Secretion of functional Renilla reniformis luciferase by mammalian cells

The soft coral Renilla reniformis luciferase enzyme is a monomeric soluble intracellular protein that is used increasingly as a marker of gene expression. Here the Renilla luciferase gene was engineered to encode a protein product secreted by mammalian cells. The 5′ end of the Renilla luciferase gene was fused in frame with the 3′ end of a short DNA sequence encoding the signal peptide from human interleukin-2 (IL-2) protein. This construct was cloned under transcriptional control of the cytomegalovirus (CMV) promoter in a mammalian expression vector. Simian COS-7 cells were transiently transfected with the construct, and light emission was measured from cell lysates and from cell culture media. The results of these experiments indicated that Renilla luciferase was secreted as a functional enzyme by mammalian cells. The advantages and disadvantages of secreted Renilla luciferase as a marker of gene expression in comparison to other secreted protein markers are discussed.