Research Assistant Professor, Division of Cancer and Developmental Biology
Current Research Focus:
1. Identification of new candidates that regulate epithelial to mesenchymal transition (EMT)
2. Role of p63 isoforms in epithelial to mesenchymal transition (EMT)
Research Focus 1: Breast cancer development involves first the appearance of non-invasive lesions followed by their transition to invasive breast cancers. A non-invasive breast cancer is one that is contained inside the milk ducts. Through unknown processes, some breast non-invasive cancers escape the boundaries of other normal breast cells and spread into the surrounding breast tissue thus become invasive. The five-year survival for patients diagnosed with breast pre-invasive cancers are significantly better than patients diagnosed with invasive breast cancers. The factors involved in the early stages of this transition are largely unknown.
A hallmark of malignant tumor progression is a migratory phenotype. The driving forces for this phenotype may be the interactions of tumor cells with their microenvironment or accumulation of genetic mutations or both. The process of epithelial to mesenchymal transition (EMT) is believed to be the initiating event promoting early invasive growth. EMT is a developmental switch where polarized epithelial cells change to a highly motile fibroblastic or mesenchymal phenotype. Repression of E-cadherin expression through transcriptional repressors such as Snail or Twist is believed to be the underlying mechanism for the initial stages of EMT. EMT is characterized by down regulation of epithelial specific markers, i.e., E-cadherin, integrins, and Zo-1, and the acquisition of a mesenchymal phenotype, i.e., expression of vimentin.
The main goal of this project is to find novel molecular candidates that play a role in EMT by using a lentiviral shRNA library approach. Identification of novel molecular candidates will be involved in slowing down or stopping the process of early invasive breast cancer progression. Recently, we have developed a novel intraductal transplantation model that closely resemble human non-invasive breast cancers. This model involves introducing human breast cancer cells inside the mouse milk ducts and studying the processes by which the cancer cells escape outside the milk ducts to spread into the surrounding breast tissue environment. These studies have high potential to develop novel therapeutic strategies for breast cancer prevention and ultimately improving survival for patients at high risk for developing breast cancer including those diagnosed with breast non-invasive cancers.
Research Focus 2: p63 is a member of the p53 family. It is critical in the development of stratified epithelial tissues such as epidermis, breast, and prostate. P63 is expressed in at least six protein isoforms with both transactivating and transcriptional repressor activities that can regulate a wide variety of target genes. It has been associated with an important role in cell proliferation, differentiation, and can exert different biologic functions in several tumors.
Only few studies have described the expression of p63 in the mammary gland. In normal breast tissue, p63 is expressed in myoepithelial cells. In highly aggressive estrogen receptor (ERα) negative breast cancers, expression of p63 is confined to a subset cells and have a poor clinical outcome. Noninvasive epithelial neoplasias, such as ductal carcinoma in-situ (DCIS), are surrounded by a p63-positive basal cell population; however, as the tumor progresses to an invasive state, p63 expression is lost in the myoepithelial cells and is acquired by the DCIS cells. These events suggest that changes in p63 expression in myoepithelial vs. epithelial cells may regulate the process of epithelial to mesenchymal transition (EMT), that is, from DCIS to mammary gland tumor invasion.
To understand the role of p63 isoforms in EMT, we have chosen two human DCIS cell lines SUM225 (Her2 overexpressing ) and MCF10A DCIS.Com (basasl type). Our preliminary observation by western blotting indicated that the SUM225 cells express both the TA and deltaN p63 whereas DCIS.com cells express only deltaN isoforms. Transplantation studies using our novel intraductal transplantation (MIND) model revealed that while the SUM225 cells grow within the mouse mammry ducts, they never invade into surrounding tissue. On the hand, DCIS.Com cells grow and invade into the surrounding tissue within 8 weeks. Based on these observations, we hypothesized that p63 isoforms may play a critical role in epithelial to mesenchymal transition (EMT). To study this hypothesis, we plan to take shRNA mediated knockdown approach to stably and specifically knockdown the TAp63 and deltaN p63 isoforms using lentiviral transduction in these two cell lines and will determine the migratory phenotype in vivo in our animal transplantation models as well as in vitro using boyden chamber assay, vimentin reporter assay and E- &N-cadherin expression profile.