KLK6 is Associated with a Neutrophil-Dominant Immunosuppressive Microenvironment and Epigenetic Deregulation in Lung Adenocarcinoma.

INTRODUCTION: Lung adenocarcinoma (LUAD) is the most prevalent histological subtype of lung cancer and is associated with poor survival despite advances in targeted therapies. Kallikrein-related peptidase 6 (KLK6) has been implicated in several malignancies, but its expression pattern, clinical relevance, and biological function in LUAD remain incompletely characterized. This study aimed to evaluate KLK6 expression and its associations with prognosis, epigenetic regulation, immune infiltration, and migratory phenotypes in LUAD. METHODS: RNA-seq expression and clinical data were obtained from The Cancer Genome Atlas (TCGA), Genotype-Tissue Expression (GTEx), and Gene Expression Omnibus (GEO) databases. KLK6 expression was analyzed in relation to clinicopathological parameters, survival outcomes, promoter methylation status (via UALCAN), and tumor-infiltrating immune cell abundance (via TIMER2.0). In vitro, KLK6 was knocked down using shRNA in A549 and H1299 LUAD cell lines. Cell migration was assessed by transwell assays, and the expression of Epithelial-Mesenchymal Transition (EMT)- and Wnt signaling-related markers was examined by qRT-PCR and Western blotting. RESULTS: KLK6 expression was significantly upregulated in LUAD tissues compared with normal lung tissues. High KLK6 expression was associated with poorer overall survival (HR = 1.52, P = 0.009) and disease-specific survival (HR = 1.55, P = 0.03). ROC analysis showed that KLK6 discriminated stage I LUAD from normal tissues with an AUC of 0.73. Promoter hypomethylation was observed in LUAD tumors and correlated with increased KLK6 expression. Immune infiltration analysis revealed that KLK6-high tumors exhibited reduced B-cell infiltration and increased neutrophil infiltration. Functional experiments demonstrated that KLK6 knockdown significantly suppressed cell migration, accompanied by increased E-cadherin and decreased N-cadherin, Vimentin, Wnt5a, and β-catenin expression. DISCUSSION: These findings suggest that KLK6 overexpression in LUAD is driven in part by promoter hypomethylation and is closely linked to a neutrophil-dominant immunosuppressive microenvironment. Furthermore, KLK6 appears to promote LUAD cell migration through EMT- and Wnt-related signaling pathways. Collectively, these multi-layered data position KLK6 as a potential driver of aggressive tumor behavior and a candidate biomarker for risk stratification. CONCLUSION: KLK6 is aberrantly overexpressed in LUAD and is associated with poor prognosis and enhanced migratory capacity. It may serve as a promising prognostic biomarker and a potential therapeutic target for LUAD.