Microsomal glutathione transferase 2 modulates LTC4 synthesis and ROS production in Apostichopus japonicus

Microsomal glutathione transferase 2 (mGST2) is an integral membrane protein involved in detoxication of xenobiotics, and has also been suggested to catalyze the biosynthesis of pro-inflammatory mediator leukotriene C4 (LTC4) as homologous to LTC4 synthase (LTC4S) in mammals. In the present study, a novel mGST2 homology was identified from Apostichopus japonicus (designated as AjmGST2) by RACE approaches. The full-length cDNA of AjmGST2 was of 1917 bp encoding a polypeptide of 161 amino acids residues. Multiple sequences alignment and phylogenetic analysis together supported that AjmGST2 belonged to a new member in invertebrate mGSTs family and close to mammalian LTC4S. Spatial expression analysis revealed that AjmGST2 was ubiquitously expressed in all examined tissues with the larger magnitude in intestine. AjmGST2 transcripts in coelomocytes were slightly induced post 6 h challenge of pathogenic Vibrio splendidus and reached the peak expression at 48 h. The increased expression profiles of AjmGST2 were also detected in lipopolysaccharide (LPS) exposed primary coelomocytes. Consistently, LTC4 contents were also induced by a 1.56-fold increase in the same condition. Functional assay further revealed that AjmGST2 might be functioned as LTC4S to promote LTC4 synthesis. AjmGST2 knock-down by specific siRNA significantly depressed LTC4 contents with 27.0% decrease at 24 h. Meantime, ROS levels were elevated by 40.1% in vitro. All of these results indicated that AjmGST2 performed dual functions roles as LTC4S and ROS eliminator in sea cucumber immune response.