. Transcriptomic profiles of pretreatment biopsies from a prospective cohort of 137 ER+ breast cancer patients were analyzed. A transgenic and an orthotopic/syngeneic obese mouse models were created to phenocopy obese patients and evaluate the effect of obesity on breast carcinogenesis and tumor progression, and to explore further direct mechanisms. Functional transcriptomic analysis of untreated human ER+ breast cancer revealed that obesity was associated with increased insulin signaling among others. Many of the functional changes in obese patients were linked to cancer hallmarks. Obese mouse models recapitulated the functional transcriptomic landscape of obesity-associated changes seen in human ER+ breast cancer and demonstrated the role of the Akt/mTOR pathway in obesity-induced breast carcinogenesis and tumor progression. Functional transcriptomic analysis identified 85 biological functions common to humans and mice. An in vitro co-culture model revealed that adipocyte-secreted adipokines (e.g., TIMP-1) regulate adipocyte-induced breast cancer cell proliferation and invasion. The human transcriptomic data provided direct evidence for the roles of hyperinsulinemia, estrogen signaling, adipokine secretion, and inflammation in the link between obesity and ER+ breast cancer. Our animal experiments provide strong evidence for the causal relationship between obesity and accelerated carcinogenesis and cancer progression and for potential therapeutic interventions by blocking these signaling pathways. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P3-01-04.

Background: Beta protein 1 (BP1), discovered in our lab, is an isoform protein of the DLX4 gene that is a member of the homeobox gene family. Previous work showed BP1 mRNA was activated in 80% of invasive ductal breast (IDC) tumors, where 100% of estrogen receptor (ER) negative tumor tissues and 73% of ER positive tumor tissues were BP1 positive. Moreover, high BP1 levels were associated with tumor cell survival, breast cancer aggressiveness and metastasis. BP1 overexpression was found to stimulate known oncogenes including BCL2 and c-Myc. Exosomes are nano-sized membrane-bound vesicles released by various cells and play important roles in intercellular communication. In addition, researchers found that exosomal proteins have unique characteristics compared to traditional biomarkers for carcinoma diagnosis and prognosis. Therefore, we hypothesized that BP1 protein may be packed in exosomes, and analysis of exosomal BP1 protein could provide a novel biomarker for diagnosis or prognosis of breast cancer. Materials and Methods: Exosomes were isolated using the commercially available Exosome Precipitation Solution. In cell line experiments, fluorescent immunohistochemistry was used to detect the location of BP1 protein. Levels of BP1 protein were determined in cell extracts (CE) and conditioned media (CM) using Western Blot analysis. The hypothesis that exosomal BP1 protein may be related to the development of breast cancer was investigated with clinical serum samples purchased from Capital Bioscience. Total exosomal protein levels in the serum were analyzed using BCA assay, and exosomal BP1 protein levels were determined using Western blot. In order to develop a method that could be easily used in the clinic, an ELISA assay was also designed to assess exosomal BP1 protein concentrations in the serum from metastatic breast cancer patients and normal controls. Results: It was observed that BP1 protein is localized to the nucleus, the cytoplasm and the conditioned media of MCF-7 cells. In addition, experiments with cell lines showed that the secreted BP1 protein could be internalized by cells and exhibited mitogenic activity, which is related to cancer metastasis. Moreover, it was observed that exosomal BP1 is included in secreted BP1 protein in the conditioned media. Experiments with serum samples demonstrated that the total exosomal protein levels have no significant differences between that in breast cancer patients and in normal controls. However, the results of Western blot and ELISA both showed exosomal BP1 protein levels were significantly higher in breast cancer samples compared to normal controls (P < 0.05). Moreover, Western blot results suggested that ER positive patients have much more (P < 0.05) exosomal BP1 protein in the serum compared to ER negative patients. Conclusion: It was shown for the first time that BP1 protein is exosomally packaged in breast cancer patients’ serum. The significant difference in the exosomal BP1 protein levels between the serum from women with metastatic breast cancer and that from normal controls indicated that exosomal BP1 protein in the serum could be a potential prognostic biomarker for breast cancer. Furthermore, the ELISA assay, designed to be easily used for exosomal BP1 protein quantification, may have many uses in the clinic through aiding in prognosis, monitoring therapy and early detection. Citation Format: Yaoxian Lou, Paul Goldsmith, Jinguen Rheey, Patricia E. Berg. Potential prognostic value of exosomal Beta Protein 1 in breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P5-01-25.