Abstract
In response to endoplasmic reticulum (ER) stress, the signaling pathway termed unfolded protein response (UPR) is activated. To investigate the role of UPR in Litopenaeus vannamei immunity, the activating transcription factor 4 (designated as LvATF4) which belonged to a branch of the UPR, the [protein kinase RNA (PKR)-like ER kinase, (PERK)]-[eukaryotic initiation factor 2 subunit alpha (eIF2α)] pathway, was identified and characterized. The full-length cDNA of LvATF4 was 1972 bp long, with an open reading frame of 1299 bp long that encoded a 432 amino acid protein. LvATF4 was highly expressed in gills, intestines and stomach. For the white spot syndrome virus (WSSV) challenge, LvATF4 was upregulated in the gills after 3 hpi and increased by 1.9-fold (96 hpi) compared to the mock-treated group. The LvATF4 knock-down by RNA interference resulted in a lower cumulative mortality of L. vannamei under WSSV infection. Reporter gene assays show that LvATF4 could upregulate the expression of the WSSV gene wsv023 based on the activating transcription factor/cyclic adenosine 3′, 5′-monophosphate response element (ATF/CRE). Another transcription factor of L. vannamei, X box binding protein 1 (designated as LvXBP1), has a significant function in [inositol-requiring enzyme-1(IRE1) – (XBP1)] pathway. This transcription factor upregulated the expression of the WSSV gene wsv083 based on the UPR element (UPRE). These results suggest that in L. vannamei UPR signaling pathway transcription factors are important for WSSV and might facilitate WSSV infection.
Highlights
The endoplasmic reticulum (ER) is the primary subcellular organelle of eukaryotic cells
We demonstrated that in L. vannamei unfolded protein response (UPR) was activated by white spot syndrome virus (WSSV) infection and L. vannamei ATF4 (LvATF4) and LvXBP1 upregulated expression of WSSV genes wsv023 and wsv083, respectively
Previous studies have demonstrated that the L. vannamei IRE1XBP1 pathway is activated under WSSV challenge [14]
Summary
The endoplasmic reticulum (ER) is the primary subcellular organelle of eukaryotic cells. This organelle is a site of lipid synthesis, protein folding and protein maturation. The unfolded protein response (UPR) is the core pathway that eukaryotic cells use to cope with ER stress [4]. It is highly conserved and has been observed in eukaryotes. UPR decreases protein translation to restore normal cell functions, increases the production of molecular chaperones involved in protein folding, and activates the signaling pathways, resulting in the ubiquitination and subsequent degradation of misfolded proteins in the ER by proteasomes [5]
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