MRTO4 (MRT4 homolog, ribosome maturation factor) is a nuclear protein that plays a critical role in ribosome biogenesis and assembly. As a component of the ribosome assembly machinery, MRTO4 functions as a nuclear paralog of ribosomal protein P0, binding to pre-60S ribosomal subunits at early stages of assembly in the nucleolus before being replaced by P0 in cytoplasmic pre-60S subunits and mature ribosomes 1. The protein undergoes phosphorylation by CK2 kinase at serines S229, S233, and S235 within its acidic C-terminal region, which regulates its molecular behavior during nucleolar stress conditions 1. MRTO4 expression is significantly dysregulated in various cancers, with high expression associated with poor prognosis in hepatocellular carcinoma and colorectal cancer 23. In hepatocellular carcinoma, MRTO4 enhances glycolysis by inhibiting ALDOB, promoting tumor progression, proliferation, and invasion while suppressing apoptosis 4. The protein also serves as an immunological biomarker, correlating with tumor microenvironment characteristics, immune checkpoint gene expression, and drug sensitivity in liver cancer 2. Additionally, MRTO4 expression is downregulated in reproductive injury models, suggesting roles beyond ribosome biogenesis 5.