Characterization of the Rana grylio virus 3β-hydroxysteroid dehydrogenase and its novel role in suppressing virus-induced cytopathic effect

The 3β-hydroxysteroid dehydrogenase (3β-HSD) isoenzymes play a key role in cellular steroid hormone synthesis. Here, a 3β-HSD gene homolog was cloned from Rana grylio virus (RGV), a member of family Iridoviridae. RGV 3β-HSD gene has 1068 bp, encoding a 355 aa predicted protein. Transcription analyses showed that RGV 3β-HSD gene was transcribed immediate-early during infection from an initiation site 19 nucleotides upstream of the translation start site. Confocal microscopy revealed that the 3β-HSD-EGFP fusion protein was exclusively colocalized with the mitochondria marker (pDsRed2-Mito) in EPC cells. Upon morphological observation and MTT assay, it was revealed that overexpression of RGV 3β-HSD in EPC cells could apparently suppress RGV-induced cytopathic effect (CPE). The present studies indicate that the RGV immediate-early 3β-HSD gene encodes a mitochondria-localized protein, which has a novel role in suppressing virus-induced CPE. All these suggest that RGV 3β-HSD might be a protein involved in host-virus interaction.