Abstract
Clinical advancement in the field of breast cancer (BC) has given access to better diagnosis and treatment. Despite these advancements,BCrelapse remains a clinical problem. The clinical and research evidence have mainly attributedBCrelapse to dormantBCcells (BCCs) in bone marrow, (BM). Research from our lab and others have shown that the dormantBCCswithin the BM niche are cancer stem cells (CSCs). The CSCs interact with the resident BM cells such as macrophages, fibroblasts and mesenchymal stem cells (MSCs), via cytokines, exosomes and/or connexin mediated gap junction intercellular communication (GJIC). This study focuses on GJIC. Connexin 43 (Cx43) has been demonstrated to be involved in GJIC between CSCs and BM supporting cells. Since Cx43 is also important for hematopoiesis, this particular molecule could not be a druggable target to reverse the dormant phase of BCC. We therefore seek for additional target to disrupt GJIC in order for the CSCs to become chemosensitive. This study tested the hypothesis that low level of N-cadherin, an epithelial to mesenchymal transition (EMT) protein, is required for Cx43-mediated GJIC. Knockdown of N-cadherin significantly reduced GJIC, based on dye transfer between CSCs and BM stromal cells. Furthermore, N-cadherin knockdown appeared to induce the differentiation of CSCs as demonstrated by decrease expression of stem cell-associated genes and reduced ability of serial passaging of spheroids. Evidence of direct interaction between N-cadherin and Cx43 was shown by single cell imaging with the Amnis, flow-cytometry, and immunoprecipitation. Cytokines such as TGFb and CXCL12 regulate the expression of N-cadherin. In vivo studies using a model ofBCdormancy indicated that the dormantCSCs was significant reduced in theBMfollowing knockdown of N-cadherin or Cx43. In summary, the molecular interaction between N-cadherin and Cx43 seems to be critical in sustaining dormancy of CSCs in BM. The results have implications to reverse BC dormancy for precise targeting.
DOI: 10.14343/JCSCR.2018.6e1006