ITGA7 interacts with FN1 to suppress the PI3K/AKT signaling pathway and inhibit thyroid cancer progression

OBJECTIVE: Thyroid cancer (TC) is the most common malignant tumor of the endocrine system, and its incidence has increased annually. Although TC generally has a favorable prognosis, some patients experience recurrence after treatment. Therefore, understanding the pathogenic mechanisms of TC is crucial for improving its treatment. It was hypothesized that ITGA7 suppresses TC by binding to FN1 and inhibiting the PI3K/AKT pathway. This study aimed to test this hypothesis and elucidate the underlying mechanism. METHODS: Expression of Integrin Subunit Alpha 7 (ITGA7) and Fibronectin 1 (FN1) was evaluated in paired samples of normal thyroid and TC tissues via reverse transcription quantitative real-time PCR (RT-qPCR) and immunohistochemistry (IHC). ITGA7 and FN1 mRNA and protein levels were further assessed using RT-qPCR and Western blot analysis. Functional assays included Cell Counting Kit-8 for cell viability, 5-Ethynyl-2'-deoxyuridine (EdU) incorporation for proliferation, Transwell for migration and invasion, and flow cytometry for apoptosis. Protein interaction and co-localization between ITGA7 and FN1 were confirmed through co-immunoprecipitation and immunofluorescence (IF). Western blot was used to examine Phosphatidylinositol 3-kinase/Protein Kinase B (PI3K/AKT) signaling pathway components, and IHC was applied to assess related protein expression in clinical specimens. A xenograft model in nude mice was established to investigate the role of ITGA7 in tumor growth in vivo. Bioinformatics tools including STRING and GEPIA were utilized to predict potential interactions involving ITGA7. RESULTS: RT-qPCR and IHC revealed decreased ITGA7 expression in TC compared to adjacent normal tissues. Consistent downregulation was observed at both mRNA and protein levels in TC cell lines. Functional loss-of-function experiments showed that ITGA7 knockdown enhanced viability, proliferation, migration, and invasion, and suppressed apoptosis. FN1 was identified as an ITGA7-binding partner with negatively correlated expression. FN1 was upregulated in TC tissues, and its silencing impeded malignant phenotypes including proliferation and migration, while promoting apoptosis. The protein interaction and co-localization between ITGA7 and FN1 were experimentally validated. Western blot analysis demonstrated that silencing ITGA7 upregulated FN1 and activated the PI3K/AKT pathway. Conversely, FN1 knockdown suppressed pathway activity. In vivo studies confirmed that ITGA7 suppressed tumor progression by inhibiting the FN1-mediated activation of the PI3K/AKT pathway. Rescue assays demonstrated that FN1 depletion counteracted the oncogenic effects of ITGA7 silencing. CONCLUSION: The expression of ITGA7 in TC tissues and cells was significantly lower than that in normal tissues and cells. ITGA7 inhibits TC progression by interacting with FN1 and suppressing PI3K/AKT signaling pathway activation.