Targeting the NR4A3-RNF139-ATF6 pathway as a therapeutic and diagnostic strategy in bladder cancer.

BACKGROUND: Bladder cancer (BCa) is a prevalent malignancy with high recurrence and metastasis rates. Nuclear receptor subfamily 4 group A member 3 (NR4A3), a member of the orphan nuclear receptor superfamily, is implicated in various cancers, but its functional role and mechanisms in BCa have not been well understood. This study aimed to explore the functional significance and diagnostic value of NR4A3 in BCa, with a focus on its regulation of endoplasmic reticulum (ER) stress and anoikis sensitivity via ATF6 and RNF139.

METHODS: NR4A3 expression in BCa cell lines was assessed by qRT-PCR and Western blot. Gain-of-function assays were performed to evaluate cell proliferation, apoptosis, and anoikis sensitivity in vitro. ER stress markers and ATF6 degradation were examined by immunoblotting, cycloheximide chase, and ubiquitination assays. The role of RNF139 and its regulation by NR4A3 via KLF2 and KLF4 were determined via various biological assays. In vivo tumorigenesis was assessed using a xenograft mouse model. Additionally, the diagnostic performance of NR4A3 was evaluated in 100 clinical patients using serum ELISA and color Doppler ultrasound.

RESULTS: NR4A3 was downregulated in BCa cells, and its overexpression suppressed cell proliferation, colony formation and promoted apoptosis and anoikis sensitivity. Mechanistically, NR4A3 inhibited ER stress by promoting ATF6 ubiquitination and degradation via transcriptional activation of RNF139 through KLF2 and KLF4. RNF139 directly interacted with ATF6 and mediated its ubiquitination at lysine 152. In vivo, NR4A3 overexpression inhibited tumor growth. Clinically, combining color Doppler ultrasound with serum NR4A3 levels significantly improved diagnostic accuracy for BCa (AUC = 0.986).

CONCLUSION: NR4A3 suppresses BCa progression via the KLF2/4-RNF139-ATF6 axis and enhances diagnostic efficacy when combined with ultrasound imaging.