Thyrospheres from B-CPAP Cell Line with BRAF and TERT promoter mutations have Different Functional and Molecular Features than Parental Cells

Human thyroid cancer derived cell lines are widely used to study the mechanisms involved in thyroid carcinogenesis. However, there is limited availability of non cross-contaminated cancer cell lines derived from papillary thyroid carcinoma (PTC), and the B-CPAP cell line is one of the few such lines. B-CPAP cells have been genetically and cytogenetically well-characterized, but details of their stemness features remain uncertain. We broaden the functional and molecular profiles as well as the tumorigenic capacity of this cell line using functional assays (sphere-forming capacity and efficiency), assessing self-renewal and propagation efficiency, and testing in vivo tumorigenicity in Hsd:Athymic Nude-Foxn1nu mice. Expression of markers of stemness, differentiation, and epithelial mesenchymal transition were estimated at RNA and protein levels in adherent parental cells and sphere-forming cells. Protein expression of xenograft tumors was evaluated by immunohistochemistry. B-CPAP sphere-forming cells were able to form thyrospheres theoretically indefinitely in an appropriate serum-free medium, reverting to the adherent parental cell phenotype when cultured in differentiation medium. Different expression of ALDH1-A1 and CD44 stemness markers and TTF-1 and CK19 differentiation markers allowed discrimination between isolated sphere-forming cells and adherent parental cells, indicating that sphere-forming cells retained stem-like features. In keeping with these observations, tumorigenicity assays confirmed that, relative to parental adherent cells, thyrospheres had enhanced capacity to initiate xenograft tumors. Our findings may constitute a useful background to develop an in vitro model for assessing the origin and progression of papillary thyroid carcinoma bearing BRAFV600E and TERT promoter mutations