Department of Dermatology, Bispebjerg Hospital, University of Copenhagen, Bispebjerg Bakke 23, Copenhagen-2400, Denmark.
Br J Dermatol. 2013 Mar;168(3):504-12. doi: 10.1111/bjd.12071.
We have previously discovered that Notch1 is expressed on malignant T cells in cutaneous T-cell lymphoma (CTCL), and is required for survival of CTCL cell lines. Notch can be inhibited by γ-secretase inhibitors (GSIs), which differ widely in their ability to induce apoptosis in CTCL.
To investigate whether GSI-I, in addition to inhibiting Notch, induces apoptosis in CTCL by proteasome inhibition, as GSI-I is very potent and has structural similarity to the proteasome inhibitor MG-132.
Cell lines derived from CTCL (MyLa, SeAx, JK, Mac1 and Mac2a) were treated with GSI-I and two other proteasome inhibitors (MG-132 and bortezomib). The effects on cell viability, apoptosis and proteasome activity were measured, as was the impact on the prosurvival, nuclear factor κB (NF-κB) pathway.
In CTCL, GSI-I had proteasome-blocking activity with a potency comparable to the proteasome inhibitors MG-132 and bortezomib. Proteasome inhibition was the main mechanism responsible for GSI-I-induced cell death, as tiron, a compound known to reverse the effect of MG-132, restored proteasome activity and largely abrogated the cytotoxic effect of GSI-I. Although inactivation of NF-κB is an important mechanism of action for proteasome inhibitors, we demonstrated an apparent activation of NF-κB. Furthermore, we showed that while the tumour suppressor protein p53 was induced during proteasome inhibition, it was dispensable for CTCL apoptosis, as both SeAx cells, which harbour p53 mutations that attenuate the apoptotic capacity, and HuT-78 cells, which have a deleted p53 gene, demonstrated potent apoptotic response.
GSI-I represents an interesting drug with a dual mechanism of action comprising inhibition of both Notch and the proteasome.
我们之前发现 Notch1 在皮肤 T 细胞淋巴瘤（CTCL）的恶性 T 细胞中表达，并且是 CTCL 细胞系存活所必需的。Notch 可以被 γ-分泌酶抑制剂（GSI）抑制，GSI 在诱导 CTCL 细胞凋亡方面的能力差异很大。
研究 GSI-I 是否除了抑制 Notch 之外，还通过蛋白酶体抑制诱导 CTCL 细胞凋亡，因为 GSI-I 非常有效，并且与蛋白酶体抑制剂 MG-132 具有结构相似性。
用 GSI-I 和另外两种蛋白酶体抑制剂（MG-132 和硼替佐米）处理源自 CTCL 的细胞系（MyLa、SeAx、JK、Mac1 和 Mac2a）。测量细胞活力、凋亡和蛋白酶体活性的变化，以及对生存促进、核因子 κB（NF-κB）途径的影响。
在 CTCL 中，GSI-I 具有与蛋白酶体抑制剂 MG-132 和硼替佐米相当的蛋白酶体阻断活性。蛋白酶体抑制是 GSI-I 诱导细胞死亡的主要机制，因为众所周知可以逆转 MG-132 作用的 tiron 恢复了蛋白酶体活性，并在很大程度上消除了 GSI-I 的细胞毒性作用。虽然 NF-κB 的失活是蛋白酶体抑制剂的重要作用机制，但我们观察到 NF-κB 的明显激活。此外，我们表明，虽然在蛋白酶体抑制期间诱导了肿瘤抑制蛋白 p53，但它对于 CTCL 细胞凋亡是可有可无的，因为既具有削弱凋亡能力的 p53 基因突变的 SeAx 细胞，也具有缺失 p53 基因的 HuT-78 细胞都表现出强烈的凋亡反应。
GSI-I 是一种具有双重作用机制的药物，包括抑制 Notch 和蛋白酶体。
