NOP56 Drives Colorectal Cancer Progression by Modulating p53 Acetylation through SIRT1/p300.

Nucleolar protein 56 (NOP56), a core component of small nucleolar ribonucleoprotein complexes, has been implicated in oncogenesis through the regulation of reactive oxygen species (ROS) homeostasis; however, its role in colorectal cancer (CRC) remains unclear. Here, we investigated the clinical relevance and biological function of NOP56 in CRC using TCGA datasets, tissue microarrays, next-generation sequencing, and in vitro and in vivo models. NOP56 expression was markedly elevated in CRC tissues compared with adjacent normal tissues and was correlated with poor patient survival. Silencing of NOP56 suppressed cell viability, colony formation, and migration, particularly in p53 wild-type HCT116 cells, and altered gene expression programs related to DNA damage response and apoptosis. Mechanistically, NOP56 depletion induced cell cycle arrest and apoptosis, accompanied by increased p53 and p21 levels and reduced expression of pro-caspase-3, c-Myc, Cyclin E, CDK2, CDK4, MDM2, and SIRT1. Conversely, NOP56 overexpression promoted p53 degradation, whereas its knockdown enhanced p53 stability and acetylation through suppression of SIRT1 and activation of p300, as supported by evidence of direct interaction and colocalization. Furthermore, NOP56 silencing synergistically enhanced the cytotoxic effect of 5-fluorouracil (5-FU). In a xenograft model, NOP56 knockdown markedly reduced tumor growth as well as PCNA and SIRT1 expression, while increasing p53 and cleaved caspase-3 levels. Collectively, these findings identify NOP56 as an oncogenic driver that promotes CRC progression by inducing p53 degradation, whereas its inhibition triggers apoptosis via p53 acetylation regulated by the SIRT1/p300 axis, highlighting NOP56 as a promising therapeutic target for p53 wild-type CRC.