BRAF V600E Transduction of an SV40-Immortalized Normal Human Thyroid Cell Line Induces Dedifferentiated Thyroid Carcinogenesis in a Mouse Xenograft Model

Background: Despite active studies of the clinical importance of BRAFV600E, suitable research models to investigate the role of this mutation in the etiopathogenesis of human thyroid cancers are limited. Thus, we generated cell lines by transducing the simian virus (SV)-40 immortalized human thyroid cell line Nthy-ori 3-1 (Nthy) with lentiviral vectors expressing either BRAFWT (Nthy/WT) or BRAFV600E. Nthy/WT and Nthy/V600E cells were then xenografted into mice to evaluate the carcinogenic role of BRAFV600E. Methods: Each cell line was subcutaneously injected into NOD.Cg-Prkdcscid Il2rgtm1Wjl/SzJ mice, and a pathological analysis was performed. The effects of the mutation were further verified by using a BRAFV600E-selective inhibitor (PLX-4032, vemurafenib). The transcriptome was analyzed by RNA sequencing and compared with data from The Cancer Cell Line Encyclopedia and Gene Expression Omnibus. Results: While Nthy/WT was not tumorigenic in vivo, Nthy/V600E formed tumors reaching 2784.343 mm3 in 4 weeks, on average. A pathological analysis indicated that Nthy/V600E tumors were dedifferentiated thyroid cancer. We found metastases in the lung, liver, and relevant lymph nodes. A transcriptomic analysis revealed 5512 differentially expressed genes (DEGs) between the mutant and wild-type cell lines, and more DEGs were shared with anaplastic thyroid cancer than with papillary thyroid cancer. BRAFV600E activated the cell cycle mainly by regulating G1/S phases. PLX-4032 treatment significantly inhibited tumor growth and metastasis. Conclusions: Our data show that BRAFV600E plays a pivotal role in the carcinogenic transformation of an SV40-transfected immortalized normal human thyroid cell line. This xenograft model is expected to contribute to studies of the etiopathogenesis and treatment of highly malignant thyroid cancers.