Rubella virus capsid protein induces apoptosis in transfected RK13 cells

Rubella virus is an enveloped positive-strand RNA virus that can cause mild to severe birth defects or death in an infected fetus. RV induction of pro grammed cell death, demonstrated in cell culture, has been implicated in th e pathogenesis. The timing of apoptosis, 48 h p.i., suggested that accumula tion of RV structural proteins might induce cell death in infected cells. E xpression of RV structural proteins, capsid, envelope glycoproteins El and E2, in transiently transfected RK13 cells was as potent an inducer of cell death as RV infection. Immunofluorescence microscopy revealed that RV struc tural protein transfected cells exhibited the condensed nuclei typical of a poptotic cell death. Transfection with the capsid protein construct, but no t E2 and El, resulted in as much cell death as joint expression of all thre e RV structural proteins. Capsid required a membrane-anchoring domain to in duce cell death, but a heterologous polypeptide fused to the capsid membran e anchor did not cause apoptosis. Deletion mutants demonstrated that the ap optosis-inducing activity resides In the N-terminal 170 amino acids of caps id. Though apoptosis-inducing capsid constructs appear to have an ER sub-ce llular localization, disruption of the ER calcium storage capacity does not correlate with cell death. Mechanisms consistent with these results are di scussed. (C) 2000 Academic Press.