Thyroid cancer (TC) is one of the most common malignancy of the human endocrine system. BRAF V600E mutation is the most frequent genetic alteration of papillary carcinoma, the most frequent TC, which effects RAS-RAF-MEK intracellular signaling pathway. These alterations in RAS-RAF-MEK pathway lead to changes in expression levels of cell membrane integrin receptors and their ligand - extracellular matrix protein osteopontin, which in turn increases the metastatic potential of tumor cells. Thus, integrins and their ligand osteopontin can be considered as potential biomarkers of tumor progression and aggressive tumor phenotypes. The aim of the study was to evaluate the expression levels of integrin receptors ITGA2, ITGA3, ITGAV, ITGA6, ITGA9, ITGB1, ITGB3 and their ligands OPNa, OPNb in the thyroid cancer with different BRAF V600E mutation status.
Methods: Thyroid tumor samples of 70 patients obtained during surgical treatment were analyzed. Expression levels of the investigated genes were evaluated by real time RT-PCR. Fluorescent immunohistochemistry (IHC) was used to confirm the PCR results and to estimate the amount of protein levels. For IHC frozen sections were used. BRAF V600E mutation was determined using allele-specific amplification. Nonparametric criteria (Kruskal Wallis, Wilcoxon and Mann-Whitney tests) were used to evaluate group differences. P values of less than 0.05 were considered as statistically significant.
Results: A higher gene expression level of ITGA2 (1.9-fold, p = 0.037), ITGA3 (21.1-fold, p = 0.041) and ITGA5 (2.08-fold, p = 0.048) was observed in papillary thyroid cancer (PTC) tissue in comparison with median expression level in control samples (conventionally normal tissue of thyroid gland). These changes were confirmed by IHC (significant changes for α2 integrin). ITGAV expression level was statistically significantly higher in follicular thyroid cancer (FTC) (2.0-fold, p = 0.040). Next, high gene expression levels in tissue samples of lymph node metastases were observed for ITGA5 (2.92-fold, p = 0.015), OPNb (4.36-fold, p = 0.037). For genes ITGA3 (37.48-fold, p = 0.017790), ITGA6 (18.76-fold, p = 0.028921) and ITGA9 (12.52-fold, p = 0.026710) higher expression level was detected in T3-4 tumors (TNM) compared to tumors classified as T1-2. Presence of BRAF V600E mutation was identified in 20 samples of PTC of 40 (50%). A significant increase of the expression level only of ITGA3 (3.1-fold, p = 0. 0422) was observed in BRAF V600E positive samples. Further, changes in expression levels of integrins and osteopontin were assessed in benign and malignant neoplasms. In PTC samples higher expression of ITGA2 (2.8-fold, p = 0.005), ITGA6 (2.11, p = 0.03) and ITGB1 (2.32-fold, p = 0.02) was detected. In FTC expression level of ITGA6 (2.67, p = 0.007) was higher than in benign thyroid nodules.
Conclusion: Identified changes in expression levels of the studied genes indicate that they could play an important role in tumor progression, and their expression could be affected by the product of mutant BRAF gene. Integrins and their ligand osteopontin might be considered as potential markers in determining prognosis and treatment of TC.
Keywords: BRAF V600E mutation; Integrins; Osteopontin; Thyroid cancer.
Copyright © 2018. Published by Elsevier Ltd.