Molecular characterization and functional analysis of Cactin gene from Litopenaeus vannamei

Cactin (Cactus interactor) is a conserved protein which was initially discovered as a novel interactor of Drosophila IkB protein Cactus. Cactin was always characterized as a negative regulator of many different developmental processes, but only found to play an immune role in humans. To better know the immune function of Cactin gene, Litopenaeus vannamei Cactin (LvCactin) was identified and characterized in this study. The full-length cDNA of LvCactin is 3, 150 bp long, with an open reading frame (ORF) encoding a Cactin_mid domain in the N-terminus 356–547 residues and a CactinC_cactus domain in the C-terminal 731–855 residues. The LvCactin protein was located in the cytoplasm and LvCactin mRNA was constitutively expressed in healthy L. vannamei, with the highest expression level in the eyestalk. LvCactin could be regulated in hemocytes after lipopolysaccharide (LPS), poly I:C, CpG-ODN2006, Vibrio parahaemolyticus, Staphylococcus aureus, and white spot syndrome virus (WSSV) challenges. Dual-luciferase reporter assays in Drosophila Schneider 2 cells revealed that LvCactin inhibited the promoters of Drosophila and shrimp antimicrobial peptide (AMP) genes. Knockdown of LvCactin by RNA interference (RNAi) increased the expression of shrimp AMP genes PEN4, crustin and ALF2 but not Lyz2. However, the mortality rates of LvCactin-knockdown shrimp in response to V. parahaemolyticus or WSSV infections were not significantly different from those of the control group. Taken together, all the results suggested that LvCactin may play a role in innate immune in L. vannamei.