默克尔细胞癌 (MCC) 是一种与默克尔细胞多瘤病毒 (MCPyV) 整合相关的高度侵袭性皮肤癌。 MCPyV 编码的 T 抗原 (TA) 对于维持 MCC 的致癌表型至关重要，即抑制 TA 会导致 RB 途径重新激活和随后的细胞周期停滞。然而，以 RB1 基因纯合缺失为特征的 MCC 细胞系 LoKe 在 shRNA 介导的 TA 抑制后表现出不间断的细胞周期进展。这一独特的功能可以深入分析 TA 对 RB 通路抑制之外的影响，揭示 panTA 敲低后干细胞相关基因表达的减少。基因调控网络分析确定 E2F 家族成员（E2F1、E2F8、TFDP1）是维持表达 TA 的 MCC 细胞中干细胞特性的关键转录调控因子。此外，编码干细胞维持所必需的 DNA 结合许可蛋白的微型染色体维持 (MCM) 基因在 panTA 敲低后受到抑制。干性的下降与神经分化同时发生，其标志是神经发生相关基因（如神经毒素、BTG2 和 MYT1L）表达增加。这种上调可归因于神经发生途径的关键调节因子 PBX1 和 BPTF 活性的增强。 LoKe 中的观察结果在另一个 MCPyV 阳性 MCC 细胞系中得到了证实，其中 RB1 在 panTA 敲低之前被沉默。此外，空间分辨转录组学证明，以神经分化为特征的 MCC 肿瘤部分原位 TA 表达减少。总之，TA 对于维持 MCC 细胞的干性和抑制神经分化至关重要，无论其对 RB 信号通路的影响如何。© 2024 作者。 《医学病毒学杂志》由 Wiley periodicals LLC 出版。

Merkel cell carcinoma (MCC) is a highly aggressive skin cancer associated with integration of Merkel cell polyomavirus (MCPyV). MCPyV-encoded T-antigens (TAs) are pivotal for sustaining MCC's oncogenic phenotype, i.e., repression of TAs results in reactivation of the RB pathway and subsequent cell cycle arrest. However, the MCC cell line LoKe, characterized by a homozygous loss of the RB1 gene, exhibits uninterrupted cell cycle progression after shRNA-mediated TA repression. This unique feature allows an in-depth analysis of the effects of TAs beyond inhibition of the RB pathway, revealing the decrease in expression of stem cell-related genes upon panTA-knockdown. Analysis of gene regulatory networks identified members of the E2F family (E2F1, E2F8, TFDP1) as key transcriptional regulators that maintain stem cell properties in TA-expressing MCC cells. Furthermore, minichromosome maintenance (MCM) genes, which encodes DNA-binding licensing proteins essential for stem cell maintenance, were suppressed upon panTA-knockdown. The decline in stemness occurred simultaneously with neural differentiation, marked by the increased expression of neurogenesis-related genes such as neurexins, BTG2, and MYT1L. This upregulation can be attributed to heightened activity of PBX1 and BPTF, crucial regulators of neurogenesis pathways. The observations in LoKe were confirmed in an additional MCPyV-positive MCC cell line in which RB1 was silenced before panTA-knockdown. Moreover, spatially resolved transcriptomics demonstrated reduced TA expression in situ in a part of a MCC tumor characterized by neural differentiation. In summary, TAs are critical for maintaining stemness of MCC cells and suppressing neural differentiation, irrespective of their impact on the RB-signaling pathway.© 2024 The Author(s). Journal of Medical Virology published by Wiley Periodicals LLC.