AGO4 (Argonaute RISC component 4) is one of four human Argonaute proteins that mediates RNA-directed gene silencing through microRNA binding and target repression 1. Unlike AGO2, AGO4 lacks endonuclease activity and cannot cleave target mRNAs due to specific structural features including inactivating elements in its catalytic center, N-terminal domain, and an AGO4-specific insertion in the catalytic domain 2. Instead, AGO4 functions primarily through translational repression mechanisms as part of RISC complexes. Beyond its canonical miRNA-mediated silencing role, AGO4 exhibits tumor suppressive functions in non-small cell lung cancer by interacting with TRIM21 and promoting ubiquitination of GRP78, which induces apoptosis and inhibits autophagy through mTOR pathway activation in a p53-independent manner 3. AGO4 also participates in RNA-directed DNA methylation (RdDM), particularly in methylating DNA sequences around HMGB1-produced DNA gaps at interspersed repetitive sequences like Alu elements 4. Importantly, while AGO2 is the primary effector for siRNA-mediated gene silencing, AGO4 does not contribute significantly to either on-target or off-target activities of GalNAc-siRNA conjugates, distinguishing its functional role from other Argonaute paralogs 5.