The Cell Fate Determination Factor DACH1 In Breast Cancer

Vladimir M Popov, Thomas Jefferson University

Abstract

Initially isolated as the dominant suppressor of the mutant epidermal growth factor receptor (ellipse), the Dachshund gene plays a key role in metazoan development as a part of the Retinal Determination Gene Network (RDGN). Drosophila dac gene encodes a well-conserved nuclear protein related to the Sno/Ski family of co-repressors. The function of dac as a part of RDGN in sex determination and arthropod complex eye formation emphasizes the importance of this gene in development. A human homologue of Drosophila dac, DACH1, encodes a protein predominantly localized to the nucleus. DACH1 contains two highly conserved domains, DachBox-N and DachBox-C, through which DACH1 has been shown to interact with different proteins. Even though no sequence-specific DNA binding activity has been indentified, DACH1 is capable of binding naked DNA. Recent studies have demonstrated an important role for human DACH1 in tumorigenesis, in particular, breast and prostate tumorigenesis. In a view of an important finding that the expression of the cell fate determination factor DACH1 was lost in poor prognosis invasive breast cancer, function of DACH1 in breast cancer cell migration and invasion was investigated. Mouse embryonic fibroblasts derived from Dach1-/- mice demonstrated endogenous Dach1 constitutively represses cellular migration. DACH1 inhibited cellular migration and invasion of oncogenetransformed human breast epithelial cells. To investigate the possible pathways involved in DACH1-mediated inhibition of migration and invasion in human cancer, an unbiased proteomic analysis was conducted. These experiments identified IL-8 as a critical target of DACH1 mediating breast cancer cellular migration and metastasis in vivo. DACH1 bound endogenous IL-8 promoter through the AP-1 and NF-κB binding site. Furthermore, following the results of the study showing a positive correlation between DACH1 expression and improved survival by 40 months in breast tumor patients, relationship between DACH1 and estrogen receptor α (ERα) was investigated. DACH1 and ERα expressions were inversely correlated in human breast cancer. Moreover, immunofluorescent staining for DACH1 in normal versus breast cancer tissue identified intra-nucleolar localization in normal and extra-nucleolar localization in breast cancer tissue. DACH1 bound and inhibited ERα function. Nuclear DACH1 expression inhibited estradiol (E2)-induced DNA synthesis and cellular proliferation. DACH1 bound ERα in immunoprecipitation western blotting, associated with ERα in chromatin immunoprecipitation, and inhibited ERα transcriptional activity, requiring a conserved DS domain. Proteomic analysis identified proline, glutamic acid, and leucine rich protein 1 (PELP1) as a DACH1-binding protein. The DACH1 COOH terminus was required for binding to PELP1. DACH1 inhibited induction or ERα signaling. E2 recruited ERα and disengaged corepressors from DACH1 at an endogenous ER response element, allowing PELP1 to serve as an ERα coactivator. DACH1 expression, which is lost in poor prognosis human breast cancer, functions as an endogenous inhibitor of ERα functions. To further investigate the function of DACH1 nucleolar localization in normal breast tissue and loss of the same in cancer, immunofluorescent staning for DACH1 and nucleolar marker nucleophosmin (NPM) in normal and breast cancer tissues was conducted. Results confirmed nucleolar localization of DACH1 in normal breast tissue. Using mass spectrometry and direct sequencing we identified nucleophosmin (NPM) as an endogenous DACH1-associated protein. DACH1 binding to NPM in immunoprecipitation western blotting required DACH1 carboxyl terminus and the C-terminus was sufficient for NPM binding. The association between DACH1 and nucleophosmin was enhanced by endogenous casein kinase 2. Inhibition of casein kinase 2 during early tumor progression may contribute to the loss of nucleolar DACH1 and its inhibitory interaction with oncogenic nucleophosmin. The loss of nucleolar DACH1 may serve as a useful marker of the early states of tumorigenesis. Our overall studies on DACH1 in breast tumorigenesis have yielded valuable conclusions and enabled us to gain a significant insight into the function of the cell fate determination factor in breast tumorigenesis. Function of DACH1 in cellular migration, invasion, hormone signaling and the importance of the cellular localization have been investigated. These studies are considered a valuable addition to the growing body of evidence supporting significance of DACH1 in the inhibition of mammary tumorigenesis.

Subject Area

Molecular biology|Cellular biology|Biochemistry|Oncology

Recommended Citation

Popov, Vladimir M, "The Cell Fate Determination Factor DACH1 In Breast Cancer" (2010). ETD Collection for Thomas Jefferson University. AAI3551852.
https://jdc.jefferson.edu/dissertations/AAI3551852

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