Although amidated forms of
gastrin-releasing peptide (GRP) have been identified as autocrine
growth factors in
small cell lung cancer, their role in the development and progression of
colorectal carcinoma is less clear. In addition, the biological activity of non-amidated
gastrin-releasing peptide has not been investigated in
colorectal carcinoma cells. We therefore investigated the effect of
bombesin (a homologue of
gastrin-releasing peptide) on proliferation, migration and
inositol phosphate production in the human
colorectal carcinoma cell line DLD-1, and determined the ability of
gastrin-releasing peptide receptor antagonists to inhibit these effects. We also compared the biological activities of amidated and non-amidated GRP in the same assays. Treatment with either
bombesin, or amidated or non-amidated GRP resulted in significant increase in proliferation, and in migration in a wound-healing assay. Both the mitogenic and migratory effects of amidated and non-amidated forms were inhibited by the GRP receptor antagonist [D-Phe(6), Leu-NHet(13), des-Met(14)]-
bombesin(6-13). The presence of GRP receptor
mRNA and GRP binding sites in three
colorectal carcinoma cell lines was demonstrated by RT-PCR and by binding of radiolabelled
bombesin, respectively. Transfection of DLD-1 cells with a dominant negative
phosphatidylinositol 3-kinase did not affect
bombesin-stimulated cell proliferation, but inhibited
bombesin-stimulated cell migration.
Bombesin and GRPgly activated
phospholipase C,
mitogen-activated protein kinase and
focal adhesion kinase. We conclude that both amidated and non-amidated forms of
gastrin-releasing peptide accelerate proliferation and migration of DLD-1 human
colorectal carcinoma cells via the
gastrin-releasing peptide receptor, but that
phosphatidylinositol 3-kinase is only involved in the cell migration signalling pathway. Our results suggest a potential role for
gastrin-releasing peptide receptor antagonists in the management of
colorectal carcinoma.