RRP9 (ribosomal RNA processing 9) is a core component of the U3 small nucleolar ribonucleoprotein (snoRNP) complex that plays essential roles in ribosomal RNA processing and ribosome biogenesis 12. The protein contains a seven-bladed WD repeat propeller domain and an N-terminal region with a nuclear localization signal 2. RRP9 specifically binds to the unique B/C motif of U3 snoRNA, with its conserved 7bc loop being crucial for this interaction and proper nucleolar localization 2. The protein undergoes neddylation modification at lysine 221 by the E3 ligase Smurf1, which is essential for pre-rRNA processing and ribosome biogenesis 1. Clinically, RRP9 is significantly overexpressed in multiple cancers including colorectal, breast, thyroid, and acute myeloid leukemia, where high expression correlates with poor prognosis and promotes tumor progression 3456. In breast cancer, RRP9 promotes progression through interaction with JUN protein and activation of AKT signaling 4. The protein's stability is enhanced by METTL1-mediated m7G methylation in colorectal cancer 7. These findings establish RRP9 as both a fundamental ribosome biogenesis factor and an important oncogene across multiple cancer types.