Expression of GLUT2 in insulin-secreting AtT20 pituitary cells

(Requests for oVprints should be addressed to C J Bailey) The importance of the glucose transporter isoform, GLUT2, in the construction of glucose-sensitive surrogate insulin-secreting cells was evaluated using murine pituitary AtT20 cells. The cells were double transfected with cDNAs for human pre-proinsulin (hppI-1) driven by the cytomegalovirus promoter, and human GLUT2 driven by the â-actin promoter. The stably transfected clone, AtTinsGLUT2.36, which strongly expressed both the hppI-1 and GLUT2 genes, constitutively released 7·5 ng/106 cells/24 h of immunoreactive insulin-like material, 75 % of which was fully processed mature human insulin. Increasing glucose concentrations in the subphysiological range up to 50 µM increased insulin release, but greater glucose concentrations did not further increase insulin release. Suppression of the low-Km glucose-phosphorylating enzyme, hexokinase, with 2-deoxy-d-glucose increased glucose-stimulated insulin release by two- to threefold in the presence of subphysiological and physiological glucose con-centrations up to 10 mM. Physiological glu-cose concentrations increased the amount of GLUT2 mRNA, indicating that the â-actin pro-moter responds in a glucose-dependent manner. Implantation of 2#107 AtTinsGLUT2.36 cells intraperitoneally into streptozotocin-diabetic nude mice slowed the progression of hyperglycaemia. The implanted cells formed vascularised tumour-like cell aggregates attached to the peritoneum. The results demonstrate that the â-actin promoter is partially regulated by glucose. Expression of GLUT2 enables glucose to enter the cell at high Km, but high-Km glucose phosphorylation is also required to signal glucose-stimulated genes aVecting insulin release