RET/PTC oncogenes, generated by chromosomal rearrangements in papillary thyroid carcinomas, are constitutively activated versions of proto-RET, a gene coding for a receptor-type tyrosine kinase (TK) whose ligand is still unknown. RET/PTCs encode fusion proteins in which proto-RET TK and C-terminal domains are fused to different donor genes. The respective Ret/ptc oncoproteins display constitutive TK activity and tyrosine phosphorylation. We found that Ret/ptcs associate with and phosphorylate the SH2-containing transducer phospholipase Cgamma (PLCgamma). Two putative PLCgamma docking sites, Tyr-505 and Tyr-539, have been identified on Ret/ptc2 by competition experiments using phosphorylated peptides modelled on Ret sequence. Transfection experiments and biochemical analysis using Tyr-->Phe mutants of Ret/ptc2 allowed us to rule out Tyr-505 and to identify Tyr-539 as a functional PLCgamma docking site in vivo. Moreover, kinetic measurements showed that Tyr-539 is able to mediate high-affinity interaction with PLCgamma. Mutation of Tyr-539 resulted in a drastically reduced oncogenic activity of Ret/ptc2 on NIH 3T3 cells (75 to 90% reduction) both in vitro and in vivo, which correlates with impaired ability of Ret/ptc2 to activate PLCgamma. In conclusion, this paper demonstrates that Tyr-539 of Ret/ptc2 (Tyr-761 on the proto-RET product) is an essential docking site for the full transforming potential of the oncogene. In addition, the present data identify PLCgamma as a downstream effector of Ret/ptcs and suggest that this transducing molecule could play a crucial role in neoplastic signalling triggered by Ret/ptc oncoproteins.

The RET proto-oncogene encodes two isoforms of a receptor type tyrosine kinase which plays a role in neural crest and kidney development. Distinct germ-line mutations of RET have been associated with the inherited cancer syndromes MEN2A, MEN2B and FMTC as well as with the congenital disorder Hirschsprung disease (HSCR), whereas somatic rearrangements (RET/PTCs) have been frequently detected in the papillary thyroid carcinoma. Despite these ®ndings, suggesting a relevant role for RET product in development and neoplastic processes, little is known about the signalling triggered by this receptor. In this study, we have demonstrated that the transducing adaptor molecule Shc is recruited and activated by both Ret isoforms and by the rearranged cytoplasmatic Ret/ptc2 oncoproteins as well as by the membrane bound receptor activated by MEN2A or by MEN2B associated mutations. Moreover, our analysis has identi®ed the Ret tyrosine residue and the Shc domains involved in the interaction. In fact, here we show that both the phosphotyrosine binding domains of Shc, PTB and SH2, interact with Ret/ptc2 in vitro. However, PTB domain binds 20 folds higher amount of Ret/ptc2 than SH2. The putative binding site for either SH2 and PTB domains has been identi®ed as Tyr586 of Ret/ptc2 (Tyr1062 on proto-Ret). In keeping with this ®nding, by using RET/PTC2-Y586F mutant, we have demonstrated that this tyrosine residue, the last amino acid but one before the divergence of the two Ret isoforms, is the docking site for Shc.

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This study aimed to identify circulating miRNAs as novel non-invasive biomarkers for prognosis and vandetanib response in advanced medullary thyroid cancer (MTC) patients. We prospectively recruited two independent cohorts of locally advanced/metastatic MTC patients including a subgroup of vandetanib-treated subjects: a discovery cohort ( = 20), including matched plasma/tissue samples ( = 17/20), and a validation cohort, yielding only plasma samples ( = 17). Plasma samples from healthy subjects ( = 36) and MTC patients in remission ( = 9) were used as controls. MTC ( = 17 from 8 patients included in discovery cohort) and non-neoplastic thyroid specimens ( = 3) were assessed by microarray profiling to identify candidate circulating miRNAs. qRT-PCR and hybridization were carried out to validate the expression and localization of a selected miRNA within tissues, and qRT-PCR was also performed to measure miRNA levels in plasma samples. By microarray analysis, we identified 51 miRNAs differentially expressed in MTC. The most overexpressed miR, miR-375, was highly expressed by C cells compared to other thyroid cells, and more expressed in MTC than in reactive C-cell hyperplasia. MTC patients had significantly higher miR-375 plasma levels than healthy controls ( < 0.0001) and subjects in remission ( = 0.0004) as demonstrated by qRT-PCR analysis. miR-375 plasma levels were not predictive of vandetanib response, but, notably, high levels were associated with significantly reduced overall survival (HR 10.61, < 0.0001) and were a strong prognostic factor of poor prognosis (HR 6.24, = 0.00025) in MTC patients. Overall, our results unveil plasma miR-375 as a promising prognostic marker for advanced MTC patients, to be validated in larger cohorts.

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.