RNF126 in Physiology and Disease: A Multifunctional RING-Type E3 Ubiquitin Ligase in Protein Homeostasis, DNA Repair, and Cancer.

Ring finger protein 126 (RNF126) is a RING-type E3 ubiquitin ligase that has recently emerged as a multifaceted regulator of cellular homeostasis, stress adaptation, and disease progression. Through its structurally distinct zinc-finger and catalytic RING domains, RNF126 orchestrates substrate recognition and ubiquitin transfer, generating diverse ubiquitin linkages with both proteolytic and nonproteolytic functions. Initially characterized as a component of the protein quality control (PQC) machinery, RNF126 cooperates with chaperones such as BAG6 and UBQLN1 to eliminate mislocalized and misfolded proteins, thereby maintaining proteostasis. Beyond PQC, RNF126 plays pivotal roles in DNA damage response pathways by regulating homologous recombination, non-homologous end joining, checkpoint signaling, and genome stability through substrates, including MRE11, Ku80, RNF168, and 14-3-3σ. Genetic studies have further demonstrated its importance in embryogenesis and male fertility, and accumulating evidence has identified RNF126 as a critical driver of malignancy in multiple cancers. RNF126 promotes tumor progression by degrading or modulating key regulators, such as p21, PTEN, p53, PDKs, and LKB1, thereby enhancing proliferation, metabolic reprogramming, anoikis resistance, metastasis, and chemo/radioresistance. Intriguingly, RNF126 exhibits context-dependent functions, acting as an oncogene or tumor suppressor depending on the tissue type and substrate selection. In addition to cancer, RNF126 has been implicated in neurodegeneration, cardiac pathology, antiviral immunity and adaptive immune regulation. This review summarizes the current knowledge of RNF126 structure, ubiquitin signaling mechanisms, physiological functions, and pathological roles, while discussing emerging therapeutic strategies and future challenges for targeting RNF126 in precision medicine.