Tumor-educated Mast Cells Induce Epithelial-to-Mesenchymal Transition and Expansion of Stem Cell Population via IL-8/CXCR1/CXCR2 Axis in Thyroid Cancer

We previously demonstrated that human papillary thyroid carcinomas (PTCs) display a MC infiltrate, whose density correlates with extrathyroidal extension. MCs (MC) are mainly found at the invasive front of human PTCs, where they may facilitate tumor cell migration and extracellular matrix degradation. The increased motility and invasiveness of tumor cells are reminiscent of the epithelial to mesenchymal transition (EMT). However, the MC-derived factors that mediate this activity and the mechanisms with which they enhance thyroid carcinoma (TC) invasive ability remain unidentified. Here, we report that MCderived conditioned media (MC CM) induce the epithelial-to-mesenchimal transition (EMT) and the gain of stemness features of TC cells. MC CMtreated thyroid cancer (TC) cells down-regulate E-cadherin expression, an epithelial protein, while up-regulating EMT transcription factors (SNAIL, SLUG, ZEB1) and mesenchimal markers (vimentin). Here we identify interleukin 8 (CXCL8/IL-8) as the main mediator produced by MCs capable of inducing both EMT and stemness in TC cells. TC cells infact express both the IL-8 receptors, CXCR1 and CXCR2. Immune depletion of IL-8 from MC CM completely abolishes EMT and stemness. Treatment of TC cells with recombinant IL-8 induces these features, and blocking molecules targeting the IL-8/CXCR1/CXCR2 axis revert them. 850-5C cells, derived from a human anaplastic thyroid carcinoma (ATC), enforced to express IL-8, undergo EMT, display increased stemness, and are more efficient in tumor formation when xenografted in immunodeficient mice with respect to parental cells. The transcription factor SLUG may be a critical mediator of IL-8-mediated biological effects in TC cells; in fact, IL-8 treatment causes persistent SLUG upregulation, and IL-8 expressing 850-5C cells constitutively express high levels of SLUG. We generated TPC-1 cells, derived from a human PTC, with enforced expression of SLUG. These cells underwent EMT and exhibited stemness features, including the capability to form spheres in low-adherence condition. By analysing a panel (n=30) of human TC surgical samples, we observed that the expression of the stemness marker OCT4 is significantly associated with tumor size and with MC density. Furthermore, we observed that IL-8 expression correlates with the presence of lymph-node metastases and with SLUG expression. The failure in the eradication of CSCs is likely one of the factors that limits the efficacy of current therapeutic approaches against cancer. Thus, novel CSCstargeted treatments are needed. In this regard, our study provides the evidence that targeting MC-derived IL-8 may be employed to directly target CSCs inadvanced thyroid cancer