Objective: To engineer 293 cells to an artificial beta cell line which secrets insulin in response to stimulation by doxycycline.
Methods: A recombined expression vector, pTRE2mINS, which contained both of the tetracycline response element and proinsulin gene, was constructed. This vector was co-transfected with plasmid pTK-Hyg encoding hygromycin in the tet293 cells, which express the reverse tetracycline-controlled transactivator stably. Following hygromycin screening, the survived cells expressing insulin were selected and enriched. Then, doxycycline one of tetracycline derivatives, was used to control the expression of insulin in these cells. At the levels of mRNA and protein, the regulating effect of doxycycline in culture medium on the expression of proinsulin gene was estimated respectively with Northern blotting, RT-PCR, and radioimmunoassay.
Results: Of the 28 hygromycin resistant cell strains, we selected one cell strain secreting insulin not only automatically, but in response to stimulation by doxycycline was selected. The cells secreted insulin at the rate of 9.7 U/24 h/1.0 x10(6) cells without doxycy cline treatment, and the amount of secreted insulin increased to 241.0 U/24 h/1.0 x 10(6) cells (25-fold) in the presence of doxycycline(1 000 ng/ml). I insulin secretion was induced by doxycycline in a dose dependent manner.
Conclusion: Human proinsulin gene was transfected successfully and expressed efficiently in 293 cells, and the expression was modulated by tetracycline and its derivatives, improving the accuracy, safety, and reliability for the gene therapy of diabetes mellitus.