Characterization of the antiproliferative signal mediated by the somatostatin receptor subtype sst5

Abstract

We investigated cell proliferation modulated by cholecystokinin (CCK) and somatostatin analogue RC-160 in CHO cells bearing endogenous CCK A receptors and stably transfected by human subtype sst5 somatostatin receptor. CCK stimulated cell proliferation of CHO cells. This effect was suppressed by inhibitor of the soluble guanylate cyclase, LY 83583, the inhibitor of the cGMP dependent kinases, KT 5823, and the inhibitor of mitogen-activated protein (MAP) kinase kinase, PD 98059. CCK treatment induced an increase of intracellular cGMP concentrations, but concomitant addition of LY 83583 virtually suppressed this increase. CCK also activated both phosphorylation and activity of p42-MAP kinase; these effects were inhibited by KT 5823. All the effects of CCK depended on a pertussis toxin-dependent G protein. Somatostatin analogue RC-160 inhibited CCK-induced stimulation of cell proliferation but it did not potentiate the suppressive effect of the inhibitors LY 83583 and KT 5823. RC-160 inhibited both CCK-induced intracellular cGMP formation as well as activation of p42-MAP kinase phosphorylation and activity. This inhibitory effect was observed at doses of RC-160 similar to those necessary to occupy the sst5 recombinant receptor and to inhibit CCK-induced cell proliferation. We conclude that, in CHO cells, the proliferation and the MAP kinase signaling cascade depend on a cGMPdependent pathway. These effects are positively regulated by CCK and negatively inf luenced by RC-160, interacting through CCK A and sst5 receptors, respectively. These studies provide a characterization of the antiproliferative signal mediated by sst5 receptor.Somatostatin and cholecystokinin are both regulatory hormones widely distributed in the body. Both these hormones participate in a variety of biological processes including neurotransmission and control of pancreatic secretion. They induce their biological effects by interacting with specific G protein-linked receptors (1, 2). The role of the two peptides in the regulation of cell growth also has been demonstrated in studies carried out both in vitro and in vivo (2-6).The effects of CCK and its related peptide, gastrin, are transduced through at least two distinct subtypes of specific cell-surface receptors, CCK A (alimentary) and CCK B (brain, also called CCK B ͞gastrin receptors), that have been cloned in human and rodents (1). CCK B ͞gastrin receptors bind CCK and gastrin with the same high affinity. In contrast, the CCK A receptors exhibit a 100-to 500-fold higher affinity for CCK than gastrin. Gastrin has trophic effects on normal digestive mucosa and stimulates the growth of colon, gastric, and pancreatic cancer cell lines in culture (7,8). This proliferative effect has been shown to be mediated by the gastrin͞CCK B receptors in different cell models (8, 9).In the rat exocrine pancreas that expresses CCK A type receptor, CCK is known to stimulate pancreatic growth both in vitro and in vivo (3-5). The CCK A receptor interacts with G proteins and thereby activates phospholipas...

Somatostatin receptors 2 and 5 are preferentially expressed in proliferating endothelium

“…Vapreotide (an analogue with sst 2 and 5 activity) has been shown to inhibit proliferation of CCK-stimulated CHO cells, which expressed endogenous CCK receptors and that were transfected with sst 5. The effects of sst 5 appeared to be due to the inhibition of guanylate cyclase, and a consequent reduction in cyclic GMP formation, which modulated the activation of the MAPK cascade (Cordelier P et al, 1997). As MAP kinase activation is associated with proliferation of endothelial cells (Bogatcheva et al, 2003;Pintus G et al, 2003), its inhibition may potentially be the mechanism by which sst 5 activation may have an antiproliferative action.…”

Activation of cGMP-dependent Protein Kinase Iβ Inhibits Interleukin 2 Release and Proliferation of T Cell Receptor-stimulated Human Peripheral T Cells

“…kinases has been demonstrated in other cell types including cGK I-transfected baby hamster kidney cells (38), 293T fibroblasts (39), CHO cells (40), Jurkat T cells (17), macrophages (41), mesangial cells (42), and also low passage rat aorta vascular smooth muscle cells (43). Responses to NO, cGMP, or cGK not only varied in different cell types with respect to activation or inhibition of MAP kinases but also proliferation.…”

Biological chemistry of reactive oxygen and nitrogen and radiation-induced signal transduction mechanisms

“…Thus, the role of PKG in cellular growth regulation has relied on the use of primary cultures, transfection to overexpress PKG or the use of pharmacological activators and inhibitors of PKG or sGC. Modulation of PKG activity by these methods has revealed significant roles for the NO -activated PKG-dependent signal transduction pathway in cell growth regulation (Cordelier et al, 1997;Chiche et al, 1998;Kim et al, 1999;Komalavilas et al, 1999;Gu et al, 2000). In many cases, this appears to be due to the intersection of PKG signaling with the MAPK and stress-activated kinase-dependent signal transduction pathways (Lander et al, 1996;Suhasini et al, 1998;Go et al, 1999;Komalavilas et al, 1999;Browning et al, 2000) and expression of the cyclindependent kinase inhibitor P21 Waf1/Cip1 (e.g.…”