Inflammation-driven Plasticity of Stromal Cells in Luminal-A Breast Cancer

Introduction: Luminal-A is the most common subtype of breast cancer, strongly affected by factors of the tumor microenvironment (TME). The breast TME is populated, among others, by stromal cells which in most research systems have been shown to promote angiogenesis, tumor growth and metastasis. In luminal-A breast cancer, the TME is also enriched with pro-inflammatory factors, including cytokines. The cytokines are expressed in the majority of breast cancer patients and have causative roles in promoting the malignant process, by acting on the tumor cells themselves and on cells of the TME. Our hypothesis is that pro-inflammatory mediators can induce pro-tumorigenic phenotypes in stromal cells, and consequently, enhance breast cancer progression.

Methods and Results: To determine the impact of inflammatory cytokines on stromal cells and on progression of luminal-A tumors thereafter, and to identify the mechanisms involved, we stimulated stromal cells with pro-inflammatory cytokines. Using live cell imaging we were able to identify and quantify significant morphological changes in the stromal cells. RNAseq profiling revealed extensive changes in gene expression, including genes related to the morphological changes, gained by the stromal cells following cytokine stimulation; moreover, changes in gene expression were noted in the cytokine-stimulated stromal cells, that may lead to their pro-tumorigenic effects on tumor cells. Indeed, factors secreted by the cytokine-stimulated stromal cells induced EMT-related morphological changes in luminal-A breast tumor cells. Moreover, tumor cell scattering, transwell chemotaxis and scratch assays indicated that factors released by cytokine-stimulated stromal cells induced increased migratory abilities of tumor cells.

Conclusions: Our results suggest that inflammatory conditions in the TME induce a pro-metastatic phenotype in stromal cells, leading to elevated aggressiveness in luminal-A tumors. Determination of the molecular mechanisms involved in the process may enable the identification of potential targets that could be inhibited and used as potential therapies in breast cancer.