Pivotal role of the RB family proteins in in vitro thyroid cell transformation

Molecular Identification of Human Papillomavirus DNA in Thyroid Neoplasms: Association or Serendipity?

Background: Human papillomavirus (HPV) is recognized as the most important cofactor in the etiology of cancers of the cervix, esophagus, larynx, and nasopharynx. Experimental evidence suggests that HPV could have an oncogenic influence on thyroid follicular cells; however, to the best of our knowledge, there is no record of its role in human thyroid gland neoplasms.

Objective: The purpose of this study is to describe the frequency and the types of HPV present in neoplastic thyroid tissue by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP).

Methods: Over 157 samples were analyzed of paraffin-embedded tissue from malignant and benign thyroid tumors. All the paraffin blocks were selected consecutively from the Pathology Tissue Bank archive of the Western Medical Center. The molecular detection and typing were performed at the Molecular Microbiology Laboratory of the Biomedical Research Center, Mexican Institute of Social Security.

Results: The frequency of HPV findings was 2.5% (four cases). HPV-6 was found in two cases of thyroid hyperplasia (2.5%), and HPV-33 in two cases of papillary cancer (4.6%).

Conclusion: The presence of HPV is not frequent in thyroid neoplasms, at least in the studied population. Due to the low prevalence of this virus in our sample, it is not possible to reach conclusions. Further research is needed.

Identification of several novel non-p.R132 IDH1 variants in thyroid carcinomas

CONTEXT

Somatic mutations at residue R132 of isocitrate dehydrogenase 1 (IDH1) were recently discovered in gliomas and leukaemia at a high frequency. IDH1 is a metabolic gene, and the R132 mutations create a new enzymatic activity.

OBJECTIVES

To determine whether IDH1 had somatically acquired mutations in thyroid carcinomas.

DESIGN

Exons 4 and 6 of IDH1 were sequenced in a large panel of thyroid tumours (n=138) and compared with the patients normal DNA (n=26). We also correlated IDH1 mutations with clinical-pathological data and BRAF and RAS mutational status.

RESULTS

We identified four novel and two previously described non-synonymous variants in thyroid carcinomas, which were absent in benign tumours and paired normal thyroid. Although IDH1 variants occurred at higher frequency in follicular thyroid carcinomas, follicular variant of papillary thyroid carcinoma (PTC) and undifferentiated thyroid carcinomas than the observed variants in classical PTC (15/72 vs 3/37), it was not significant (P=0.1). Sequence alignment across several species shows that all IDH1 genetic alterations occurred at evolutionarily conserved residues located within the active site, and therefore, are likely to affect protein function. Unlike other tumours, IDH1 and BRAF or RAS mutations are not mutually exclusive. There was no association between IDH1 mutational status and clinical characteristics.

CONCLUSION

IDH1-acquired genetic alterations are highly prevalent in thyroid carcinomas (16%). Our findings not only extend our understanding of the molecular mechanism underlying pathogenesis of thyroid tumours, but also emphasize the biological differences between tumour types. Those tumours with IDH1 mutations might benefit from therapies that exploit this alteration.

Bevacizumab increases viral distribution in human anaplastic thyroid carcinoma xenografts and enhances the effects of E1A-defective adenovirus dl922-947

PURPOSE

Anaplastic thyroid carcinoma is a prime target for innovative therapy because it represents one of the most lethal human neoplasms and is refractory to conventional treatments such as chemotherapy and radiotherapy. We have evaluated a novel therapeutic approach based on the oncolytic replication-selective adenovirus dl922-947.

EXPERIMENTAL DESIGN

The antitumor efficacies of the E1ADeltaCR2 (dl922-947) and DeltaE1B55K (dl1520) mutants were compared in human thyroid anaplastic carcinoma cells in culture and in xenografts in vivo. To enhance the effects of dl922-947, anaplastic thyroid carcinoma tumor xenografts were treated with dl922-947 in combination with bevacizumab.

RESULTS

We showed that the efficacy of dl922-947 exceeded that of dl1520 in all tested anaplastic thyroid carcinoma cells in vitro and in vivo. Furthermore, bevacizumab in combination with dl922-947 significantly reduced tumor growth compared with single treatments alone. Bevacizumab treatment significantly improved viral distribution in neoplastic tissues.

CONCLUSIONS

Our data showed that dl922-947 had a higher oncolytic activity compared with dl1520 in anaplastic thyroid carcinoma cell lines and might represent a better option for virotherapy of anaplastic thyroid carcinoma. Moreover, bevacizumab increased the oncolytic effects of dl922-947 by enhancing viral distribution in tumors. The results described herein encourage the use of the dl922-947 virus in combination with bevacizumab.

Human thyroid tumours, the puzzling lessons from E7 and RET/PTC3 transgenic mice

Human rearranged RET/PTC3 (papillary thyroid carcinoma) proto-oncogene and high-risk human papillomavirus (HPV) type 16 E7 oncogene induces in the mouse a neoplastic transformation of thyroid follicular cells. We present a detailed immuno-histological study (170 mouse thyroids: RET/PTC3, E7, wild type, 2- to 10-month-old) with cell cycle proliferation and signalling pathway indicators. The characteristics of both models are different. There is an 'oncogene dependent' cellular signature, maintained at all studied ages in the E7 model, less in the RET/PTC3 model. During tumour development a large heterogeneity occurred in the Tg-RET/PTC3 model within a same tumour or within a same thyroid lobe. The Tg-E7 model was less heterogeneous, with a dominant goitrous pattern. The solid tumour already described in the RET/PTC3 models associated with cribriform patterns, suggested 'PTC spindle cell changes' as in humans PTC rather than the equivalent of the solid human PTC. Proliferation and apoptosis in the two thyroid models are related to the causal oncogene rather than reflect a general tumorigenic process. The thyroids of RET/PTC3 mice appeared as a partial and transient model of human PTCs, whereas the Tg-E7 mice do not belong to the usual PTC type.

Thyroid-stimulating hormone/cAMP-mediated proliferation in thyrocytes

Current research on thyrotropin-activated proliferation in the thyrocyte needs to be aimed at a better understanding of crosstalk and negative-feedback mechanisms with other proliferative pathways, especially the insulin/IGF-1-induced phosphoinositol-3 kinase pathway and the serum-induced MAPK or Wnt pathways. Convergence of proliferative pathways in mTOR is a hotspot of current research, and combined treatment using double class inhibitors for thyroid cancer may bring some success. New thyroid-stimulating hormone receptor (TSHR)-interacting proteins, a better picture of cAMP targets, a deeper knowledge of the action of the protein kinase A regulatory subunits, especially their interactions with the replication machinery, and a further understanding of mechanisms that lead to cell cycle progression through G₁/S and G₂/M checkpoints are areas that need further elucidation. Finally, massive information coming from microarray data analysis will prompt our understanding of thyroid-stimulating hormone-promoted thyrocyte proliferation in health and disease.

Retinoblastoma protein acts as Pax 8 transcriptional coactivator

Control of cell proliferation and differentiation by the retinoblastoma protein (pRb) depends on its interactions with key cellular substrates. Available data indicate that pRb and the transcription factor Pax 8 play a crucial role in the differentiation of thyroid follicular cells. In this study, we show that pRb takes part in the complex assembled on the thyroperoxidase gene promoter acting as a transcriptional coactivator of Pax 8. Accordingly, pRb interacts with and potentiates Pax 8 transcriptional activity. In addition, we show that the downregulation of pRb gene expression, in thyrocytes, through RNA interference results in a reduction of the thyroperoxidase gene promoter activity mediated by the Pax 8-binding site. In agreement with these results and with the ability of the adenoviral protein E1A to bind pRb, we show that E1A downregulates Pax 8 activity and that such inhibition requires the E1A-Rb interaction. Furthermore, we show that the Pax 8/pRb synergy plays a role on the sodium/iodide symporter gene expression as well.