pp60c-Src Kinase mediates growth effects of the full-length precursor progastrin1-80 peptide on rat intestinal epithelial cells, in vitro

Progress in Research on Colorectal Cancer-Related Microorganisms and Metabolites

Intestinal flora is an important component in the human body, which have been reported to be involved in the occurrence and development of colorectal cancer (CRC). Indeed, changes in the intestinal flora in CRC patients compared to those in control subjects have been reported. Several bacterial species have been shown to exhibit the pro-inflammatory and pro-carcinogenic properties, which could consequently have an impact on colorectal carcinogenesis. In this review, we summarize the current knowledge on the potential links between the intestinal microbiota and CRC. We illustrated the mechanisms by which intestinal flora imbalance affects CRC, mainly focusing on inflammation, microbial metabolites, and specific bacteria species. In addition, we discuss how a diet exhibits a strong impact on microbial composition and provides risks for developing CRC. Finally, we describe the potential future directions that are based on intestinal microbiota manipulation for CRC diagnosis and treatment.

The G-protein coupled receptor 56, expressed in colonic stem and cancer cells, binds progastrin to promote proliferation and carcinogenesis

Overexpression of human progastrin increases colonic mucosal proliferation and colorectal cancer progression in mice. The G-protein coupled receptor 56 (GPR56) is known to regulate cell adhesion, migration, proliferation and stem cell biology, but its expression in the gut has not been studied. We hypothesized that the promotion of colorectal cancer by progastrin may be mediated in part through GPR56. Here, we found that GPR56 expresses in rare colonic crypt cells that lineage trace colonic glands consistent with GPR56 marking long-lived colonic stem-progenitor cells. GPR56 was upregulated in transgenic mice overexpressing human progastrin. While recombinant human progastrin promoted the growth and survival of wild-type colonic organoids in vitro, colonic organoids cultured from GPR56^−/− mice were resistant to progastrin. We found that progastrin directly bound to, and increased the proliferation of, GPR56-expressing colon cancer cells in vitro, and proliferation was increased in cells that expressed both GPR56 and the cholecystokinin-2 receptor (CCK2R). In vivo, deletion of GPR56 in the mouse germline abrogated progastrin-dependent colonic mucosal proliferation and increased apoptosis. Loss of GPR56 also inhibited progastrin-dependent colonic crypt fission and colorectal carcinogenesis in the azoxymethane (AOM) mouse model of colorectal cancer. Overall, we found that progastrin binds to GPR56 expressing colonic stem cells, which in turn promotes their expansion, and that this GPR56-dependent pathway is an important driver and potential new target in colorectal carcinogenesis.

Targeting progastrin enhances radiosensitization of colorectal cancer cells

A high percentage of advanced rectal cancers are resistant to radiation. Therefore, increasing the efficacy of radiotherapy by targeting factors involved in radioresistance seems to be an attractive strategy. Here we demonstrated that the pro-hormone progastrin (PG), known to be over-expressed in CRC, and recognized as a pro-oncogenic factor, is a radioresistance factor that can be targeted to sensitize resistant rectal cancers to radiations. First, we observed an increase in PG mRNA expression under irradiation. Our results also demonstrated that down-regulating PG mRNA expression using a shRNA strategy, significantly increases the sensitivity to irradiation (IR) in a clonogenic assay of different colorectal cancer cell lines. We also showed that the combination of PG gene down-regulation and IR strongly inhibits tumours progression in vivo. Then, we demonstrated that targeting PG gene radiosensitizes cancer cells by increasing radio-induced apoptosis shown by an increase in annexin V positive cells, caspases activation and PARP cleavage. We also observed the up-regulation of the pro-apoptotic pathway, JNK and the induction of the expression of pro-apoptotic factors such as BIM. In addition, we demonstrated in this study that inhibition of PG gene expression enhances radiation-induced DNA damage. Our data also suggest that, in addition to increase radio-induced apoptosis, targeting PG gene also leads to the inhibition of the survival pathways, AKT and ERK induced by IR. Taken together, our results highlight the role of PG in radioresistance and provide a preclinical proof of concept that PG represents an attractive target for sensitizing resistant rectal tumours to irradiation. .

Activation of pro-oncogenic pathways in colorectal hyperplastic polyps

Background

In contrast to sessile serrated adenomas and traditional serrated adenomas which are associated with a significant cancer risk, the role of hyperplastic polyps (HP) in colorectal carcinogenesis as well as the molecular mechanisms underlying their development remain controversial and still need to be clarified. Several reports suggest that a subset of HP may represent precursor lesions of some colorectal cancers. However, biomarkers are needed to identify the subset of HP that may have a malignant potential. The hormone precursor, progastrin (PG) has been involved in colon carcinogenesis and is known to activate pro-oncogenic pathways such as the ERK or the STAT3 pathway. We therefore analyzed PG expression and the activation of these signaling factors in HP.

Methods

We retrospectively analyzed PG expression as well as the phosphorylation of ERK and STAT3 by immunohistochemistry in HP from 48 patients.

Results

Mean percentages of epithelial cells positive for PG or phospho-ERK were respectively, 31% and 33% in HP and were significantly higher in these lesions compared to normal colon (3%, p = 0.0021 and 7%, p = 0.0008, respectively). We found a significant correlation between PG and phospho-ERK expression in HP with ERK activation significantly stronger in lesions with high progastrin expression (p = 0.015). In contrast, STAT3 was not significantly activated in HP compared to normal colon and we did not observe a significant correlation with PG expression.

Conclusions

HP overexpressing PG that have the highest activation of the ERK pathway might reflect less latent lesions that might have a malignant potential.

Progastrin Peptides Increase the Risk of Developing Colonic Tumors: Impact on Colonic Stem Cells

Pre-neoplastic lesions (ACF, aberrant-crypt-foci; Hp, hyperplastic/dysplastic polyps) are believed to be precursors of sporadic colorectal-tumors (Ad, adenomas; AdCA, adenocarcinomas). ACF/Hp likely originate due to abnormal growth of colonic-crypts in response to aberrant queues in the microenvironment of colonic-crypts. Thus identifying factors which regulate homeostatic vs aberrant proliferation/apoptosis of colonocytes, especially stem/progenitor cells, may lead to effective preventative/treatment strategies. Based on this philosophy, role of growth-factors/peptide-hormones, potentially available in the circulation/microenvironment of colonic-crypts is being examined extensively. Since the time gastrins were discovered as trophic (growth) factors for gastrointestinal-cells, the effect of gastrins on the growth of normal/cancer cells has been investigated, leading to many discoveries. Seminal discoveries made in the area of gastrins and colon-cancer, as it relates to molecular pathways associated with formation of colonic tumors will be reviewed, and possible impact on diagnostic/preventative/treatment strategies will be discussed.

Elevated risk of recurrent colorectal neoplasia with Helicobacter pylori-associated chronic atrophic gastritis: A follow-up study of patients with endoscopically resected colorectal neoplasia

In a previous population-based case-control study, we demonstrated an elevated risk of colorectal neoplasia with Helicobacter pylori (H. pylori) infection. The present study investigated the effects of H. pylori-associated chronic gastritis on the development of colorectal neoplasia by analyzing the recurrence of colorectal neoplasia subsequent to endoscopic resection. Ninety-nine patients who had undergone endoscopic resection of colorectal neoplasia were monitored under colonoscopy, and the recurrence of colorectal neoplasia was prospectively investigated. The stage of H. pylori-associated chronic gastritis in each subject was evaluated using a combination of two serum tests: H. pylori antibody and pepsinogen. In the present cohort, colorectal neoplasia recurred at a rate of 15,296/100,000 person-years during the study period. After adjusting for the confounding factors, chronic atrophic gastritis (CAG) was identified as an independent risk factor [adjusted hazard ratio (HR), 2.72; 95% confidence interval, 1.33-5.57], while H. pylori-infected non-atrophic gastritis was not identified as an independent risk factor for recurrent colorectal neoplasia. Colorectal neoplasia recurred earlier and was significantly more frequent in patients with CAG (22,573/100,000 person-years) compared to patients without CAG (11,089/100,000 person-years; P=0.029, log-rank test). Patients with more extensive CAG showed a higher risk of recurrence. These results demonstrated a significant elevation of the risk of recurrent colorectal neoplasia with the establishment and progression of CAG, indicating the involvement of H. pylori infection in the development of colorectal neoplasia. The two serum tests were useful clinical markers for noninvasively evaluating the risk of each individual for recurrent colorectal neoplasia subsequent to endoscopic resection.

P53 gene mutation increases progastrin dependent colonic proliferation and colon cancer formation in mice

Transgenic mice overexpressing human progastrin (hGAS) show colonic crypt hyper-proliferation and elevated susceptibility to colon carcinogenesis. We aimed to investigate effects of p53 mutation on colon carcinogenesis in hGAS mice. We show that introducing a p53 gene mutation further increases progastrin dependent BrdU labeling and results in markedly elevated number of aberrant crypt foci (ACF) and colonic tumors. We demonstrate that hGAS/Lgr5-GFP mice have higher number of Lgr5+ colonic stem cells per crypt when compared to Lgr5-GFP mice indicating that progastrin changes crypt biology through increased stem cell numbers and additional p53 mutation leads to more aggressive phenotype in this murine colon cancer model.

Clathrin mediates endocytosis of progastrin and activates MAPKs: role of cell surface annexin A2

Cell-surface-associated annexin A2 (CS-ANXA2) is a nonconventional "receptor" for progastrin; expression levels of both are elevated in colon cancers, and downregulation of either reduces tumorigenic potential of cells. We recently reported internalization of progastrin in target cells. Here, mechanisms mediating internalization of progastrin were examined. Initially, we confirmed that cell-surface ANXA2 mediates binding and internalization of progastrin in intestinal cells. Progastrin, covalently linked to sepharose beads, failed to activate p38MAPK/ERKs, suggesting internalization of progastrin was required for eliciting biological effects; importantly annexin A2 expression and availability of CS-ANXA2 were required for internalization of progastrin. Clathrin expression and formation of clathrin-coated pits were critically required for endocytotic internalization of progastrin; in the absence of clathrin, progastrin failed to activate p38MAPK/ERKs. Downregulation of caveolin had no effect on binding or internalization of progastrin. We therefore demonstrate for the first time that progastrin binds CS-ANXA2 and is rapidly internalized via clathrin-mediated endocytotic pathway, resulting in activation of MAPKinases. Targeting clathrin-mediated endocytosis of progastrin may thus inhibit previously reported co-carcinogenic/tumorigenic effects of progastrin on intestinal cells.

A new biomarker that predicts colonic neoplasia outcome in patients with hyperplastic colonic polyps

The most frequently occurring lesions in the colon are the hyperplastic polyps. Hyperplastic polyps have long been considered as lesions with no malignant potential and colonoscopy for these patients is not recommended. However, recent works suggest that hyperplastic polyps may represent precursor lesions of some sporadic colorectal cancers. Until now, no biomarker allows to identify the subset of hyperplastic polyps that may have a malignant potential. Because the hormone precursor progastrin has been involved in colon carcinogenesis, we investigated whether its expression in hyperplastic polyps predicts the occurrence of colonic neoplasm after resection of hyperplastic polyps. We retrospectively analyzed progastrin expression in hyperplastic polyps from 74 patients without history of colorectal pathology. In our study, 41% of patients presenting an initial hyperplastic polyp subsequently developed adenomatous polyps, recognized as precursor lesions for colorectal adenocarcinomas. Progastrin was overexpressed in the hyperplastic polyps in 40% of the patients. We showed a significant association between progastrin overexpression and shortened neoplasm-free survival (P = 0.001). Patients with high overexpression of progastrin had a 5-year neoplasm-free survival rate of 38% as compared with 100% for the patients with low progastrin expression. In addition, we established a predictive test on the basis of progastrin staining and patients' age that predicts occurrence of neoplasm after developing a first hyperplastic polyp with a sensitivity of 100% [95% confidence interval (CI), 79%-100%] and a specificity of 74% (51%-90%). We show that progastrin expression evaluation in hyperplastic polyps is an efficient prognostic tool to determine patients with higher risk of metachronous neoplasms who could benefit from an adapted follow-up.

Inactivating cholecystokinin-2 receptor inhibits progastrin-dependent colonic crypt fission, proliferation, and colorectal cancer in mice

Hyperproliferation of the colonic epithelium, leading to expansion of colonic crypt progenitors, is a recognized risk factor for colorectal cancer. Overexpression of progastrin, a nonamidated and incompletely processed product of the gastrin gene, has been shown to induce colonic hyperproliferation and promote colorectal cancer in mice, but the mechanism of pathogenesis has not been defined. Cholecystokinin-2 receptor (CCK2R) is the primary receptor for cholecystokinin (CCK) and amidated gastrin. Here, we show that Cck2r was expressed in murine colonic crypts and upregulated in the transgenic mice that overexpress human progastrin. Murine deletion of Cck2r abrogated progastrin-dependent increases in colonic proliferation, mucosal thickness, and beta-catenin and CD44 expression in the colon tumor. In addition, either deletion or antagonism of Cck2r resulted in the inhibition of progastrin-dependent increases in progenitors expressing doublecortin and CaM kinase-like-1 (DCAMKL1), stem cells expressing leucine rich repeat-containing G protein-coupled receptor 5 (LgR5), and colonic crypt fission. Furthermore, in the azoxymethane mouse model of colorectal carcinogenesis, Cck2r deletion in human progastrin-overexpressing mice resulted in markedly decreased aberrant crypt foci formation and substantially reduced tumor size and multiplicity. Taken together, these observations indicate that progastrin induces proliferative effects, primarily in colonic progenitor cells, through a CCK2R-dependent pathway. Moreover, our data suggest that CCK2R may be a potential target in the treatment or prevention of colorectal cancer.

Flow cytometric detection of progastrin interaction with gastrointestinal cells

The unprocessed gastrin precursor, progastrin (PG), is often overexpressed in colon cancer and other malignancies where it appears to stimulate colonic growth. Overexpression of progastrin also stimulates proliferation of normal colonic mucosa, but the receptors mediating these effects have not been identified. Here we report the development of a non-radioactive assay for assessment of PG binding to normal and transformed cells. Progastrin was labeled using biotinylation, and binding of biotinylated PG to cells was assessed using flow cytometry. Using this approach, we show strong and specific binding of PG to some cell lines (IEC-6, IEC-18, HT-29, COLO320) and minimal binding to others (HeLa, DC2.4, Jurkat). We also found PG binding to several non-gut epithelial lines, such as CHO-K1, COS-6 and HEK293 cells. The specificity of binding was confirmed by competition with cold, unlabeled PG but not with glycine-extended gastrin or amidated gastrin-17. Binding was not influenced by the presence of the classical CCK-2 receptor, but was partially dependent on the charged glycosaminoglycans (GAG). The analysis of primary colonic tissues isolated from wild type C57BL/6 mouse, revealed a small epithelial subpopulation of non-hematopoietic (CD45-negative) cells that strongly interacted with PG. Surprisingly, this population was greatly expanded in gastrin knockout mice. This non-radioactive, FACS-based assay should prove useful for further characterization of cells expressing the progastrin receptor.

Antiapoptotic effects of progastrin on pancreatic cancer cells are mediated by sustained activation of nuclear factor-{kappa}B

Progastrin (PG) exerts proliferative and antiapoptotic effects on intestinal epithelial and colon cancer cells via Annexin II (ANX-II). In here, we show that ANX-II similarly mediates proliferative and antiapoptotic effects of PG on a pancreatic cancer cell line, AR42J. The role of several signaling molecules was examined in delineating the biological activity of PG. PG (0.1-1.0 nmol/L) caused a significant increase (2- to 5-fold) in the phosphorylation of phosphatidylinositol 3-kinase (PI3K), Akt (Thr(308)), p38 mitogen-activated protein kinase (MAPK; Thr(180)/Tyr(182)), extracellular signal-regulated kinases (ERK; Thr(202)/Tyr(204)), IkappaB kinase alpha/beta (IKKalpha/beta; Ser(176)/(180)), IkappaBalpha (Ser(32)), and p65 nuclear factor-kappaB (NF-kappaB; Ser(536)). Inhibition of p44/42 ERKs (PD98059), p38 MAPK (SB203580), Akt, and PI3K (LY294002), individually or combined, partially reversed antiapoptotic effects of PG. The kinetics of phosphorylation of IKKalpha/beta in response to PG matched the kinetics of phosphorylation and degradation of IkappaBalpha and correlated with phosphorylation, nuclear translocation, and activation of p65 NF-kappaB. NF-kappaB essential modulator-binding domain peptide (an inhibitor of IKKalpha/beta) effectively blocked the activity of p65 NF-kappaB in response to PG. Activation of p65 NF-kappaB, in response to PG, was 70% to 80% dependent on phosphorylation of MAPK/ERK and PI3K/Akt molecules. Down-regulation of p65 NF-kappaB by specific small interfering RNA resulted in the loss of antiapoptotic effects of PG on AR42J cells. These studies show for the first time that the canonical pathway of activation of p65 NF-kappaB mediates antiapoptotic effects of PG. Therefore, targeting PG and/or p65 NF-kappaB may be useful for treating cancers, which are dependent on autocrine or circulating PGs for their growth.

Role of Annexin-II in GI cancers: interaction with gastrins/progastrins

The role of the gastrin peptide hormones (G17, G34) and their precursors (progastrins, PG; gly-extended gastrin, G-gly), in gastrointestinal (GI) cancers has been extensively reviewed in recent years [W. Rengifo-Cam, P. Singh, Role of progastrins and gastrins and their receptors in GI and pancreatic cancers: targets for treatment, Curr. Pharm. Des. 10 (19) (2004) 2345-2358; M. Dufresne, C. Seva, D. Fourmy, Cholecystokinin and gastrin receptors, Physiol. Rev. 86 (3) (2006) 805-847; A. Ferrand, T.C. Wang, Gastrin and cancer: a review, Cancer Lett. 238 (1) (2006) 15-29]. A possible important role of progastrin peptides in colon carcinogenesis has become evident from experiments with transgenic mouse models [W. Rengifo-Cam, P. Singh, (2004); A. Ferrand, T.C. Wang, (2006)]. It is now known that growth stimulatory and co-carcinogenic effects of gastrin/PG peptides are mediated by both proliferative and anti-apoptotic effects of the peptides on target cells [H. Wu, G.N. Rao, B. Dai, P. Singh, Autocrine gastrins in colon cancer cells Up-regulate cytochrome c oxidase Vb and down-regulate efflux of cytochrome c and activation of caspase-3, J. Biol. Chem. 275 (42) (2000) 32491-32498; H. Wu, A. Owlia, P. Singh, Precursor peptide progastrin(1-80) reduces apoptosis of intestinal epithelial cells and upregulates cytochrome c oxidase Vb levels and synthesis of ATP, Am. J. Physiol. Gastrointest. Liver Physiol. 285 (6) (2003) G1097-G1110]. Several receptor subtypes have been described that mediate growth effects of gastrin peptides [W. Rengifo-Cam, P. Singh (2004); M. Dufresne, C. Seva, D. Fourmy, (2006)]. Recently, we identified Annexin II as a high affinity binding protein for gastrin/PG peptides [P. Singh, H. Wu, C. Clark, A. Owlia, Annexin II binds progastrin and gastrin-like peptides, and mediates growth factor effects of autocrine and exogenous gastrins on colon cancer and intestinal epithelial cells, Oncogene (2006), doi:10.1038/sj.onc.1209798]. Importantly, the expression of Annexin II was required for mediating growth stimulatory effects of gastrin and PG peptides on intestinal epithelial and colon cancer cells [P. Singh, H. Wu, C. Clark, A. Owlia, Annexin II binds progastrin and gastrin-like peptides, and mediates growth factor effects of autocrine and exogenous gastrins on colon cancer and intestinal epithelial cells, Oncogene (2006), doi:10.1038/sj.onc.1209798], suggesting that Annexin-II may represent the elusive novel receptor for gastrin/PG peptides. The importance of this finding in relation to the structure and function of Annexin-II, especially in GI cancers, is described below. Since this surprising finding represents a new front in our understanding of the mechanisms involved in mediating growth effects of gastrin/PG peptides in GI cancers, our current understanding of the role of Annexin-II in proliferation and metastasis of cancer cells is additionally reviewed.

Annexin II binds progastrin and gastrin-like peptides, and mediates growth factor effects of autocrine and exogenous gastrins on colon cancer and intestinal epithelial cells

We and others have reported the presence of novel progastrin (PG)/gastrin receptors on normal and cancerous intestinal cells. We had earlier reported the presence of 33-36 kDa gastrin-binding proteins on cellular membranes of colon cancer cells. The goal of the current study was to identify the protein(s) in the 33-36 kDa band, and analyse its functional significance. A carbodiimide crosslinker was used for crosslinking radio-labeled gastrins to membrane proteins from gastrin/PG responsive cell lines. Native membrane proteins, crosslinked to the ligand, were solubulized and enriched by >1000-fold, and analysed by surface-enhanced laser desorption/ionization-time of flight-mass spectrometry. The peptide masses were researched against the NCBInr database using the ProFound search engine. Annexin II (ANX II) was identified, and confirmed by matrix-assisted laser desorption/ionization-time of flight-mass spectrometry. As HCT-116 cells express autocrine PG, the in situ association of PG with ANX II was demonstrated in pulldown assays. Direct binding of PG with ANX II was confirmed in an in vitro binding assay. In order to confirm a functional importance of these observations, sense and anti-sense (AS) ANX II RNA-expressing clones of intestinal epithelial (IEC-18) and human colon cancer (HCT-116) cell lines were generated. AS clones demonstrated a significant loss in the growth response to exogenous (IEC-18) and autocrine (HCT-116) PG. We have thus discovered that membrane-associated ANX II binds PG/gastrins, and partially mediates growth factor effects of the peptides.

The gastrin gene promoter is regulated by p73 isoforms in tumor cells

p73, a new p53 family member, is a transcription factor that is increasingly recognized in cancer research as an important player in tumorigenesis as well as in chemotherapeutic drug sensitivity. Despite the substantial structural and functional similarities to p53, accumulating evidence suggests that p53 and p73 may differently regulate their transcriptional targets. In this study, we have investigated the role of p73 in regulation of the gastrin gene promoter. Gastrin is a peptide hormone and an important factor in determining the progression of a number of human malignancies. Our results show that p73 can bind to the gastrin promoter. This leads to transcriptional upregulation of gastrin mRNA. We also found that the levels of gastrin and p73 transcripts correlate in primary gastric tumors. Taken together, our results demonstrate a novel mechanism for regulation of gastrin gene transcription and support a concept that p53 and p73 may have different biological roles in tumors.

Gastrin and cancer: a review

In 1905, a Cambridge physiologist, John Sydney Edkins, initially identified a hormone responsible of gastric acid secretion, which he called gastric secretin, or gastrin. While gastrin's role in acid secretion is now well defined, more recent studies have implicated the various isoforms of gastrin in cancer. Important advances in the last decade have included the recognition of biological activity for processing intermediates such as progastrin and the glycine-extended gastrin. Here, we give an overview of the roles of these peptides in cancer, highlighted by molecular, cellular and integrated studies on animal models for progastrin-derived peptides and their receptors.

Signaling pathways associated with colonic mucosa hyperproliferation in mice overexpressing gastrin precursors

MTI/G-Gly mice and hGAS mice, overexpressing glycine-extended gastrin (G-Gly) and progastrin, respectively, display colonic mucosa hyperplasia, hyperproliferation, and an increased susceptibility to intestinal neoplasia. Here, we have used these transgenic mice to analyze in vivo the modulation of intracellular signaling pathways that may be responsible for the proliferative effects of gastrin precursors. The expression, activation, and localization of signaling and cell-to-cell adhesion molecules were studied using immunofluorescence and Western blot techniques on colonic tissues derived from MTI/G-Gly, hGAS, or wild-type FVB/N mice. These analyses revealed an up-regulation of Src tyrosine kinase and related signaling pathways [phosphatidyl inositol 3'-kinase (PI3K)/Akt, Janus-activated kinase (JAK) 2, signal transducer and activator of transcription (STAT) 3, and extracellular-signal regulated kinases (ERK)] in both MTI/G-Gly and hGAS mice compared with the wild-type control animals as well as an overexpression of transforming growth factor-alpha (TGF-alpha). In contrast, overexpression of the gastrin precursors did not affect the activation status of STAT1 nor the expression and the distribution of adhesion proteins (focal adhesion kinase, cadherins, and catenins). We report for the first time that the transition from a normal colonic epithelium to a hyperproliferative epithelium in MTI/G-Gly and hGAS mice may be a consequence of the up-regulation of Src, PI3K/Akt, JAK2, STAT3, ERKs, and TGF-alpha. Deregulation of cell adhesion, a late event in tumor progression, does not occur in these transgenic models.

Two essential but distinct functions of the mammalian abasic endonuclease

The mammalian abasic endonuclease, APE1, has two distinct roles in the repair of oxidative DNA damage and in gene regulation. Here we show that both functions are essential for cell survival. Deletion of the APE1 gene causes embryonic lethality in mice, and no nullizygous embryo fibroblasts have been isolated. We have now established nullizygous embryo fibroblast lines from APE1(-/-) mouse embryos that are transgenic with the "floxed" human APE1 (hAPE1) gene. Removal of hAPE1 by Cre expression through nuclear microinjection elicited apoptosis in these cells within 24 h, which was blocked by coinjection of the wild-type hAPE1 gene. In contrast, mutant hAPE1 alleles, lacking either the DNA repair or acetylation-mediated gene regulatory function, could not prevent apoptosis, although the combination of these two mutants complemented APE deficiency induced by Cre. These results indicate that distinct and separable functions of APE1 are both essential for mammalian cells even in vitro and provide the evidence that mammalian cells, unlike yeast or Escherichia coli, absolutely require APE for survival, presumably to protect against spontaneous oxidative DNA damage.

Gastrin: old hormone, new functions

It is exactly a century since the gastric hormone gastrin was first described as a blood-borne regulator of gastric acid secretion. The identities of the main active forms of the hormone (the "classical gastrins") and their cellular and molecular sites of action in regulating acid secretion have all attracted sustained attention. However, recent work on peptides derived from the gastrin precursor that do not stimulate acid secretion ("non-classical gastrins"), together with studies on mice over-expressing the gene, or in which the gastrin gene has been deleted, suggest hitherto unsuspected roles in regulating cell proliferation, migration, and differentiation. Moreover, microarray and proteomic studies have identified previously unsuspected target genes of the classical gastrins. Some of the newer actions have implications for our understanding of the progression to cancer in oesophagus, stomach, pancreas and colon, all of which have recently been linked in one way or another to dysfunctional signalling involving products of the gastrin gene. The present review focuses on recent progress in understanding the biology of both classical and non-classical gastrins.

Transfection with 4-hydroxynonenal-metabolizing glutathione S-transferase isozymes leads to phenotypic transformation and immortalization of adherent cells

4-Hydroxy-2-trans-nonenal (4-HNE), one of the major end products of lipid peroxidation, has been shown to induce apoptosis in a variety of cell lines. It appears to modulate signaling processes in more than one way because it has been suggested to have a role in signaling for differentiation and proliferation. We show for the first time that incorporation of 4-HNE-metabolizing glutathione S-transferase (GST) isozyme, hGSTA4-4, into adherent cell lines HLE B-3 and CCL-75, by either cDNA transfection or microinjection of active enzyme, leads to their transformation. The dramatic phenotypic changes due to the incorporation of hGSTA4-4 include rounding of cells and anchorage-independent rapid proliferation of immortalized, rounded, and smaller cells. Incorporation of the inactive mutant of hGSTA4-4 (Y212F) in cells by either microinjection or transfection does not cause transformation, suggesting that the activity of hGSTA4-4 toward 4-HNE is required for transformation. This is further confirmed by the fact that mouse and Drosophila GST isozymes (mGSTA4-4 and DmGSTD1-1), which have high activity toward 4-HNE and subsequent depletion of 4-HNE, cause transformation whereas human GST isozymes hGSTP1-1 and hGSTA1-1, with minimal activity toward 4-HNE, do not cause transformation. In cells overexpressing active hGSTA4-4, expression of transforming growth factor beta1, cyclin-dependent kinase 2, protein kinase C betaII and extracellular signal regulated kinase is upregulated, whereas expression of p53 is downregulated. These studies suggest that alterations in 4-HNE homeostasis can profoundly affect cell-cycle signaling events.

Glycine-extended gastrin promotes the growth of lung cancer

The less processed forms of gastrin have recently been shown to act as trophic factors for both normal and malignant colonic cells. Although incompletely processed forms of gastrin such as glycine-extended gastrin and progastrin are also expressed in human lung cancers, the clinical significance of this expression has not been addressed. Consequently, we investigated the effects of overexpression of glycine-extended gastrin in a mouse strain that is prone to developing lung cancer and also examined the expression of incompletely processed gastrins in primary human lung cancers. We found that transgenic overexpression of glycine-extended gastrin in FVB/N mice resulted in a significant increase in the prevalence and growth of bronchoalveolar carcinoma. In addition, a substantial subset of human lung cancers was found to express progastrin and/or glycine-extended gastrin. Overexpression of glycine-extended gastrin by human lung cancers was associated with a significantly decreased survival. Taken together, these results suggest that glycine-extended gastrin may play a role in the growth and progression of some human lung cancers.

Precursor peptide progastrin(1-80) reduces apoptosis of intestinal epithelial cells and upregulates cytochrome c oxidase Vb levels and synthesis of ATP

We recently reported that downregulation of gastrin gene expression in colon cancer cells significantly suppresses relative levels of mitochondrial cytochrome c (cyt c) oxidase Vb (Cox Vb) RNA and protein. These unexpected findings suggested the possibility that gastrin gene products [mainly progastrin (PG)] may be directly or indirectly mediating the observed effects in colon cancer cells. Because colon cancer cells do not respond to exogenous PG, we examined the possibility of whether PG regulates Cox Vb expression in gastrin-responsive intestinal epithelial cells (IECs) in vitro. Levels of Cox Vb RNA and protein were significantly increased in a dose-dependent manner in response to PG. Mitochondrial synthesis of ATP was also increased by approximately three- to fivefold in response to optimal concentrations (0.1-1.0 nm) of PG. Possible antiapoptotic effects of PG were additionally examined, because activation of caspases 9 and 3 had been noted in colon cancer cells downregulated for gastrin gene expression. We measured a significant loss in the levels of cyt c in the cytosol of PG-treated vs. control IEC cells, which correlated with a significant loss in the activation of caspases 9 and 3, resulting in a significant loss in DNA fragmentation on PG treatment of the cells. Our results thus suggest the novel possibility that the precursor PG peptide exerts direct antiapoptotic effects on IECs, which may contribute to the observed growth effects of PG on these cells. Additionally, Cox Vb gene appears to be an important intracellular target of PG, resulting in an increase in ATP levels, which may also contribute to the observed increase in the growth of target cells in response to PG.