COEXPRESSION OF THE PLATELET-DERIVED GROWTH-FACTOR (PDGF) B-CHAIN AND THE PDGF BETA-RECEPTOR IN ISOLATED PANCREATIC-ISLET CELLS STIMULATES DNA-SYNTHESIS

Suspensions rich in pancreatic β cells were transfected by means of electroporation or by using the liposome technique with DNA constructs coding for the B chain of platelet-derived growth factor (PDGF) and the PDGF α and β receptors to induce a mitotic response in this slowly replicating cell type. Transfection with the B-chain construct induced synthesis of the PDGF B-chain homodimer (PDGF-BB) as assessed by the presence of 125I-labeled PDGF-BB competing activity in the conditioned medium of the transfected islet cells. Moreover, islet cells transfected with the PDGF β-receptor construct exhibited increased immunofluorescence staining with a PDGF β-receptor antibody. These cells also displayed increased 125I-labeled PDGF-BB binding compared with control transfected cells. Cotransfection with the B-chain construct or the addition of 10% fetal bovine serum or purified PDGF all induced DNA synthesis in islet cells transfected with the PDGF β-receptor construct. Islet cells transfected with the PDGF α-receptor construct did not respond with stimulation of [3H]thymidine incorporation to any of the PDGF isoforms (PDGF-AA, -AB, or -BB). Cotransfection of the PDGF α- and β-receptor constructs resulted in a loss of the DNA synthesis response to PDGF. The β cells exhibited elevated levels of [3H]inositol trisphosphate after transfection with the B-chain and β-receptor constructs, indicating activation of phospholipase C. Islet cells transfected with the different receptor constructs exhibited different patterns of tyrosine phosphorylation upon ligand activation. The results demonstrate that pancreatic islet cells can be stimulated to increase DNA synthesis by transfection with the PDGF β-receptor gene, whereas cotransfection with the α-receptor gene may attenuate the growth response.