The apoptosis-inducing effect of gastrin on colorectal cancer cells relates to an increased IEX-1 expression mediating NF-κB inhibition

Addressing the puzzling role of amidated gastrin(17) (G17) and the gastrin/CCKB/CCK2 receptor in colorectal carcinogenesis, we analysed potential candidate genes involved in G17-dependent NF-kappaB inhibition and apoptosis. The colorectal carcinoma cell line Colo320 overexpressing the wild-type CCK2 receptor (Colo320wt) underwent G17-induced apoptosis along with suppressed NF-kappaB activation and decreased expression of the antiapoptotic NF-kappaB target genes cIAP1 and cIAP2, whereas G17 was without effect on Colo320 cells expressing a CCK2 receptor bearing a loss of function mutation (Colo320mut). Gene microarray analysis revealed an elevated expression of the stress response gene IEX-1 in G17-treated Colo320wt but not Colo320mut cells. Quantitative real-time PCR and conventional RT-PCR confirmed this G17-dependent increase of IEX-1 expression in Colo320wt cells. If these cells were subjected to IEX-1 knockdown by small interfering RNA transfection, the apoptosis-inducing effect of G17 was abolished. Moreover, tumor necrosis factor alpha (TNFalpha)- or 5-FU-induced apoptosis that is greatly enhanced by G17 treatment in Colo320wt cells was prevented if IEX-1 expression was repressed. Under these conditions of blocked IEX-1 expression, the NF-kappaB activity remained unaffected by G17, in particular in Colo320wt cells co-treated with TNFalpha and also the suppressive effect of G17 on cIAP1 and cIAP2 expression was not observed anymore if IEX-1 expression was blocked. Conversely, IEX-1 overexpression in Colo320mut cells caused an increase of basal and TNFalpha- or 5-FU-induced apoptosis, an effect not further triggered by G17 treatment. Using a xenograft tumor model in severe combined immune deficiency mice, we could show that experimental systemic hypergastrinemia induced by the administration of omeprazole led to enhanced apoptosis as well as to a marked increase of IEX-1 expression in Colo320wt tumors, but not in Colo320mut tumors. These observations indicate that the proapoptotic effect of G17 on human colon cancer cells expressing the wild-type CCK2 receptor is mediated by IEX-1, which modulates NF-kappaB-dependent antiapoptotic protection and thereby exerts tumor-suppressive potential.

Gender specific effects of ethanol in mice, lacking CCK2 receptors

Neuropeptide cholecystokinin (CCK) has been reported to suppress ethanol intake, but there is contradictory evidence about the role of CCK(2) receptors. In the present study anxiolytic, hypolocomotor and sedative effects of acute ethanol administration, but also voluntary ethanol consumption were studied in male and female mice, lacking CCK(2) receptors (-/-). Ethanol (1.0 and 2.0 g/kg) induced a significant reduction of anxiety-related behaviours in the elevated plus-maze, but this effect was statistically significant only in female homozygous mice (-/-). In male mice, lacking CCK(2) receptors (-/-), but not in their wild-type littermates (+/+), the suppression of vertical locomotor activity was caused by ethanol at a dose 0.5 g/kg. The highest dose of ethanol (2.0 g/kg) produced statistically significant reduction of horizontal locomotor activity only in female wild-type (+/+) mice, but this effect was related to increased basal activity when compared to female mutant (-/-) mice. Duration of the loss of righting reflex was not significantly affected by genotype or gender, but blood ethanol levels at regain of righting reflex were significantly lower in female homozygous mice (-/-) compared to their wild-type (+/+) littermates, indicating increased sensitivity to the sedative effect of ethanol. Ethanol intake, but not preference, at concentration 10% was significantly increased in female mice, lacking CCK(2) receptors (-/-). The present study revealed an altered response to the acute effects of ethanol in CCK(2) receptor deficient mice (-/-). These changes are gender-specific and could be attributed to the altered activity of dopaminergic system in male mice and increased activity of GABA-ergic system in female mice as established in our previous studies.

Is the CCK2 receptor essential for normal regulation of body weight and adiposity?

Cholecystokinin (CCK) is a gastrointestinal satiety signal released from the duodenum to terminate feeding, via CCK1 receptors. CCK2 receptors are considered to be involved in anxiety. CCK2 receptor knockout mice have increased body weight and food intake. Little is known regarding the effects of CCK2 receptor deficiency on adipose distribution and hypothalamic feeding regulators such as neuropeptide Y (NPY), a powerful stimulator of feeding. Adult (10 week) CCK2 receptor knockout and wild-type mice were anaesthetized and killed by decapitation. Brain sections, organs and fat tissue were dissected. Plasma leptin, insulin and brain NPY content were measured by radioimmunoassay. Female CCK2 receptor knockout mice weighed more than control mice (22.0 +/- 0.2 vs. 19.9 +/- 0.4 g, P < 0.05), with this difference being less marked in male mice (26.4 +/- 0.4 vs. 25.6 +/- 0.6 g). Fat masses in all locations sampled were significantly smaller in CCK2 receptor knockout mice of both genders (P < 0.05), resulting in lower plasma leptin and insulin levels. NPY concentrations were significantly increased in arcuate nucleus and anterior hypothalamus in both male and female CCK2 receptor knockout mice, and total hypothalamic NPY content was increased by 7 and 9% in males and females, respectively (P < 0.05). CCK2 receptor deletion was associated with increased body weight and hypothalamic NPY content, but reduced fat masses and plasma leptin and insulin. Increased NPY might contribute to increased food intake in CCK2 receptor knockout mice. Further work needs to focus on the metabolic changes.

Cat odour exposure decreases exploratory activity and alters neuropeptide gene expression in CCK2 receptor deficient mice, but not in their wild-type littermates

An attempt was made to establish whether the anxiogenic effect of cat odour differs in female wild-type and CCK(2) receptor deficient mice, having different exploratory activity in the elevated plus-maze. The exposure of wild-type and homozygous CCK(2) receptor deficient mice to cat odour did not reveal substantial differences between the two genotypes. The number of contacts with the cat odour impregnated cloth was reduced and the frequency of stretch-attend postures was increased similarly in wild-type and homozygous mice. However, the following exposure of mice to the elevated plus-maze established differences as homozygous mice displayed increased exploratory activity in the plus-maze. The cat odour exposure significantly reduced exploratory activity only in homozygous mice. Together with the increased exploratory activity we established in homozygous mice significantly increased expression of the Oprm1 gene in the frontal cortex and mesencephalon. The exposure of mice to cat odour caused only minor changes in the gene expression of wild-type mice, whereas in homozygous animals a significantly increased expression of the Mc3r gene in the frontal cortex and temporal lobe, and the Pomc1 gene in the temporal lobe, mesencephalon and mesolimbic area was established. In conclusion, CCK(2) receptor deficient mice displayed reduced anxiety compared to their wild-type littermates in the plus-maze test. This behavioural effect seems to be related, at least partly, to an increased tone of opioid system in the brain. Moreover, homozygous mice respond to the exposure of cat odour with an increased anxiety. This effect seems to be related to the increased function of the melanocortin system in the brain structures of genetically modified mice.

Targeted invalidation of CCK2 receptor gene induces anxiolytic-like action in light-dark exploration, but not in fear conditioning test

RATIONALE

Evidence suggests that gamma-aminobutyric acid (GABA) and cholecystokinin (CCK) have opposite roles in the regulation of anxiety.

OBJECTIVES

The aim of our work was to study the behaviour of CCK(2) receptor deficient mice in light-dark exploration and fear conditioning tests. Moreover, the action of diazepam and methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM), having the opposite effect on GABA(A) receptors, was evaluated on the exploratory behaviour in these mice. Expression levels of GABA(A) receptor subunit genes were also measured.

METHODS

Light-dark exploration and fear conditioning tests were used to determine changes in anxiety of mice. The action of diazepam (0.5-2 mg/kg i.p.) and DMCM (0.25-1 mg/kg i.p.) was studied in the light-dark box. The effect of DMCM was also evaluated in the motor activity test to demonstrate that its anti-exploratory action was not related to motor suppression. Expression levels of GABA(A) receptor subunit genes were determined by means of real-time polymerase chain reaction (qRT-PCR).

RESULTS

Female mice lacking CCK(2) receptors displayed increased exploratory activity in the light-dark box compared to their wild-type (+/+) littermates. Locomotor activity in the motility boxes and the intensity of freezing did not differ in wild-type (+/+) and homozygous (-/-) mice. Treatment with diazepam (0.5 mg/kg) increased the number of transitions in wild-type (+/+) animals, whereas in homozygous (-/-) mice diazepam (0.5-2 mg/kg) reduced exploratory activity. Administration of DMCM (0.25-1 mg/kg) induced an anxiogenic-like effect in homozygous (-/-) mice, but did not change their locomotor activity. Gene expression analysis established a 1.6-fold increase in the expression of the alpha2 subunit of GABA(A) receptors in the frontal cortex of homozygous (-/-) mice.

CONCLUSION

Genetic invalidation of CCK(2) receptors induced an anxiolytic-like action in exploratory, but not in conditioned models of anxiety. The observed reduction in anxiety in homozygous (-/-) mice is probably related to an increased function of GABAergic system in the brain.

Cholecystokinin-2 (CCK2) receptor-mediated anxiety-like behaviors in rats

Cholecystokinin (CCK) is a neurotransmitter in the brain closely related to anxiety. Of the two CCK receptor subtypes, CCK(2) receptors are most implicated in the control of anxiety-related behavior. CCK(2) receptor activation causes anxiogenic effects while the blockade of this receptor has anxiolytic effects. This review focuses on the molecular mechanisms of CCK(2) receptors underlying anxiety-related behaviors of PVG hooded and Spraque-Dawley (SD) rats in two anxiety models (elevated plus-maze [EPM] and cat exposure test). PVG hooded rats showed prolonged freezing behavior in the cat exposure test while SD rats showed very low levels of freezing. A CCK(2) receptor antagonist (LY225910) attenuated freezing behavior in PVG hooded rats while a CCK(2) receptor agonist (CCK-4) increased freezing behavior in SD rats. In contrast, the two strains behaved similarly on the EPM. CCK-4 caused a pronounced anxiogenic effect in PVG hooded rats but only a slight effect in SD rats. CCK(2) antagonists also showed more pronounced anxiolytic effects in PVG hooded rats than in SD rats. CCK(2) receptor expression was greater in PVG hooded than in SD rats in the cortex and hippocampus. Genetic studies also demonstrated four differences in the DNA sequence of the CCK(2) receptor gene between the two rat strains.

Differences in ethanol ingestion between cholecystokinin-A receptor deficient and -B receptor deficient mice

AIMS

Cholecystokinin (CCK) modulates dopamine release in the nucleus accumbens through the CCK-A receptor (CCK-AR). The dopaminergic neurotransmission between the ventral tegmental area and the limbic forebrain is a critical neurobiological component of alcohol and drug self-administration. Based on the evidence of interaction between CCK and dopamine, we had found previously that the CCK-AR gene -81A/G polymorphism was associated with alcohol dependence. Since the precise mechanism underlying this association has not been elucidated, the role of CCK-AR in ethanol ingestion was examined using CCK-AR gene deficient (-/-) mice and compared with those of CCK-BR(-/-) and wild-type mice.

METHODS

The two-bottle choice protocol was conducted and the righting reflex was examined in these three genotypes. Furthermore, the protein level of dopamine 2 receptor (D2R) in the nucleus accumbens was determined by western blotting.

RESULTS

CCK-AR(-/-) mice consumed more ethanol than CCK-BR(-/-) and wild-type mice, and showed no aversion to high concentrations of ethanol solution. However, the difference was actually in the total fluid consumption and alcohol preference remained unchanged, indicating that the differences were not specific to alcohol. Behavioral sensitivity to ethanol, examined using the righting reflex, did not differ significantly between the groups. D2R expression in the nucleus accumbens was significantly lower in the CCK-BR(-/-) mice and was significantly higher in CCK-AR(-/-) mice than in wild-type mice.

CONCLUSIONS

Voluntary ingestion of ethanol differed between CCK-AR(-/-) and CCK-BR(-/-) mice. The difference might be attributable in part to the different levels of D2R expression in the nucleus accumbens.

Unique roles of G protein-coupled histamine H2 and gastrin receptors in growth and differentiation of gastric mucosa

Disruption of histamine H2 receptor and gastrin receptor had different effects growth of gastric mucosa: hypertrophy and atrophy, respectively. To clarify the roles of gastrin and histamine H2 receptors in gastric mucosa, mice deficient in both (double-null mice) were generated and analyzed. Double-null mice exhibited atrophy of gastric mucosae, marked hypergastrinemia and higher gastric pH than gastrin receptor-null mice, which were unresponsive even to carbachol. Comparison of gastric mucosae from 10-week-old wild-type, histamine H2 receptor-null, gastrin receptor-null and double-null mice revealed unique roles of these receptors in gastric mucosal homeostasis. While small parietal cells and increases in the number and mucin contents of mucous neck cells were secondary to impaired acid production, the histamine H2 receptor was responsible for chief cell maturation in terms of pepsinogen expression and type III mucin. In double-null and gastrin receptor-null mice, despite gastric mucosal atrophy, surface mucous cells were significantly increased, in contrast to gastrin-null mice. Thus, it is conceivable that gastrin-gene product(s) other than gastrin-17, in the stimulated state, may exert proliferative actions on surface mucous cells independently of the histamine H2 receptor. These findings provide evidence that different G-protein coupled-receptors affect differentiation into different cell lineages derived from common stem cells in gastric mucosa.

Deletion of the CCK2 receptor gene reduces mechanical sensitivity and abolishes the development of hyperalgesia in mononeuropathic mice

Previous studies suggest that cholecystokinin (CCK) is implicated in the modulation of pain sensitivity and the development of neuropathic pain. We used CCK(2) receptor deficient (CCK(2) (-/-)) mice and assessed their mechanical sensitivity using Von Frey filaments, as well as the development and time course of mechanical hyperalgesia in a model of neuropathic pain. We found that CCK(2) (-/-) mice displayed mechanical hyposensitivity, which was reversed to the level of wild-type animals after administration of naloxone (0.1-10 mg/kg). On the other hand, injection of L-365260 (0.01-1 mg/kg), an antagonist of CCK(2) receptors, decreased dose-dependently, mechanical sensitivity in wild-type mice. The mechanism of reduced mechanical sensitivity in CCK(2) (-/-) mice may be explained by changes in interactions between CCK and opioid systems. Indeed, CCK(2) (-/-) mice natively expressed higher levels of lumbar CCK(1), opioid delta and kappa receptors. Next, we found that CCK(2) (-/-) mice did not develop mechanical hyperalgesia in the Bennett's neuropathic pain model. Induction of neuropathy resulted in decrease of lumbar pro-opiomelanocortin (POMC) gene expression in wild-type mice, but increase of POMC expression in CCK(2) (-/-) mice. In addition, induction of neuropathy resulted in further increase of opioid delta receptor in CCK(2) (-/-) mice. Gene expression results indicate up-regulation of opioid system in CCK(2) (-/-) mice, which apparently result in decreased neuropathy score. Our study suggests that not only pain sensitivity, but also mechanical sensitivity and the development of neuropathic pain are regulated by antagonistic interactions between CCK and opioid systems.

Targeted mutation of CCK(2) receptor gene antagonises behavioural changes induced by social isolation in female, but not in male mice

Neuropeptide cholecystokinin (CCK) regulates the adaptation of rodents in the novel environment. In the present study we analysed the behavioural changes induced by the individual housing in mice, lacking CCK(2) receptors. The wild-type (+/+) and homozygous (-/-) CCK(2) receptor deficient mice of both gender were used throughout the study. The weight gain during the 21-day isolation period and changes in the locomotor activity following the social separation were measured. The elevated plus-maze and resident/intruder tests were also performed to test alterations in the emotional behaviour. Social isolation induced locomotor hyperactivity, reduced weight gain and increased aggressiveness in the wild-type (+/+) and homozygous (-/-) male mice. In the wild-type (+/+) female mice the significant reduction of exploratory activity in the plus-maze was evident. By contrast, in female mice, lacking CCK(2) receptors, the exploration of the plus-maze was not significantly affected by the individual housing. This finding demonstrates that the social isolation does not cause anxiety-like state in the CCK(2) receptor deficient mice. Moreover, the targeted invalidation of CCK(2) receptors increased in male mice the affinity of dopamine D(2) receptors in the sub-cortical structures, whereas in female mice the increased affinity of 5-hydroxytryptamine(2) (5-HT(2)) receptors in the frontal cortex was established. The increased affinity of 5-HT(2) receptors is probably the compensatory change to the lack of CCK(2) receptors in female mice and probably reflects the reduced sensitivity of these animals to the anxiogenic manipulations. In conclusion, targeted mutation of CCK(2) receptors selectively antagonised the behavioural changes induced by the individual housing in females, but not in male mice.

The role of CCK2 receptors in energy homeostasis: insights from the CCK2 receptor-deficient mouse

The present study explored the contribution of type 2 cholecystokinin (CCK) receptors in energy regulation. A total of 78 CCK2 receptor-deficient mice and 80 wild-type controls were acclimated to a 12:12 light-dark cycle at 30 +/- 1 degrees C. Using a computer-monitored biotelemetry system, circadian patterns of body temperature, food intake, and activity were monitored for 4 days. Body weight and water consumption were manually recorded during this period. Results indicate that CCK2 receptor invalidation produces elevated body temperature during both the photophase and scotophase (by 0.38 and 0.12 degrees C, respectively), increased body weight (29.3 +/- 0.2 vs. 26.8 +/- 0.2 g) and water consumption (4.1 +/- 0.1 vs. 3.2 +/- 0.1 ml), and decreased scotophase locomotor activity (WT: 7.0 +/- 0.2 vs. KO: 6.1 +/- 0.2 counts/min). These findings suggest an important role for CCK2 receptors in processes underlying energy regulation during basal and possibly pathological states.

Deletion of the CCK2 receptor gene reduces mechanical sensitivity and abolishes the development of hyperalgesia in mononeuropathic mice

Previous studies suggest that cholecystokinin (CCK) is implicated in the modulation of pain sensitivity and the development of neuropathic pain. We used CCK(2) receptor deficient (CCK(2) (-/-)) mice and assessed their mechanical sensitivity using Von Frey filaments, as well as the development and time course of mechanical hyperalgesia in a model of neuropathic pain. We found that CCK(2) (-/-) mice displayed mechanical hyposensitivity, which was reversed to the level of wild-type animals after administration of naloxone (0.1-10 mg/kg). On the other hand, injection of L-365260 (0.01-1 mg/kg), an antagonist of CCK(2) receptors, decreased dose-dependently, mechanical sensitivity in wild-type mice. The mechanism of reduced mechanical sensitivity in CCK(2) (-/-) mice may be explained by changes in interactions between CCK and opioid systems. Indeed, CCK(2) (-/-) mice natively expressed higher levels of lumbar CCK(1), opioid delta and kappa receptors. Next, we found that CCK(2) (-/-) mice did not develop mechanical hyperalgesia in the Bennett's neuropathic pain model. Induction of neuropathy resulted in decrease of lumbar pro-opiomelanocortin (POMC) gene expression in wild-type mice, but increase of POMC expression in CCK(2) (-/-) mice. In addition, induction of neuropathy resulted in further increase of opioid delta receptor in CCK(2) (-/-) mice. Gene expression results indicate up-regulation of opioid system in CCK(2) (-/-) mice, which apparently result in decreased neuropathy score. Our study suggests that not only pain sensitivity, but also mechanical sensitivity and the development of neuropathic pain are regulated by antagonistic interactions between CCK and opioid systems.

[Functional analyses of gastric mucosa using mice deficient in both histamine H2 receptor and CCKB/gastrin receptor]

Histamine H2 and cholecystokinin (CCK)-B/gastrin receptors are very important in both acid secretion and growth and differentiation of the gastric mucosa. Generations of mice deficient in each of these receptors have provided information on the structure and function of the gastric mucosa, respectively. To examine the gastric mucosa in further detail, we generated mice deficient in both receptors. This review discusses the roles of histamine H2 and CCK-B/gastrin receptors in gastric mucosa based on data from our double-null mice.

Reduced anxious behavior in mice lacking the CCK2 receptor gene

Cholecystokinin 2 (CCK2) receptors have been implicated as mediators of anxiety in standard mouse models such as exploratory behavior both in black and white test boxes and in elevated plus-mazes. We investigated the role of the CCK2 receptor in anxiety by evaluating the behavior of mice lacking the gene for this receptor in these standard anxiety models (i.e., exploratory behavior in a black and white test box and exploratory behavior in an elevated plus-maze). In the black and white test box, mice lacking the CCK2 receptor gene showed significantly increased numbers of transitions between the boxes compared to control mice. In the elevated plus-maze, mice lacking the CCK2 receptor gene displayed significantly more head dips than control mice. These results suggest that mice lacking the CCK2 receptor gene are less anxious than normal mice.

Targeted mutation of CCK2 receptor gene modifies the behavioural effects of diazepam in female mice

RATIONALE

Evidence suggests that GABA and CCK have opposite roles in the regulation of anxiety.

OBJECTIVE

The aim of the present work was to study diazepam-induced anxiolytic-like action and impairment of motor co-ordination, and the parameters of benzodiazepine receptors in mice lacking CCK2 receptors.

METHODS

The action of diazepam (0.5-3 mg/kg i.p.) was studied in the elevated plus-maze model of anxiety and rotarod test using mice lacking CCK2 receptors. The parameters of benzodiazepine receptors were analysed using [3H]-flunitrazepam binding.

RESULTS

In the plus-maze test, the exploratory activity of the homozygous (-/-) mice was significantly higher compared to their wild-type (+/+) littermates. However, the wild-type (+/+) mice displayed higher sensitivity to the anxiolytic-like action of diazepam. Even the lowest dose of diazepam (0.5 mg/kg) induced a significant increase of open arm entries in the wild-type (+/+) mice. A similar effect in the homozygous (-/-) mice was established after the administration of diazepam 1 mg/kg. The highest dose of diazepam (3 mg/kg) caused a prominent anxiolytic-like effect in the wild-type (+/+) mice, whereas in the homozygous (-/-) animals suppression of locomotor activity was evident. The performance of the homozygous (-/-) mice in the rotarod test did not differ from that of the wild-type (+/+) littermates. However, a difference between the wild-type (+/+) and homozygous (-/-) animals became evident after treatment with diazepam. Diazepam (0.5 and 3 mg/kg) induced significantly stronger impairment of motor co-ordination in the homozygous (-/-) mice compared to their wild-type (+/+) littermates. The density of benzodiazepine binding sites was increased in the cerebellum, but not in the cerebral cortex and hippocampus, of the homozygous (-/-) mice.

CONCLUSIONS

Female mice lacking CCK2 receptors are less anxious than their wild-type (+/+) littermates. The reduced anxiety in homozygous (-/-) mice probably explains why the administration of a higher dose of diazepam is necessary to induce an anxiolytic-like action in these animals. The highest dose of diazepam (3 mg/kg) induced significantly stronger suppression of locomotor activity and impairment of motor co-ordination in the homozygous (-/-) mice compared to the wild-type (+/+) littermates. The increase in the action of diazepam is probably related to the elevated density of benzodiazepine receptors in the cerebellum of homozygous (-/-) mice. The present study seems to be in favour of increased tone of the GABAergic system in mice without CCK2 receptors.