Breast carcinoma escape from the primary site leads to mortality. Recently, it has been found that tumor properties of aggressiveness required for dissemination may revert within metastatic microenvironment to enable seeding, in part through reversal of methylation of E-cadherin. The initial mesenchymal transition that allows breast cancer cells to disseminate from the primary tumor is driven via EGFR family signaling (HER1 and HER2). However, during metastatic seeding, EGFR family signaling is downregulated and E-cadherin is re-expressed. We present preliminary data showing that downregulation of Kaiso, or restricting Kaiso from the nucleus, drives breast cancer cells towards a differentiated epithelial-like phenotype. Thus, our novel foundational model of metastatic seeding posits a key molecular link that enables the breast carcinoma cells to incorporate into the ectopic environment and even become dormant, that of retaining Kaiso out of the nucleus so that E-cadherin can be re-expressed. In this proposal we will establish that both metastatic seeding and tumor dormancy can be minimized if not eliminated by modulating this molecular cascade.
The aims to be tested are Specific Aim 1. Determine how EGF receptor signaling causes relocalization of Kaiso into the nucleus and whether this alters DNA methylation and the carcinoma cell phenotype. In this aim, we will 1) Determine the influence of autocrine EGFR signaling on Kaiso localization/expression and methylation status of E-cadherin in breast cancer, and 2) Determine breast cancer phenotype upon sequestration of Kaiso outside of the nucleus, using pharmacological and molecular constructs, and 3) Determine how EGF receptor signaling/cascade coordinately alters Kaiso subcellular localization and DNA methylation in breast cancer cell lines.
Specific Aim 2. 1) Determine whether disruption of Kaiso relocalization into the nucleus alters entry into the metastatic niche and/or the development of tumor dormancy. We will introduce the carcinoma cells into the bioreactor and determine the localization of Kaiso along with the expression of E-cadherin during initial metastatic seeding. 2) Determine the influence of sequestering Kaiso localization outside of the nucleus on tumor dormancy within the organotypic liver microenvironment. 3) Determine the role of nuclear Kaiso on the two steps of escape from the primary tumor and seeding of the metastatic microenvironment in animals. In summary, through the use of primary human explants, established lines, and an innovative human organotypic liver bioreactor as well as animal models, we will determine Kaiso localization and expression levels and that correlate with cell phenotype and cellular behaviors with the tumor microenvironment. Successful completion of these studies would could have immediate impact be on the basic science of tumor biology, and provide paradigm shifting insights into the molecular mechanisms by which breast carcinomas metastasize and enter dormancy, one of the most chilling aspects of progression.
In this proposal we are focusing on a novel transcriptional repressor Kaiso, as the regulator of DNA molecular machinery that enables successful metastasis and entrance and exit of tumor dormancy. This molecule is uniquely positioned as it shuttles between the membrane and the nucleus to alter the DNA structure. Its movement into the nucleus is controlled, at least in part by HER-family members, and its retention out of the nucleus by receptors that bind to the cells of the metastatic organ. This proposal will determine Kaiso's role and whether this can be targeted to limit tumor metastasis or dormancy.