Integrated single‐cell transcriptomics reveals miR‐941 targets CLDN4 to inhibit malignant progression of thyroid cancer through the PI3K/AKT signaling pathway

Abstract Claudin‐4 (CLDN4), a key tight junction protein, has been implicated in tumor progression; however, its functional role and regulatory mechanisms in thyroid cancer remain unclear. This study aimed to investigate the contribution of CLDN4 to malignant progression and its interaction with the tumor–immune microenvironment. Single‐cell and bulk transcriptomic data were integrated to identify CLDN4‐associated malignant epithelial subpopulations. CLDN4 expression was validated in 25 paired papillary thyroid carcinoma (PTC) tissues by qRT‐PCR, western blotting, and immunohistochemistry. Functional assays were performed using CLDN4‐overexpressing and CLDN4‐knockdown B‐CPAP and TPC‐1 cells. The miR‐941–CLDN4 interaction was verified by luciferase reporter assays. PI3K/AKT signaling and macrophage polarization were evaluated in vitro, and tumor growth was assessed in a xenograft mouse model. A CLDN4‐high epithelial subpopulation was identified and associated with advanced tumor stage and PI3K/AKT activation. CLDN4 was upregulated in PTC tissues, whereas miR‐941 was downregulated. High CLDN4 expression correlated with larger tumor size, lymphatic metastasis, and vascular migration. CLDN4 overexpression promoted proliferation, migration, colony formation, and apoptosis resistance, whereas knockdown produced the opposite effects. miR‐941 directly targeted CLDN4 and attenuated its oncogenic effects. CLDN4 activated PI3K/AKT signaling, while PI3K inhibition reversed these phenotypes. CLDN4 also promoted M2 macrophage polarization and suppressed M1 polarization. In vivo, CLDN4 enhanced tumor growth, which was inhibited by PI3K blockade. miR‐941 suppresses CLDN4 to inhibit PTC progression through modulation of the PI3K/AKT pathway. These findings provide mechanistic insights into tumor progression and immune microenvironment remodeling, highlighting CLDN4 as a potential therapeutic target.