JNK and PI3k/Akt signaling pathways are required for establishing persistent SARS-CoV infection in Vero E6 cells

Persistence was established after most of the SARS-CoV-infected Vero E6 cells died. RNA of the defective interfering virus was not observed in the persistently infected cells by Northern blot analysis. SARS-CoV diluted to 2 PFU failed to establish persistence, suggesting that some particular viruses in the seed virus did not induce persistent infection. Interestingly, a viral receptor, angiotensin converting enzyme (ACE)-2, was down-regulated in persistently infected cells. G418-selected clones established from parent Vero E6 cells, which were transfected with a plasmid containing the neomycin resistance gene, were infected with SARS-CoV, resulting in a potential cell population capable of persistence in Vero E6 cells. Our previous studies demonstrated that signaling pathways of extracellular signal-related kinase (ERK1/2), c-Jun N-terminal protein kinase (JNK), p38 mitogen-activated protein kinase (MAPK), and phosphatidylinositol 3'-kinase (PI3K)/Akt were activated in SARS-CoV-infected Vero E6 cells. Previous studies also showed that the activation of p38 MAPK by viral infection-induced apoptosis, and a weak activation of Akt was not sufficient to protect from apoptosis. In the present study, we showed that the inhibitors of JNK and PI3K/Akt inhibited the establishment of persistence, but those of MAPK/ERK kinase (MEK; as an inhibitor for ERK1/2) and p38 MAPK did not. These results indicated that two signaling pathways of JNK and PI3K/Akt were important for the establishment of persistence in Vero E6 cells.