Article

Conditional BRAF(V600E) expression induces DNA synthesis, apoptosis, dedifferentiation, and chromosomal instability in thyroid PCCL3 cells

University of Cincinnati, Cincinnati, Ohio, United States
Cancer Research (Impact Factor: 9.28). 04/2005; 65(6):2465-73. DOI: 10.1158/0008-5472.CAN-04-3314
Source: PubMed

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.

0 Followers
 · 
61 Views
  • [Show abstract] [Hide abstract]
    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
  • [Show abstract] [Hide abstract]
    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
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A number of reports indicated that Aurora-A or Aurora-B overexpression represented a negative prognostic factor in several human malignancies. In thyroid cancer tissues a deregulated expression of Aurora kinases has been also demonstrated, butno information regarding its possible prognostic role in differentiated thyroid cancer is available. Here, weevaluated Aurora-A and Aurora-B mRNA expression and its prognostic relevance in a series of 87 papillary thyroid cancers (PTC), with a median follow-up of 63 months. The analysis of Aurora-A and Aurora-B mRNA levels in PTC tissues, compared to normal matched tissues, revealed that their expression was either up- or down-regulatedin the majority of cancer tissues. In particular, Aurora-A and Aurora-B mRNA levels were altered, respectively, in 55 (63.2%) and 79 (90.8%) out of the 87 PTC analyzed.A significant positive correlation between Aurora-A and Aurora-B mRNAswas observed (p=0.001). The expression of both Aurora genes was not affected by the BRAFV600E mutation. Univariate, multivariate and Kaplan-Mayer analyses documented the lack of association between Aurora-A or Aurora-B expression and clinicopathological parameterssuch as gender, age, tumor size, histology, TNM stage, lymph node metastasis and BRAF status as well asdisease recurrences or disease-free interval. Only Aurora-B mRNA was significantly higher in T(3-4) tissues, with respect to T(1-2) PTC tissues. The data reported here demonstrate that the expression of Aurora kinases is deregulated in the majority of PTC tissues, likely contributing to PTC progression. However, differently from other human solid cancers, detection of Aurora-A or Aurora-B mRNAs is not a prognostic biomarker inPTC patients.
    PLoS ONE 01/2015; 10(3):e0121514. DOI:10.1371/journal.pone.0121514 · 3.53 Impact Factor