Dermatology Center, Xinhua Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China.
Department of Dermatology, Shanghai Jiaotong University School of Medicine, Shanghai, China.
Cell Death Dis. 2024 Apr 8;15(4):252. doi: 10.1038/s41419-024-06626-5.
Cutaneous squamous carcinoma is the second most common epithelial malignancy, associated with significant morbidity, mortality, and economic burden. However, the mechanisms underlying cSCC remain poorly understood. In this study, we identified TGM3 as a novel cSCC tumor suppressor that acts via the PI3K-AKT axis. RT-qPCR, IHC and western blotting were employed to assess TGM3 levels. TGM3-overexpression/knockdown cSCC cell lines were utilized to detect TGM3's impact on epithelial differentiation as well as tumor cell proliferation, migration, and invasion in vitro. Additionally, subcutaneous xenograft tumor models were employed to examine the effect of TGM3 knockdown on tumor growth in vivo. Finally, molecular and biochemical approaches were employed to gain insight into the tumor-suppressing mechanisms of TGM3. TGM3 expression was increased in well-differentiated cSCC tumors, whereas it was decreased in poor-differentiated cSCC tumors. Loss of TGM3 is associated with poor differentiation and a high recurrence rate in patients with cSCC. TGM3 exhibited tumor-suppressing activity by regulating cell proliferation, migration, and invasion both in vitro and in vivo. As a novel cSCC tumor differentiation marker, TGM3 expression was positively correlated with cell differentiation. In addition, our results demonstrated an interaction between TGM3 and KRT14 that aids in the degradation of KRT14. TGM3 deficiency disrupts keratinocytes differentiation, and ultimately leads to tumorigenesis. Furthermore, RNA-sequence analysis revealed that loss of TGM3 enhanced EMT via the PI3K-AKT signaling pathway. Deguelin, a PI3K-AKT inhibitor, blocked cSCC tumor growth induced by TGM3 knockdown in vivo. Taken together, TGM3 inhibits cSCC tumor growth via PI3K-AKT signaling, which could also serve as a tumor differentiation marker and a potential therapeutic target for cSCC. Proposed model depicted the mechanism by which TGM3 suppress cSCC development. TGM3 reduces the phosphorylation level of AKT and degrades KRT14. In the epithelial cell layer, TGM3 exhibits a characteristic pattern of increasing expression from bottom to top, while KRT14 and pAKT are the opposite. Loss of TGM3 leads to reduced degradation of KRT14 and activation of pAKT, disrupting keratinocyte differentiation, and eventually resulting in the occurrence of low-differentiated cSCC.
皮肤鳞状细胞癌是第二大常见的上皮恶性肿瘤，与显著的发病率、死亡率和经济负担有关。然而，cSCC 的发病机制仍知之甚少。在这项研究中，我们发现 TGM3 是一种新型的 cSCC 肿瘤抑制因子，通过 PI3K-AKT 轴发挥作用。我们采用 RT-qPCR、免疫组化和 Western blot 来评估 TGM3 水平。利用 TGM3 过表达/敲低的 cSCC 细胞系检测 TGM3 对上皮分化以及体外肿瘤细胞增殖、迁移和侵袭的影响。此外，我们还利用皮下异种移植肿瘤模型检测 TGM3 敲低对体内肿瘤生长的影响。最后，我们采用分子和生化方法深入研究了 TGM3 的肿瘤抑制机制。结果表明，TGM3 在分化良好的 cSCC 肿瘤中表达增加，而在分化差的 cSCC 肿瘤中表达降低。TGM3 的缺失与 cSCC 患者的低分化和高复发率相关。TGM3 在体外和体内均通过调节细胞增殖、迁移和侵袭发挥肿瘤抑制作用。作为一种新型的 cSCC 肿瘤分化标志物，TGM3 的表达与细胞分化呈正相关。此外，我们的研究结果表明，TGM3 与 KRT14 之间存在相互作用，有助于 KRT14 的降解。TGM3 缺乏会破坏角质形成细胞的分化，最终导致肿瘤发生。此外，RNA 测序分析表明，TGM3 的缺失通过 PI3K-AKT 信号通路增强 EMT。PI3K-AKT 抑制剂 Deguelin 阻断了体内 TGM3 敲低诱导的 cSCC 肿瘤生长。综上所述，TGM3 通过 PI3K-AKT 信号抑制 cSCC 肿瘤生长，同时也可作为 cSCC 的肿瘤分化标志物和潜在治疗靶点。提出的模型描绘了 TGM3 抑制 cSCC 发展的机制。TGM3 降低 AKT 的磷酸化水平并降解 KRT14。在上皮细胞层，TGM3 的表达从底部到顶部呈递增特征模式，而 KRT14 和 pAKT 则相反。TGM3 的缺失导致 KRT14 降解减少和 pAKT 激活，破坏角质形成细胞分化，最终导致低分化 cSCC 的发生。
