RSPO2-induced ferroptosis via PTBP1-mediated FSP1 mRNA decay suppresses breast cancer progression.

Introduction: Breast cancer is the most common malignant tumor worldwide, and its high heterogeneity limits the efficacy of current clinical therapies. R-spondin 2 (RSPO2) expression is closely associated with breast cancer subtypes, but the precise mechanisms by which it drives disease progression, particularly its relationship with ferroptosis, remain unclear. Methods: RSPO2 expression was examined in primary breast cancer specimens and in MCF-7 and MDA-MB-231 cell lines. Functional assays, including proliferation, migration, and invasion tests, were performed following RSPO2 overexpression. Results: RSPO2 was consistently downregulated in malignant breast cancer tissues. Restoring RSPO2 expression markedly suppressed cell proliferation, migration, and invasion in vitro and inhibited tumor growth in vivo. Mechanistically, RSPO2 recruited the E3 ubiquitin ligase TRIM21 to promote PTBP1 ubiquitination and proteasomal degradation. RNA-seq and validation assays revealed that PTBP1 bound the 3'UTR of ferroptosis suppressor protein 1 (FSP1) mRNA, enhancing its stability. RSPO2 overexpression reduced PTBP1 levels, leading to decreased FSP1 mRNA stability and expression. Consequently, RSPO2 overexpression triggered ferroptosis, as evidenced by ROS accumulation, GSH depletion, and elevated MDA and Fe Discussion: This study demonstrates that RSPO2 functions as a tumor suppressor in breast cancer by recruiting TRIM21 to degrade PTBP1, thereby reducing FSP1 mRNA stability and promoting ferroptosis. The RSPO2/PTBP1/FSP1 signaling axis is identified for the first time in breast cancer and represents a promising novel therapeutic target.