INHBB promotes liver metastasis of colorectal cancer via regulation of TGF-β/Smad signaling, EMT and anoikis resistance.

[BACKGROUND] Colorectal cancer (CRC) is the third most prevalent malignancy worldwide, with liver metastasis being a major cause of mortality. Although Inhibin β B (INHBB) is associated with tumor progression, its specific role in CRC liver metastasis remains poorly understood.

[METHODS] Transcriptomic analysis of GEO/TCGA datasets identified INHBB as a key regulator of anoikis resistance and liver metastasis in colorectal cancer. Comprehensive bioinformatics analyses were performed, including clinicopathological correlation assessment, prognostic evaluation, immune landscape characterization, drug sensitivity prediction, and functional enrichment studies. Functional validation included: (1) molecular profiling (qPCR/Western blot/IHC), (2) siRNA-mediated knockdown in HCT116/Caco-2 cells with functional assays (transwell migration/invasion, calcein AM/EthD-1 anoikis detection), and (3) mechanistic interrogation of TGF-β/Smad signaling, EMT markers, and anoikis-related proteins. In vivo validation was performed using a mouse model with spleen injection.

[RESULTS] Our study systematically characterized the expression profile of INHBB in primary CRC and liver metastases, revealing significantly elevated expression in both tissue types (P < 0.01). Clinicopathological analysis demonstrated that high INHBB expression correlated significantly with advanced TNM stage (III-IV), lymph node metastasis (N1-2), and poor prognosis (P < 0.001). Functionally, INHBB knockdown reduced CRC cell migration, invasion, and hepatic metastasis formation (all P < 0.01) through three distinct mechanisms: (1) attenuating TGF-β/Smad2/3/Smad4 signaling (evidenced by decreased Smad2/3 phosphorylation, P < 0.01), (2) reversing EMT progression (E-cadherin upregulation concomitant with N-cadherin and vimentin downregulation), and (3) sensitizing cells to anoikis (INHBB interference significantly increased the anoikis rate). Immune profiling revealed that INHBB positively correlated with M0/M1 macrophages and resting NK cells (P < 0.05), but negatively with resting dendritic cells, mast cells, eosinophils, and plasma cells (P < 0.05), suggesting its potential role in remodeling the immune microenvironment to facilitate tumor immune escape. Our in vivo studies demonstrated that INHBB silencing significantly inhibited colorectal cancer liver metastasis in a xenograft mouse model.

[CONCLUSION] Our study demonstrates that INHBB drives CRC liver metastasis by upregulating the TGF-β/Smad2/3/Smad4 pathway and anoikis resistance, highlighting its potential as a therapeutic target and prognostic biomarker for metastatic CRC.