Bombesin receptor subtype-3 agonists stimulate the growth of lung cancer cells and increase EGF receptor tyrosine phosphorylation

The effects of bombesin receptor subtype-3 (BRS-3) agonists were investigated on lung cancer cells. The BRS-3 agonist (DTyr(6), (Ala(11), Phe(13), Nle(14)) bombesin(6-14) (BA1), but not gastrin releasing peptide (GRP) or neuromedin B (NMB) increased significantly the clonal growth of NCI-H1299 cells stably transfected with BRS-3 (NCI-H1299-BRS-3). Also, BA1 addition to NCI-H727 or NCI-H1299-BRS-3 cells caused Tyr(1068) phosphorylation of the epidermal growth factor receptor (EGFR). Similarly, (DTyr(6), R-Apa(11), Phe(13), Nle(14)) bombesin(6-14) (BA2) and (DTyr(6), R-Apa(11), 4-Cl,Phe(13), Nle(14)) bombesin(6-14) (BA3) but not gastrin releasing peptide (GRP) or neuromedin B (NMB) caused EGFR transactivation in NCI-H1299-BRS-3 cells. BA1-induced EGFR or ERK tyrosine phosphorylation was not inhibited by addition of BW2258U89 (BB2R antagonist) or PD168368 (BB1R antagonist) but was blocked by (DNal-Cys-Tyr-DTrp-Lys-Val-CysNal)NH2 (BRS-3 ant.). The BRS-3 ant. reduced clonal growth of NCI-H1299-BRS-3 cells. BA1, BA2, BA3 and BRS-3 ant. inhibit specific I-126-BA1 binding to NCI-H1299-BRS-3 cells with an IC50 values of 1.1, 21, 15 and 750 nM, respectively. The ability of BRS-3 to regulate EGFR transactivation in NCI-H1299-BRS-3 cells was reduced by AG1478 or gefitinib (EGFR tyrosine kinase inhibitors), GM6001 (matrix metalloprotease inhibitor), PP2 (Src inhibitor), N-acetylcysteine (anti-oxidant), Tiron (superoxide scavenger) and DPI (NADPH oxidase inhibitor). These results demonstrate that BRS-3 agonists may stimulate lung cancer growth as a result of EGFR transactivation and that the transactivation is regulated by BRS-3 in a Src-, reactive oxygen and matrix metalloprotease-dependent manner. Published by Elsevier Inc.