Unveiling PAK4 as a Key Biomarker in Adrenocortical Carcinoma: Insights from Bioinformatics and Experimental Evidence

Adrenocortical carcinoma (ACC) is a rare and fatal adrenal cortex cancer with a poor prognosis and high mortality rate. Although surgical resection is the primary treatment for ACC, recurrence is still common. p21-activated kinase 4 (PAK4) is linked to tumour development and progression, being overexpressed in various cancers. However, the role of PAK4 in ACC remains unclear.

In this study, PAK4 expression in ACC was analysed using sequencing data from the Gene Expression Omnibus (GEO) and The Cancer Genome Atlas (TCGA) databases, assessing its clinical relevance with Kaplan-Meier, Cox regression, receiver operating characteristic (ROC) curve and prognostic nomogram models. Functional enrichment of PAK4-related genes was explored using protein-protein interaction (PPI) networks, Gene Ontology (GO)/Kyoto Encyclopedia of Genes and Genomes (KEGG) and gene set enrichment analysis (GSEA). The association between PAK4 messenger RNA (mRNA) expression and immune infiltration was examined via Tumor Immune System Interaction Database (TISIDB). Finally, immunohistochemistry was used for tissue validation.

In the GEO and TCGA databases, PAK4 expression was significantly higher in ACC tissues than in normal samples (p < 0.05). High PAK4 levels were associated with poor prognosis, including shorter overall survival, disease-specific survival and progression-free interval (p < 0.05). Elevated PAK4 expression correlated with advanced T, N and M stages (p < 0.05), indicating increased malignancy in ACC. A PPI network predicted associations between PAK4 and its targets, whereas GSEA linked PAK4 to the Hedgehog signalling pathway and cell proliferation (p < 0.05). The upregulation of PAK4 was also connected to immune regulation and tumour-infiltrating immune cells such as T cells, B cells and mast cells (p < 0.05). Immunohistochemistry confirmed high PAK4 expression in ACC (p < 0.001).

PAK4 is significantly overexpressed in ACC, and it may play a carcinogenic role, showing great application potential as a potential therapeutic target and an independent prognostic biomarker of ACC.