Evidence of oncogene-induced senescence in thyroid carcinogenesis.
ABSTRACT Oncogene-induced senescence (OIS) is a growth arrest triggered by the enforced expression of cancer-promoting genes and acts as a barrier against malignant transformation in vivo. In this study, by a combination of in vitro and in vivo approaches, we investigate the role of OIS in tumours originating from the thyroid epithelium. We found that expression of different thyroid tumour-associated oncogenes in primary human thyrocytes triggers senescence, as demonstrated by the presence of OIS hallmarks: changes in cell morphology, accumulation of SA-β-Gal and senescence-associated heterochromatic foci, and upregulation of transcription of the cyclin-dependent kinase inhibitors p16(INK4a) and p21(CIP1). Furthermore, immunohistochemical analysis of a panel of thyroid tumours characterised by different aggressiveness showed that the expression of OIS markers such as p16(INK4a), p21(CIP1) and IGFBP7 is upregulated at early stages, and lost during thyroid tumour progression. Taken together, our results suggest a role of OIS in thyroid carcinogenesis.
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ABSTRACT: Thyroid cancer is a heterogeneous disease with several subtypes characterized by cytological, histological and genetic alterations, but the involvement of epigenetics is not well understood. Here, we investigated the role of aberrant DNA methylation in the development of well-differentiated thyroid tumors. We performed genome-wide DNA methylation profiling in the largest well-differentiated thyroid tumor series reported to date, comprising 83 primary tumors, as well as 8 samples of adjacent normal tissue. The epigenetic profiles were closely related to not only tumor histology but also the underlying driver mutation; we found that follicular tumors had higher levels of methylation, which seemed to accumulate in a progressive manner along the tumorigenic process from adenomas to carcinomas. Furthermore, tumors harboring a BRAF or RAS mutation had a larger number of hypo- or hypermethylation events, respectively. The aberrant methylation of several candidate genes potentially related to thyroid carcinogenesis was validated in an independent series of 52 samples. Furthermore, through the integration of methylation and transcriptional expression data, we identified genes whose expression is associated with the methylation status of their promoters. Finally, by integrating clinical follow-up information with methylation levels we propose etoposide-induced 2.4 and Wilms tumor 1 as novel prognostic markers related to recurrence-free survival. This comprehensive study provides insights into the role of DNA methylation in well-differentiated thyroid cancer development and identifies novel markers associated with recurrence-free survival. © 2013 Wiley Periodicals, Inc.International Journal of Cancer 12/2013; · 6.20 Impact Factor
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ABSTRACT: Aims: RAS-induced tumorigenesis has been suggested to follow a three-stage model consisting of an initial RAS activation, senescence induction, and evasion of p53-dependent senescence checkpoints. While reactive oxygen species (ROS) act as second messengers in RAS-induced senescence, they are also involved in oncogenic transformation by inducing proliferation and promoting mutations. In the current work, we investigated the role of extracellular superoxide dismutase (SOD3) in RAS-induced senescence and immortalization in vitro and in vivo. We used a mouse embryonic fibroblast (MEF) primary cell model together with immortalized and transformed human cell lines derived from papillary and anaplastic thyroid cancer. Results: Based on our data, sod3 RNA interference in H-RasV12-transduced cells markedly inhibited cell growth, while sod3 over-expression in MEFs initially caused a proliferative burst followed by the activation of DNA damage checkpoints, induction of p53-p21 signal transduction, and senescence. Subsequently, sod3-transduced MEF cells developed co-operative p21-p16 down-regulation and acquired transformed cell characteristics such as increased telomerase activity, loss of contact inhibition, growth in low-nutrient conditions, and in vivo tumorigenesis. Interestingly, as reported previously with RAS, we showed a dose-dependent response to SOD3 in vitro and in vivo involving transcriptional and non-transcriptional regulatory mechanisms. Innovation: SOD3 may mediate H-RasV12-induced initiation of primary cell immortalization. Conclusions: Our results indicate that SOD3 influences growth signaling in primary and cancer cells downstream of the ras oncogene and could serve as a therapy target at an early tumorigenesis phase.Antioxidants & Redox Signaling 12/2013; · 8.20 Impact Factor
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ABSTRACT: Abstract The clonal/neoplastic nature of Langerhans' cell histiocytosis (LCH) has been recently demonstrated by the high prevalence of BRAF mutations, including pulmonary LCH (PLCH). We hypothesized that BRAF-induced senescence, as demonstrated in nevi and melanoma, is involved in the pathogenesis of LCH and PLCH. In a series of pulmonary (19 cases) and non-pulmonary LCH (19 cases), including five aggressive cases, we investigated the occurrence of the BRAF-V600E mutation by molecular analysis and/or by immunohistochemistry using a validated antibody (VE1). The expression of cell-senescence markers p16(INK4a) and p21(CIP1/WAF1) were also immunohistochemically investigated. We demonstrated that 6/19 LCH and 12/19 PLCH cases were VE1 positive, matching with molecular analysis, and in all cases both p16(INK4a) and p21(CIP1/WAF1) were expressed, irrespective of BRAF mutation status. Interestingly, all the aggressive cases did not express p16(INK4a) thus suggesting that the loss of senescence control could be related to clinical aggressiveness of LCH, as in melanoma.Leukemia & lymphoma 01/2014; · 2.61 Impact Factor