Laboratory for Experimental Oncology and Radiobiology, Center for Experimental and Molecular Medicine, Cancer Center Amsterdam and Academic Medical Center, Meibergdreef 9, 1105AZ, Amsterdam, The Netherlands.
Oncode Institute, Academic Medical Center, Amsterdam, The Netherlands.
Cell Oncol (Dordr). 2018 Aug;41(4):427-437. doi: 10.1007/s13402-018-0381-9. Epub 2018 Jun 4.
Basal cell carcinoma (BCC) is one of the most common skin cancers, and is typically driven by an aberrantly activated Hedgehog (Hh) pathway. The Hh pathway is regulated by interactions between the Patched-1 (Ptch1) and Smoothened (Smo) receptors. Smo is an activating receptor and is subject to inhibition by Ptch1. Following ligand binding to Ptch1, its inhibitory action is relieved and pathway activation occurs. This receptor interaction is pivotal to restraining uncontrolled cellular growth. Both receptors have been found to be frequently mutated in BCCs. Ptch2 is a Ptch1 paralog that exhibits overlapping functions in both normal development and tissue homeostasis. As yet, its contribution to cancer growth is poorly defined. Here we set out to assess how Ptch2 inhibits BCC growth.
We used several in vitro readouts for transcriptional and chemotactic Hh signaling in BCC-derived ASZ001 cells, and a novel xenograft model to assess in vivo BCC tumor growth. Gene editing by TALEN was used to untangle the different Ptch2-dependent responses to its ligand sonic hedgehog (Shh).
We first defined the signaling competence of Ptch2 in Ptch1-deficient ASZ001 cells in vitro, and found that Ptch2 ligand binding drives their migration rather than eliciting a transcriptional response. We found that subsequent targeting of Ptch2 abrogated the chemotaxic effect. Next, we tested the contribution of Ptch2 to in vivo tumor growth using a xenograft model and found that reduced Ptch function results in increased tumor growth, but that selective pressure appatently acts against complete Ptch2 ablation.
We conclude that like Ptch1, Ptch2 exerts a tumor-suppressive function in BCC cells, and that after targeting of both paralogs, ligand-independent activation of the Hh pathway contributes to tumor growth.
基底细胞癌（BCC）是最常见的皮肤癌之一，通常由异常激活的 Hedgehog（Hh）信号通路驱动。Hh 信号通路受 Patched-1（Ptch1）和 Smoothened（Smo）受体之间的相互作用调节。Smo 是一种激活受体，受 Ptch1 抑制。配体与 Ptch1 结合后，其抑制作用被解除，通路被激活。这种受体相互作用对于抑制不受控制的细胞生长至关重要。在 BCC 中，这两种受体都经常发生突变。Ptch2 是 Ptch1 的旁系同源物，在正常发育和组织稳态中具有重叠功能。然而，它对癌症生长的贡献还不清楚。在这里，我们着手评估 Ptch2 如何抑制 BCC 生长。
我们使用几种体外转录和趋化性 Hh 信号的测定方法来评估 BCC 衍生的 ASZ001 细胞，并用一种新的异种移植模型来评估体内 BCC 肿瘤生长。使用 TALEN 进行基因编辑来理清 Ptch2 对其配体 sonic hedgehog（Shh）的不同依赖反应。
我们首先在体外定义了 Ptch1 缺陷的 ASZ001 细胞中 Ptch2 的信号转导能力，发现 Ptch2 配体结合驱动它们的迁移而不是引发转录反应。我们发现随后靶向 Ptch2 会消除趋化作用。接下来，我们使用异种移植模型测试了 Ptch2 对体内肿瘤生长的贡献，发现降低 Ptch 功能会导致肿瘤生长增加，但选择性压力显然不利于 Ptch2 的完全缺失。
我们得出结论，与 Ptch1 一样，Ptch2 在 BCC 细胞中发挥肿瘤抑制功能，并且在靶向两个旁系同源物后，配体非依赖性激活 Hh 通路有助于肿瘤生长。
