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C Stewart, N A Taylor, K Docherty, and C J Bailey


The feasibility of somatic cell gene therapy as a method of insulin delivery has been studied in mice. Murine pituitary AtT20 cells were transfected with a human preproinsulin DNA in a plasmid containing a metallothionein promoter and a gene conferring resistance to the antibiotic G418. The AtT20MtIns-1·4 clone of cells was selected because of its higher insulin-releasing activity compared with other clones. After culturing for 24 h in Dulbecco's medium containing 10 mM glucose, the AtT20MtIns-1·4 cells released human insulin at about 5 ng/106 cells per 24 h. Insulin release was not significantly altered by raised concentrations of glucose, potassium or calcium, but insulin release was increased by 20 mm arginine, 5 mm isomethylbutylxanthine and 90 μm zinc.

AtT20MtIns-1·4 cells (2 × 106) were implanted intraperitoneally into non-diabetic athymic nude (nu/nu) mice, and the mice were made diabetic by injection of streptozotocin after 7 days. Release of human insulin in vivo was assessed using a specific plasma human C-peptide assay. Human C-peptide concentrations were maintained at about 01 pmol/ml throughout the 29 days of the study. The development of streptozotocin-induced hyperglycaemia was delayed in recipients of the cells releasing human insulin, compared with a control group receiving an implant of non-transfected cells. At autopsy the implanted AtT20MtIns-1·4 cells in each recipient had formed a tumour-like aggregation, with an outer region of insulin-containing cells. The study suggests that somatic cell gene therapy offers a feasible approach to insulin delivery.

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R A Sporici, J S Hodskins, D M Locasto, L B Meszaros, A L Ferry, A M Weidner, C A Rinehart, J C Bailey, I M Mains, and S E Diamond

The POU-homeodomain transcription factor Pit-1 is required for the differentiation of the anterior pituitary cells and the expression of their hormone products. Pit-1β, an alternate splicing isoform, has diametrically different outcomes when it is expressed in different cell types. Pit-1β acts as a transcriptional repressor of prolactin (PRL) and growth hormone genes in pituitary cells, and as a transcriptional activator in non-pituitary cells. In order to explore these differences, we: (1) identified the transcriptional cofactors necessary for reconstitution of repression in non-pituitary cells; (2) tested the effect of the β-domain on heterodimerization with Pit-1 and physical interaction with the co-activator CREB binding protein (CBP); and (3) determined the β-domain sidechain chemistry requirements for repression. Co-expression of both Pit-1 isoforms reconstituted the repression of the PRL promoter in non-pituitary cells. The β-domain allowed heterodimerization with Pit-1 but blocked physical interaction with CBP, and specific chemical properties of the β-domain beyond hydrophobicity were dispensable. These data strongly suggest that Pit-1β represses hormone gene expression by heterodimerizing with Pit-1 and interfering with the assembly of the Pit-1–CBP complex required for PRL promoter activity in pituitary cells.

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Jarrod Bailey, Alison J Tyson-Capper (née Pollard), Kate Gilmore, Stephen C Robson, and G Nicholas Europe-Finner

cAMP-response element (CRE) binding (CREB) and modulator (CREM) proteins, activated by protein kinase A-mediated phosphorylation, bind as homo- and heterodimers to promoters containing CRE and activator protein 1 (AP-1) sites to alter target-gene expression. We have previously reported differential expression of CREB and CREM splice variants CREMα and CREMτ2α in human myometrium during pregnancy and labour. Via microarray studies with cultured myometrial cells stably transfected with CREB, CREMα and CREMτ2α cDNAs, CREB affected the expression of 958 genes; 522 being up-regulated and 436 down-regulated. CREMα altered the expression of 118 genes; 71 were increased and 47 decreased. CREMτ2α affected 220 genes; 148 were activated and 72 repressed. Notably, genes affected by CREB, CREMα and CREMτ2α belong to largely discrete groups: less than 9% were affected by more than one factor. Genes involved in regulation of cell death and apoptosis, growth and maintenance, signal transduction, physiological and developmental processes, protein kinase cascades, extracellular matrix, cytoskeleton, cell-cycle regulation, transport, and a variety of enzymes, intracellular components and nucleic acid-binding proteins have been described, many of which are involved in the modulation of myometrial activity during pregnancy and parturition.