RNF125 suppresses stem cell-like properties and metastasis in non-small cell lung cancer by promoting ubiquitination and degradation of DDX5.

Non-small cell lung cancer (NSCLC) is the most frequent subclass of lung cancer with a gloomy prognosis. Ring finger protein 125 (RNF125), as a ubiquitin E3 ligase, functions on the progression and development of various tumors. This study attempted to address the function and mechanism of RNF125 in NSCLC. The level of RNF125 was predicted with GEPIA2 website and verified in tumor tissues from NSCLC patients. The role of RNF125 in the malignant processes of NSCLC was determined by cell counting kit-8, the 5-ethynyl-2'-deoxyuridine (EdU) incorporation, transwell, flow cytometry and sphere‑formation experiments. The ubiquitinated role of RNF125 on DEAD-box helicase 5 (DDX5) was assessed by co-immunoprecipitation, ubiquitination and cycloheximide assays. The function of RNF125 was revealed in xenografted mice. Low RNF125 expression predicted poor prognosis in NSCLC. RNF125 inhibited the levels of indexes involved in proliferation, migration, invasion and stemness, but promoted apoptosis rate in both A549 and H1299 cells. Mechanically, RNF125 directly bound to DDX5. Overexpression of RNF125 enhanced the DDX5 ubiquitination, but knockdown of RNF125 reduced the degradation of endogenous DDX5. The inhibitory role of RNF125 overexpression in the malignant progressions of A549 cells was recovered with the upregulation of DDX5, vice versa. Besides, overexpression of RNF125 declined tumor weight and volume, the level of Ki-67 and the numbers of liver metastasis foci in vivo, vice versa. Also, RNF125 overexpression reduced the protein expressions of invasion markers and stemness markers in vivo. Collectively, low expression of RNF125 predicted poor prognosis of NSCLC patients. Upregulation of RNF125 repressed proliferation, mobility, invasion and stemness of NSCLC through the ubiquitinated degradation of DDX5.