Genes affected by Ret activation during estrogen stimulation or inhibition in MCF7/Aro cells

Endocrine therapy is the main therapeutic option for patients with estrogen receptor alpha positive (ER+) breast cancer. Nevertheless, most of them become estrogen-independent and relapse after the treatment. Ret is a tyrosine kinase receptor that shows elevated expression levels in ER+ human breast tumors. In this study, we demonstrate that activation of the Ret receptor promotes proliferation as well as cell migration irrespective of endocrine therapy. Microarray data show that Ret activation involves changes in the expression of inflammatory- and motility-related genes. In vivo treatment with a Ret pathway inhibitor in a ER+/Ret+ mouse mammary cancer model, reduces tumor growth and lung metastasis even after endocrine therapy. Additionally, we show a connection between Ret and inflammatory pathways. The pro-inflamatory cytokine IL6 lies at the core of this regulation, which involves a positive feedback loop with IL6 and the Ret pathway reciprocally stimulating each other to further leading metastasis risk. Our findings provide insight into endocrine resistance mechanism and point at the Ret pathway as a potential target for future therapies. In order to model letrozole-sensitive breast cancer we use aromatase expressing MCF7 cells (MCF7/Aro). Six-day treatment (6 days) of cultures with letrozole (L) or fulvestrant (F) reversed the proliferative effects of the exposure to the estrogen (E2) precursor androstenedione (D4A). The addition of only EtOH (E) to the cells was used as control condition of deprivation. Treatment with the Ret ligand GDNF (G) partially rescues the inhibition of estrogen-dependent proliferation in these cells. To go deeper insight into the pathways involved, we decided to perform a microarray following different treatments (1-8: E, E+G, D, D+G, L, L+G, F, F+G) used in proliferation assays. Three biological replicates (rep 1-3) were used to the array.