The role of miR‐335‐5p in the redifferentiation of BRAF p. V600E thyroid cancers

The BRAF p.V600E mutation activates the RAS/BRAF/MEK/ERK pathway, leading to cancer cell dedifferentiation and uncontrolled growth. In radioiodine-refractory thyroid cancers, MEK and/or BRAF inhibitors can induce redifferentiation, resensitizing tumors to radioiodine. However, compensatory mechanisms limit this efficacy. We used the SWitchMiner software to identify a small pool of regulatory genes, called switch genes, critically associated with drastic changes in cell phenotypes, using TCGA transcriptomic data from BRAF-mutant papillary thyroid carcinoma and normal thyroid tissues, which highlighted miR-335-5p. Restoring miR-335-5p in thyroid cancer cell lines harboring the BRAF mutation increased expression of thyroid-specific genes and proteins, especially in well-differentiated cell lines, with enhanced sodium-iodide symporter localization and iodine uptake confirmed in organoids. Due to the connection between thyroid-specific and EMT-related genes in the protein–protein interaction network, we examined how miR-335-5p overexpression affects EMT pathway genes that modulate thyroid-specific genes and Kinase Inhibitor (KI) resistance. miR-335-5p inhibited the expression of nearly all analyzed genes in less-differentiated thyroid cell lines. Thus, miR-335-5p may be a viable therapeutic target to restore radioiodine avidity in BRAF-mutant metastatic thyroid cancer and enhance KI treatment redifferentiation.