C/EBPβ Drives Anaplastic Thyroid Cancer Dedifferentiation and Radioiodine Resistance via IL-6/JAK/STAT and EMT Activation

Abstract Anaplastic thyroid carcinoma (ATC) is among the most lethal human malignancies, with a median survival of four months. While ATC is thought to arise from papillary thyroid carcinoma (PTC) through dedifferentiation, the molecular drivers underlying this transition remain poorly defined. Here, we integrated single-cell transcriptomics (43,866 cells; PTC, n = 5; ATC, n = 3) with spatial transcriptomics from independent cohorts across the disease spectrum. We identified CCAAT/enhancer-binding protein beta (C/EBPβ) as a transcriptionally hyperactivated, genomically amplified master regulator of thyroid cancer dedifferentiation. Trajectory analysis positioned C/EBPβ upregulation as an early molecular switch. Mechanistically, C/EBPβ activates IL-6/JAK/STAT signaling and epithelial-mesenchymal transition (EMT). In PTC cell lines, inducible C/EBPβ expression phenocopied ATC-like aggressive features, enhancing proliferation, migration, and invasion, and conferring radioiodine refractoriness by suppressing the sodium-iodide symporter (NIS). These phenotypes were abrogated by a DNA-binding-deficient mutant and reversed upon withdrawal of C/EBPβ. In vivo , induction of C/EBPβ accelerated xenograft tumor growth. Furthermore, immunohistochemistry confirmed marked C/EBPβ overexpression in clinical ATC specimens (mean H-score: 166.7) compared with advanced PTC (mean H-score: 18.8). Spatial analysis revealed ATC-associated microenvironmental remodeling, highlighted by CST1-expressing myofibroblastic cancer-associated fibroblasts (myCAFs) at tumor boundaries and the expansion of SPP1 + tumor-associated macrophages linked to hypoxia and EMT. Collectively, these integrated findings establish C/EBPβ as a critical mechanistic driver and candidate therapeutic target in aggressive thyroid cancer.