Secretion of enzymatically active human renin from mammalian cells using an avian retroviral vector

Recombinant plasmid-based retroviral expression vectors were constructed using a modified spleen necrosis virus (SNV) containing the Herpes simplex virus thymidine kinase gene promoter controlling the expression of the Tn5 neomycin phosphotransferase II gene (NPTII gene). The human renin (HRn) gene (hrn) was inserted into the 5' end of the SNV sequences such that in concatemeric plasmid DNA its expression was controlled by the strong promoter in the SNV long terminal repeat (LTR). Dog cells transfected with the concatemeric plasmid DNA secreted a small amount of a HRn-like 43-kDa protein. After cotransfection of chicken cells with concatemeric plasmid DNA and proviral DNA of reticuloendotheliosis virus strain A, infectious stocks of viruses were recovered. Cells infected with the virus carrying the viral LTR-hrn gene oriented for expression secreted the 43-kDa HRn-like protein at about 100-fold higher levels than the cells transfected with the plasmid DNAs. Biological activity of secreted HRn was determined by measuring levels of angiotensin I generated by incubating culture media with either a porcine or human angiotensinogen substrate. Infected dog cells produce about 40 ng of enzymatically active HRn per 10(6) cells per 24 h. These data indicate that retroviral expression vectors provide a good system for obtaining the secretion of high levels of enzymatically active heterologous proteins from mammalian cells.