Mutation analysis of the Epac--Rap1 signaling pathway in cold thyroid follicular adenomas

Abstract

Objective: The cyclic AMP (cAMP) cascade is the main regulatory pathway in thyrocytes. Whilst activating mutations in the TSH receptor or in the Gs a-subunit, which increase cAMP levels, have been shown to be responsible for 80% of the autonomous adenomas, no such mutations have been observed in the other types of thyroid tumors, suggesting that other mechanisms exist. The discovery of Epac (`exchange nucleotide protein directly activated by cAMP'), a novel cAMP-binding protein, which is strongly expressed in the thyroid, raised the possibility of a role for this protein in the generation of the unexplained cold thyroid follicular adenomas. Thus, we investigated whether activating mutations in either Epac or Rap (the downstream target of Epac) could be responsible for the generation of these thyroid nodules. Design: Epac and Rap1 (Rap1A and Rap1B) cDNAs were sequenced in 10 patients. The sequencing of the cDNAs was realized on both strands in the cold nodule and the juxtanodular tissue of each patient. Results: No mutations in either Epac or Rap1 cDNAs were found. For five patients, a polymorphism in Epac at codon 332 (Gly±Ser) was observed. Conclusions: In this report, we show that the cAMP±Epac±Rap1 signaling pathway in the thyroid gland does not play a major role in the generation of cold thyroid follicular adenomas, since no mutations in either Epac or Rap1 could be observed in the 10 nodules studied.

Gene expression analysis reveals evidence for inactivation of the TGF-β signaling cascade in autonomously functioning thyroid nodules

“…Interestingly, a recent study of Ribeiro-Neto et al (2002) indicates that Rap1 is able to transduce the mitogenic cAMP signal while maintaining differentiation in thyroid epithelial cells. Vanvooren et al (2001) investigated the role of Epac and Rap1 in the development of cold thyroid nodules by sequencing, but they found no mutations in these genes indicating that the cAMP-Epac-Rap1 pathway is not a major target for mutations in the development of cold thyroid nodules. However, our expression data suggest the participation of Rap1 in the signal transduction in AFTNs and further investigations, preferentially at the protein level are necessary to understand the role of Rap1 in nodular development.…”

RET/Papillary Thyroid Carcinoma Oncogenic Signaling through the Rap1 Small GTPase

“…Recently, it has been shown that Rap1b has mitogenic activity in rat thyroid cells (21). However, microinjection of the Rap1 protein failed to induce proliferation of dog thyrocytes showing that Rap1 alone is not sufficient to trigger thyroid cell growth (22); no mutations in Rap1 have been found in thyroid follicular adenomas (23). Here, we show that RET/PTC1 activates Rap1 in a Tyr 1062 -dependent fashion and we provide evidence that Rap1 is required for RET/ PTC1-induced BRAF activation, mitogenesis, and actin cytoskeleton rearrangement.…”

Mutation Analysis of RAP1 Gene in Papillary Thyroid Carcinomas

“…These data suggest that RAP1 might be a good candidate as a target of oncogenic mutation in PTCs. Although Vanvooren et al investigated mutational status of RAP1 in follicular thyroid adenomas and did not find any mutations [11], it remains to be clarified whether RAP1 is activated by somatic mutation in PTCs. In this study, therefore, the possibility that RAP1 mutation plays a role in PTC pathogenesis was explored.…”