Breast cancer cells which metastasize to bone marrow can remain dormant and survive multiple rounds of adjuvant chemotherapy. The re-awakening of dormant populations, particularly in estrogen receptor (ER)-positive patients, has been associated with tumor cell proliferation and poor patient outcomes. Tumor dormancy can be modelled in vitro by exposing cancer cells on fibronectin-coated plates to bFGF-2, a mammary differentiation factor abundant in the bone marrow stroma, which causes partial re-differentiation, cell spreading and re-expression of integrin-α5β1. Ligation of integrin-α5β1 by fibronectin and activation of the PI3K pathway both contribute to dormant cell survival. Our study has uncovered a novel potential role for the adhesion protein Junctional Adhesion Molecule-A (JAM-A) in tumor dormancy. JAM-A overexpression has previously been linked to increased risk of metastasis in breast cancer patients, and its expression regulates the angiogenic functions of bFGF-2. Furthermore, since loss of JAM-A causes down-regulation of the α5β1 downstream effector FAK, we hypothesized that JAM-A is required for maintenance of breast cancer cell dormancy. To investigate this, JAM-A was transiently silenced using siRNA in MCF-7 breast cancer cells grown on fibronectin-coated plates and exposed to FGF-2. JAM-silenced cells exhibited downregulations in the protein expression of integrin-α5β1 and FAK in this model, and failed to exhibit the cortical actin redistribution and morphological spreading which characterize dormant cells. We next investigated a potential relationship between JAM-A expression and pro-inflammatory cytokines which have been linked with the re-awakening of dormant cells in post-menopausal women. Exposure of MCF-7 cells to the pro-inflammatory cytokines IL-1β, TNF-α, IL-6 and IL-8 decreased JAM-A expression in in a concentration-dependent fashion, suggesting that the loss of JAM-A could be associated with re-awakening from tumor dormancy. We are currently probing alterations in JAM-A expression and that of integrin-α5β1 in matched human primary breast tumor specimens and bone marrow metastases. Since JAM-high dormant cells express high mRNA levels of the stemness factors (Sox2, Oct3/4, Nanog) and have high Aldefluor activity, our data also suggest that JAM-A may be required for a stem-like phenotype. To conclude, our data support a model whereby JAM-A is important for the maintenance of dormancy in breast cancer cells in a simulated bone marrow microenvironment, and represents a novel therapeutic target worthy of investigation in breast cancer.

Citation Format: Sri Harikrishna Vellanki, Rodrigo G. Cruz, Ann M. Hopkins. The adhesion protein JAM-A is important for maintenance of tumor dormancy in breast cancer cells, and JAM-A high-dormant cells have stem cell characteristics [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4921. doi:10.1158/1538-7445.AM2017-4921