Triple-Negative Breast Cancers (TNBCs) are considered to be among the most drug resistant, virulent and difficult to treat subtype of breast cancer and often associated with the Epithelial Mesenchymal Transition (EMT) and a high propensity for early metastasis. EMT is a complex process that regulates embryogenesis, organogenesis, and wound repair [1] and is characterized by cells transforming from epithelial cells that are cuboidal and adherent to mesenchymal cells that are spindle-shaped and migratory leading to increased invasion and migration [2]. Snail (Snail1) promotes EMT, is expressed at high levels in tumors and has been associated with breast tumor recurrence [3]. We have previously shown that Snail expression can be inhibited by muscadine grape skin extract (MSKE), a natural grape product rich in anthocyanins that is currently in Phase II clinical trials for treatment of localized prostate cancer and is non-toxic to normal cells [4,5]. It is now well accepted that cysteine proteases such as Cathepsin L (Cat L) promote the degradation of basement membranes and extracellular matrix, thereby facilitating invasion and metastasis [6]. The presence of Cat L in nucleus of triple-negative breast and colon cancer have been associated with poor prognosis [7,8]. Recent evidence has challenged the intracellular lysosome-restricted role of this cysteine protease with the demonstration that Cat L functions in the regulation of cell cycle progression through its presence in the nucleus and is able to proteolytically process the CDP/Cux (also commonly known as p110Cux1) transcription factor [9] . Additionally, CDP/Cux has been shown to increase Snail transcription leading to repression of E cadherin and increased tumor migration and invasion in mouse mammary epithelial cells [10]. Preliminary data indicate that Snail overexpression in breast cancer cells increases Cat L expression and activity that can be antagonized by treatment with MSKE or Cat L inhibitor, Z-FY-CHO. Our data also indicates that in MCF-7 cells overexpressing Snail, Cat L is localized to the nucleus compared to the empty vector where Cat L is cytoplasmic. We hypothesize that Snail may promote nuclear Cat L expression and activity allowing cleavage of CDP/CUX which by positive feedback increases Snail transcription leading to increased EMT and tumor progression in TNBCs; these effects can be abrogated by MSKE. Our objectives are (1) To determine whether Snail promotes the nuclear localization of Cat L, which promotes EMT in TNBC (2) To determine the mechanism by which Snail promotes nuclear localization of Cat L and test whether that can be overcome by MSKE. These studies will identify the novel role of Snail in promoting TNBC via nuclear Cat L and investigate natural products such as MSKE that can be used in the treatment of TNBC that will not affect normal cells.
In the first aim on this proposal we propose a concept that Snail transcription factor can promote the nuclear localization of Cathepsin L (Cat L) and that African American women may express higher Snail and nuclear Cat L that may lead to increased breast cancer cell invasion and migration. In the second aim we want to examine the mechanism by which Snail promotes nuclear localization of Cat L and target nuclear Cat L and Snail with a natural product, muscadine grape skin extract (MSKE). Using the following proposed aims we hope to determine the importance of nuclear Cat L, and Snail transcription factor in breast cancer progression.
| Burton, Liza J; Henderson, Veronica; Liburd, Latiffa et al. (2017) Snail transcription factor NLS and importin ?1 regulate the subcellular localization of Cathepsin L and Cux1. Biochem Biophys Res Commun 491:59-64 |
