Prusiner S B
Department of Neurology, University of California, San Francisco 94143.
Dev Biol Stand. 1991;75:55-74.
Considerable progress has been made in deciphering the role of an abnormal isoform of the prion protein (PrP) in scrapie of animals and Gerstmann-Sträussler syndrome (GSS) of humans. Transgenic (Tg) mice expressing both Syrian hamster (Ha) and mouse (Mo) PrP genes, which encode proteins differing at 16 residues out of 254, were used to probe the mechanism of scrapie prion replication. Four Tg lines expressing HaPrP exhibited distinct incubation times ranging from 48 to 277 days after Ha prion inoculation, which were inversely correlated with the steady-state levels of HaPrP mRNA and HaPrPc. Bioassays of brain extracts from two scrapie-infected Tg lines showed that the prion inoculum dictates which prions are synthesized de novo, even though the cells express both PrP genes. Tg mice inoculated with Ha prions had approximately 10(9) ID50 units of Ha prions per gram of brain while less than 10 units of Mo prions were found. Conversely, Tg mice inoculated with Mo prions had approximately 10(6) ID50 units of Mo prions and less than 10 units of Ha prions. Consistent with the analysis of prion synthesis, Tg mice inoculated with Ha prions exhibited neuropathologic changes characteristic of hamsters with scrapie while Mo prions produced changes similar to those in non-Tg mice with scrapie. Our results argue that species specificity of scrapie prions resides in the primary structure of PrP and formation of infectious prions is initiated by a species-specific interaction between PrPSc in the inoculum and homologous, cellular PrP. Studies on Syrian, Armenian and Chinese hamsters suggest that the domain of the PrP molecule between codons 100 and 120 controls both the length of the incubation time and the deposition of PrP in amyloid plaques. Ataxic GSS in families shows genetic linkage to a mutation in the PrP gene leading to the substitution of Leu for Pro at codon 102. Discovery of a point mutation in the PrP gene from humans with GSS established that GSS is unique among human diseases--it is both genetic and infectious. These results have revised thinking about sporadic Creutzfeldt-Jakob disease (CJD) suggesting it may arise from a somatic mutation. Pulse-chase radiolabeling experiments of scrapie-infected cultures of mouse neuroblastoma cells indicate that protease-resistant PrPSc is synthesized during the chase period with t1/2 approximately 15 h from a protease-sensitive precursor, consistent with the conclusion that PrPc and PrPSc differ due to a post-translational event.(ABSTRACT TRUNCATED AT 400 WORDS)
在破译朊病毒蛋白（PrP）异常异构体在动物瘙痒病和人类格斯特曼-施特劳斯勒综合征（GSS）中的作用方面已取得了相当大的进展。表达叙利亚仓鼠（Ha）和小鼠（Mo）PrP基因的转基因（Tg）小鼠被用于探究瘙痒病朊病毒复制的机制，这两种基因编码的蛋白质在254个氨基酸中有16个不同。四个表达HaPrP的Tg品系在接种Ha朊病毒后，潜伏期从48天到277天不等，这与HaPrP mRNA和HaPrPc的稳态水平呈负相关。对两个感染瘙痒病的Tg品系脑提取物的生物测定表明，尽管细胞同时表达两种PrP基因，但朊病毒接种物决定了从头合成哪种朊病毒。接种Ha朊病毒的Tg小鼠每克脑中约有10⁹ ID50单位的Ha朊病毒，而Mo朊病毒不到10单位。相反，接种Mo朊病毒的Tg小鼠有大约10⁶ ID50单位的Mo朊病毒，Ha朊病毒不到10单位。与朊病毒合成分析一致，接种Ha朊病毒的Tg小鼠表现出仓鼠瘙痒病特有的神经病理变化，而Mo朊病毒产生的变化与非Tg瘙痒病小鼠相似。我们的结果表明，瘙痒病朊病毒的种属特异性存在于PrP的一级结构中，传染性朊病毒的形成是由接种物中的PrPSc与同源细胞PrP之间的种属特异性相互作用引发的。对叙利亚、亚美尼亚和中国仓鼠的研究表明，PrP分子中密码子100至120之间的区域控制潜伏期的长短以及PrP在淀粉样斑块中的沉积。家族性共济失调性GSS与PrP基因中的一个突变存在遗传连锁，该突变导致密码子102处的亮氨酸被脯氨酸取代。从患有GSS的人类中发现PrP基因的一个点突变，证实GSS在人类疾病中是独特的——它既是遗传性的又是传染性的。这些结果改变了对散发性克雅氏病（CJD）的看法，表明它可能由体细胞突变引起。对感染瘙痒病的小鼠神经母细胞瘤细胞培养物进行脉冲追踪放射性标记实验表明，蛋白酶抗性PrPSc在追踪期由蛋白酶敏感的前体合成，半衰期约为15小时，这与PrPc和PrPSc因翻译后事件而不同的结论一致。（摘要截短于400字）
