Abstract

BACKGROUND
Type 1 diabetes mellitus is an autoimmune disease resulting in destruction of the pancreatic beta cells. Insulin gene therapy for these patients has been vigorously researched. The strategy for achieving glucose-dependent insulin secretion in gene therapy relies on glucose-responsive transcription of insulin mRNA and the constitutive secretory pathway of target non-beta cells. We observed that genetically engineered K-cells using Epstein-Barr virus (EBV)-based episomal vector can produce glucose-regulated insulin production. METHODS: Green fluorescent protein (GFP) or rat-preproinsulin (PPI) expression cassette transcriptionally controlled by the promoter of glucose dependent insulinotropic peptide (GIPP) is fused to pCEP4 containing the origin of replication (oriP) and Epstein-Barr virus nuclear antigen 1 (EBNA-1). CMV promoter was replaced by subcloning the GIPP into pCEP4 to generate pGIPP/CEP4. Two recombinant EBV-based episomal vectors, pGIPP/GFP/CEP4 and pGIPP/PPI/CEP4, were constructed. pGIPP/GFP/CEP4 and pGIPP/PPI/CEP4 containing K-cell specific GIPP were co-transfected into STC-1. K-cell was isolated from the clonal expansion of the fluorescent cells selected by hygromycin treatment in STC-1, and were analyzed for the expression of glucokinase (GK) or transcription factors involved in pancreas development. K-cells concurrently transfected with pGIPP/PPI/CEP4 and pGIPP/GFP/CEP4 were analyzed for the transcripts of PPI by RT-PCR, and for the glucose dependent insulin expression by immunocytochemistry or insulin assay using ultra-sensitive rat-specific insulin ELISA kit. RESULT: STC-1 was stably-transfected with pGIPP/GFP/CEP4 along with pGIPP/PPI/CEP4. Genetically selected fluorescent K-cells expressed GK and transcription factors involved in pancreas development. And K-cells transfected with pGIPP/PPI/CEP4 contained detectable levels of PPI transcripts and showed glucose-dependent immunoreactive insulin secretion. CONCLUSION: We identified genetically engineered K-cells which exert a glucose-dependent insulin expression using EBV-based episomal vector. The similarities between K-cells and pancreatic beta cells support that K-cells may make effective and ideal targeting cells for insulin gene therapy or alternative cell therapy.

• Keywords: Epstein-Barr virus-based episomal vector;GIP promoter;Insulin gene therapy;K-cell