A study on the mechanism of action of B7H4 in HER2-positive gastric cancer and its sensitivity to trastuzumab therapy.

Background: Human epidermal growth factor receptor 2 (HER2)-positive gastric cancer (GC) is characterized by high malignancy and a poor prognosis. Trastuzumab is the first-line targeted therapy for this disease, but the frequent development of primary and acquired resistance severely compromises treatment efficacy and impedes improvements in patient outcomes. B7H4 is a critical negative immune checkpoint molecule that has been demonstrated to contribute to tumor progression and targeted therapy resistance in multiple cancers. However, the specific mechanisms by which B7H4 regulates sensitivity to trastuzumab in HER2-positive GC remain unclear. This study aims to investigate the expression and biological functions of B7H4 in HER2-positive GC, elucidate the molecular mechanisms underlying B7H4-mediated trastuzumab resistance, and thereby provide a theoretical basis for targeted resistance intervention and therapeutic optimization for this malignancy. Methods: The study began with an analysis of The Cancer Genome Atlas (TCGA) database and immunohistochemical staining of tissue sections to assess the expression levels of B7H4 and HER2, as well as the correlation between their expression. Furthermore, the correlation between B7H4 expression and various pathological parameters in patients with HER2-positive GC was analysed. Western blot analysis was used to screen for co-expressing cells, and short hairpin RNA (shRNA) was employed to knockdown B7H4. The effects of B7H4 knockdown on the proliferation, migration and invasion of HER2-positive GC cells were assessed using colony formation assays, Cell Counting Kit-8 (CCK-8) assays, cell scratch assays and Transwell assays, respectively. RNA sequencing (RNA-Seq) was utilised to analyse the biological processes and signalling pathways regulated by B7H4 and to detect relevant biomarkers. Colony formation assays and CCK-8 assays were employed to evaluate the therapeutic sensitivity of trastuzumab to HER2-positive GC cells following B7H4 knockdown. Results: Analysis of the TCGA database and immunohistochemical staining of tissue sections revealed that B7H4 and HER2 were co-expressed in GC tissues, and their expression levels were positively correlated. Clinical correlation analysis revealed that B7H4 expression was significantly associated with tumor size, grade, depth of invasion, lymph node metastasis, distant metastasis, vascular invasion and nerve invasion in HER2-positive GC patients. Western blot analysis demonstrated co-expression of B7H4 and HER2 in NCI-N87 cells. Knockdown of B7H4 resulted in varying degrees of inhibition of proliferation, migration and invasion in NCI-N87 cells. RNA-seq results indicated that B7H4 knockdown affected biological processes such as cell proliferation, migration, invasion and epithelial-mesenchymal transition (EMT), and was significantly associated with the nuclear factor κB (NF-κB) signalling pathway. Knockdown of B7H4 significantly enhanced the sensitivity of HER2-positive GC cells to trastuzumab. Conclusions: B7H4 is highly expressed in HER2-positive GC and is associated with poor prognosis. B7H4 promotes tumor cell proliferation, migration and invasion by activating the NF-κB signalling pathway and driving the EMT process. B7H4 expression influences the sensitivity of HER2-positive GC cells to trastuzumab; inhibition of B7H4 significantly enhances the antitumor efficacy of trastuzumab.