Nucleolar and spindle-associated protein 1 (NUSAP1) promotes thyroid cancer dedifferentiation via BCAT1-mediated metabolic-epigenetic crosstalk.

Thyroid cancer (TC) dedifferentiation contributes to tumor progression, treatment resistance, and poor survival, yet the underlying molecular mechanisms remain elusive. Genetic alterations, copy number variations, and epigenetic modifications may contribute to this process. Here, we conducted an integrated analysis to screen for critical molecules involved in TC dedifferentiation, identifying nucleolar and spindle-associated protein 1 (NUSAP1) as a candidate. NUSAP1 is overexpressed in TC and associated with poor prognosis. Upregulation of NUSAP1 enhances TC cell proliferation, migration, and dedifferentiation, evidenced by the suppression of thyroid differentiation genes and the induction of epithelial-mesenchymal transition. Mechanistically, branched-chain amino acid (BCAA) catabolism is a potential mechanism of dedifferentiation in TC mediated by NUSAP1 through RNA sequencing enrichment analysis. Specifically, NUSAP1 forms a transcriptional complex with bromodomain containing 4 (BRD4), which activates branched-chain amino acid transaminase 1 (BCAT1) transcription and leads to accelerated BCAA catabolism and reduced α-ketoglutarate (α-KG) levels. This metabolic shift increases histone H3 lysine 27 trimethylation (H3K27me3) levels by impairing histone demethylation, thereby suppressing the expression of thyroid differentiation genes. Pharmacologic inhibition of NUSAP1 with entinostat suppresses downstream target levels, suggesting a novel treatment modality. In summary, NUSAP1 promotes dedifferentiation through the BCAT1/α-KG/H3K27me3 axis by forming a transcriptional complex with BRD4, which indicates that NUSAP1 is a potential therapeutic target in TC.