Characteristics analyses of Eimeria tenella 14-3-3 protein and verification of its interaction with calcium-dependent protein kinase 4

Abstract

Avian coccidiosis is a common disease caused by Eimeria spp. In the genus Eimeria, the species Eimeria tenella is an obligate intracellular parasite that invades mostly chicken cecal epithelial cells. The 14-3-3 protein is one of the most common adaptor proteins. It is involved in regulating protein phosphorylation and is associated with phosphorylated proteins to regulate signal transduction. Previous reports have shown that 14-3-3 protein has a direct regulatory effect on calcium-dependent protein kinases (CDPKs) activity by interacting with CDPKs. In this study, the characteristics of the E. tenella 14-3-3 protein including transcription and translation analyses, localization in different developmental stages etc were analyzed. The interaction between E. tenella 14-3-3 (Et14-3-3) and E. tenella calcium-dependent protein kinase 4 (EtCDPK4) which is a critical molecule in E. tenella invasion of host cells was verified by Bimolecular Fluorescent Complimentary (BiFC), Co-Immunoprecipitation (co-IP), and Glutathione S-transferase (GST) pull-down. The transcription and translation levels were analyzed using real-time quantitative PCR and western blot. The results showed that the mRNA transcription level of Et14-3-3 was highest in the sporozoite, and the translation level was higher in the unsporulated oocyst than in the other stages. Indirect immunolocalization found that Et14-3-3 was located mainly at the anterior of sporozoites and on the surface of second-generation merozoites. As the sporozoites developed in cells, the fluorescence intensity of Et14-3-3 gradually darkened. BiFC results showed green fluorescence under microscopy in 293T cells co-transfected with pBiFC-VN155-Et14-3-3 and pBiFC-VC155-EtCDPK4. Co-IP and GST pull-down showed that Et14-3-3 interacted with EtCDPK4, which is consistent with the BiFC results. These results indicated that Et14-3-3 had significant interactions with EtCDPK4. Co-localization of Et14-3-3 with EtCDPK4 in sporozoites revealed that they were located in the same position. The secretion assay results indicated that Et14-3-3 was a secreted protein but was not secreted from micronemes. These results lay the foundation for further research on the mechanism of action of EtCDPK4 with Et14-3-3 and the functions of Et14-3-3 in the lifecycle of E. tenella.