Colorectal Cancer Cell's Weapon: RNF32 Engages SPP1+ Macrophages to Foster Liver Metastasis, Targeted by Indole-3-Acetic Acid.

Colorectal cancer liver metastasis (CRLM) involves complex molecular mechanisms. By integrating The Cancer Genome Atlas (TCGA) data and employing Cox regression, Weighted Gene Co-expression Network Analysis (WGCNA), and single-cell RNA sequencing, this study identifies RNF32 as a key gene linking poor prognosis to metastasis. Functional assays demonstrate that RNF32 promotes tumor cell proliferation, invasion, and epithelial-mesenchymal transition (EMT) in vitro, and drives tumor growth and liver metastasis in vivo. Mechanistically, RNF32 catalyzes K48-linked ubiquitination at the K60 site of GSK3β, stabilizing β-catenin and activating the Wnt signaling pathway, thereby upregulating CCL2. Mass cytometry and other experiments further reveal that RNF32 recruits SPP1+ macrophages via CCL2 to remodel the metastatic niche, a process dependent on the CCR2/FABP1/PPARG axis. Macrophage depletion abrogates metastasis, while the FABP1 inhibitor orlistat reverses SPP1 upregulation in macrophages. Moreover, SPP1+ macrophages interact with tumor cell CD44, synergizing with RNF32 to enhance cancer stemness via Wnt signaling. Importantly, virtual screening identifies indole-3-acetic acid (IAA) as an RNF32 inhibitor that suppresses liver metastasis and reverses immunosuppression in vivo. This study establishes RNF32 as a dual-functional driver of metastasis and proposes IAA as a promising therapeutic agent, offering new hope for targeting both tumor-intrinsic EMT and the immune microenvironment in CRC liver metastasis.