Schnitger Anna K D, Kafatos Fotis C, Osta Mike A
Imperial College London, Division of Cell and Molecular Biology, Exhibition Road, London, UK.
J Biol Chem. 2007 Jul 27;282(30):21884-8. doi: 10.1074/jbc.M701635200. Epub 2007 May 30.
The melanization reaction of insects requires activation of pro-phenoloxidase by a proteolytic cascade leading to melanin production. Studies in adult mosquitoes have shown that bacteria are efficiently melanized in the hemocoel, but the contribution of melanization to survival after bacterial infections has not been established. Here we show that the Anopheles gambiae noncatalytic serine protease CLIPA8, an essential factor for Plasmodium ookinete melanization, is also required for melanization of bacteria in adult mosquitoes. CLIPA8 silencing by RNA interference inhibits pro-phenoloxidase activation and melanization of bacteria in the hemolymph following microbial challenge. However, CLIPA8 is not required for wound melanization nor for melanotic pseudotumor formation in serpin2 knockdown mosquitoes, suggesting a specific role for pathogen melanization. Surprisingly, CLIPA8 knockdown mosquitoes are as resistant to bacterial challenge as controls, indicating that melanization is not essential for defense against bacteria and questions its precise role in mosquito immunity.
昆虫的黑化反应需要通过蛋白水解级联反应激活前酚氧化酶，从而产生黑色素。对成年蚊子的研究表明，细菌在血腔中能有效地被黑化，但黑化对细菌感染后生存的贡献尚未明确。在此，我们表明冈比亚按蚊的非催化性丝氨酸蛋白酶CLIPA8是疟原虫卵囊黑化的关键因子，在成年蚊子中细菌的黑化过程中也不可或缺。通过RNA干扰使CLIPA8沉默会抑制微生物攻击后血淋巴中前酚氧化酶的激活和细菌的黑化。然而，在丝氨酸蛋白酶抑制剂2基因敲低的蚊子中，伤口黑化和黑色素瘤假瘤形成并不需要CLIPA8，这表明其在病原体黑化中具有特定作用。令人惊讶的是，CLIPA8基因敲低的蚊子对细菌攻击的抵抗力与对照蚊子相同，这表明黑化对于抵御细菌并非必不可少，并对其在蚊子免疫中的精确作用提出了质疑。
