PCV2 Triggers PK-15 Cell Apoptosis Through the PLC-IP3R-Ca²⁺ Signaling Pathway

The endoplasmic reticulum (ER) plays an essential role in Ca²⁺ concentration balance and protein biosynthesis. During infection, the virus needs to complete its life process with the help of ER. At the same time, ER also produces ER stress (ERS), which induces apoptosis to resist virus infection. Our study explored the Ca²⁺ concentration, ERS, and the apoptosis mechanism after porcine circovirus 2 (PCV2) infection. We show here that PCV2 infection induces the increased cytoplasmic Ca²⁺ level and PK-15 cell ER swelling. The colocalization of phospholipase C (PLC) and inositol 1,4,5-trisphosphate receptor (IP3R) in the cytoplasm was observed by laser confocal microscopy. Western blot and quantitative polymerase chain reaction experiments confirmed that PLC and IP3R expression levels increased after PCV2 infection, and Ca²⁺ concentration in the cytoplasm increased after virus infection. These results suggest that PCV2 infection triggers ERS of PK-15 cells via the PLC-IP3R-Ca²⁺ signaling pathway to promote the release of intracellular Ca²⁺ and led to cell apoptosis.