Study Of Apoptosis Induced By Infectious Spleen And Kidney Necrosis Virus (ISKNV) Open Reading Frame111L

Infectious Spleen and Kidney Necrosis Virus (ISKNV) is a type speciesof Megalocytivirus genera, Iridoviridae family, which causes a seriousand pandemic disease in wild and cultured mandarin fish. ISKNVinfection resulted in an acute and high mortality disease, while themechanism is still poorly understood. Here we demonstrated that ISKNVinfection induced significant apoptosis in MFF-1mandarin fish cell line.Particularly, ISKNV open reading frame111L (ORF111L), as a viralTRAF homologue, also induced evident apoptosis in vitro MFF-1mandarin fish cell line and in vivo zebrafish embryos, mainly through theTRADD/FADD/Caspase-8apoptotic axis. Intriguingly, ORF111L notonly triggered profound apoptosis, but also activated the NF-κB andup-regulated the transcription of the anti-apoptotic gene c-flip in zebrafish.Subsequent analysis showed that ORF111L directly interacted withc-FLIP, while co-expression of ORF111L with c-FLIP in293T celldecreased the total c-FLIP protein. Notably, the over-expression of theCOOH terminus of ORF111L (TRAF domain, ORF111L-C) resulted insimilar pro-apoptotic effect as that of the full-length ORF111L inzebrafish embryos, but no effect in over-expression of the NH2terminus(Ring finger domain, ORF111L-N). Moreover, co-injection of c-FLIPmRNA effectively rescued ORF111L-C-induced apoptotic phenotype in zebrafish embryos, but had no effect on the full-length ORF111Lover-expression. In conclusion, this study provides novel insight intoregulatory mechanism of ISKNV ORF111L, particularly highlighting itspro-apoptotic effect in the ISKNV infection.