A novel integrin function in innate immunity from Chinese mitten crab (Eriocheir sinensis)

Integrins belong to a superfamily of conserved α β heterodimeric cell surface receptors that have critical function in cell migration, differentiation, and survival. In this study, an integrin called EsIntegrin was identified from Chinese mitten crab Eriocheir sinensis. EsIntegrin cDNA is 4415 bp long with a 2457 bp open reading frame that encodes an 818 amino acid protein. EsIntegrin contains a signal peptide, an integrin beta subunit (N-terminal portion of extracellular region) INB domain, an epidermal growth factor (hEGF) domain, an integrin B tail domain, a transmembrane region, and an integrin b cyt domain. EsIntegrin was mainly expressed in hemocytes and the heart, with a relatively lower expression level in gills, nerves, intestine, hepatopancreas, muscles, and eyestalk. When healthy crabs were challenged with LPS, PGN, Staphyloccocus aureus, or Vibrio parahaemolyticus, EsIntegrin expression level was upregulated significantly. Recombinant EsIntegrin has agglutination activity to Gram-positive (e.g., S. aureus and Bacillus subtilis) and Gram-negative bacteria (e.g., V. parahaemolyticus and Aeromonas hydrophila) in the presence of calcium. Furthermore, rEsIntegrin could not only bind to various bacteria such as S. aureus, Micrococcus luteus, B. subtilis, Bacillus megaterium, Bacillus thuringiensis, V. parahaemolyticus, Vibrio anguillarum, A. hydrophila, Vibrio natriegens, and Escherichia coli, but this compound also helped crabs in clearing virulent Gram-negative bacterium, V. parahaemolyticus, in vivo. These data suggested that EsIntegrin might function as cellular receptor that is involved in anti-bacterial immunity from E. sinensis.