Conditional BRAF(V600E) expression induces DNA synthesis, apoptosis, dedifferentiation, and chromosomal instability in thyroid PCCL3 cells
ABSTRACT The activating mutation BRAF(T1796A) is the most prevalent genetic alteration in papillary thyroid carcinomas (PTC). It is associated with advanced PTCs, suggesting that this oncoprotein confers thyroid cancers with more aggressive properties. BRAF(T1796A) is also observed in thyroid micropapillary carcinomas and may thus be an early event in tumor development. To explore its biological consequences, we established doxycycline-inducible BRAF(V600E)-expressing clonal lines derived from well-differentiated rat thyroid PCCL3 cells. Expression of BRAF(V600E) did not induce growth in the absence of thyrotropin despite increasing DNA synthesis, which is likely explained because of a concomitant increase in apoptosis. Thyrotropin-dependent cell growth and DNA synthesis were reduced by BRAF(V600E) because of decreased thyrotropin responsiveness associated with inhibition of thyrotropin receptor gene expression. These results are similar to those obtained following conditional expression of RET/PTC. However, in contrast to RET/PTC, BRAF activation did not impair key activation steps distal to the thyrotropin receptor, such as forskolin-induced adenylyl cyclase activity or cyclic AMP-induced DNA synthesis. We reported previously that acute RET/PTC expression in PCCL3 cells did not induce genomic instability. By contrast, induction of BRAF(V600E) expression increased the frequency of micronuclei by both clastogenic and aneugenic events. These data indicate that BRAF(V600E) expression confers thyroid cells with little growth advantage because of concomitant activation of DNA synthesis and apoptosis. However, in contrast to RET/PTC, BRAF(V600E) may facilitate the acquisition of secondary genetic events through induction of genomic instability, which may account for its aggressive properties.
SourceAvailable from: Eftychia Oikonomou[Show abstract] [Hide abstract]
ABSTRACT: As the increased knowledge of tumour heterogeneity and genetic alterations progresses, it exemplifies the need for further personalized medicine in modern cancer management. Here, the similarities but also the differential effects of RAS and BRAF oncogenic signalling are examined and further implications in personalized cancer diagnosis and therapy are discussed. Redundant mechanisms mediated by the two oncogenes as well as differential regulation of signalling pathways and gene expression by RAS as compared to BRAF are addressed. The implications of RAS vs BRAF differential functions, in relevant tumour types including colorectal cancer, melanoma, lung cancer are discussed. Current therapeutic findings and future viewpoints concerning the exploitation of RAS-BRAF-pathway alterations for the development of novel therapeutics and efficient rational combinations, as well as companion tests for relevant markers of response will be evaluated. The concept that drug-resistant cells may also display drug dependency, such that altered dosing may prevent the emergence of lethal drug resistance posed a major therapy hindrance.Oncotarget 10/2014; · 6.63 Impact Factor
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ABSTRACT: B-RafV600E oncogene mutation occurs most commonly in papillary thyroid carcinoma (PTC) and is associated with tumor initiation. However, a genetic modification by B-RafV600E in thyrocytes results in oncogene-induced senescence (OIS). In the present study, we explored the factors involved in the senescence overcome program in PTC. First of all, we observed down-regulation of p-extracellular signal-regulated kinases 1/2 and up-regulation of dual specific phosphatase 6 (DUSP6) in the PTC with B-RafV600E mutation. DUSP6 overexpression in vitro induced extracellular signal-regulated kinases 1/2 dephosphorylation and inhibited B-RafV600E-induced senescence in thyrocytes. Although DUSP6 protein was degraded by B-RafV600E-induced reactive oxygen species (ROS), thyroid-stimulating hormone (TSH) stabilized DUSP6 protein by increasing Mn superoxide dismutase expression and inhibited B-RafV600E-induced senescence. Although serum TSH was not increased, its receptor was markedly upregulated in PTC with B-RafV600E. Furthermore, TSH together with DUSP6 reactivated Ras signaling, resulted in activation of Ras/AKT/glycogen synthase kinase 3β, and stabilized c-Myc protein by inhibiting its degradation. These observations led us to conclude that increased TSH signaling overcomes OIS and is essential for B-RafV600E-induced papillary thyroid carcinogenesis. Copyright © 2014 Neoplasia Press, Inc. Published by Elsevier Inc. All rights reserved.Neoplasia (New York, N.Y.) 12/2014; 16(12):1107-20. DOI:10.1016/j.neo.2014.10.005 · 5.40 Impact Factor
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ABSTRACT: Background: The aim of this study was to evaluate the prognosis of the classic variant of papillary thyroid carcinomas with the BRAF(V600E) mutation and I-131 treatment failure in those tumors due to lower functional sodium iodide symporter expression. Methods: 109 papillary thyroid carcinomas were associated with clinicopathologic features. The BRAF(V600E) mutation was evaluated by direct sequencing and sodium iodide symporter protein was determined by immunohistochemistry. Results: We found that the BRAF(V600E) mutation was significantly associated with the classic variant of papillary thyroid carcinomas and was independent of tumor size, the presence of extrathyroid invasion and lymph node metastasis, advanced TMN stages, and a high risk of disease recurrence. Moreover, the BRAF(V600E) mutation was associated with a statistically significant lower functional NIS protein expression in the classic variant of papillary thyroid carcinomas. However, those statistically significant relationships were not found in the follicular variant of papillary thyroid carcinomas. Conclusions: The BRAF(V600E) mutation might be associated with a more aggressive phenotype and a poor prognosis, causing less NIS-mediated I-131 uptake due to a lower functional NIS protein expression in the classic variant of papillary thyroid carcinomas. Our current study appears to be valuable for predicting prognosis and is of important clinical significance for surgery and 1311 treatment in patients with the classic variant of papillary thyroid carcinomas. (Clin. Lab. 2012;58:919-926. DOT: 10.7754/Clin.Lab.2012.111217)Clinical laboratory 01/2013; 59(01+02/2013). DOI:10.7754/Clin.Lab.2012.111217 · 1.08 Impact Factor