POU5F1B is responsible for the acquired resistance to dabrafenib in papillary thyroid cancer cells with the BRAF V600E mutation.

[BACKGROUND] Dabrafenib, an inhibitor of the B-Raf proto-oncogene (BRAF) V600E mutant, has become the major drug for targeted therapy of papillary thyroid cancer (PTC) with the BRAF V600E mutant; however, acquired resistance is inevitable.

[OBJECTIVE] To identify key transcription factors (TFs) involved in dabrafenib resistance and identify targets to reverse dabrafenib resistance.

[METHODS] Dabrafenib-resistant PTC cell lines BCPAP/DabR and K1/DabR were established, and phenotypic assays were performed to validate the malignant phenotype. RNA sequencing and bioinformatics analyses were used to identify differentially expressed genes (DEGs) and screen TFs involved in resistant phenotype-related pathways. The role of the key TF POU5F1B in dabrafenib resistance was further validated using gene gain-and-loss assays.

[RESULTS] BCPAP/DabR and K1/DabR were resistant to dabrafenib, with a resistance index of 5-8. Resistant cells exhibited slower proliferation, strong migration, and spheroid-forming abilities. RNA sequencing screened 6233 DEGs in the resistant group, including 2687 protein-coding RNA (mRNA). Venn analysis indicated that three genes, E2F2, WNT4, and POU5F1B, were involved in resistant phenotype-related pathways and were included in the TF regulatory network. Four TFs of the three genes, POU5F1B, TBX4, FOXO4, and FOXP3, were validated, and POU5F1B showed the highest validated fold-change. Overexpression of POU5F1B in sensitive cells resulted in resistance to dabrafenib and induced a malignant phenotype, whereas silencing it sensitized the resistant cells and reversed the resistant phenotype.

[CONCLUSION] This study successfully established two dabrafenib-resistant PTC cell lines, and POU5F1B could be a potential target for reversing dabrafenib resistance.