ARIH1 (ariadne RBR E3 ubiquitin protein ligase 1) functions as an atypical E3 ubiquitin ligase that works cooperatively with cullin-RING ubiquitin ligase (CRL) complexes to initiate substrate ubiquitination 1. ARIH1 associates with CRL complexes and specifically mediates addition of the first ubiquitin on CRL targets, which is then elongated by CDC34/UBE2R1 and UBE2R2 1. The protein catalyzes both conventional and non-conventional ubiquitination reactions, including K63-linked ubiquitination and oxyester bond-mediated ubiquitination through cooperation with SCFFBS2 23. ARIH1 plays critical roles in immune regulation by catalyzing mono-ISGylation of cGAS at K187, promoting its oligomerization and activation for antiviral immunity and autoimmunity 4. In cancer, ARIH1 demonstrates context-dependent functions: it promotes colorectal cancer progression by facilitating K63-linked ubiquitination of PHB1, enhancing mitochondrial oxidative phosphorylation 3, while also activating STING-mediated T-cell responses that sensitize tumors to immune checkpoint blockade through DNA-PKcs degradation 5. The protein exhibits high evolutionary conservation, sharing 70% amino acid identity with Drosophila ariadne and 98% identity between human and mouse orthologs 6. This conservation suggests fundamental biological importance in cellular regulation through the ubiquitin-proteasome system.