Ku proteins play a positive role in the immune response against WSSV infection in Litopenaeus vannamei

Ku proteins (Ku70 and Ku80) are essential components of the DNA-dependent protein kinase (DNA-PK), and they play a critical role in DNA double-strand break repair. Several studies in recent years have shown that Ku proteins can bind to DNA and are involved in regulating innate immune responses to DNA viruses. In present study, two Ku proteins subunits, Ku70 and Ku80 homologues (named LvKu70 and LvKu80, respectively) were cloned and identified from Litopenaeus vannamei. Both LvKu70 and LvKu80 encoded proteins with a VWA domain, a Ku78 domain and a Ku_C domain, and both are constitutively expressed in healthy L. vannamei, with high levels of expression in immune organs such as the hemocytes. Besides, LvKu70 and LvKu80 expression were up-regulated in haemocytes and hepatopancreas after white spot syndrome virus (WSSV) infection, and RNAi-mediated knockdown of LvKu70 and LvKu80 both enhanced the sensitivity of shrimps to WSSV challenge, manifested by higher virus loads and lower survival rate compared with the control group. Moreover, silencing of LvKu70 and LvKu80 resulted in decreased expression levels of IRF-Vago pathway components and several antimicrobial peptides (penaeidins and ALFs). All of these results suggest that Ku proteins play a positive role in antiviral immunity in L.vannamei and are probably involved in the regulation of STING-mediated IRF-Vago and NF-κB pathway.