Regulated expression of a Sindbis virus replicon by herpesvirus promoters

We describe the use of herpesvirus promoters to regulate the expression of a Sindbis virus replicon (SINrep/LacZ). We isolated cell lines that contain the cDNA of SINrep/LacZ under the control of a promoter from a herpesvirus early gene which requires regulatory proteins encoded by immediate-early g enes for expression. Wild-type Sindbis virus and replicons derived from thi s virus cause death of most vertebrate cells, but the cells discussed here grew normally and expressed the replicon and P-galactosidase only after inf ection with a herpesvirus. Vero cell lines in which the expression of SINre p/LacZ was regulated by the herpes simplex virus type 1 (HSV-1) infected-ce ll protein 8 promoter were generated. One Vero cell line (V3-45N) contained , in addition to the SINrep/LacZ cDNA, a Sindbis virus-defective helper cDN A which provides the structural proteins for packaging the replicon. Infect ion of V3-45N cells with HSV-1 resulted in the production of packaged SINre p/LacZ replicons. HSV-1 induction of the Sindbis virus replicon and packagi ng and spread of the replicon led to enhanced expression of the reporter ge ne, suggesting that this type of cell could be used to develop sensitive as says to detect herpesviruses. We also isolated a mink lung cell line that w as transformed with SINrep/LacZ cDNA under the control of the promoter from the human cytomegalovirus (HCMV) early gene UL45. HCMV carries out an abor tive infection in mink lung cells, but it was able to induce the SINrep/Lac Z replicon. These results, and those obtained with an HSV-1 mutant, demonst rate that this type of signal amplification system could be valuable for de tecting herpesviruses for which a permissive cell culture system is not ava ilable.