Wang, Xiao-FanYao, Tso-PangMa, Zhehao2025-07-022025-07-022025https://hdl.handle.net/10161/32715<p>Amyloid precursor protein (APP) has been extensively studied in the context of neurodegenerative diseases, particularly in Alzheimer’s disease (AD), where its amyloidogenic processing contributes to the formation of amyloid-β (Aβ) plaques. However, the physiological functions of full-length APP and its proteolytic fragments outside the central nervous system remain poorly understood. Emerging evidence suggests that APP is highly expressed in various cancers, yet its role in tumor progression and immune regulation remains largely unexplored. Given the complex interplay between cancer and immune responses, we investigated whether APP contributes to tumor immune evasion and modulates the tumor microenvironment (TME), particularly in non-small cell lung cancer (NSCLC).NSCLC remains a leading cause of cancer-related mortality worldwide, with most patients diagnosed at advanced stages. Immunotherapy, particularly immune checkpoint blockade (ICB), has revolutionized NSCLC treatment by enhancing anti-tumor immune responses. However, many patients exhibit resistance to ICB, often associated with the presence of an immune-excluded or “cold” TME, where tumor-infiltrating lymphocytes are scarce. The mechanisms underlying this immune exclusion remain incompletely understood, necessitating further research into tumor-intrinsic factors that actively suppress immune infiltration. Type I interferons (IFN-Is) play a pivotal role in anti-tumor immunity by enhancing antigen presentation, promoting cytotoxic T lymphocyte recruitment, and modulating immune cell activation. However, their production and activity can be suppressed within the TME, contributing to immune evasion. While IFN-I signaling has been extensively studied in viral immunity and autoimmunity, its regulation by tumor-intrinsic factors in NSCLC remains poorly defined. Given that APP has been implicated in immune modulation in neurodegenerative diseases, we hypothesized that APP might exert a similar function in NSCLC by influencing IFN-I signaling and shaping the immune landscape of the TME. To investigate the role of APP in NSCLC immune regulation, we employed a combination of in vitro and in vivo approaches. APP expression was analyzed in human and murine NSCLC cell lines, as well as in tumor tissues, using immunohistochemistry, RNA sequencing, and Western blotting. Functional assays, including co-culture experiments with cytotoxic T lymphocytes and NK cells, were conducted to assess the impact of APP on immune-mediated tumor cell killing. CRISPR-mediated APP knockout and overexpression systems were utilized to examine APP’s effects on IFN-I signaling and chemokine expression. In vivo tumor models were established in syngeneic mice, and tumor growth was monitored following APP depletion or inhibition. Additionally, chemokine neutralization and integrin-targeting strategies were employed to delineate the APP–IFN-I regulatory axis. These integrated methodologies enabled a comprehensive characterization of APP’s role in shaping the tumor immune microenvironment. Analysis of NSCLC tumors revealed that APP is highly expressed in malignant cells, with elevated APP levels correlating with reduced CD8+ T cell infiltration and poorer patient prognosis, suggesting its role in maintaining an immune-excluded TME. Mechanistically, APP suppresses tumor-intrinsic IFN-I production through the integrin αVβ3–FAK–AKT–GSK3β signaling pathway. Specifically, APP engagement with integrin αVβ3 activates AKT, leading to GSK3β inhibition and subsequent downregulation of IFN-I production. As IFN-Is are key inducers of CXCL9 and CXCL10—chemokines crucial for effector T cell recruitment—APP-mediated suppression of IFN-I impairs CXCL9/10 expression, thereby restricting T cell infiltration. In APP-deficient tumors, IFN-I production was restored, CXCL9 and CXCL10 expression increased, and CD8+ T cell infiltration was enhanced. Neutralizing CXCR3, the receptor for CXCL9/10, abolished these effects, confirming that APP restricts immune infiltration via this chemokine axis.</p><p>These findings position APP as a key regulator of immune exclusion in NSCLC, linking tumor-intrinsic signaling to impaired T cell infiltration. Given the critical role of immune exclusion in immunotherapy resistance, targeting APP could provide a novel strategy to enhance immune infiltration and improve therapeutic outcomes. Future research should explore how APP interacts with other immune components in the TME, including its potential impact on T cell activation, memory formation, and cytotoxic function. From a translational perspective, APP’s E1 domain represents a promising target for cancer immunotherapy. Given its extracellular localization, this domain is well-suited for antibody-based or vaccine-based therapeutic approaches. Vaccines targeting APP’s E1 domain could be explored as a strategy to transform immune-cold tumors into inflamed ones, ultimately enhancing responsiveness to current immunotherapies. Furthermore, targeting APP could not only enhance immune infiltration but also potentially modulate T cell function within the TME, influencing their activation and cytotoxicity. Investigating whether APP influences immune cell interactions within tumors could provide further insight into its broader immunosuppressive roles.In summary, this study reveals a novel role for APP in regulating tumor immunity by suppressing IFN-I signaling and restricting T cell infiltration. By elucidating the molecular mechanisms through which APP mediates immune exclusion, these findings provide a foundation for future research aimed at targeting APP as a therapeutic strategy. Overcoming immune resistance remains a major challenge in solid tumor treatment, and APP represents a promising avenue for enhancing the efficacy of cancer immunotherapy. </p>https://creativecommons.org/licenses/by-nc-nd/4.0/Molecular biologyDissertation