Molecular Basis for Safety Assessment of Microbial Pesticides

杆状病毒和Bt(苏云金芽孢杆菌)是世界上广泛使用的微生物农药，杆状病毒也为真核生物提供了一个最有效的外源基因表达系统(baculovector系统)。我们研究了这些昆虫病原微生物安全性的分子基础。最近的研究表明，杆状病毒(AcMNPV)可以独立于细胞周期进入哺乳动物的细胞核，不需要增殖，也可以在不表达自身基因的情况下有效地表达外源基因，这表明杆状病毒可以作为一种低风险的病毒载体应用于基因治疗领域。与一般的认识相反，我们阐明了AcMNPV至少部分地通过通常的感染途径在哺乳动物细胞中表达病毒基因。此外，细胞基因(至少β-肌动蛋白)在接种AcMNPV的哺乳动物细胞中表达上调。然而，病毒基因在哺乳动物细胞中的表达被抑制到低水平，部分原因是组蛋白去乙酰化机制，进而导致一些病毒基因的转录从错误的位置开始(S)。对于苏云金芽孢杆菌(Bt)菌株，我们主要研究了非溶血性肠毒素C(NheC)对Vero细胞的毒性机制，该毒素被认为是导致食物中毒的最重要的肠毒素。从具有Vero细胞毒性的蜡样芽孢杆菌临床分离株(BC株)分泌的NheC可通过30个氨基酸的N末端区域附着于Vero细胞表面。另一方面，相应的N-末端区域可能被商品用Bt菌株分泌的NheC的翻译后切割所截断。此外，NheC的N端截短不再表现出Vero细胞毒性。

Baculovirus and Bt (Bacillus thuringiensis) are used as microbial pesticides all over the world and the former also provide a most efficient foreign gene expression system in eukaryotes (baculovector system). We studied the molecular basis in the safety of these entomopathogenic microorganisms. Recent studies demonstrated that a baculovirus (AcMNPV) can enter the nucleus of mammalian cells independently of the cell cycle without multiplication and effectively express foreign genes without expressing its own genes, suggesting that the baculovirus can be used as a low risk viral vector in the field of gene therapy. Contrary to the general perception, we elucidated that AcMNPV expressed viral genes at least partly in mammalian cells through the usual infection pathway. In addition, the expression of cellular gene (at least β-actin) was upregulated in the mammalian cells inoculated with AcMNPV. However, the expression of viral genes was inhibited to low level in mammalian cells partly by histone deacetylation mechanism and further the transcription of some viral genes started at incorrect site(s).As for the B. thuringiensis (Bt) strains, we investigated mainly the mechanisms of Vero cell toxicity by non-hemolytic enterotoxin C (NheC) that was thought to be the most important enterotoxin causing food-poisoning. It was elucidated that NheC secreted from a clinical isolate of B. cereus (Bc) strain possessing Vero cell toxicity could attach to the surface of Vero cells through the N-terminal region of 30 amino acids. On the other hand, the corresponding N-terminal region was truncated possibly by post-translational cleavage in the NheC secreted from Bt strains used in the commercial products. In addition, the N-terminal truncated from of NheC didn't show Vero cell toxicity any more.