Infectious pancreatic necrosis virus induces apoptosis due to down-regulation of survival factor MCL-1 protein expression in a fish cell line

Infectious pancreatic necrosis virus (IPNV), a member of the virus family B irnaviridae, causes an acute, contagious disease in a number of economicall y important fish species. CHSE-214, a Chinook salmon embryonic cell line, w hen infected by IPNV showed morphological and biochemical features of apopt osis, including an intense DNA laddering pattern and blebbing of the plasma membrane, followed by formation of apoptotic bodies. The Mcl-1 gene produc t proved to be a member of the Bcl-2 gene family, and like Bcl-2 had the ca pacity to promote cell viability. Here, we investigated the pattern of expr ession of Mcl-1 in CHSE-214 cells infected by IPNV. We found that the Mcl-1 level decreased markedly in cells undergoing apoptosis after IPNV infectio n. This decrease was rapid during the first 8 h postinfection and preceded cell death. Furthermore, we found that drugs including cycloheximide, genis tein and EDTA either prevented the decline in Mcl-1 levels or blocked the i ntense DNA laddering pattern. Other drugs like serine proteinase inhibitor, 400 mu g/ml aprotinin, 400 mu g/ml leupeptin and 100 mu g/ml tryphostin di d not. The virus gene expression pattern was examined by Western blot using antivirion polyclonal antibody and was blocked during treatment with cyclo heximide, genistein and EDTA but not by serine proteinase, aprotinin, leupe ptin or tryphostin. Together the data showed a striking correlation between virus replication and Mcl-1 expression in CHSE-214 cells, suggesting that the virus gene expression has a possible involvement with Mcl-1 in the regu lation of apoptosis in these cells. (C) 1999 Elsevier Science B.V. All righ ts reserved.