title: Tetracycline-regulated secretion of human insulin in a transfected non-endocrine cell line.
abstract: Long-term constitutive secretion of insulin by implantation of ex vivo transfected cells such as fibroblasts or myoblasts or in situ by intramuscular injection of naked plasmid DNA provides a potential approach to gene therapy for diabetes mellitus. A mechanism for regulating insulin secretion will be necessary to realize the therapeutic potential of this approach. A second obstacle is the inability of non-endocrine host cells to fully process proinsulin. Therefore, alteration of the wild-type cDNA will be necessary to achieve processing of proinsulin by endogenous endoproteases within these cells. The cDNAs for beta-galactosidase (beta), human wild-type proinsulin (hppI1) and a mutated construct (hppI4), in which the dibasic PC2 and PC3 cleavage sites had been altered to form furin cleavage sites, were sub-cloned into four vectors (pCR3, pVR1012, pIRES, pTRE), including a tetracycline responsive plasmid (pTRE) that requires co-transfection with another plasmid encoding a transactivator (pTet-off) for transgene expression. Transient transfection of the COS-7 fibroblast cell line with these constructs was performed using DEAE-dextran and liposomes. Analysis of vector efficiencies revealed that pTRE/pTet-off>pIRES>pCR3>pVR1012. Further analysis demonstrated total pro/insulin secretion of 2.33 ng/10(6) cells/24 h with > or =25% processed to insulin in hppI-1.pTRE/pTet-off-transfected cells compared with 0.39 ng/10(6) cells/24 h and >70% processing in hppI-4.pTRE/pTet-off-transfected cells. In co-transfection studies with pTRE-hppI1/pTet-off and pTRE-hppI4/pTet-off constructs, pro/insulin secretion was inhibited to 65-66% and 36-38% of control (100%) in the presence of 0.01 and 0.1 microg/ml tetracycline respectively over a 24-h incubation period. Furthermore, reversal of tetracycline inhibition was demonstrated for pTRE-hppI1/pTet-off- and pTRE-hppI4/pTet-off-transfected cells. After a 48-h incubation with 1.0 microg/ml tetracycline, total pro/insulin levels were 10 and 14% compared with untreated cells respectively. On tetracycline removal, total proinsulin levels increased and were equivalent to untreated groups 72 h later. In conclusion, regulation of fully processed human insulin secretion has been achieved in a transiently transfected non-endocrine cell line.
authors.affiliation: Department of Medicine and Therapeutics, University of Aberdeen, Institute of Medical Sciences, Foresterhill, Aberdeen, Scotland, UK.
authors.forename: K T
authors.initials: KT
authors.lastname: Scougall
authors.forename: C A
authors.initials: CA
authors.lastname: Maltin
authors.forename: J A M
authors.initials: JA
authors.lastname: Shaw
mesh_terms: D000818:Animals; D015152:Blotting, Northern; D019556:COS Cells; D002460:Cell Line; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D007150:Immunohistochemistry; D007328:Insulin / Q000235:genetics / Q000378:metabolism*; D000078790:Insulin Secretion; D012333:RNA, Messenger / Q000235:genetics; D011863:Radioimmunoassay; D013754:Tetracyclines / Q000494:pharmacology*; D014162:Transfection
chemical_list: D007328:Insulin; D012333:RNA, Messenger; D013754:Tetracyclines