Circular RNA EIF3I promotes papillary thyroid cancer progression by interacting with AUF1 to increase Cyclin D1 production.

Circular RNAs (circRNAs) play an important role in regulating the development of human cancers through diverse biological functions. However, the exact molecular mechanisms underlying the role of circRNAs in papillary thyroid cancer (PTC) remain largely unknown. Here, we found that hsa_circ_0011385, designated as circular eukaryotic translation initiation factor 3 subunit I (circEIF3I), preferentially localized in the cytoplasm of PTC cells and was more stable than its linear counterpart, EIF3I. Gain- and loss-of-function studies indicated that circEIF3I promoted PTC progression by facilitating cell proliferation, cell cycle, cell migration, and invasion in vitro, as well as PTC cell proliferation in vivo. Mechanistically, circEIF3I interacted with AU-rich element (ARE) RNA-binding factor 1 (AUF1) in the cytoplasm of PTC cells, thus reducing the degradation of Cyclin D1 mRNA and increasing Cyclin D1 protein production, ultimately resulting in PTC progression. Collectively, our results demonstrate the vital role of circEIF3I in PTC progression, supporting its significance as a potential therapeutic target.