Dose-dependent expression of CLIP2 in post-Chernobyl papillary thyroid carcinomas.
Bottom Line: A clear positive dose-response relationship was found for young PTC cases [age at operation (AaO) < 20 years, AaE < 5 years].In the elder age group a higher proportion of sporadic tumors is assumed due to a negligible dose response, suggesting different molecular mechanisms in sporadic and radiation-induced cases.This is further supported by the association of elder patients (AaO > 20 years) with positivity for BRAF V600E mutation.
Affiliation: Research Unit Radiation Cytogenetics and.Show MeSH
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Mentions: Scatter plots of binary CLIP2 data and their dependence on thyroid dose and either AaO or AaE are shown in Figure 1. AIC values of the tested models are listed in Tables 2 and 3 for the data sets that contained 141 PTCs and 117 PTCs, respectively. Our main results are derived from the larger data set since inclusion of non-exposed controls provides additional information on the age-dependence of sporadic PTC incidence. For this data set a model with four independent variables, which includes a multiplicative interaction of the continuous variables dose and AaO provides the fit with the lowest AIC (Table 2). The dose-response exhibits an inflexion point at an AaO of 23 years that separates a response with a positive slope at young AaO from a response with a negative slope at elder AaO. With this model the sensitivity of goodness-of-fit with respect to a variation of the categorical boundary was tested. The goodness-of-fit of the preferred model 1 using a categorical boundary at an AaO of 20 years, which was fixed a priori for biological reasons, decreased only slightly by 3.7 points. Parameter estimates of the preferred model 1 are given in Table 4, dose-response relations for the two categories of AaO are shown in the upper panels of Figure 2. For the reduced data set (n = 117) AaE could be additionally included as a covariable since all patients were exposed. Generally, improvements in quality of fit after introduction of additional model parameters were less pronounced in contrast to the results for the larger data set (Table 3). Using AaE as a covariable yielded a better description of the smaller data set compared to using covariable AaO. However, applying the preferred model 1 with two AaO categories to the smaller data set produced the same parameter estimates of Table 4 (left panel) in view of their uncertainties. The preferred model 2 with the lowest AIC used two categories of AaE < 5 years and ≥5 years together with thyroid dose as a continuous variable. Table 4 contains the parameter estimates and the dose-responses, which are depicted in the lower panels of Figure 2. Replacing the two categories for AaE with a continuous variation in AaE yielded a model that described the data almost equally well. For the model with continuous AaE the dose-response had a positive slope below an AaE of 6 years, whilst above AaE 6 years the slope was negative. Again, with the latter model the sensitivity of goodness-of-fit with respect to a variation of the categorical boundary was tested. All findings were consistent between UkrAm and Genrisk-T cohorts (results not shown). Figure 3 shows the thyroid doses for CLIP2 positive and negative cases in box plot representation for the larger data set (141 PTCs) with two categories AaO < 20 years and ≥20 years in the upper panels and for the reduced data set (117 PTCs) with two categories AaE < 5 years and ≥5 years in the lower panels. The hypothesis that the two arithmetic means of log-transformed dose estimates for PTCs with a positive and negative CLIP2 marker status assumed equal values has been tested with two-sample t-tests. On a 95% confidence level the hypothesis was rejected only in the larger data set for AaO < 20. The comparison of CLIP2 mRNA expression levels of 32 tumor and corresponding normal samples showed a significantly increased expression in the tumor samples (P < 0.001). An association of the dose estimates and the expression levels in normal tissues was not observed. In a group of 14 PTCs, BRAF V600E mutations were detected whilst the mean AaO was 22 years and the geometric/arithmetic dose means were 0.20/0.66 Gy. The level of CLIP2 protein abundance using the immunohistochemistry visual scoring level (Supplementary Table 1, available at Carcinogenesis Online) was analyzed. According to staining intensity, tumors were classified as having negative staining (score 0), weak staining (score 1), intermediate staining (score 2), or strong staining (score 3). The results, based on a comparison of dose distribution in tumors with intermediate and strong staining relative to tumors with negative/weak staining, were consistent with those based on a binary scale and there was a clear trend towards higher doses with higher CLIP2 protein expression for AaE < 5 years and AaO < 20 years. This trend was not visible for AaE ≥ 5 years and AaO ≥ 20 years (Supplementary Figure 2, available at Carcinogenesis Online).