Identification of functional GRP‐preferring bombesin receptors on human melanoma cells

Bombesin was originally isolated from amph- ibian skin, wherease its mammalian counterpart, gastrin- releasing peptide (GRP), was first identified in the nervous system of the gastrointestinal tract. Whether GRP is present in the human skin is not known. Bombesin-like peptides are also known to modulate growth. We therefore investigated whether human mel- anoma cell lines express functional GRP-preferring bom- besin receptors and whether they alter growth or other specific cellular functions of these tumour cells. GRP receptor mRNA was found in HBL, D-10, Me-28 and A375-6 cell lines, but only A375-6 cells express a large number of high-affinity binding sites for ( 125 I)-(Tyr 4 ) bombesin (Kd 0 . 31 6 0 . 04 nmol L π1 , 3880 6 429 binding sites per cell). Bombesin dose-dependently increased cytosolic calcium, but did not alter interleukin (IL) 1b-induced reduction of cell viability or IL-6 secretion, both A375-6-specific cell functions. Growth of A375-6 cells was not altered by bombesin or the specific GRP receptor antagonist BIM26226 as measured by ( 3 H)- thymidine incorporation or methylene blue assay, whereas insulin alone or in combination with other potential growth factors dose-dependently stimulated growth of these cells. The newly characterized GRP-preferring bombesin receptors on highly malignant human melanoma cells could initiate studies of growth effects on solid tumours or in vivo scanning using radiolabelled tracers.