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

## TL;DR

This study shows how RNF32 promotes liver metastasis in colorectal cancer by altering immune cells and suggests indole-3-acetic acid as a potential treatment.

## Contribution

The study identifies RNF32 as a dual-functional metastasis driver and proposes IAA as a novel therapeutic agent.

## Key findings

- RNF32 promotes tumor growth and liver metastasis by stabilizing β-catenin and activating Wnt signaling.
- RNF32 recruits SPP1+ macrophages to the metastatic niche, enhancing tumor stemness via CD44.
- Indole-3-acetic acid inhibits RNF32, suppressing metastasis and reversing immunosuppression in vivo.

## Abstract

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.

Cytoplasmic RNF32 fuels CRC liver metastasis by degrading GSK3β, which stabilizes β‐catenin and activates Wnt/EMT. Moreover, RNF32 rewires the metastatic niche: it depletes CD8+/CD4+ T and NK cells while recruiting SPP1+ macrophages (which boost tumor stemness via CD44), fibroblasts, and immunosuppressive monocytes to aid colonization. Importantly, indole‐3‐acetic acid (IAA) counteracts RNF32, reversing tumor progression and immunosuppression.