Background Thyroid carcinoma includes several variants characterized by different biological and clinical features: from indolent microcarcinoma to undifferentiated and aggressive anaplastic carcinoma. Inflammation plays a critical role in thyroid tumors. Conditions predisposing to cancer, as well as oncogene activity, contribute to the construction of an inflammatory microenvironment that facilitates thyroid tumor progression. Moreover, oncogene-induced senescence, a mechanism tightly connected with inflammation, and able to restrain or promote cancer progression, is involved in thyroid cancer. The interactions between thyroid tumor cells and the microenvironment are not completely clarified. Methods We characterize in vitro the interplay between macrophages and senescent thyrocytes and tumor-derived cell lines, modeling early and late thyroid tumor stages, respectively. Purified peripheral blood-derived human monocytes were exposed to thyroid cell-derived conditioned medium (CM) and assessed for phenotype by flow cytometry. The factors secreted by thyroid cells and macrophages were identified by gene expression analysis and ELISA. The protumoral effect of macrophages was assessed by wound healing assay on K1 thyroid tumor cells. The expression of PTGS2 and M2 markers in thyroid tumors was investigated in publicly available datasets. Results Human monocytes exposed to CM from senescent thyrocytes and thyroid tumor cell lines undergo M2-like polarization, showing high CD206 and low MHC II markers, and upregulation of CCL17 secretion. The obtained M2-like macrophages displayed tumor-promoting activity. Among genes overexpressed in polarizing cells, we identified the prostaglandin-endoperoxide synthase enzyme (PTGS2/COX-2), which is involved in the production of prostaglandin E2 (PGE2). By using COX-2 inhibitors we demonstrated that the M2-like polarization ability of thyroid cells is related to the production of PGE2. Co-expression of PTGS2 and M2 markers is observed a significant fraction of human thyroid tumors. Conclusions Our results demonstrate that both senescent thyrocytes and thyroid tumor cell lines trigger M2-like macrophage polarization that is related to PGE2 secretion. This suggests that the interaction with the microenvironment occurs at both early and late thyroid tumor stages, and favors tumor progression. The co-expression of PTGS2 gene and M2 markers in human thyroid carcinoma highlights the possibility to counteract tumor growth through COX-2 inhibition. Electronic supplementary material The online version of this article (10.1186/s13046-019-1198-8) contains supplementary material, which is available to authorized users.

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Inflammation plays a critical role in thyroid cancer onset and progression. We previously characterized the in vitro interplay between macrophages and senescent human thyrocytes and thyroid tumor-derived cell lines, modeling the early and the late thyroid tumor phases, respectively. We reported that both models are able to induce pro-tumoral M2-like macrophage polarization, through the activation of the COX2-PGE2 axis. Here, we investigated the presence of macrophage infiltrating cells in mouse xenografts derived from the above described cells models. We showed that subcutaneous injection in immunodeficient mice of both senescent human thyrocytes and thyroid tumor-derived cell lines elicits macrophage recruitment. Furthermore, considering the type of macrophage infiltrate, we observed a stronger infiltration of Arginase I positive cells (M2-like). Overall, these results demonstrate the in vivo capability of senescent and tumor thyroid cells to recruit and polarize macrophages, suggesting that the promotion of a pro-tumoral microenvironment through tumor associated macrophages may occurs in late as well as in early thyroid tumor stages, favoring tumor onset and progression.

Background: Despite thyroid tumors are generally curable, a fraction of patients develops resistance to therapy and tumors progress towards undifferentiated forms, which have a poor prognosis and whose treatment is still a demanding challenge. To identify potential novel targets for thyroid cancer treatment, especially for those aggressive forms, we faced the non-oncogene addiction paradigm, which states that tumor cells become addicted to stress support pathway genes, not required to the same degree by normal ones. To this aim, in a previous study we screened a siRNA library on normal and tumor thyroid cell lines and found several genes essential for the growth of tumor but not normal cells; among the top-ranking hits we found MASTL, a serine/threonine kinase involved in mitosis regulation. Here, we investigated the mechanisms of growth inhibition mediated by MASTL silencing in thyroid tumor cells, in order to identify whether it could represent a potential target for tumor treatment. Methods: MASTL gene expression profile was assessed in 58 normal thyroid tissue samples and 72 papillary (PTC), 17 poorly differentiated (PDTC) and 31 anaplastic (ATC) thyroid carcinoma samples, derived from a meta-analysis of different publicly available datasets. HTC/C3 and 8505C cell lines (ATC-derived) were transfected with MASTL and control siRNAs and tested for cell growth, nuclear aberrations, DNA damage and cell death. Results: By gene expression data analysis, we found that MASTL expression levels in PTC and PDTC samples were similar to those observed in control group, while the highest levels were evidenced in ATC. We next tested by different growth assays the effects of MASTL depletion on HTC/C3 and 8505C cells and found that MASTL silencing impaired their proliferation capacity. Notably, MASTL depletion increased the percentage of cells presenting nuclear anomalies, such as micronuclei, multiple nuclei and lobular nuclei, which are indicative of mitotic catastrophe. We observed that MASTL depletion was associated with increased phosphorylation of CDK1 (Y15), supportive of impairment of cell growth, and of H2AX (Ser139), indicative of increase of DNA damage. Furthermore, MASTL depletion was associated with increased expression of the apoptotic markers cleaved caspase 3 and cleaved PARP, thus suggesting that MASTL inhibition may cause thyroid tumor cell death through apoptosis. These finding was further corroborated by Annexin V assay, which showed an increase of apoptotic and necrotic cells upon MASTL silencing, compared to control. Conclusions: Our results demonstrated that MASTL inhibition is able to impair the growth of thyroid tumor cell lines and is associated with mitotic catastrophe and tumor cell death, thus suggesting that it may represent a valuable candidate for validation as therapeutic target in thyroid cancer. Citation Format: Elena Cetti, Maria Chiara Anania, Katia Todoerti, Giuseppe Mauro, Antonino Neri, Angela Greco. Identification of MASTL as novel mitotic vulnerability of thyroid tumor cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 770.