Protein Prenylation and Progeria

摘要 包括Hutchinson-Gilford早衰症(HGPS)在内的几种孕激素紊乱症是由 导致法尼基-前层蛋白A在核缘积聚的缺陷。积攒的 法尼基-前层素A导致培养细胞的细胞核严重畸形。我们建议法尼化的 前层蛋白A对细胞有毒性，并预测抑制蛋白质法尼化将减少 一对早衰症小鼠模型中核畸形和疾病表型改善的频率 我们实验室创造的-Zmpste24缺陷小鼠和杂合子HGPS“敲入”突变的小鼠 (Lmna HG/+)。这些关于蛋白质法尼化重要性的预测得到了支持： 法尼基转移酶抑制剂(FTI)减少培养细胞中畸形核的频率，还 改善了两种早衰症小鼠模型的疾病表型。这些研究结果令人欣慰。 因为他们建议FTI可以有效地治疗患有HGPS的人类。然而， 这些研究给我们留下了关于FTI改善疾病的机制的重要问题 表型。 FTI疗法在改善疾病表型方面明确有效，但它只有一个 对小鼠前层素A的加工影响较小。因此，疾病表型的改善如何 会被解释吗？一种可能性是，对前层蛋白A法尼化的极小影响足以 改善疾病表型；另一种是FTI可以独立于其效果而改善疾病 关于前层蛋白A的加工。我们的第一个目标将是通过分析其他基因来详细研究这个问题- 通过更好地确定FTI对体内前层蛋白A代谢的影响，我们将研究目标小鼠模型。我们的 第二个目标将是进一步检查我们的HGPS小鼠的一个意外发现--核的形状 与Lmna HG等位基因相关的异常和疾病表型可以通过以下方式显著减少 通过替换Lmna HG/+小鼠的野生型LmNA等位基因减少野生型层粘连蛋白A的合成 与“层粘连蛋白C-唯一”等位基因)。对这一发现的一种解释是，野生型前层蛋白A(或层粘连蛋白A) 会恶化早衰症，而层粘连蛋白C不会。在接下来的几年里，我们将在 通过检查Lmna HG等位基因在两个“仅层粘连蛋白C”存在时的影响，提供了相当详细的信息 疾病表型和核力学上的等位基因和“仅层粘连蛋白A”等位基因。我们的第三个目标是探索 非法呢化前层蛋白A的生理影响用FTI治疗早衰症将导致 非法尼化前层蛋白A的积累(来自野生型Lmna等位基因)。它的属性是 不正常的蛋白质以及它是否表现出自身的毒性尚不清楚。我们将通过以下方式解决这一问题 分析非法尼化Prelamin A纯基因小鼠，并检测Lamin蛋白对细胞和 组织生理学。

ABSTRACT Several progeroid disorders, including Hutchinson-Gilford progeria syndrome (HGPS), are caused by defects that lead to the accumulation of farnesyl-prelamin A at the nuclear rim. The accumulation of farnesyl-prelamin A causes grossly misshapen nuclei in cultured cells. We proposed that the farnesylated form of prelamin A is toxic to cells and predicted that inhibiting protein farnesylation would reduce the frequency of misshapen nuclei and ameliorate disease phenotypes in a pair of progeria mouse models created in our laboratory-Zmpste24-deficient mice and mice heterozygous for a HGPS "knock-in" mutation (LmnaHG/+). These predictions regarding the importance of protein farnesylation were upheld: farnesyltransferase inhibitors (FTIs) reduced the frequency of misshapen nuclei in cultured cells and also ameliorated disease phenotypes in both of the progeria mouse models. These studies have been gratifying because they have suggested that FTIs could be efficacious for treating humans with HGPS. However, these studies left us with important questions regarding the mechanisms by which FTIs improve disease phenotypes. The FTI treatment was unequivocally efficacious in ameliorating disease phenotypes, yet it had only a small effect on prelamin A processing in mice. How, therefore, can an improvement in disease phenotypes be explained? One possibility is that an extremely small effect on prelamin A farnesylation is sufficient to ameliorate disease phenotypes; another is that FTIs could ameliorate disease independently of their effect on prelamin A processing. Our first aim will be to examine this issue in detail, by analyzing additional gene- targeted mouse models and by better defining the effects of FTIs on prelamin A metabolism in vivo. Our second aim, will be to further examine an unexpected finding in our HGPS mice-that the nuclear shape abnormalities and disease phenotypes associated with the LmnaHG allele can be reduced significantly by decreasing the synthesis of wild-type lamin A (by replacing the wild-type Lmna allele in the LmnaHG/+ mice with a "lamin C-only" allele). One interpretation of this finding is that wild-type prelamin A (or lamin A) worsens progeria, while lamin C does not. During the next few years, we will examine this concept in considerable detail by examining the impact of the LmnaHG allele in the presence of both a "lamin C-only" allele and a "lamin A-only" allele on disease phenotypes and nuclear mechanics. Our third aim will explore the physiological impact of nonfarnesylated prelamin A. Treatment of progeria with an FTI will lead to the accumulation of nonfarnesylated prelamin A (from the wild-type Lmna allele). The properties of this abnormal protein and whether it exhibits its own toxicities are unknown. We will address this issue by analyzing nonfarnesylated prelamin A-only mice and examining the impact of the lamin protein on cell and tissue physiology.