A novel putative lipoprotein receptor (CasLpR) in the hemocytes of the blue crab, Callinectes sapidus: cloning and up-regulated expression after the injection of LPS and LTA

The full-length cDNA encoding a putative lipoprotein receptor (CasLpR) was isolated from the hemocytes of Callinectes sapidus using 5′ and 3′ RACEs. The open reading frame for CasLpR contains a precursor of putative CasLpR consisting of 1710 amino acid residues including 22 amino acid residues of the signal peptide (22 amino acids). Mature CasLpR (1688 amino acids with 5.6% of phosphorylation sites) has multiple, putative functional domains: five low-density lipoprotein receptor domains in the N-terminus, and a G-protein-coupled receptor proteolysis site domain and a 7 transmembrane receptor (secretin family) domain in the C-terminus. To date, there are no proteins with a similar domain structure in the GenBank. The expression pattern of CasLpR was exclusive in hemocytes among all tested tissues obtained from a juvenile female at intermolt stage: brain, eyestalk ganglia, pericardial organs, and thoracic ganglia complex (nervous system); hepatopancreas (digestive system); heart, artery and hemocytes (circulatory system); gill and antennal gland (excretory system), hypodermis; and Y-organ (endocrine organ). There was no CasLpR expression in the ovary of an adult female. A putative function of CasLpR was examined after challenges of lipopolysaccharides (LPS) and lipoteichoic acid (LTA) in vivo using qRT-PCR assays. Animals at 24 h after injection of LPS or LTA up-regulated the expression of CasLpR in hemocytes by ∼3.5 and 1.4 folds, respectively, compared to the controls that received saline injection. LPS challenge also caused the greatest increment (∼55 folds) of heat shock protein 90 (Hsp90) expression in these samples. These data indicate that putative CasLpR and CasHsp90 may be involved in the defense system or the stress response of C. sapidus.