Porcine reproductive and respiratory syndrome virus infection triggers autophagy via ER stress-induced calcium signaling to facilitate virus replication

Author summaryPorcine reproductive and respiratory syndrome virus (PRRSV) infection results in a serious swine disease and causes a severe economic threat to the global swine industry. However, commercial vaccines do not provide satisfactory protection against PRRSV due to its genetic variation. Well understanding the mechanism of PRRSV replication is helpful to develop the effective strategies to control the disease. Calcium signaling has been reported to play an important role in the life cycles of viruses. In this study, we describe the picture that PRRSV infection induces ER stress, opens the store operated calcium entry (SOCE) channel and destroys host calcium homeostasis, further exploits CaMKII-AMPK-mTOR signaling mediated autophagy to benefit self-replication. Conversely, pharmacological inhibition ER stress or Ca2+ signaling suppresses PRRSV replication. Our work is the first report to link ER stress, Ca2+ signaling mediated autophagy, and PRRSV replication, which provides the new insights into virus-host interactions and controlling measures for future PRRSV outbreaks. Calcium (Ca2+), a ubiquitous second messenger, plays a crucial role in many cellular functions. Viruses often hijack Ca2+ signaling to facilitate viral processes such as entry, replication, assembly, and egress. Here, we report that infection by the swine arterivirus, porcine reproductive and respiratory syndrome virus (PRRSV), induces dysregulated Ca2+ homeostasis, subsequently activating calmodulin-dependent protein kinase-II (CaMKII) mediated autophagy, and thus fueling viral replication. Mechanically, PRRSV infection induces endoplasmic reticulum (ER) stress and forms a closed ER-plasma membrane (PM) contacts, resulting the opening of store operated calcium entry (SOCE) channel and causing the ER to take up extracellular Ca2+, which is then released into the cytoplasm by inositol trisphosphate receptor (IP3R) channel. Importantly, pharmacological inhibition of ER stress or CaMKII mediated autophagy blocks PRRSV replication. Notably, we show that PRRSV protein Nsp2 plays a dominant role in the PRRSV induced ER stress and autophagy, interacting with stromal interaction molecule 1 (STIM1) and the 78 kDa glucose-regulated protein 78 (GRP78). The interplay between PRRSV and cellular calcium signaling provides a novel potential approach to develop antivirals and therapeutics for the disease outbreaks.