Glycine-Extended Gastrin Exerts Growth-Promoting Effects on Human Colon Cancer Cells

Abstract

Background: Since human colon cancers often contain significant quantities of progastrin-processing intermediates, we sought to explore the possibility that the biosynthetic precursor of fully processed amidated gastrin, glycine-extended gastrin, may exert trophic effects on human colonic cancer cells. Materials and Methods: Binding of radiolabeled glycine-extended and amidated gastrins was assessed on five human cancer cell lines: LoVo, HT 29, HCT 116, Colo 320DM, and T 84. Trophic actions of the peptides were assessed by increases in [3H]thymidine incorporation and cell number. Gastrin expression was determined by northern blot and radioimmunoassay. Results: Amidated gastrin did not bind to or stimulate the growth of any of the five cell lines. In contrast, saturable binding of radiolabeled glycine-extended gastrin was seen on LoVo and HT 29 cells that was not inhibited by amidated gastrin (10-6 M) nor by a gastrin/ CCKB receptor antagonist (PD 134308). Glycine-extended gastrin induced a dose-dependent increase in [3H]thymidine uptake in LoVo (143 ± 8% versus control at 10-10 M) and HT 29 (151 ± 11% versus control at 10-10 M) cells that was not inhibited by PD 134308 or by a mitogen-activated protein (MAP) or ERK kinase (MEK) inhibitor (PD 98509). Glycine-extended gastrin did stimulate jun-kinase activity in LoVo and HT 29 cells. The two cell lines expressed the gastrin gene at low levels and secreted small amounts of amidated gastrin and glycine-extended gastrin into the media. Conclusions: Glycine-extended gastrin receptors are present on human colon cancer cells that mediate glycine-extended gastrin's trophic effects via a MEK-independent mechanism. This suggests that glycine-extended gastrin and its novel receptors may play a role in colon cancer cell growth.

Use of interfering RNA to investigate the role of endogenous gastrin in the survival of gastrointestinal cancer cells

“…Whereas amidated gastrin acts through the CCK-2 receptor (CCK-2R) (Shulkes and Baldwin, 1997), progastrin and gly-gastrin bind with low affinity to this receptor (Baldwin et al, 2001;Dockray et al, 2001). Furthermore, the biological effects of progastrin and gly-gastrin are not blocked by CCK-B receptor antagonists (Seva et al, 1994;Stepan et al, 1999;Baldwin et al, 2001), and amidated gastrin and gly-gastrin stimulate different downstream signalling events (Todisco et al, 2001). Potential alternative receptors for progastrin and gly-gastrin have been suggested (Seva et al, 1994;Baldwin, 1995a;Singh et al, 1995;Smith et al, 2002;Ahmed et al, 2004).…”

“…Amidated gastrin, glygastrin and progastrin promote growth of a range of cell lines in vitro and in vivo (Watson et al, 1989;Seva et al, 1994;Baldwin, 1995b;Stepan et al, 1999;Baldwin et al, 2001) and upregulate expression of a range of anti-apoptotic proteins, including Akt and bcl-2 (Konturek et al, 2003;Harris et al, 2004a;Ramamoorthy et al, 2004). Gly-gastrin promotes invasion of human colon cancer cells by upregulating expression of matrix metalloproteinases (Baba et al, 2004), by increasing the rate of metastasis formation in vivo (Kermorgant and Lehy, 2001) and by promoting blood vessel formation through the stimulation of endothelial cells (Clarke et al, 2006).…”

Gastrin stabilises β-catenin protein in mouse colorectal cancer cells

“…However, in addition to its recognised role in the physiological regulation of acid secretion, another biological property attributed to gastrin is its trophic effects. A prospective study by Thorburn et al (1998) suggested that hypergastrinemia is associated with an increased risk for colorectal cancer (CRC), and numerous studies have demonstrated that gastrin stimulates the growth of malignant colorectal adenocarcinomas (Wang et al, 1996;Malecka-Panas et al, 1997;Baldwin & Shulkes, 1998;Nakata et al, 1998;Koh et al, 1999;Stepan et al, 1999;Smith & Watson, 2000). Transgenic mice overexpressing progastrin and glycine-extended gastrin demonstrate enhanced colonic proliferation (Wang et al, 1996;Koh et al, 1999), and conversely, gastrin-deficient mice manifest decreased colonic proliferation (Koh et al, 1997).…”

COX-2 selective inhibition reverses the trophic properties of gastrin in colorectal cancer

“…Another biological property attributed to gastrin is its trophic effect on gastrointestinal (GI) mucosa, including its role in the pathogenesis of GI carcinogenesis (Koh et al, 1999;Stepan et al, 1999;Koh and Chen, 2000). Previous epidemiological studies have indicated that chronic hypergastrinaemia constitutes a risk factor for the development of colorectal cancer Sundler et al, 1986;Wolfe, 1992;Lamberts et al, 1999;Singh et al, 2000;Watson and Smith, 2001).…”