# Loss of Epithelial Homeostasis Driven by TMBIM1 Depletion via E-Cadherin Junction Disassembly

## TL;DR

This study shows that reduced TMBIM1 levels in colorectal cancer disrupt epithelial cell structure and promote tumor growth by lowering E-cadherin, a key protein for cell adhesion.

## Contribution

The study reveals a novel context-dependent tumor-suppressive role of TMBIM1 through E-cadherin suppression in microsatellite instability-high colorectal cancer cells.

## Key findings

- TMBIM1 deficiency in normal colonic cells causes morphological changes and growth suppression.
- TMBIM1 knockdown in HCT-116 cells enhances proliferation and pro-tumorigenic traits.
- E-cadherin (CDH1) is a key downstream target of TMBIM1 suppression, leading to loss of epithelial integrity.

## Abstract

Mounting evidence from large-scale association studies has identified transmembrane BAX inhibitor motif-containing 1 (TMBIM1) as a promising candidate gene in colorectal cancer (CRC) pathogenesis. Our clinical analysis confirmed this association, demonstrating significantly reduced TMBIM1 expression in human colon cancer tissues. To elucidate its functional role, we employed complementary experimental approaches across different cellular contexts. In normal colonic epithelial cells (NCM460), TMBIM1 deficiency triggered distinct morphological changes and suppressed cellular growth. Conversely, in malignant HCT-116 cells, TMBIM1 knockdown paradoxically enhanced proliferation and other pro-tumorigenic characteristics, suggesting context-dependent functions. Transcriptomic profiling via RNA-seq revealed that TMBIM1 suppression enhances cell viability, and the specific mutational background of HCT-116 cells appears to exploit the consequent loss of E-cadherin to further drive progression. Mechanistic investigations further identified E-cadherin (CDH1) as a key downstream effector, showing significant down-regulation following TMBIM1 knockdown. We therefore define a context-dependent tumor-suppressive mechanism for TMBIM1, wherein its loss in MSI-H cells promotes tumorigenesis via E-cadherin suppression and the consequent loss of epithelial integrity.