Iron Regulatory Protein 1 Inhibits Ferritin Translation Responding to OsHV-1 Infection in Ark Clams, Scapharca Broughtonii .

Elemental iron is an indispensable prosthetic group of DNA replication relative enzymes. The upregulation of ferritin translation by iron regulatory proteins (IRP1) in host cells is a nutritional immune strategy to sequester available iron to pathogens. The efficient replication of Ostreid herpesvirus 1 (OsHV-1), a lethal dsDNA virus among bivalves, depends on available iron. OsHV-1 infection was found to trigger iron limitation in ark clams; however, it is still an enigma how OsHV-1 successfully conducted rapid replication, escaping host iron limitations. In this study, we identified the IRP1 protein (designated as Sb IRP-1) in the ark clam ( Scapharca broughtonii ) and found it could bind to the iron-responsive element (IRE) of ferritin ( Sb Fn) mRNA based on electrophoretic mobility shift assay (EMSA). Knockdown of Sb IRP-1 expression (0.24 ± 1.82-fold of that in NC group, p < 0.01) by RNA interference resulted in the accumulation of Sb Fn in hemocytes (1.79 ± 0.01-fold, p < 0.01) post-24 h of enhanced RNA interference injection. During OsHV-1 infection, Sb Fn mRNA was significantly upregulated in hemocytes from 24 h to 60 h, while its protein level was significantly reduced from 24 h to 48 h, with the lowest value at 36 h post-infection (0.11 ± 0.01-fold, p < 0.01). Further analysis by RNA immunoprecipitation assays showed that OsHV-1 could enhance the binding of Sb IRP-1 with the Sb Fn IRE, which was significantly increased (2.17 ± 0.25-fold, p < 0.01) at 36 h post-infection. Consistently, Sb IRP-1 protein expression was significantly increased in hemocytes from 12 h to 48 h post OsHV-1 infection ( p < 0.01). In conclusion, the results suggest that OsHV-1 infection could suppress post-transcriptional translation of Sb Fn through the regulation of Sb IRP-1, which likely contributes to OsHV-1 evasion of Sb Fn-mediating host iron limitation.