Functional expression of bombesin receptor in most adult and pediatric human glioblastoma cell lines; role in mitogenesis and in stimulating the mitogen-activated protein kinase pathway

Functional bombesin receptors were identified in most human glioblastoma cell lines examined (85% of lines). Bombesin stimulated the release of intracellular Ca²⁺ in human adult (U-373MG, D-247MG, U-118MG, U-251MG, D-245MG, U-105MG, D-54MG, A-172MG, and D-270MG lines) and pediatric (SJ-S6 and SJ-G2 lines) glioblastoma cell lines. Stimulation of the glioblastoma cell line U-373MG with bombesin or gastrin-releasing peptide (GRP) induced mitogenesis, measured by [³H]thymidine incorporation into DNA, and stimulated the tyrosine phosphorylation of the mitogen-activated protein (MAP) kinases (Erk1 and Erk2). The stimulation of the MAP kinase phosphorylation in U-373MG cells was time- and peptide concentration-dependent. Both bombesin and GRP showed similar potencies in stimulation of intracellular Ca²⁺ release and activation of the MAP kinase pathway in U-373MG cells, whereas neuromedin B (NMB) peptide was less potent. Bombesin and GRP induced the release of cytosolic Ca²⁺ in a concentration-dependent manner. Because bombesin and GRP were more potent than NMB peptide in increasing the cytosolic Ca²⁺ levels in U-373MG cells, we concluded that the BB₂ subtype (also known as GRP-preferring receptor subtype) of the bombesin receptor is expressed in this cell line. The bombesin receptor antagonist ([Leu¹³-ψ(CH₂NH)Leu¹⁴]bombesin) blocked bombesin induced Ca²⁺ release and attenuated MAP kinase activation in U-373MG cells demonstrating that bombesin is acting through a receptor-dependent mechanism. This study indicates that functional bombesin receptors are widely expressed in human glioblastoma cell lines.