Protein Prenylation and Progeria

摘要 包括哈钦森-吉尔福德早老综合征（HGPS）在内的几种早老性疾病是由以下原因引起的： 导致法尼基-前核层蛋白A在核边缘积累的缺陷。的积累 法呢基-前核层蛋白A在培养的细胞中引起严重畸形的细胞核。我们认为法尼基化的 前层蛋白A的形式对细胞是有毒的，并预测抑制蛋白法尼基化将减少细胞的增殖。 一对早衰小鼠模型中畸形细胞核的频率和改善疾病表型 Zmpste 24缺陷小鼠和HGPS“敲入”突变杂合子小鼠 （LmnaHG/+）。这些关于蛋白质法尼基化的重要性的预测得到了支持： 法尼基转移酶抑制剂（FTIs）减少了培养细胞中畸形细胞核的频率， 在两种早衰小鼠模型中改善疾病表型。这些研究令人欣慰 因为他们认为FTIs可以有效治疗人类HGPS。然而，在这方面， 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治疗在改善疾病表型方面是明确有效的，但它只有一个优点， 对小鼠中前层蛋白A加工的影响较小。因此，疾病表型的改善 被解释？一种可能性是，对前核层蛋白A法尼基化的极小影响足以 另一种观点认为FTIs可以独立于其作用而改善疾病 前层蛋白A的加工我们的第一个目标将是详细研究这个问题，通过分析额外的基因- 靶向小鼠模型，并通过更好地定义FTIs对体内前层蛋白A代谢的影响。我们 第二个目标，将是进一步研究我们的HGPS小鼠的一个意想不到的发现-核形状 与LmnaHG等位基因相关的异常和疾病表型可以通过以下方式显著降低： 减少野生型核纤层蛋白A的合成（通过替换LmnaHG/+小鼠中的野生型Lmna等位基因 具有“仅核纤层蛋白C”等位基因）。对这一发现的一种解释是，野生型前核纤层蛋白A（或核纤层蛋白A） 而核纤层蛋白C则不存在。在未来几年中，我们将研究这一概念， 通过检查LmnaHG等位基因在“仅核纤层蛋白C”和“仅核纤层蛋白C”两者存在下的影响， 等位基因和“仅核纤层蛋白A”等位基因对疾病表型和核力学的影响。我们的第三个目标是探索 非法尼基化前核纤层蛋白A的生理影响。用FTI治疗早衰症将导致 非法尼基化的前核纤层蛋白A（来自野生型Lmna等位基因）的积累。这个的属性 异常的蛋白质和它是否表现出其自身的毒性是未知的。我们将通过以下方式解决这一问题： 分析非法尼基化的仅核纤层蛋白A前体的小鼠并检查核纤层蛋白对细胞的影响， 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.