NEUROMEDIN-B RECEPTOR TRANSFECTED BALB 3T3 CELLS - SIGNAL-TRANSDUCTION AND EFFECTS OF ECTOPIC RECEPTOR EXPRESSION ON CELL-GROWTH/

Bombesin-like peptides including neuromedin B have been proposed as au tocrine or paracrine growth factors for carcinomas. To examine signal transduction and regulation of cell growth by NMB, transfectants were created with the rat NMB receptor (NMB-R) gene in BALB/3T3 cells which do not express an endogenous bombesin peptide receptor. The resultant cell line, NMB-8, expresses 800,000 NMB binding sites/cell. Addition of NMB has a biphasic effect on [H-3]thymidine ([H-3]dT) incorporation in confluent and quiescent cells: up to 10 nM of NMB causes a 1.5-3-f old stimulation of [H-3]dT incorporation, but at greater than 10 nM th ere is inhibition of [H-3]dT incorporation, and at 100 nM of NMB there is inhibition of cell growth. NMB causes protracted increases in intr acellular Ca2+, and pertussis toxin (PT)-insensitive phosphatidylinosi tol (PI) turnover. NMB-mediated increase in membrane phospholipase-C a ctivity is stimulated by guanosine 5'-O-(3-thiotriphosphate). Arachido nate release is also activated by NMB in a PT-insensitive manner. Brie f exposure to 12-tetradecanoylphorbol 13-acetate inhibits NMB-mediated PI turnover but not arachidonate release. Thus, in NMB-8 cells, disti nct mechanisms govern NMB-mediated phospholipase-C activation and arac hidonate release. Also, neuromedin-B is potentially a bifunctional reg ulator of cell growth.