High-density seedling expression system for the production of bioactive human cardiotrophin-1, a potential therapeutic cytokine, in transgenic tobacco chloroplasts.

Histidine-tagged human cardiotrophin-1 (hCT-1), a recently discovered cytokine with excellent therapeutic potential, was expressed in tobacco chloroplasts under the transcriptional and translational control of two different promoters (rrn and psbA) and 5'-untranslated regions (5'-UTRs) (psbA and phage T7 gene 10). The psbA 5'-UTR promotes recombinant hCT-1 (rhCT-1) accumulation in chloroplasts at higher levels (eight-fold) than those obtained for the phage T7 gene 10 5'-UTR, regardless of the promoter used, indicating that the correct choice of translational control element is most important for protein production in chloroplasts. The maximum level of rhCT-1 achieved was 1.