mTOR activation in medullary thyroid carcinoma with RAS mutation

Abstract

Objective: Rearranged during transfection (RET) mutations are well-known genetic events in sporadic and familial medullary thyroid carcinoma (FMTC). The presence of RAS mutations in sporadic cases, challenging the RET paradigm in these tumors, has been recently reported. We intend to evaluate mTOR pathway activation in RET-and RAS-mutated MTC. Materials and methods: In this study, we analysed the presence of RET, H-RAS, and K-RAS mutations in a series of 87 MTCs (82 apparently sporadic and five FMTCs; five apparently sporadic MTCs were eventually found to be familial). We also evaluated mTOR activation -using the expression of its downstream effector phospho-S6 ribosomal protein (p-S6) and the expression of the mTOR inhibitor, phosphatase and tensin homologue deleted on chromosome 10 (PTEN) -by immunohistochemistry. Results: Our results revealed that RET mutations were present in 52.9% of the cases (46/87) and RAS mutations in 12.6% (11/87) of the whole series of MTCs and 14.3% of the 77 sporadic MTCs. The presence of RET and RAS mutations was mutually exclusive. RAS mutations were significantly associated with higher intensity of p-S6 expression (PZ0.007), suggesting that the mTOR pathway is activated in such MTCs. We observed also an increased expression of p-S6 in invasive tumors (PZ0.042) and in MTCs with lymph node metastases (PZ0.046). Cytoplasmic PTEN expression was detected in 58.8% of the cases; cases WT for RAS showed a significantly lower expression of PTEN (PZ0.045). Conclusions: We confirmed the presence of RAS mutation in 14.3% of sporadic MTCs and report, for the first time, an association between such mutations and the activation of the mTOR pathway. The evaluation of the mTOR activation by pS6 expression may serve as an indicator of invasive MTC.

Osteopontin expression is correlated with differentiation and good prognosis in medullary thyroid carcinoma

“…The OPN staining score (range from 0 to 7) corresponds to the sum of staining intensity and the proportion of positive-stained cells (Table 3). OPN staining score was correlated with data previously obtained by our group in this tumour series with regards to PTEN and pS6 IHC expression (25).…”

“…As higher levels of OPN were significantly associated with higher levels of nuclear PTEN in MTCs, these two molecules can probably act together in the maintenance of the differentiation of C-cells, thus contributing to prevent tumour progression. In sporadic MTC, RAS mutations are often detected in HRAS and KRAS genes (25), representing an alternative genetic event to RET mutation. Casson et al (50) showed that RAS mutation induces expression of OPN in human esophageal cancer, and other authors reported that OPN promoter have target sequences for RAS binding, inducing OPN expression in both human (51) and mouse (52).…”

“…Formalin-fixed, paraffinembedded tissue and clinical data were retrieved from the files of Centro Hospitalar São João (CHSJ)/Medical Faculty of Porto (FMUP)/Ipatimup (56 cases), Portuguese Institute of Oncology, Coimbra (IPO-C) (19 cases), and Portugueseof the Department of Pathology and Oncology of CHSJ and from IPO databases (Table 1). RET and RAS genetic characterisation of the series had been done previously and reported in two publications (25,26). The study was approved by the Hospital Ethical Committees, and National Ethical rules were followed in every procedure.…”

Prognostic Impact of miR-224 and RAS Mutations in Medullary Thyroid Carcinoma

“…It remains to be seen whether RAS mutations can also lead to the activation of both of these signaling pathways in sporadic MTC, or whether there is a preferential activation pathway. Lyra et al examined mTOR activation in a series of 87 MTCs (10 familial and 77 sporadic) and found RAS mutations significantly associated with a more intense expression of phospho-S6 ribosomal protein (p-S6, a downstream effector of mTOR) [44], pointing to an association between mTOR pathway activation and the presence of RAS mutations in MTC. We consequently conducted a recent study and demonstrated that MTC-harboring RAS mutations showed a preferential activation of the PI3K/Akt/mTOR pathway, revealed by an intense phospho-Akt reactivity pattern on Western blot analysis [24].…”

Sorafenib in the treatment of thyroid cancer

“…Also, other genetic events are determinant for the pathogenesis of MTC, as indicated by the recent findings of H-RAS mutations in 13-56% of RET-negative sporadic MTC and the activation of the mTOR intracellular signaling pathway in hereditary MTC [42][43][44].…”