TRIM21

Tripartite motif-containing 21 (TRIM21) is a cytosolic E3 ubiquitin ligase that functions in intracellular immunity and protein homeostasis^[1][2]. Mechanistically, TRIM21 mediates K48- and K11-linked ubiquitination of target proteins, including viral antigens and transcription factors, modulating their stability, signaling, and degradation^[3][4][5]. TRIM21 regulates protein translation by interacting with PKR and promoting K6-linked ubiquitination of PP1α, thereby controlling eIF2α dephosphorylation and protein synthesis under stress conditions^[6]. In cancer models, TRIM21 suppresses tumorigenesis by promoting cuproptosis in esophageal squamous cell carcinoma through ID1 ubiquitination and inhibits ovarian cancer cell proliferation and migration via cell cycle regulation^[3][7]. TRIM21 also contributes to hepatocarcinogenesis by negatively regulating the p62-Keap1-Nrf2 antioxidant pathway, enhancing oxidative stress and tumor progression^[8]. Compared with related TRIM isoforms, TRIM21 specifically targets interferon regulatory factors, such as IRF3 and IRF5, with differential isoform-specific degradation, thereby modulating innate immunity and autoimmune responses^[9][10]. Experimental applications exploit TRIM21’s antibody-binding Fc domain to degrade specific intracellular proteins, enabling precise protein depletion in cell and zebrafish models^[1][11]. Small molecules or inhibitors targeting upstream regulators, like Sorafenib, can enhance TRIM21-mediated ubiquitination, highlighting its potential in therapeutic intervention and functional studies^[3][5]. Collectively, TRIM21 integrates immune defense, protein quality control, and disease modulation, making it a versatile tool for mechanistic and translational research.