Endocrine Abstracts

Objective: Focal adhesion kinase (FAK) is non-receptor tyrosine kinase that has been shown to affect cell motility, adhesion, invasion, cell survival, proliferation and de-differentiation. Its increased expression has been reported for various types of malignancies and is associated with cancer progression. However, there are less information regarding its posttranslational form, phosphorylated at Tyrosine 397 (pY397-FAK), which represents a key event for complete protein activation. In order to determine the possible role of the activated form of FAK in progression of papillary thyroid carcinoma (PTC), we analyzed expression levels of pY397-FAK. We aimed to investigate its presence in tumor and adjacent normal thyroid tissue and its localization in tumor cells, as well as its expression levels in relation to clinicopathological parameters of PTC patients.

Material and methods: Proteins were extracted from 68 snap-frozen malignant and 14 corresponding non-malignant adjacent thyroid tissue for the purpose of pY397-FAK expression analysis by western blot method. Immunohistochemistry was also applied with the aim of investigating the localization of pY397-FAK in terms of presence in the cytoplasm, membrane and nucleus. All the expression levels were correlated separately with the clinicopathological parameters, to test the prognostic capacity.

Results: Densitometric analysis of western blot results showed that the levels of pY397- FAK are significantly higher in the malignant tissue than in paired non-malignant (P < 0.001). We detected the presence of pY397- FAK in all three compartments, with the strongest staining observed in the cytosol. Nuclear staining was noticed in 26.5% (18/68) of the cases. Furthermore, we detected nuclear staining predominantly in the follicular variant of PTC. Western blot analysis revealed that increased expression of pY397-FAK correlated with lymph node metastasis, degree of tumor infiltration, extrathyroid invasion, pT, pTNM and tumor aggressiveness. Immunohistochemistry displayed similar results in terms of cytoplasmic and membranous staining, except that high expression of pY397-FAK originating from cytoplasm significantly correlated with intraglandular dissemination as well. Moreover, the best results have been achieved when the mean score (mean values of cytoplasmic, membranous and nuclear scores) was used for the statistical analysis.

Conclusions: Our results showed that post-translational modifcation of FAK is important event during malignant progression of PTC and that its elevated expression is promising candidate in prognostic assessment. The mean pY397-FAK immunohistochemical score displayed the best performances in stratification of highrisk PTC patients.