Identification of binding sites for C-terminal pro-gastrin-releasing peptide ( GRP)-derived peptides in renal cell carcinoma: a potential target for future therapy.

Objective To determine the expression and biology of the neuroendocrine growth factor gastrin-releasing peptide ( GRP) and other proGRP-derived peptides in renal cancer. Materials and Methods Receptor binding studies, enzyme-linked immunosorbent assay ( ELISA) and radioimmunoassay, were used to quantitate the presence of proGRP-derived peptide receptors and their ligands in renal cancer cell lines and human renal cancers. Biological activity of proGRP peptides was confirmed with proliferation, migration, and extracellular-signal-regulated kinases 1 and 2 ( ERK1/2) activation assays in vitro. In vivo, ACHN renal cancer xenografts were treated with proGRP-derived peptides to assess tumour size and necrosis. hypoxia-inducible factor 1α ( HIF1α) and vascular endothelial growth factor ( VEGF) expression were investigated with Western blotting and ELISA respectively, to determine the possible contribution of the proGRP peptides to tumour viability. Results In ACHN cells that expressed both proGRP- and GRP-receptors, the expression of proGRP binding sites was 80-fold greater than the GRP-receptor ( GRPR). C-terminal proGRP-derived peptides stimulated the activation of ERK1/2, but with a different time course to GRP, consistent with the suggestion that these peptides may have unique cellular functions. Both GRP and proGRP47-68 stimulated proliferation and migration of ACHN cells in vitro, but only GRP reduced the extent of tumour necrosis in ACHN xenografts. GRP, but not proGRP47-68, was able to induce HIF1α and VEGF expression in ACHN cells. This may account in part for the reduction in necrosis after GRP treatment. C-terminal proGRP-derived peptides were present in all three renal cancer cell lines and a panel of human renal cancers, but mature amidated GRP was absent. Conclusion C-terminal proGRP peptides are more abundant in renal cancers and their cell lines than the more extensively studied amidated peptide, GRP. These results suggest that C-terminal proGRP-derived peptides may be a better target for novel renal cancer treatments. [ABSTRACT FROM AUTHOR]