TAT-mediated delivery of human glutamate dehydrogenase into PC12 cells

Human glutamate dehydrogenase (GDH) gene was fused with a gene fragment encoding the nine amino acid (RKKRRQRRR) protein transduction domain of human immunodeficiency virus TAT protein in bacterial expression vector to produce genetic in-frame TAT-GDH fusion protein. The TAT-GDH protein can enter PC12 cells efficiently when added exogenously in culture media as determined by Western blot analysis and enzyme activities. Once inside the cells, the transduced denatured TAT-GDH protein showed a full activity of GDH indicating that the TAT-GDH fusion protein was correctly refolded after delivery into cells and the activities of GDH in the TAT-GDH fusion protein was not affected by the addition of the TAT sequence. TAT-GDH fusion protein and TAT itself showed no cytotoxicity in PC12 cells. Although the exact mechanism of transduction across a membrane remains unclear, the transduction activity of TAT-GDH into PC12 cells may suggest new possibilities for direct delivery of GDH into the patients with the GDH-deficient disorders.