A QM protein from Bombyx mori negatively regulates prophenoloxidase activation and melanization by interacting with Jun protein.

The QM gene that encodes for the ribosomal protein L10 was firstly identified from human tumor cells as a tumor suppressor. In this study, a QM gene was identified in silkworm Bombyx mori (BmQM) and its immunomodulatory function was explored. BmQM mRNA and protein were highly expressed in the silk gland and fat body, and expressed in all stages of silkworm growth. After challenged with four different microorganisms, the expression levels of BmQM mRNA in fat body or hemocytes were significantly upregulated compared with the control. After knock-down of BmQM gene, the expressions of some immune genes (PGRPS6, Gloverin0, Lysozyme, and Moricin) were affected, and the transcripts of prophenoloxidase1 and prophenoloxidase2, have different degrees of increased. The phenoloxidase activity was significantly reduced when injected the purified recombinant BmQM protein. Recombinant BmQM protein inhibited systemic melanization and suppressed prophenoloxidase activation stimulated by M. luteus, but did not affect phenoloxidase activity. Far Western blotting assays showed that the BmQM protein interacted with silkworm BmJun protein which negatively regulates AP-1 expression. Our results indicated that BmQM protein could affect some immune gene expression and negatively regulate the prophenoloxidase-activating system, and it may play an important role in regulation of the innate immunity in insects. This article is protected by copyright. All rights reserved.