Tyrosine dephosphorylation of STAT3 in SARS coronavirus-infected Vero E6 cells

Severe acute respiratory syndrome (SARS) has become a global public health emergency. p38 mitogen-activated protein kinase (MAPK) and its downstream targets are activated in SARS coronavirus (SARS-CoV)-infected Vero E6 cells and activation of p38 MAPK enhances the cytopathic effects of SARS-CoV infection. In addition, weak activation of Akt cannot prevent SARS-CoV infection-induced apoptosis in Vero E6 cells. In the present study, we demonstrated that signal transducer and activator of transcription (STAT) 3, which is constitutively phosphorylated at tyrosine (Tyr)-705 and slightly phosphorylated at serine (Ser)-727 in Vero E6 cells, was dephosphorylated at Tyr-705 on SARS-CoV infection. In addition to phosphorylation of p38 MAPK in virus-infected cells, other MAPKs, i.e., extracellular signal-regulated kinase (ERK) 1/2 and c-Jun N-terminal kinase (JNK), were phosphorylated. Although inhibitors of ERK1/2 and JNK (PD98059 and SP600125) had no effect on phosphorylation status of STAT3, inhibitors of p38 MAPK (SB203580 and SB202190) partially inhibited dephosphorylation of STAT3 at Tyr-705. Tyr-705-phosphorylated STAT3 was localized mainly in the nucleus in mock infected cells, whereas STAT3 disappeared from the nucleus in virus-infected cells. As STAT3 acts as an activator of transcription in the nucleus, these results suggest that STAT3 lacks its activity on transcription in SARS-CoV-infected Vero E6 cells.