A clip domain serine protease stimulates melanization activation and expression of antimicrobial peptides in the Chinese oak silkworm, Antheraea pernyi

Abstract

Abstract Clip domain serine proteases (Clips) mediate various biological processes, especially in insect immune responses such as prophenoloxidase (proPO) activation and Toll pathway initiation. In the present study, we cloned and studied the functions of a clip domain serine protease from Antheraea pernyi (ApSnake). ApSnake contains a typical clip domain and a trypsin-like serine protease domain. It shares high similarity with serine protease snake in Bombyx mori, and groups into the CLIPC family. ApSnake mRNA expressions were detected in all tested tissues, particularly high in the hemocytes. Challenged with four different microorganisms (Escherichia coli, Beauveria bassiana, Micrococcus luteus or Nuclear polyhedrosis virus), the expressions of ApSnake mRNA were induced significantly compared with control, particularly challenged by B. bassiana and M. luteus. Recombinant ApSnake protein stimulated melanization reaction and prophenoloxidase activation in A. pernyi hemolymph, but had no effect on phenoloxidase activity. Injection of recombinant ApSnake into A. pernyi larvae increased the transcript levels of proPO and antimicrobial peptides (AMPs) in hemocytes significantly. Our results suggested that ApSnake might be a modulating protein that both stimulate the melanization activation process and AMPs synthesis, and plays an important role in the innate immunity of A. pernyi.