CLIP2 as biomarker of long-term effect in radiation-associated thyroid cancer.

One of the major consequences of the Chernobyl nuclear power plant accident in 1986 has been a significant increase in the incidence of papillary thyroid carcinoma (PTC) among children exposed to the radioiodine fallout, particularly to iodine-131. Thus, young age at exposure is a significant risk factor for the development of radiation-induced PTC. Previously, the investigation of PTC from young exposed patients and non-exposed controls that were matched as closely as possible for potential confounders revealed a radiation-specific DNA copy number gain on chromosomal band 7q11.23 and the radiation-associated mRNA overexpression of the gene CLIP2, located on chromosome 7q11.23 (Hess et al., PNAS, 2011). We confirmed the radiation-associated CLIP2 overexpression at the protein level in PTCs from independent tumor cohorts and established a standardized procedure for CLIP2 typing, an essential step in integrating a molecular biomarker into epidemiological studies for improved risk estimation and modeling of radiation-induced carcinogenesis (Selmansberger et al., Oncogene, 2015). Moreover, a reconstruction of the CLIP2 gene regulatory network suggests the involvement of CLIP2 in the fundamental carcinogenic processes apoptosis, MAPK signalling, and genomic instability, indicating a functional role of CLIP2 in the carcinogenesis of radiation-associated PTC. In a further study, the association between the binary CLIP2 typing and continuous thyroid dose with logistic regression was analysed. The clear dose-response relationship for the CLIP2 radiation marker in two PTC cohorts (UkrAm and Genrisk-T) for young patients with age at operation less than 20 years and age at exposure less than 5 years demonstrates the importance of this biomarker in low-dose radiation research and suggests different molecular mechanisms depending on age (Selmansberger et al., Carcinogenesis, 2015)

Genomic copy number analysis of Chernobyl papillary thyroid carcinoma in the Ukrainian-American Cohort.

One of the major consequences of the 1986 Chernobyl reactor accident was a dramatic increase in papillary thyroid carcinoma (PTC) incidence, predominantly in patients exposed to the radioiodine fallout at young age. The present study is the first on genomic copy number alterations (CNAs) of PTCs of the Ukrainian American cohort (UkrAm) generated by Array Comparative Genomic Hybridization (aCGH). Unsupervised hierarchical clustering of CNA profiles revealed a significant enrichment of a subgroup of patients with female gender, long latency (> 17 years) and negative lymph node status. Further, we identified single CNAs that were significantly associated with latency, gender, radiation dose and BRAF status. Multivariate analysis revealed no interactions but additive effects of parameters gender, latency and dose on CNAs. The previously identified radiation-associated gain of the chromosomal bands 7q11.22-11.23 was present in 29% of cases. Moreover, comparison of our radiation-associated papillary thyroid carcinoma (PTC) data set with the TCGA data set on sporadic PTCs revealed altered copy numbers of the tumor driver genes NF2 and CHEK2. Further, we integrated the CNA data with transcriptomic data that were available on a subset of the herein analyzed cohort and did not find statistically significant associations between the two molecular layers. However, applying hierarchical clustering on a "BRAF-like/RAS-like" transcriptome signature split the cases into four groups, one of which containing all BRAF-positive cases validating the signature in an independent data set

Integration of a radiation biomarker into modelling of thyroid carcinogenesis and post-Chernobyl risk assessment.

Strong evidence for the statistical association between radiation exposure and disease has been produced for thyroid cancer by epidemiological studies after the Chernobyl accident. However limitations of the epidemiological approach in order to explore health risks especially at low doses of radiation appear obvious. Statistical fluctuations due to small case numbers dominate the uncertainty of risk estimates. Molecular radiation markers have been searched extensively to separate radiation- induced cancer cases from sporadic cases. The overexpression of the CLIP2 gene is the most promising of these markers. It was found in the majority of papillary thyroid cancers (PTCs) from young patients included in the Chernobyl tissue bank. Motivated by the CLIP2 findings we propose a mechanistic model which describes PTC development as a sequence of rate-limiting events in two distinct paths of CLIP2-associated and multi-stage carcinogenesis. It integrates molecular measurements of the dichotomous CLIP2 marker from 141 patients into the epidemiological risk analysis for about 13,000 subjects from the Ukrainian-American cohort which were exposed below age 19 yr and were put under enhanced medical surveillance since 1998. For the first time a radiation risk has been estimated solely from marker measurements. Cross checking with epidemiological estimates and model validation suggests that CLIP2 is a marker of high precision. CLIP2 leaves an imprint in the epidemiological incidence data which is typical for a driver gene. With the mechanistic model we explore the impact of radiation on the molecular landscape of PTC. The model constitutes a unique interface between molecular biology and radiation epidemiology

Comparative transcriptomic analysis of temozolomide resistant primary GBM stem-like cells and recurrent GBM identifies up-regulation of the carbonic anhydrase CA2 gene as resistance factor.

About 95% of patients with Glioblastoma (GBM) show tumor relapse, leaving them with limited therapeutic options as recurrent tumors are most often resistant to the first line chemotherapy standard Temozolomide (TMZ). To identify molecular pathways involved in TMZ resistance, primary GBM Stem-like Cells (GSCs) were isolated, characterized, and selected for TMZ resistance in vitro. Subsequently, RNA sequencing analysis was performed and revealed a total of 49 differentially expressed genes (log2-fold change> 0.5 and adjusted p-value < 0.1) in TMZ resistant stem-like cells compared to their matched DMSO control cells. Among up-regulated genes, we identified carbonic anhydrase 2 (CA2) as a candidate gene correlated with glioma malignancy and patient survival. Notably, we describe consistent up-regulation of CA2 not only in TMZ resistant GSCs on mRNA and protein level, but also in patient-matched clinical samples of first manifest and recurrent tumors. Co-treatment with the carbonic anhydrase inhibitor Acetazolamid (ACZ) sensitized cells to TMZ induced cell death. Cumulatively, our findings illustrate the potential of CA2 as a chemosensitizing target in recurrent GBM and provide a rationale for a therapy associated inhibition of CA2 to overcome TMZ induced chemoresistance