Identification of IQGAP3 prognostic potential and involvement in immune cell infiltration in LUAD.

BACKGROUND: Although IQGAP3 has been identified as a prognostic biomarker in various cancers, its mechanistic role in lung adenocarcinoma (LUAD) progression and modulation of the tumor immune microenvironment remains poorly defined. METHODS: We integrated bulk RNA sequencing and single-cell RNA sequencing (scRNA-seq) analyses of clinical specimens to quantify IQGAP3 expression in LUAD. Survival analyses correlated expression levels with patient outcomes. Functional assays including CCK-8, colony formation, EdU incorporation, migration, and invasion assays were performed to evaluate the role of IQGAP3 in LUAD cells. Enrichment analyses (KEGG, GO, and GSEA) were used to identify relevant biological pathways. Immune infiltration analyses evaluated correlations with cytotoxic T-cell exhaustion markers, validated via RT-qPCR, Western blotting, co-culture systems, and multiplex immunofluorescence staining. Mechanistic studies examined RAS-ERK pathway activation, and therapeutic efficacy was tested using IQGAP3-knockdown combined with anti-PD-1 therapy in C57BL/6 subcutaneous xenograft models. RESULTS: IQGAP3 was significantly upregulated in LUAD tumor tissues compared to adjacent non-tumor tissues, and its high expression was associated with poor patient prognosis. IQGAP3 promoted LUAD cell proliferation, migration, and invasion. Enrichment analyses revealed IQGAP3-associated differentially expressed genes (DEG) involvement in cell cycle dysregulation and MAPK signaling. Crucially, IQGAP3 expression positively correlated with T-cell exhaustion markers, coinciding with tumor cell PD-L1 upregulation. Mechanistic studies revealed that these effects were mediated through activation of the RAS-ERK signaling cascade. In vivo, the combination of IQGAP3 knockdown and anti-PD-1 therapy significantly suppressed tumor growth in LUAD-bearing mice. CONCLUSIONS: Overexpression of IQGAP3 in LUAD is associated with poor clinical outcomes and promotes tumor progression by regulating cell cycle and inducing T cell exhaustion via RAS-ERK signaling pathway.