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

Bowen Huang,Lusheng Xin,Changming Bai,Qin Liu,Xiang Zhang,Chen Li,Chongming Wang

doi:10.3390/cells11060982

Abstract

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 SbIRP-1) in the ark clam (Scapharca broughtonii) and found it could bind to the iron-responsive element (IRE) of ferritin (SbFn) mRNA based on electrophoretic mobility shift assay (EMSA). Knockdown of SbIRP-1 expression (0.24 ± 1.82-fold of that in NC group, p < 0.01) by RNA interference resulted in the accumulation of SbFn in hemocytes (1.79 ± 0.01-fold, p < 0.01) post-24 h of enhanced RNA interference injection. During OsHV-1 infection, SbFn 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 SbIRP-1 with the SbFn IRE, which was significantly increased (2.17 ± 0.25-fold, p < 0.01) at 36 h post-infection. Consistently, SbIRP-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 SbFn through the regulation of SbIRP-1, which likely contributes to OsHV-1 evasion of SbFn-mediating host iron limitation.

Highlights

Iron performs a critical role in cellular metabolism as a component of prosthetic groups in electron transport proteins and various enzymes involved in DNA synthesis, ATP production, etc. [1,2]
To ensure that infected cells are enriched with iron and favor viral rapid replication, some viruses selectively infect iron-rich cells by targeting transferrin receptor 1 (TfR1) [7] or disrupt host iron homeostasis by interfering with the regulation of host iron-metabolism-related proteins, such as hepcidin, MHC class I-like protein HFE (Homeostatic Iron Regulator), TfR1, and ferritin [8–12]
Multiple sequence comparisons showed that SbIRP-1 possessed 83% similarity to IRP1 form Crassostrea virginica (XP_022311890.1) and 69% similarity to IRP1 form Homo sapiens (NP_001265281.1), but the aconitase domain (Ser138-Gly189) of SbIRP-1 exhibited low homology with those of other molluscan IRP1s and was absent in vertebrate IRP1s (Figure 2)

Summary

Introduction

Iron performs a critical role in cellular metabolism as a component of prosthetic groups in electron transport proteins and various enzymes involved in DNA synthesis, ATP production, etc. [1,2]. To ensure that infected cells are enriched with iron and favor viral rapid replication, some viruses selectively infect iron-rich cells by targeting transferrin receptor 1 (TfR1) [7] or disrupt host iron homeostasis by interfering with the regulation of host iron-metabolism-related proteins, such as hepcidin, MHC class I-like protein HFE (Homeostatic Iron Regulator), TfR1, and ferritin [8–12]. Pathogens such as bacteria and fungi have parallelly evolved various strategies against iron limitation in hosts, such as secreting siderophores to compete for available iron in the host, or directly acquiring host iron via heme/hemoprotein receptors [2,13]

Methods

Results

Conclusion