A Serine Proteinase Homologue, SPH-3, Plays a Central Role in Insect Immunity

Abstract

Numerous vertebrate and invertebrate genes encode serine proteinase homologues (SPHs) similar to members of the serine proteinase family, but lacking one or more residues of the catalytic triad. These SPH proteins are thought to play a role in immunity, but their precise functions are poorly understood. In this study, we show that SPH-3 (an insect non-clip domain–containing SPH) is of central importance in the immune response of a model lepidopteran, Manduca sexta. We examine M. sexta infection with a virulent, insect-specific, Gram-negative bacterium Photorhabdus luminescens. RNA interference suppression of bacteria-induced SPH-3 synthesis severely compromises the insect’s ability to defend itself against infection by preventing the transcription of multiple antimicrobial effector genes, but, surprisingly, not the transcription of immune recognition genes. Upregulation of the gene encoding prophenoloxidase and the activity of the phenoloxidase enzyme are among the antimicrobial responses that are severely attenuated on SPH-3 knockdown. These findings suggest the existence of two largely independent signaling pathways controlling immune recognition by the fat body, one governing effector gene transcription, and the other regulating genes encoding pattern recognition proteins.

Caspase-1-Like Regulation of the proPO-System and Role of ppA and Caspase-1-Like Cleaved Peptides from proPO in Innate Immunity

“…Intriguingly, recently we succeeded in showing that all of the steps in the proPO-cascade in Tenebrio molitor are shared with the proteinase cascade that leads to the activation of the Toll pathway for the production of antimicrobial peptides [10]. This shared cascade has been confirmed in several other insects [11], [12]. In the present study, we found that caspases are very important for the rapid degradation of proPO, which prevents oxidation in places where it is not appropriate.…”

Dynamics of transcriptomic response to infection by the nematode Heterorhabditis bacteriophora and its bacterial symbiont Photorhabdus temperata in Heliothis virescens larvae

“…Both genes were induced at 11 h postexposure, but the gene encoding tyrosine-protein phosphatase non-receptor type 23-like, which is involved in positive regulation of the Toll pathway, was repressed at 12 h postexposure. The Toll pathway is generally triggered by a cascade of serine proteases upon immunological challenge and PGRP-based recognition (Lemaitre & Hoffmann, 2007;Felfoldi et al, 2011). In insects, serine proteases are known to perform functions of digestion, embryonic development and defence responses towards both microbial and parasite invaders (Rawlings & Barrett, 1993;Kanost, 1999;Krem & Di Cera, 2002).…”

A Pathogenic Nematode Targets Recognition Proteins to Avoid Insect Defenses

“…Recent investigations based on RNAi studies of genes encoding defense effector proteins and genes encoding the PRPs suggest that the PRP signaling pathway has a much greater impact on an insect’s survival after infection than does the effector gene pathway [58,59]. Thus, it is reasonable to assume that the ability of S .…”