gastrins and Hypoxia

Hypoxia, or a low concentration of O2, is encountered in humans undertaking activities such as mountain climbing and scuba diving and is important pathophysiologically as a limiting factor in tumor growth. Although data on the interplay between hypoxia and gastrins are limited, gastrin expression is upregulated by hypoxia in gastrointestinal cancer cell lines, and gastrins counterbalance hypoxia by stimulating angiogenesis in vitro and in vivo. The aim of this study was to determine if higher concentrations of the gastrin precursor progastrin are protective against hypoxia in vivo. hGAS mice, which overexpress progastrin in the liver, and mice of the corresponding wild-type FVB/N strain were exposed to normoxia or hypoxia. Iron status was assessed by measurement of serum iron parameters, real-time PCR for mRNAs encoding critical iron regulatory proteins, and Perls' stain and atomic absorption spectrometry for tissue iron concentrations. FVB/N mice lost weight at a faster rate and had higher sickness scores than hGAS mice exposed to hypoxia. Serum iron levels were lower in hGAS than FVB/N mice and decreased further when the animals were exposed to hypoxia. The concentration of iron in the liver was strikingly lower in hGAS than FVB/N mice. We conclude that increased circulating concentrations of progastrin provide a physiological advantage against systemic hypoxia in mice, possibly by increasing the availability of iron stores. This is the first report of an association between progastrin overexpression, hypoxia, and iron homeostasis.

Topics: Animals; Colon; Erythropoietin; Female; Gastrins; Gene Expression; Hypoxia; Iron; Liver; Male; Mice; Real-Time Polymerase Chain Reaction; RNA, Messenger

Gastrin and its precursors have been shown to promote mitogenesis and angiogenesis in gastrointestinal tumors. Hypoxia stimulates tumor growth, but its effect on gastrin gene regulation has not been examined in detail. Here we have investigated the effect of hypoxia on the transcription of the gastrin gene in human gastric cancer (AGS) cells. Gastrin mRNA was measured by real-time PCR, gastrin peptides were measured by RIA, and gastrin promoter activity was measured by dual-luciferase reporter assay. Exposure to a low oxygen concentration (1%) increased gastrin mRNA concentrations in wild-type AGS cells (AGS) and in AGS cells overexpressing the gastrin receptor (AGS-cholecystokinin receptor 2) by 2.1 ± 0.4- and 4.1 ± 0.3-fold (P < 0.05), respectively. The hypoxia mimetic, cobalt chloride (300 μM), increased gastrin promoter activity in AGS cells by 2.4 ± 0.3-fold (P < 0.05), and in AGS-cholecystokinin receptor 2 cells by 4.0 ± 0.3-fold (P < 0.05), respectively. The observations that either deletion from the gastrin promoter of the putative binding sites for the transcription factor hypoxia-inducible factor 1 (HIF-1) or knockdown of either the HIF-1α or HIF-1β subunit did not affect gastrin promoter inducibility under hypoxia indicated that the hypoxic activation of the gastrin gene is likely HIF independent. Mutational analysis of previously identified Sp1 regulatory elements in the gastrin promoter also failed to abrogate the induction of promoter activity by hypoxia. The observations that hypoxia up-regulates the gastrin gene in AGS cells by HIF-independent mechanisms, and that this effect is enhanced by the presence of gastrin receptors, provide potential targets for gastrointestinal cancer therapy.

Topics: Aryl Hydrocarbon Receptor Nuclear Translocator; Cell Line, Tumor; Cobalt; Colorectal Neoplasms; Gastrins; Gastrointestinal Neoplasms; Gastrointestinal Tract; Humans; Hypoxia; Hypoxia-Inducible Factor 1; Hypoxia-Inducible Factor 1, alpha Subunit; Models, Biological; Promoter Regions, Genetic; RNA, Messenger; Sp1 Transcription Factor

As the hormone gastrin promotes gastrointestinal (GI) cancer progression by triggering survival pathways, regulation of gastrin expression at the translational level was explored. Sequence within the 5' untranslated region of a gastrin transcript expressed in GI cancer cells was investigated, then cloned into a bicistronic vector upstream of firefly luciferase and transfected into a series of GI cancer cell lines. Firefly luciferase activity was measured relative to that of a cap-dependent Renilla luciferase. A gastrin transcript that was different from that described in Ensembl was expressed in GI cancer cells. Its transcription appears to be initiated within the region designated as the gene's first intron. In GI cancer cells transfected with the bicistronic construct, firefly luciferase activity increased 8-15-fold compared with the control vector, and there was a further induction of the signal (up to 25-fold) following exposure of the cells to genotoxic stress or hypoxia, suggesting that the sequence acts as an internal ribosome entry site. These data suggest that the gastrin transcript within GI cancer cells contains an internal ribosome entry site that may allow continued expression of gastrin peptides when normal translational mechanisms are inactive, such as in hypoxia, thereby promoting cancer cell survival.

Topics: 5' Untranslated Regions; Adenocarcinoma; Apoptosis; Cell Survival; Gastrins; Gastrointestinal Neoplasms; Gene Expression Regulation, Neoplastic; HCT116 Cells; Humans; Hypoxia; Luciferases; Luciferases, Renilla; Pancreatic Neoplasms; Protein Biosynthesis; Reverse Transcriptase Polymerase Chain Reaction; Ribosomes; Survival Analysis; Transcription, Genetic; Transfection

This study examines the effects of hypoxia in the gastric function in conscious rats which adapted to a meal-feeding schedule, that allowed free access to a high protein (HP) diet (550 g casein/kg diet, Exp.1,2 and 4), a normal protein (NP) diet (200 g casein/kg diet, Exp.3) or a nonpurified rat (NPR) diet (Exp. 5 and 6) for 4 h every day for 2 wk. In Exp. 1, after 4 h of consuming the HP diet, rats were exposed to 7.6 or 10.5% O2 normobaric hypoxia. Hypoxia delayed the excretion of urinary urea for 12 h. In Exp.2 and 3, when rats were exposed to 7.6%O2 after 4 h of consuming the HP diet and exposed to 10.5% O2 after 4 h of consuming the NP diet, respectively, a significant delay in gastric emptying was found in the hypoxic rats. In Exp. 4, when rats were exposed to 7.6 O2 hypoxia after 4 hr of eating the HP diet, the plasma gastrin concentration in the 7.6% O2 hypoxic rats was 2.3-fold that of the normoxic rats after 6 h of hypoxia. Furthermore, when rats that did not consume any HP diet on the day of the experiment were exposed to 7.6 or 10.5% O2 hypoxia, the plasma gastrin concentration was higher in both hypoxic groups than in the normoxic group after 3 and 6 of hypoxia. In Exp. 5, rats that were not fed the NPR diet on the day of study were exposed to 7.6 or 10.5% O2 hypoxia for 3 h after pylorus ligation. Hypoxia inhibited the secretion of gastric acid and elevated the plasma gastrin concentration. In Exp. 6, unfed rats that had been consuming the NPR diet were exposed to 7.6% O2 hypoxia for 3 h after pylorus ligation and were orally administered HCl. The rise of the gastrin concentration due to hypoxia was completely inhibited by oral HCl. These results demonstrate that hypoxia inhibits gastric emptying and gastric acid secretion and that the inhibitory effect of hypoxia on gastric acid secretion stimulates gastrin release through positive feedback regulation.

Topics: Analysis of Variance; Animals; Consciousness; Dietary Proteins; Feedback; Gastric Acid; Gastric Emptying; Gastrins; Hydrochloric Acid; Hypoxia; Male; Oxygen; Rats; Rats, Wistar; Time Factors; Urea

Calves were subjected to experimental hypoxia from 0.5 to 4 h after birth. The plasma level of immunoreactive gastric inhibitory polypeptide was higher (P less than 0.05) than in control calves during hypoxia and 2 and 7 h later. However, the gastrin level was not lower during treatment and was higher (P less than 0.05) 3, 6, and 13 h later. Hypoxia could have changed circulating levels or degradation rates of these peptides and could have delayed abomasal emptying.

Topics: Animals; Animals, Newborn; Cattle; Gastric Inhibitory Polypeptide; Gastrins; Hypoxia; Male

Topics: Animals; Atmospheric Pressure; Cats; Female; Gastric Juice; Gastric Mucosa; Gastrins; Humans; Hypercapnia; Hypoxia; Male; Peptic Ulcer; Peptic Ulcer Hemorrhage; Pulmonary Heart Disease; Pyloric Stenosis

Topics: Anesthesia; Animals; Blood Flow Velocity; Fasting; Gastrins; Histamine; Hydrogen; Hypoxia; Norepinephrine; Platinum; Rats; Regional Blood Flow; Stomach

Topics: Acetylcholine; Animals; Cocaine; Colon; Female; Gastrins; Guinea Pigs; Hexamethonium Compounds; Histamine; Histamine H1 Antagonists; Hypoxia; Intestine, Small; Methysergide; Morphine; Muscle, Smooth; Physostigmine; Piperazines; Rats; Scopolamine; Serotonin; Stomach; Uterus