Regulation of shrimp PjCaspase promoter activity by WSSV VP38 and VP41B

Members of the Caspase family play essential roles in apoptosis. In kuruma shrimp Marsupenaeus japonicus the caspase gene (PjCaspase) was previously found dramatically up-regulated in viral-challenged and -resistant shrimp, suggesting that PjCaspase plays an important role in protecting host from viral infection. In order to further delineate the transcriptional regulation of PjCaspase in response to viral infection, the promoter activity was confirmed by fusing the 5′-flanking promoter region of the PjCaspase gene to the enhanced green fluorescence protein (EGFP) gene and transformed to Trichoplusia ni High Five™ cell line. With streptavidin-bead pulldown assay, two envelope proteins VP38 and VP41B of white spot syndrome virus (WSSV) were found to bind to PjCaspase promoter in vitro. Luciferase reporter assay by cotransfection of PjCaspace promoter with VP38 or VP41B revealed that the proteins act as repressor and activator of PjCaspase transcription respectively. Our study suggested a potential role for the two WSSV proteins on shrimp PjCaspase regulation in response to WSSV challenge. To our knowledge this is the first report on WSSV envelope proteins found to be involved in gene regulation. These results provide insights into the molecular regulation of PjCaspase gene expression, which will be helpful for shrimp viral disease control.