Lamprey TFE3 exhibits evolutionarily conserved activation mechanisms and regulates autophagy and immune responses

The microphthalmia-associated transcription factor/transcription factor E (MiT/TFE) family belongs to the basic group of helix-loop-helix leucine zipper (bHLH-ZIP)-containing transcription factors. Although MiT/TFE family members, especially TFEB and TFE3, have been extensively studied in higher vertebrates, little is known about their roles in basal vertebrates such as lampreys. Here, we show that lamprey TFE3 and TFEC retain conserved structural features, including key domains, motifs, and serine residues, consistent with the evolutionary history of vertebrates. Expression profiling revealed that lamprey TFE3 is broadly expressed across tissues, with the highest level in the heart. Treatment with Torin1 induced nuclear translocation of TFE3, indicative of its activation. Torin1 also led to a time-dependent increase in TFE3 expression, and upregulation of downstream target genes associated with autophagy, stress responses, and inflammation. Furthermore, we observed elevated LC3-II levels and reduced p62 expression following Torin1 treatment, indicating that activated lamprey TFE3 enhances autophagic activity. Notably, TFE3 activation also promoted cholesterol mobilization and efflux, as evidenced by decreased Bodipy fluorescence intensity and upregulated expression of ABCA1. In vivo stimulation with LPS or poly (I:C) induced significant changes in Lj-TFE3 expression, indicating that lamprey TFE3 is responsive to pathogen-associated molecular patterns and may participate in immune stress responses. Together, these findings demonstrate that lamprey TFE3 exhibits conserved structural and functional features and plays a key role in immune and metabolic regulation, providing important evolutionary insights into the MiT/TFE transcription factor family in early vertebrates.