Mytilus galloprovincialis Myticin C: A Chemotactic Molecule with Antiviral Activity and Immunoregulatory Properties

Previous research has shown that an antimicrobial peptide (AMP) of the myticin class C (Myt C) is the most abundantly expressed gene in cDNA and suppressive subtractive hybridization (SSH) libraries after immune stimulation of mussel Mytilus galloprovincialis. However, to date, the expression pattern, the antimicrobial activities and the immunomodulatory properties of the Myt C peptide have not been determined. In contrast, it is known that Myt C mRNA presents an unusual and high level of polymorphism of unidentified biological significance. Therefore, to provide a better understanding of the features of this interesting molecule, we have investigated its function using four different cloned and expressed variants of Myt C cDNA and polyclonal anti-Myt C sera. The in vivo results suggest that this AMP, mainly present in hemocytes, could be acting as an immune system modulator molecule because its overexpression was able to alter the expression of mussel immune-related genes (as the antimicrobial peptides Myticin B and Mytilin B, the C1q domain-containing protein MgC1q, and lysozyme). Moreover, the in vitro results indicate that Myt C peptides have antimicrobial and chemotactic properties. Their recombinant expression in a fish cell line conferred protection against two different fish viruses (enveloped and non-enveloped). Cell extracts from Myt C expressing fish cells were also able to attract hemocytes. All together, these results suggest that Myt C should be considered not only as an AMP but also as the first chemokine/cytokine-like molecule identified in bivalves and one of the few examples in all of the invertebrates.

既往研究证实，在对地中海贻贝（Mytilus galloprovincialis）实施免疫刺激后，肌蒂素C型（myticin class C, Myt C）抗菌肽（antimicrobial peptide, AMP）是互补脱氧核糖核酸（complementary DNA, cDNA）文库与抑制性消减杂交（suppressive subtractive hybridization, SSH）文库中表达丰度最高的基因。然而截至目前，Myt C肽的表达模式、抗菌活性及免疫调节特性仍未得到明确阐释。与之相对，学界已探明Myt C信使核糖核酸（messenger RNA, mRNA）存在异常高水平的多态性，但其对应的生物学意义至今不明。为深入解析这一极具研究价值的分子的特性，本研究借助四种经克隆与重组表达的Myt C cDNA变体，以及多克隆抗Myt C血清，对其功能开展了系统性研究。体内实验结果显示，该抗菌肽主要表达于血淋巴细胞中，或可作为免疫系统调节分子发挥功能：其过表达能够改变贻贝免疫相关基因的表达谱，涵盖抗菌肽肌蒂素B（Myticin B）、贻贝素B（Mytilin B）、含C1q结构域蛋白MgC1q以及溶菌酶。此外，体外实验结果表明，Myt C肽兼具抗菌活性与趋化特性。将该肽在鱼类细胞系中进行重组表达后，可使细胞获得针对两种不同类型鱼类病毒（有包膜病毒与无包膜病毒）的抗性。表达Myt C的鱼类细胞提取物同样可趋化血淋巴细胞。综合上述实验结果，Myt C不仅可被归为抗菌肽，同时也是双壳类动物中首个被鉴定的趋化因子/细胞因子样分子，且属于所有无脊椎动物中为数不多的同类分子之一。