Obstetrics and Gynecology Department, The Second Hospital of Jilin University, 218 Zi Qiang Street, Changchun, Jilin, 130041, China.
National Engineering Laboratory for Druggable Gene and Protein Screening, Northeast Normal University, Changchun, Jilin, 130024, China.
J Exp Clin Cancer Res. 2023 Sep 1;42(1):222. doi: 10.1186/s13046-023-02758-2.
FAT4 (FAT Atypical Cadherin 4) is a member of the cadherin-associated protein family, which has been shown to function as a tumor suppressor by inhibiting proliferation and metastasis. The Wnt/β-catenin pathway activation is highly associated with PD-L1-associated tumor immune escape. Here, we report the mechanism by which FAT4 overexpression regulates anti-tumor immunity in cervical cancer by inhibiting PD-L1 N-glycosylation and cell membrane localization in a β-catenin-dependent manner.
FAT4 expression was first detected in cervical cancer tissues and cell lines. Cell proliferation, clone formation, and immunofluorescence were used to determine the tumor suppressive impact of FAT4 overexpression in vitro, and the findings were confirmed in immunodeficient and immunocomplete mice xenografts. Through functional and mechanistic experiments in vivo and in vitro, we investigated how FAT4 overexpression affects the antitumor immunity via the β-catenin/STT3/PD-L1 axis.
FAT4 is downregulated in cervical cancer tissues and cell lines. We determined that FAT4 binds to β-catenin and antagonizes its nuclear localization, promotes phosphorylation and degradation of β-catenin by the degradation complexes (AXIN1, APC, GSK3β, CK1). FAT4 overexpression decreases programmed death-ligand 1 (PD-L1) mRNA expression at the transcriptional level, and causes aberrant glycosylation of PD-L1 via STT3A at the post-translational modifications (PTMs) level, leading to its endoplasmic reticulum (ER) accumulation and polyubiquitination-dependent degradation. We found that FAT4 overexpression promotes aberrant PD-L1 glycosylation and degradation in a β-catenin-dependent manner, thereby increasing cytotoxic T lymphocyte (CTL) activity in immunoreactive mouse models.
These findings address the basis of Wnt/β-catenin pathway activation in cervical cancer and provide combination immunotherapy options for targeting the FAT4/β-catenin/STT3/PD-L1 axis. Schematic cartoons showing the antitumor immunity mechanism of FAT4. (left) when Wnts bind to their receptors, which are made up of Frizzled proteins and LRP5/6, the cytoplasmic protein DVL is activated, inducing the aggregation of degradation complexes (AXIN, GSK3β, CK1, APC) to the receptor. Subsequently, stable β-catenin translocates into the nucleus and binds to TCF/LEF and TCF7L2 transcription factors, leading to target genes transcription. The catalytically active subunit of oligosaccharyltransferase, STT3A, enhances PD-L1 glycosylation, and N-glycosylated PD-L1 translocates to the cell membrane via the ER-to-Golgi pathway, resulting in immune evasion. (Right) FAT4 exerts antitumor immunity mainly through following mechanisms: (i) FAT4 binds to β-catenin and antagonizes its nuclear localization, promotes phosphorylation and degradation of β-catenin by the degradation complexes (AXIN1, APC, GSK3β, CK1); (ii) FAT4 inhibits PD-L1 and STT3A transcription in a β-catenin-dependent manner and induces aberrant PD-L1 glycosylation and ubiquitination-dependent degradation; (iii) Promotes activation of cytotoxic T lymphocytes (CTL) and infiltration into the tumor microenvironment.
FAT4（非典型钙黏蛋白 4）是钙黏蛋白相关蛋白家族的成员，已被证明通过抑制增殖和转移来发挥肿瘤抑制作用。Wnt/β-连环蛋白通路的激活与 PD-L1 相关的肿瘤免疫逃逸高度相关。在这里，我们报告了 FAT4 过表达通过抑制 PD-L1 N-糖基化和 β-连环蛋白依赖性的细胞膜定位来调节宫颈癌中的抗肿瘤免疫的机制。
首先在宫颈癌组织和细胞系中检测 FAT4 的表达。细胞增殖、克隆形成和免疫荧光用于体外确定 FAT4 过表达的肿瘤抑制作用，并在免疫缺陷和免疫完整的小鼠异种移植中得到证实。通过体内和体外的功能和机制实验，我们研究了 FAT4 过表达如何通过 β-连环蛋白/STT3/PD-L1 轴影响抗肿瘤免疫。
FAT4 在宫颈癌组织和细胞系中下调。我们确定 FAT4 与 β-连环蛋白结合并拮抗其核定位，通过降解复合物（AXIN1、APC、GSK3β、CK1）促进 β-连环蛋白的磷酸化和降解。FAT4 过表达在转录水平上降低程序性死亡配体 1（PD-L1）mRNA 的表达，并通过 STT3A 在翻译后修饰（PTMs）水平上导致 PD-L1 的异常糖基化，导致其内质网（ER）积累和多聚泛素化依赖性降解。我们发现 FAT4 过表达以 β-连环蛋白依赖性方式促进 PD-L1 的异常糖基化和降解，从而在免疫反应性小鼠模型中增加细胞毒性 T 淋巴细胞（CTL）的活性。
这些发现解决了宫颈癌中 Wnt/β-连环蛋白通路激活的基础，并为针对 FAT4/β-连环蛋白/STT3/PD-L1 轴的联合免疫治疗提供了选择。显示 FAT4 抗肿瘤免疫机制的示意图。（左）当 Wnts 与其受体结合时，该受体由 Frizzled 蛋白和 LRP5/6 组成，细胞质蛋白 DVL 被激活，诱导降解复合物（AXIN、GSK3β、CK1、APC）聚集到受体上。随后，稳定的 β-连环蛋白易位到细胞核并与 TCF/LEF 和 TCF7L2 转录因子结合，导致靶基因转录。多萜基转移酶的催化活性亚基 STT3A 增强 PD-L1 的糖基化，并且 N-糖基化的 PD-L1 通过内质网-高尔基体途径易位到细胞膜，导致免疫逃逸。（右）FAT4 主要通过以下机制发挥抗肿瘤免疫作用：（i）FAT4 与 β-连环蛋白结合并拮抗其核定位，通过降解复合物（AXIN1、APC、GSK3β、CK1）促进 β-连环蛋白的磷酸化和降解；（ii）FAT4 在 β-连环蛋白依赖性方式下抑制 PD-L1 和 STT3A 的转录，并诱导 PD-L1 的异常糖基化和泛素化依赖性降解；（iii）促进细胞毒性 T 淋巴细胞（CTL）的激活和浸润到肿瘤微环境中。
