Catalytic and regulatory subunits of casein kinase 2 in Penaeus vannamei: Cloning, identification, expression profiles and functional analysis

As a highly conserved serine/threonine kinase with catalytic and regulatory subunits distributed ubiquitously in eukaryotic organisms, casein kinase 2 (CK2) is involved in multiple cellular functions, including immune regulation. In this study, two variants of the catalytic subunit (designated PvCK2α-1 and PvCK2α-2) and the regulatory subunit homologs (designated PvCK2β-1 and PvCK2β-2) in Penaeus vannamei were cloned and characterised. PvCK2α-1 and PvCK2α-2 shared the same genomic sequence consisting of six exons and five introns and encoded the same protein of 350 amino acids with an S_TKc domain, although there was a sequence deletion in 3'-UTR in PvCK2α-2 when compared with PvCK2α-1. Because of the sequence deletion in the ORF, PvCK2β-1 and PvCK2β-2 encoded different proteins with a CK_II_beta domain. The gene structures of PvCK2β-1 and PvCK2β-2 were identical and consisted of four exons and three introns. Semi-quantitative RT-PCR analyses revealed that PvCK2α and PvCK2β were constitutively expressed in all P. vannamei tissues tested, with higher levels detected in the immune-related tissues including hemocytes, hepatopancreas, gills and intestine. In these four tissue types, all variants of PvCK2α and PvCK2β were induced upon challenge with white spot syndrome virus (WSSV), Vibrio parahaemolyticus and Staphyloccocus aureus. The inhibition of PvCK2α, PvCK2β-1 and PvCK2βComb (the amount of PvCK2β-1 and PvCK2β-2) significantly reduced the survival rates of P. vannamei after WSSV infection and significantly increased the WSSV viral loads. Knockdown of PvCK2 by RNAi could distinctly decrease the expression of NF-κB related genes. All of these results suggest that PvCK2 plays an important role in the innate immune response to pathogen challenges in P. vannamei, with a positive role in anti-WSSV response which may be mediated through regulating the expression of NF-κB drived antimicrobial peptide genes.