Genetic status and expression of the cyclin-dependent kinase inhibitors in human gastric carcinoma cell lines

Infection with a hypervirulent strain of Helicobacter pylori primes gastric cells toward intestinal transdifferentiation

BACKGROUND

Intestinal metaplasia, gastric-to-intestinal transdifferentiation, occurs as a result of the misexpression of certain regulatory factors, leading to genetic reprogramming. Here, we have evaluated the H. pylori-induced expression patterns of these candidate genes.

METHODS

The expression levels of 1) tissue-specific transcription factors (RUNX3, KLF5, SOX2, SALL4, CDX1 and CDX2), 2) stemness factors (TNFRSF19, LGR5, VIL1) and 3) tissue-specific mucins (MUC5AC, MUC2) were evaluated by quantitative real-time PCR in gastric primary cells (GPCs), in parallel with two gastric cancer (MKN45 and AGS) cell lines, up to 96h following H. pylori infection.

RESULTS

Following H. pylori infection of GPCs, RUNX3 declined at 24h post infection (-6.2 ± 0.3) and remained downregulated for up to 96h. Subsequently, overexpression of self-renewal and pluripotency transcription factors, KLF5 (3.6 ± 0.2), SOX2 (7.6 ± 0.5) and SALL4 (4.3 ± 0.2) occurred. The expression of TNFRSF19 and LGR5, demonstrated opposing trends, with an early rise of the former (4.5 ± 0.3) at 8h, and a simultaneous fall of the latter (-1.8 ± 0.5). This trend was reversed at 96h, with the decline in TNFRSF19 (-5.5 ± 0.2), and escalation of LGR5 (2.6 ± 0.2) and VIL1 (1.8 ± 0.3). Ultimately, CDX1 and CDX2 were upregulated by 1.9 and 4.7-fold, respectively. The above scenario was, variably observed in MKN45 and AGS cells.

CONCLUSION

Our data suggests an interdependent gene regulatory network, induced by H. pylori infection. This interaction begins with the downregulation of RUNX3, upregulation of self-renewal and pluripotency transcription factors, KLF5, SOX2 and SALL4, leading to the downregulation of TNFRSF19, upregulation of LGR5 and aberrant expression of intestine-specific transcription factors, potentially facilitating the process of gastric-to-intestinal transdifferentiation.

Tumor-suppressing potential of stingless bee propolis in in vitro and in vivo models of differentiated-type gastric adenocarcinoma

The protective property of propolis across a wide spectrum of diseases has long been realized, yet the anti-tumor efficacy of this bioactive substance from Philippine stingless bees has remained poorly understood. Here, we showed the tumor-suppressing potential of crude ethanolic extract of Philippine stingless bee propolis (EEP) in in vitro models of gastric cancer highlighting the first indication of remarkable subtype specificity towards differentiated-type human gastric cancer cell lines but not the diffuse-type. Mechanistically, this involved the profound modulation of several cell cycle related gene transcripts, which correlated with the prominent cell cycle arrest at the G0/G1 phase. To reinforce our data, a unique differentiated-type gastric cancer model, A4gnt KO mice, together with age-matched 60 week-old C57BL/6 J mice were randomly assigned to treatment groups receiving distilled water or EEP for 30 consecutive days. EEP treatment induced significant regression of gross and histological lesions of gastric pyloric tumors that consistently corresponded with specific transcriptional regulation of cell cycle components. Also, the considerable p21 protein expression coupled with a marked reduction in rapidly dividing BrdU-labeled S-phase cells unequivocally supported our observation. Altogether, these findings support the role of Philippine stingless bee propolis as a promising adjunct treatment option in differentiated-type gastric cancer.

The significance of scirrhous gastric cancer cell lines: the molecular characterization using cell lines and mouse models

Scirrhous gastric cancer (SGC) exhibits aggressiveness of the rapid infiltrating tumor cells with abundant fibroblasts. Experimental studies using SGC cell lines have obtained useful information about this cancer. Our literature search divulged a total of 18 SGC cell lines; two cell lines were established from primary SGC and the other lines were established from a metastatic lesion of SGC. Fibroblast growth factor receptor 2 (FGFR2) and transforming growth factor-beta receptor (TβR) are linked to the rapid development of SGC. Cross-talk between the cancer cells and cancer-associated fibroblasts (CAFs) has been shown to contribute to the progression of SGC. Chemokine (C-X-C motif) receptor 1 (CXCR1) from SGC cells might be associated with the abundant CAFs in cancer microenvironments. The in vivo models established using SGC cell lines are expected to serve as a useful tool for the development of drugs such as FGFR2 inhibitors, TβR inhibitors, and CXCR1 inhibitors, which might be promising as SGC treatments. However, the number of available SGC cell lines is insufficient for the clarification of the entire biologic behavior of SGC. Since the mechanisms responsible for the characteristic aggressiveness of SGC are not fully elucidated, the establishment of new SGC cell lines could help clarify the biological behavior of SGC and contribute to its treatment.

Astaxanthin Inhibits Proliferation of Human Gastric Cancer Cell Lines by Interrupting Cell Cycle Progression

Background/Aims

Astaxanthin is a carotenoid pigment that has antioxidant, antitumoral, and anti-inflammatory properties. In this in vitro study, we investigated the mechanism of anticancer effects of astaxanthin in gastric carcinoma cell lines.

Methods

The human gastric adenocarcinoma cell lines AGS, KATO-III, MKN-45, and SNU-1 were treated with various concentrations of astaxanthin. A cell viability test, cell cycle analysis, and immunoblotting were performed.

Results

The viability of each cancer cell line was suppressed by astaxanthin in a dose-dependent manner with significantly decreased proliferation in KATO-III and SNU-1 cells. Astaxanthin increased the number of cells in the G0/G1 phase but reduced the proportion of S phase KATO-III and SNU-1 cells. Phosphorylated extracellular signal-regulated kinase (ERK) was decreased in an inverse dose-dependent correlation with astaxanthin concentration, and the expression of p27^kip-1 increased the KATO-III and SNU-1 cell lines in an astaxanthin dose-dependent manner.

Conclusions

Astaxanthin inhibits proliferation by interrupting cell cycle progression in KATO-III and SNU-1 gastric cancer cells. This may be caused by the inhibition of the phosphorylation of ERK and the enhanced expression of p27^kip-1.

A synergic inhibitory-effect of combination with selective cyclooxygenase-2 inhibitor and S-1 on the peritoneal metastasis for scirrhous gastric cancer cells

An inhibitory-effect of a selective cyclooxygenase-2 (COX-2) inhibitor on peritoneal metastasis of scirrhous gastric carcinoma was investigated in vivo. Peritoneal metastasis had developed after intraperitoneal inoculation of scirrhous gastric cancer cells, OCUM-2MD3, in nude mice. COX-2 inhibitor and/or S-1 were administered orally in nude mice with peritoneal metastasis. Oral administration of COX-2 inhibitor and S-1 significantly prolonged survival rates of these nude mice, compared with either alone. These findings suggested that combining S-1 and COX-2 inhibitor administration obtain a synergistic inhibitory-effect on the peritoneal metastasis of scirrhous gastric carcinoma.

ADAM23, a possible tumor suppressor gene, is frequently silenced in gastric cancers by homozygous deletion or aberrant promoter hypermethylation

Array-based comparative genomic hybridization (CGH-array) has a powerful potential for high-throughput identification of genetic aberrations in cell genomes. We identified a homozygous loss of ADAM23 (2q33.3) in the course of a program to screen a panel of gastric cancer (GC) cell lines (1/32, 3.1%) for genomic copy-number aberrations using our custom-made CGH-array. Infrequent homozygous deletion of ADAM23 was also seen in primary gastric tumors (1/39, 2.6%). ADAM23 mRNA was expressed in normal stomach tissue, but not in the majority of GC cell lines without homozygous deletion of this gene. Expression of ADAM23 mRNA was restored to gene-silenced GC cells after treatment with 5-aza 2'-deoxycytidine. The methylation status of the ADAM23 CpG island, which showed promoter activity, correlated inversely with its expression. Methylation of this CpG island was observed both in GC cell lines and in primary GC tissues; in primary tumors with a hypermethylated CpG island, expression of ADAM23 was lower than in adjacent noncancerous tissues. Moreover, restoration of ADAM23 in GC cells reduced their numbers in colony-formation assays. These results suggest that genetic or epigenetic silencing by hypermethylation of the ADAM23 CpG-rich promoter region leads to loss of ADAM23 function, which may be a factor in gastric carcinogenesis.

Inhibitory effect of a selective cyclooxygenase inhibitor on the invasion-stimulating activity of orthotopic fibroblasts for scirrhous gastric cancer cells

The cyclooxygenase (COX)-2 inhibitor has been reported to impede the progression of gastric cancer, but underlying mechanisms remain unclear. We therefore investigated the effect of a COX-2 inhibitor, JTE-522, on the ability of orthotopic fibroblasts to stimulate invasion of scirrhous gastric carcinoma cells. The human scirrhous gastric cancer cell lines OCUM-2D or OCUM-2M, and human gastric fibroblasts (NF-21) were cultured in the absence or presence of JTE-522 at various concentrations. Cancer cells were then assayed for invasiveness in vitro by invasion assay. The effect of prostaglandins (PG) on growth factor production in NF-21 cells was examined by ELISA. Finally, the effects of orally administrated JTE-522 on orthotopically transplanted tumors were examined in nude mice. NF-21 cells stimulated invasion by OCUM-2D cells, an effect suppressed by JTE-522 at 5 x 10(-6) M. Hepatocyte growth factor (HGF) and PGE2 production by NF-21 cells were suppressed by JTE-522 (P < 0.01). PGE2 stimulated HGF production by NF-21 cells in a dose-dependent manner. JTE-522 significantly suppressed orthotopic tumor growth and lymph node metastasis, and also decreased HGF expression by fibroblasts within the gastric tumor. In conclusion, we found that gastric fibroblasts stimulated invasiveness in scirrhous gastric cancer cells, whereas a selective COX-2 inhibitor inhibited this paracrine effect by decreasing fibroblast PGE2 production, resulting in downregulation of HGF production.

Cyclin E

E-type cyclins (cyclin E1 and cyclin E2) are expressed during the late G1 phase of the cell cycle until the end of the S-phase. The activity of cyclin E is limiting for the passage of cells through the restriction point "R" which marks a "point of no return" for cells entering the division cycle from a resting state or passing from G1 into S-phase. Expression of cyclin E is regulated on the level of gene transcription mainly by members of the E2F trrnscription factor family and by its degradation via the proteasome pathway. Cyclin E binds and activates the kinase Cdk2 and by phosphorylating its substrates, the so-called "pocket proteins", the cyclic/Cdk2 complexes initiate a cascade of events that leads to the expression of S-phase specific genes. Aside from this specific function as a regulator of S-phase-entry, cyclin E plays a direct role in the initiation of DNA replication, the control of genomic stability, and the centrosome cycle. Surprisingly, recent studies have shown that the once thought essential cyclin E is dispensable for the development of higher eukaryotes and for the mitotic division of eukaryotic cells. Nevertheless, high level cyclin E expression has been associated with the initiation or progression of different human cancers, in particular breast cancer but also leukemia, lymphoma and others. Transgenic mouse models in which cyclin E is constitutively expressed develop malignant diseases, supporting the notion of cyclin E as a dominant onco-protein.

Screening of DNA copy-number aberrations in gastric cancer cell lines by array-based comparative genomic hybridization

We performed genome-wide screening for deoxyribonucleic acid copy-number aberrations in 31 gastric cancer (GC) cell lines by using custom-made comparative genomic hybridization (CGH)-array. Copy-number gains were frequently detected at 1q, 3q, 5p, 7p, 7q, 8q, 11q, 17q, 20p, 20q, Xp and Xq, and losses at 3p, 4p, 4q, 8p, 9p, 18p and 18q. With respect to histological subtypes, copy-number gains at 1p, 16p, 20p, 20q and 22q, and losses at 8p, 10p, 10q and 18q were significantly frequent in cell lines derived from tumors of the well-differentiated type, whereas copy-number gains at 1q, 7p, 7q, Xp and Xq were frequent in the undifferentiated type. Homozygous deletions were seen at five loci, whereas high-level amplifications were detected in 15 of the 31 GC cell lines; these had occurred at 24 loci, including the segment containing CDK6 (7q21.2). Amplification of that gene had never been reported in GC before. Immunohistochemical studies showed increased levels of CDK6 protein in 54 of the 292 primary GC samples we examined (18.5%). Cytoplasmic localization of CDK6, as well as CDK6 over-expression, was more frequent in well-differentiated GC than in undifferentiated tumors. Nuclear expression of CDK6 was more frequent in early stage GC than in advanced tumors, suggesting that nuclear localization of CDK6 is likely to be a prognostic factor for GC. Taken together, our data indicate that CDK6 might be involved in the pathogenesis of GC and, more generally, that CGH-arrays have a powerful potential for identifying novel cancer-related genetic changes in a variety of tumors.

Expression of p21(WAF1) and p53 and polymorphism of p21(WAF1) gene in gastric carcinoma

AIM

To investigate the relationship between expression of p21(WAF1) and p53 gene, and to evaluate the deletion and polymorphism of p21(WAF1) gene in gastric carcinoma (GC).

METHODS

Expression of p21 and p53 proteins, and deletion and polymorphism of p21 gene in GC were examined by streptavidin-peroxidase conjugated method (SP) and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) respectively.

RESULTS

The expression of p21 and p53 was found in 100% (20/20) and 0% (0/20) of normal gastric mucosae(NGM), 92.5% (37/40) and 15.0% (6/40) of dysplasia (DP) and 39.8% (43/108) and 56.5% (61/108) of GC, respectively. The positive rate of p21 in GC was lower than that in NGM and DP (P<0.05), while the positive rate of p53 in GC was higher than that in NGM and DP (P<0.05). p21 and p53 were significantly expressed in 63.3% (19/30) and 36.7% (11/30), 35.0% (14/40) and 77.5% (31/40), 26.7% (4/15) and 80.0% (12/15), 30.8% (4/13) and 30.8% (4/13), and 20.0% (2/10) and 30.0% (3/10) of well-differentiated, poorly-differentiated, undifferentiated carcinomas, mucoid carcinomas and signet ring cell carcinomas. The expression of p21 in well-differentiated carcinomas was significantly higher than that in poorly-differentiated, un-differentiated, mucoid carcinomas and signet ring cell carcinomas (P<0.05). Contrarily, The expression of p53 was increased from well-differentiated to poorly-differentiated and un-differentiated carcinomas (P<0.05). The expression of p21 and p53 in paired primary and metastatic GC (35.3% and 70.6%) was different from non-metastatic GC (62.5% and 42.5%) markedly (P<0.05). The expression of p21 in invasive superficial muscle (60.0%) was higher than that in invasive deep muscle or total layer (35.2%) (P<0.05) and was higher in TNM stages I (60.0%) and II (56.2%) than in stages III (27.9%) and IV (22.2%) (P<0.05), whereas the expression of p53 did not correlate to invasion depth or TNM staging (P>0.05). The exoression patterns of p53+/p21-, and of p53-/p21+ were found in 5.0% and 82.5% of DP. There was a significant correlation between expression of p21 and p53 (P<0.05). But there was no significant correlation between expression of both in GC (P>0.05). There was no deletion in exon 2 of p21 gene in 30 cases of GC and 45 cases of non-GC, but polymorphism of p21 gene at exon 2 was found in 26.7% (8/30) of GC and 8.9% (4/45) of non-GC, a significant difference was found between GC and non-GC (P<0.05). There was no significant relation between p21 expression of polymorphism (37.5%, 3/8) and non-polymorphism (45.5%, 10/22) in GC (P>0.05).

CONCLUSION

The loss of p21 protein and abnormal expression of p53 are related to carcinogenesis, differentiation and metastasis of GC. The expression of p21 is related to invasion and clinical staging in GC intimately. The expression of p21 protein depends on p53 protein largely in NGM and DP, but not in GC. No deletion of p21 gene in exon 2 can be found in GC. The polymorphism of p21 gene might be involved in gastric carcinogenesis.There is no significant association between polymorphism of p21 gene and expression of p21 protein.

PPAR gamma ligand-induced apoptosis through a p53-dependent mechanism in human gastric cancer cells

We have recently demonstrated that the PPAR gamma ligand troglitazone induced cell growth arrest and evoked apoptosis in a gastric cancer cell line, MKN-45. Since in general, p53 plays an important role in the induction of apoptosis and growth inhibition, we tried to clarify whether or not p53 mediates troglitazone-induced apoptosis and growth arrest in gastric cancer cells. Troglitazone increased the number of apoptoic cells in MKN-28, MKN-45 and MKN-74, but not in KATO-III cells. The troglitazone-induced apoptotic change was significantly reduced by coincubation with bisphenol A digycidyl ether (BADGE), a synthetic PPAR gamma antagonist, in MKN-74 cells, suggesting that PPAR gamma mediates the apoptotic effect of troglitazone. Since KATO-III lacks the p53 gene, we speculated that p53 might be implicated in the PPAR gamma ligand-induced apoptosis. Western blot analysis revealed that p53 expression was increased by troglitazone in a time-dependent manner in MKN-74 cells, further suggesting that p53 may mediate the apoptotic process induced by troglitazone. We next established a dominant-negative p53 mutant by stable transfection of p53 mutant into MKN-74 cells. In the dominant-negative p53 mutant cells, troglitazone failed to induce apoptosis, strongly supporting the hypothesis that p53 indeed mediates the process of the troglitazone-induced apoptosis. In the dominant-negative p53 mutant cells, troglitazone significantly induced cell growth arrest and increased expression of p27(Kip1) protein, which is thought to be the key molecule to evoke growth arrest, suggesting that p53 is not involved in the growth inhibition by troglitazone. All these results suggest that p53 mediates the PPAR gamma ligand-induced apoptosis, but not the cell growth inhibition.

p16Ink4a is overexpressed in H. pylori-associated gastritis and is correlated with increased epithelial apoptosis

BACKGROUND

Cell cycle regulatory proteins may be critical targets during carcinogenesis. We have previously shown that chronic H. pylori infection is associated with decreased expression of the cyclin dependent kinase inhibitor (CDI) p27kip1. Loss of p27kip1 and p16Ink4a (p16) expression, another CDI, has been reported during the progression of gastric tubular adenomas to advanced gastric cancer. The aim of the current study was to examine whether H. pylori infection also affects the expression of p16 in the gastric mucosa of H. pylori-infected patients.

METHODS

p16 expression was evaluated in gastric antral biopsies by immunohistochemistry in 50 patients with nonulcer dyspepsia (n = 18 uninfected, n = 32 H. pylori infected, 24 by cagA+ strains). Adjacent sections were stained for proliferating epithelial cells (by Ki67) and for apoptotic cells (by TUNEL assay).

RESULTS

Both in H. pylori infected and uninfected patients the expression of p16 was higher in the neck and base of the gland than in the foveolar region. Epithelial staining for p16 was increased with H. pylori infection (31.3% vs. 11.1% in the foveolar region, 68.8% vs. 27.8% in the neck and 75% vs. 50% in the glandular base). There was no correlation between the expression of 16 and proliferation but there was a significant positive correlation between apoptosis and 16 immunostaining.

CONCLUSIONS

The tumor suppressor gene 16 is over expressed in gastric epithelial cells of H. pylori infected patients and this is associated with an increase in apoptosis. These findings suggest a possible role for this cell cycle regulator in the increase in gastric cell turnover that is associated with H. pylori infection.

Expression of manganese superoxide disumutase influences chemosensitivity in esophageal and gastric cancers

The purpose of this study was to examine whether the increased sensitivity of cancer cells to adriamycin (ADM), which is known to produce superoxide radicals, was brought through suppressed manganese superoxide disumutase (MnSOD) expression in the presence of transforming growth factor beta1 (TGFbeta1). T.T., MKN28, and MKN45 cell lines were treated with TGFbeta1 before exposure to ADM. Athymic female mice bearing the MKN28 cells were treated with TGFbeta1, ADM, or TGFbeta1 + ADM. Pretreatment of T.T., MKN28, and MKN45 cell lines with TGFbeta1 resulted in increased sensitivity to ADM. In contrast, simultaneous exposure to TNFalpha, which increased MnSOD expression, decreased sensitivity of cancer cells to ADM. In vivo studies demonstrated that the combined administration of TGFbeta1 and ADM delayed tumor growth better than either treatment alone. Our results suggest that the synergistic antitumor effects of TGFbeta1 and ADM may be due to decreased MnSOD expression in cancer cells. Thus, combined administration of TGFbeta1 and ADM might prove useful for treatment of malignant disease.

Troglitazone induces G1 arrest by p27(Kip1) induction that is mediated by inhibition of proteasome in human gastric cancer cells

We examined in the present study whether human gastric cancer cells express peroxisome proliferator-activated receptor gamma (PPARgamma), the effect of PPARgamma activation by troglitazone, a selective ligand, on cellular growth, and the mechanism of the growth arrest by troglitazone in gastric cancer cells. RT-PCR, northern blot and western blot analysis demonstrated that all four tested human gastric cancer cell lines, MKN-28, MKN-45, MKN-74 and KATO-III, expressed PPARgamma mRNA and protein. WST-1 assay and flow cytometric analysis revealed that troglitazone inhibited the growth and induced G1 arrest in all four gastric cancer cell lines. To examine the role of p27(Kip1), a cyclin-dependent kinase inhibitor, in the G1 arrest by troglitazone, we determined p27(Kip1) protein expression by western blot analysis in gastric cancer cells that had been treated with troglitazone. Troglitazone increased p27(Kip1) in all four gastric cancer cell lines. Since it has been reported that the ubiquitin-proteasome system plays a vital role in the degradation of p27(Kip1) protein, we evaluated the hypothesis that inhibition of proteasome mediates the troglitazone-induced p27(Kip1) accumulation. Lactacystin, a proteasome inhibitor, inhibited cell growth and increased p27(Kip1) expression in MKN-74 cells. It was further demonstrated that troglitazone inhibited proteasome activity in a dose-dependent manner in MKN-74 cells. All these results suggest that troglitazone inhibited proteasome activity, followed by induction of p27(Kip1), which arrests cells at the G1 phase of the cell cycle in gastric cancer cells. The troglitazone-mediated inhibition of the proteasome suggests a novel mechanism for the anti-proliferative effect of this agent in cancer cells.

Role of Helicobacter pylori and p53 in regulation of gastric epithelial cell cycle phase progression

H. pylori disrupts gastric mucosal homeostasis by altering gastric epithelial cell cycle distribution, and this may contribute to the diverse disease outcomes associated with this infection. The effect of H. pylori on gastric epithelial cells and the role of p53 were assessed in this study by incubating H. pylori strains with gastric epithelial cells. During a 72-hr coincubation, H. pylori induced a time- and dose-dependent inhibition of cell growth and induction of apoptosis. However, at low inocula, H. pylori stimulates cell DNA synthesis compared to untreated controls. Although there was no difference in the induction of AGS cell line apoptosis and cell proliferation between cells exposed to cagA+/vacA+ and cagA-/vacA- strains, an interstrain variation on H. pylori-induced cell cycle events was noted. Serum starvation enhanced the sensitivity of gastric epithelial cells to H. pylori-induced apoptosis. H. pylori induced apoptosis in all the cell lines regardless of their p53 status, but cells with wild-type p53 had higher apoptosis rates. Therefore, bacterial density, diversity, local nutrient levels, and host cell p53 status may contribute to the regulation of H. pylori-induced cell cycle events.

Role of Helicobacter pylori and p53 in regulation of gastric epithelial cell cycle phase progression

H. pylori disrupts gastric mucosal homeostasis by altering gastric epithelial cell cycle distribution, and this may contribute to the diverse disease outcomes associated with this infection. The effect of H. pylori on gastric epithelial cells and the role of p53 were assessed in this study by incubating H. pylori strains with gastric epithelial cells. During a 72-hr coincubation, H. pylori induced a time- and dose-dependent inhibition of cell growth and induction of apoptosis. However, at low inocula, H. pylori stimulates cell DNA synthesis compared to untreated controls. Although there was no difference in the induction of AGS cell line apoptosis and cell proliferation between cells exposed to cagA+/vacA+ and cagA-/vacA- strains, an interstrain variation on H. pylori-induced cell cycle events was noted. Serum starvation enhanced the sensitivity of gastric epithelial cells to H. pylori-induced apoptosis. H. pylori induced apoptosis in all the cell lines regardless of their p53 status, but cells with wild-type p53 had higher apoptosis rates. Therefore, bacterial density, diversity, local nutrient levels, and host cell p53 status may contribute to the regulation of H. pylori-induced cell cycle events.

Cyclin D1 antisense oligonucleotide inhibits cell growth stimulated by epidermal growth factor and induces apoptosis of gastric cancer cells

The cyclin D1 protein is one of the cell cycle regulators required for cell cycle progression through G1 phase to S phase. The cyclin D1-cyclin-dependent kinase (CDK) system is thought to control the cell cycle through mediating extracellular signals from mitogens, such as epidermal growth factor (EGF). In this study, we attempted to examine the therapeutic effect of cyclin D1 antisense oligonucleotides (AS/D1) on cell proliferation and apoptosis of the gastric cancer cell line MKN-74, in the presence and absence of EGF-stimulation. Evaluation of cell survival and DNA synthesis revealed that enhanced cell growth following EGF-stimulation was completely inhibited by a 24 h pre-incubation with 100 nM AD/D1. This inhibition was down to 19.3% compared with maximal DNA synthesis after stimulation with 3 nM EGF alone. Western blotting demonstrated that while EGF-stimulation led to cyclin D1 over-expression, AS/D1 inhibited cyclin D1 protein expression. We also demonstrated the induction of apoptosis in MKN-74 cells by AS/D1. In conclusion, EGF-stimulated MKN-74 cell proliferation was inhibited by AS/D1, which could overcome EGF-induced cyclin D1 over-expression. AS/D1 also affected cell survival by inducing apoptosis through cell cycle arrest following cyclin D1 depletion. Thus, AS/D1 may be a candidate for use as a novel cancer therapy specifically targeted against the over-expression of cyclin D1 enhanced by EGF in malignant cells.

High-density allelotype of the commonly studied gastric cancer cell lines

Gastric cancer is one of the leading causes of death from cancer throughout the world, and studies to elucidate the genetic defects found in this type of cancer are growing in number. Increasingly sophisticated techniques and the sequencing of the human genome have had an impact on the scope of such studies. While the use of tumor specimens remains popular, more emphasis is being placed on cell lines as model systems where specific data can be directly combined with results from other studies. This article describes a genetic survey of the most widely used gastric adenocarcinoma cell lines. The allelotype at 351 polymorphic loci in 14 cell lines was obtained, and the results from the 4,900 polymerase chain reactions are displayed. In addition to confirming loss of heterozygosity on chromosome arms 6p, 7q, 17p, and 18, additional deletions on arm 5p and the pericentromeric regions of chromosomes 1 and 10 were detected. Areas that might contain homozygous deletions or amplifications also were mapped. The rate of microsatellite instability was quantified and shown to vary greatly among the different cell lines. Most important, this study serves as a genetic scaffold for the integration of past and future studies on the nature of the genetic defects in gastric cancer.

Genetic and epigenetic changes in stomach cancer

Genetic and epigenetic alterations of multiple cancer-related genes and molecules are implicated in the development and progression of human gastric carcinomas. Reactivation of telomerase, inactivation of p53 tumor suppressor gene, overexpression of cyclin E, and reduced expression of p27 KIP1 by disorganized degradation in proteasome are common events of both well-differentiated and poorly differentiated gastric adenocarcinomas. Inactivation of hMLH1 mismatch repair gene by CpG hypermethylation resulting in microsatellite instability, amplification of c-erbB2 oncogene, inactivation of APC tumor suppressor gene, and K-ras mutations are preferentially associated with well-differentiated gastric cancer. Conversely, reduction or loss of E-cadherin and catenins by both mutation and CpG hypermethylation and K-sam and c-met oncogene amplification are necessary for the development and progression of poorly differentiated or scirrhous gastric carcinomas. Interaction between cancer cells expressing c-met and hepatocyte growth factor from stromal cells is implicated in morphogenesis of gastric cancer.

Molecular characteristics of eight gastric cancer cell lines established in Japan

Molecular characterization of eight gastric cancer cell lines established in Japan are summarized according to the genetic and epigenetic alterations and growth factor status. TMK-1 poorly differentiated adenocarcinoma cell line harbors mutant p53 tumor suppressor gene and rearrangement of p15MTS2. MKN-1 adenosquamous carcinoma line with mutant p53 reveals silencing of E-cadherin by promoter CpG hypermethylation. MKN-7 well-differentiated adenocarcinoma cell line has amplification of c-erbB2 oncogene and cyclin E gene. MKN-28 well-differentiated adenocarcinoma cell line reveals mutations in p53 and APC tumor suppressor genes and silencing of CD44. The MKN-45 poorly differentiated adenocarcinoma cell line with wild-type p53 is characterized by homozygous deletion of p16CDKN2/MTS1/INK4A and p15MTS2, amplification of c-met oncogene and promoter mutation of E-cadherin. MKN-74 derived from moderately differentiated tubular adenocarcinoma has wild-type p53. KATO-III signet ring cell carcinoma line has genomic deletion of p53, amplification of K-sam and c-met oncogene and mutation of E-cadherin. HSC-39 signet ring cell carcinoma cell line harboring p53 missense mutation has homozygous deletion of p16CDKN2/MTS1/INK4A and p15MTS2, amplifications of c-myc, c-met, K-sam and CD44 gene and mutation in beta-catenin gene.

Topoisomerase I inhibitor (camptothecin)-induced apoptosis in human gastric cancer cells and the role of wild-type p53 in the enhancement of its cytotoxicity

Camptothecin (CPT), a human topoisomerase I inhibitor, blocks DNA replication in human cancer cells. It represents a promising new class of chemotherapeutic agents with broad anti-tumor activity. However, its effect on gastric cancer cells remains unknown. We examined cell growth, apoptosis and cell cycle phase distribution in gastric cancer cells by exposing these cells to CPT for up to 72 h. Cell viability was determined by the Trypan blue exclusion assay. Cell cycle phase distribution and apoptosis were measured using flow cytometry, fluorescence microscopy and DNA ladder assay. Exposure of exponentially growing gastric AGS cancer cells to CPT induced time-dependent apoptosis and growth inhibition. Serum starvation-synchronized AGS cells (about 60% cells in G0/G1 phase) showed similar cellular responses. Analysis of cell cycle phase distribution of AGS cells treated with CPT for up to 72 h showed no obvious differences compared to untreated control cells. Although the induction of apoptosis was noticed in gastric cancer cell lines both with and without p53, cells lacking p53 showed less apoptosis compared to those cell lines possessing p53. Our data show that CPT is capable of inducing gastric cancer cell growth inhibition and apoptosis. Wild-type p53 may enhance the cytotoxicity of CPT against gastric carcinoma.

Correlation of p16 hypermethylation with p16 protein loss in sporadic gastric carcinomas

Hypermethylation of p16 has been detected frequently in a variety of cancer cells and is known to repress the level of p16 transcription. In human gastric carcinoma (GC) cells, p16 protein loss has often been detected, but genetic alterations of p16 are infrequent. To investigate the molecular mechanism of p16 gene inactivation in gastric carcinogenesis, we examined the methylation status of p16 in GC using methylation-specific PCR. Thirty-seven of eighty-eight (42%) GC showed p16 hypermethylation. Immunohistochemical analysis of 41 cases of GC showed a complete loss of p16 immunoreactivity in 19 of 22 (86%) methylation-positive cases, but in only 2 of 19 (11%) methylation-negative cases. Of 88 GC, 21 cases were previously identified as having microsatellite instability (MSI). Interestingly, 13 of 21 (62%) MSI-positive tumors and 24 of 67 (36%) MSI-negative tumors had hypermethylation on p16. The relatively high frequency of hypermethylation on p16 and the strong correlation between the immunoreactivity and methylation patterns suggest that methylation is an important mechanism for p16 gene inactivation in GC.

Integrin alpha6beta4 as a suppressor and a predictive marker for peritoneal dissemination in human gastric cancer

BACKGROUND & AIMS

Because alterations of integrin expression in cancers contribute to cancer cell biology, we analyzed the association between the potential for peritoneal dissemination and integrin expression.

METHODS

The dissemination potential of 10 human gastric cancer cell lines in mice with severe combined immunodeficiency (SCID) was compared with the expression of various integrins. The relationship between integrin expression and peritoneal dissemination was also investigated in surgically resected gastric cancer cases.

RESULTS

The level of integrin beta4 subunit expression was inversely correlated with dissemination potential. Introduction of a full-length complementary DNA (cDNA) for beta4 subunit into cancer cells showing negligible beta4 subunit expression markedly suppressed peritoneal dissemination and inhibition of endogenous integrin alpha6beta4 by introduction of a cytoplasmic domain-deleted beta4 subunit cDNA into cells showing high expression of beta4 subunit promoted peritoneal dissemination. Apoptosis, which was histologically evident in peritoneal nodules of SCID mice, was induced in the cells with high beta4 subunit expression by attachment to laminin and stimulation with growth factors in vitro. An immunohistochemical study of specimens from 120 cases of primary gastric cancer showed that patients with beta4 subunit-positive tumors exhibited peritoneal dissemination only infrequently (P < 0.0001) and had a better outcome (P < 0.01).

CONCLUSIONS

These results indicate that integrin alpha6beta4 is both a suppressor and a predictive marker for peritoneal dissemination in gastric cancer.

Expressions of cell-cycle regulatory gene products in conventional gastric adenomas: possible immunohistochemical markers of malignant transformation

In 54 lesions of gastric adenomas consisting of 31 low-grade adenomas (LGAs) and 23 high-grade adenomas (HGAs), 28 intramucosal carcinomas (IMCs), and 23 carcinomas invading the submucosa (SMCs), the expression of cell-cycle regulatory gene products (p53, p21/waf1, p27/kip1, and Ki-67) was studied using immunohistochemical techniques. Several lesions were also analyzed by the fluorescence in situ hybridization method. The overexpression of p53 was found in no LGAs and in 9% of HGAs, whereas a considerable number of cases showed an overexpression in IMCs (39%) and SMCs (43%). A reduced expression of p21/waf1 was present in only 4% of HGAs. Superficial eccentric positivity was present in all LGAs and 74% of HGAs, whereas it was present in 46% of IMCs and 4% of SMCs. P53-positive and p21/waf1-negative lesions, which were supposed to have a mutated p53 gene, were observed in no LGAs, in 4% of HGAs, in 11% of IMCs, and in 26% of SMCs. The expression of cyclin E was more frequently present in carcinomas than in adenomas. However, no high expression of cyclin E was observed among the adenomas. A reduced expression of p27/kip1 was encountered more frequently in carcinoma than adenoma. By a semiquantitative evaluation comparing adenoma and carcinoma in the same stomach, the increased degrees of both p21/waf1 and cyclin E were highlighted. A chromosome gain was detected among 7% of the adenomas and 85% of the carcinomas. In conclusion, the expressions of p53, p21/waf1, p27/kip1, and cyclin E were considered to be of great value for estimating the dysplastic progression of gastric adenomas. Especially, various aspects of protein expression, including its distribution and semiquantitative evaluation of positive cells, and a combined analysis with several proteins, may thus be useful as possible markers of dysplastic evolution in gastric adenomas.

Targeting molecular pathways with camptothecin as novel therapy for gastric cancer

Novel chemotherapeutic agents are needed to treat gastric cancer for which the prognosis remains dismal. The antitumor alkaloid camptothecin (CPT) may be useful in the treatment of certain solid tumors; however, its effects on gastric cancer are largely undefined. The purpose of our study was to characterize the effects of CPT on human gastric tumors in vivo and to determine the cellular mechanisms involved in CPT-mediated inhibition. Two human gastric cancers, WIL and TOR, were transplanted subcutaneously into athymic nude mice. After tumors reached 50 to 100 mm(2), mice were randomized into three groups to receive injections of either low-dose CPT (5 mg/kg), high-dose CPT (10 mg/kg), or vehicle (control) intraperitoneally 3 days a week for 3 weeks. Tumors were measured and weighed, and protein levels of the cell cycle inhibitor, p21Waf1/Cip1, and the antiapoptotic protein, Bcl-2, were assessed. Both dosages of CPT significantly inhibited growth of WIL and TOR gastric tumors. CPT (10 mg/kg) reduced tumor size compared to baseline, establishing this as a tumoricidal dosage. Treatment with CPT was associated with increased levels of p21Waf1/Cip1 and decreased levels of Bcl-2. CPT effectively kills human gastric cancers associated with increased levels of p21Waf1/Cip1 and decreased levels of Bcl-2. By activating cell cycle withdrawal and cell death through induction of p21Waf1/Cip1 and downregulation of Bcl-2, CPT may be an effective agent for gastric cancer.

Differential apoptosis by indomethacin in gastric epithelial cells through the constitutive expression of wild-type p53 and/or up-regulation of c-myc

Nonsteroidal anti-inflammatory drug (NSAID)-induced apoptosis is considered to be an important mechanism in the antineoplastic effects and damage produced by the drugs in the gastrointestinal tract. In this study, two different gastric cancer cell lines, MKN28 (mutant-type p53) and AGS (wild-type p53), were compared as to growth inhibition, apoptosis, and cell cycle and apoptosis-related gene expression in response to indomethacin treatment. Cell growth was measured by MTT (3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyl tetrazolium bromide) assay. Apoptosis was characterized by acridine orange staining and DNA fragmentation, and cell cycle kinetics by flow cytometry. The mRNA and protein levels of p53, p21waf1/cip1, and c-myc were determined by Northern and Western blotting. The results showed that indomethacin initiated growth inhibition and apoptosis in both cell lines without cell cycle shifting. AGS cells were more sensitive to growth inhibitory activity and apoptosis of indomethacin than MKN28 cells. In MKN28 cells, the levels of p53, p21waf1/cip1, and c-myc mRNA remained unchanged over the 24-hr treatment with indomethacin, but the p53 protein level was elevated after 4 hr. There was no change in the p21waf1/cip1 and c-myc protein levels in the MKN28 cells. In AGS cells, a progressive increase in c-myc mRNA and protein levels was noted, while p53 and p21waf1/cip1 remained unchanged. It can be concluded that wild-type p53 and/or up-regulation of c-myc is associated with indomethacin-mediated differential apoptosis in gastric epithelial cells.

Effect of 3,4-dihydro-6-[4-(3,4-dimethoxybenzoyl)-1-piperazinyl]-2(1H)- quinolinone (vesnarinone) on the growth of gastric cancer cell lines

Vesnarinone (OPC-8212; 3,4-dihydro-6-[4-(3,4-dimethoxybenzoyl)-1-piperazinyl]-2(1H)-quinolinone ) is a synthetic oral cardiotonic agent that has been used for the treatment of patients with congestive heart failure. Six days of treatment with 30 microg/ml of vesnarinone induced 20-80% growth inhibitions in five out of six gastric carcinoma cell lines examined. Cell cycle analysis revealed that the vesnarinone-sensitive TMK-1 gastric cancer cell line exhibited a significant G0-G1 arrest without evidence of apoptotic cell death induction after 48 h of treatment. Interestingly, this phenomenon was preceded by a marked reduction in the expression of cyclin A, D1 and E as well as cyclin-dependent kinase 2 (CDK2). On the other hand, no significant change was observed in the expression of p21(Waf1/Cip1), p27Kip1 nor various growth factors and their receptor genes. Overall these results indicate that vesnarinone inhibits the growth of gastric cancer cells by down-regulating G1 cyclins and CDK2 to induce G0-G1 arrest through a pathway different from that of cyclin inactivation by p21(Waf1/Cip1) or p27Kip1.

Mapping of chromosomal imbalances in gastric adenocarcinoma revealed amplified protooncogenes MYCN, MET, WNT2, and ERBB2

Gastric adenocarcinoma is a malignant tumor with a high incidence and a low survival rate. In order to identify genetic alterations associated with this tumor, we screened 23 gastric adenocarcinomas for recurrent chromosomal imbalances by using comparative genomic hybridization (CGH). The most common gains of chromosomal material were found on chromosome arms 20q (10 cases), 16p (7 cases), and 1q (4 cases) and on chromosome 11 (4 cases). Losses were observed on chromosome arms 4q, 5q, 9p, and 21q (3 cases each). Four tumors exhibited high-level amplifications localized on chromosome regions 2p23-p24, 7q31-q32, 8p21-p22, 10q25-q26, 11q13, 17q11-q21, and 20q. Based on the position of these amplifications, candidate (onco)genes were selected and subsequently tested by Southern blot analysis of the respective tumors. Of the seven tested candidates, MYCN, MET, WNT2, and ERBB2 were found to participate in the amplicons of the respective tumor samples. Of these four presumably activated oncogenes, two, MYCN and WNT2, were previously not assumed to play a pathogenic role in stomach cancer. Among the other regions of imbalance, gain of 20q seems particularly interesting, because it is found in almost half of the analyzed cases and is highly amplified. Our data allowed us to narrow the relevant region down to the commonly gained bands 20q12-q13.1. This and other imbalanced regions provide a basis for searching new putative oncogenes and tumor suppressor genes involved in the development or progression of gastric adenocarcinoma.

Positive correlation between p27Kip1 expression and progression of human esophageal squamous cell carcinoma

p27Kip1, one of the cyclin-dependent kinase (CDK) inhibitors (CDKIs), blocks progression from G1 to S phase by binding cyclin D1-CDK4 and/or cyclin E-CDK2 and inhibiting their activities. Reflecting the function of p27 as a CDKI in vitro, a reduced expression of protein p27 has recently been reported to be associated with tumor aggressiveness in some types of human cancers. In the present study, we examined the relationships between immunohistochemically detected expression of p27, cyclin D1, cyclin E proteins and clinicopathological findings in 77 patients with esophageal squamous cell carcinoma (SCC). Using specific monoclonal antibodies to p27, cyclin DI and cyclin E proteins, positive immunostaining in the nuclei was observed in 32.5% (25/77), 27.3% (21177) and 29.6% (21/71) of patients, respectively. There were no statistically significant relationships among the expressions of these 3 proteins. Using the Kaplan-Meier's method, p27 and cyclin D1 expressions were found to be independently associated with poor prognosis. When all parameters were combined into a multivariate regression analysis using the Cox model, the expressions of p27 and cyclin D1 retained a predictive value for survival. In contrast to former reports supporting a tumor-suppressive function of p27, our results suggest that altered expression of p27 and cyclin D1 may be associated with the progression of human esophageal SCC, in which cyclin E may well not play any central role.

Prognostic significance of cyclin E and p53 protein overexpression in carcinoma of the renal pelvis and ureter

Cyclin E gene alteration in the cell cycle plays an important role in carcinogenesis, while p53 protein affects different phase checkpoint pathways by activating p21WAF1/CIP1 in the normal cell cycle. We immunohistochemically examined the expression of cyclin E and p53 proteins in 121 patients with transitional cell carcinoma (TCC) of the renal pelvis and ureter to determine their significance for tumour behaviour and patient prognosis. Cyclin E and p53 immunostaining of the nucleus was observed in 36 tumours (29.8%) and 35 tumours (28.9%) respectively. A significant percentage, 69.4% (25 out of 36 tumours), of the cyclin E-positive tumours exhibited simultaneous labelling for p53 (P < 0.05). Mirror-section technique was performed in five selected double-positive tumours to identify cancer cells that were nuclei positive for both cyclin E and p53. The prevalence of cases simultaneously exhibiting both cyclin E and p53 immunostaining was higher in the high-grade tumours (P < 0.01) than in the other types of tumours. Patients with TCCs coexpressing cyclin E and p53 had a significantly poorer prognosis than those expressing neither cyclin E nor p53 (P < 0.001). These in vivo findings provide evidence for cyclin E protein overexpression in TCCs intimately associated with p53 alteration and suggest that simultaneous overexpression of both cyclin E and p53 is related to tumour behaviour and poor prognosis.

Overexpression of cyclin-dependent kinase-activating CDC25B phosphatase in human gastric carcinomas

CDC25 phosphatases activate cyclin-dependent kinases by removing inhibitory phosphate groups on the molecules and positively regulate the cell cycle progression. The expression of CDC25A, B and C was examined in gastric carcinoma cell lines and gastric carcinoma tissues by northern blotting and immunohistochemistry. The gastric carcinoma cell lines expressed CDC25A, B and C mRNA at various levels. The expression levels of CDC25B were generally higher than those of CDC25A and C. Of the 40 gastric carcinomas, 70% of the tumors expressed CDC25B mRNA at higher levels than the corresponding normal mucosas, while 38% overexpressed CDC25A mRNA. The CDC25C expression was at very low or undetectable levels. No obvious correlation was detected between the expression of CDC25B and p53 gene mutations. Immunohistochemically, CDC25-positive tumor cells were detected in 43 (78%) of 55 gastric carcinoma cases, of which 27 (49%) were strongly positive. Strong expression of CDC25B protein was associated with advanced stage and deep invasion. Furthermore, the incidence of strong expression was significantly higher in carcinomas with nodal metastasis than in those without metastasis. These findings suggest that overexpression of CDC25B may favor development and progression and may be an indicator of malignant behavior of gastric carcinomas.

The pattern of p53 and p21WAF1/CIP1 immunoreactivity in non-Hodgkin's lymphomas predicts p53 gene status

P53 and p21WAF1/CIP1 (p21) immunostaining was performed on 92 non-Hodgkin's lymphomas (NHLs), and the staining pattern correlated with the presence or absence of p53 hot spot mutations as detected by PCR-SSCP of exons 5-8 and direct sequencing. Twenty-nine of 92 lymphomas overexpressed p53, and 17 overexpressed p21. Of the p53 overexpressing lymphomas, 14 also overexpressed p21, and none of these 14 harbored a detectable hot spot mutation. However, mutations were detected in 13 (87%) of 15 p53 overexpressing, p21 negative lymphomas. One of the 63 p53-negative lymphomas harbored a detectable hot spot mutation, and it was also negative for p21. These results demonstrate that among NHLs that overexpress p53 protein, those which also show p21 overexpression do not harbor p53 hot spot mutations, and furthermore, provide evidence that the transactivating function of p53 is retained. On the other hand, p53 overexpression in NHLs that lack p21 expression is usually indicative of p53 gene mutation.

Expression of p21WAF1/CIP1 in colorectal adenomas and adenocarcinomas and its correlation with p53 protein expression

The expression of p53-inducible cyclin-dependent kinase inhibitor, p21WAF1/CIP1 in non-neoplastic mucosa, adenoma and adenocarcinoma of the colorectum was examined by immunohistochemistry and western blotting and its relation with the expression of p53 protein was analyzed. Non-neoplastic epithelial cells at the surface area showing no proliferative activity expressed p21WAF1/CIP1. The expression of p21WAF1/CIP1 was immunohistochemically detected in 55% (206/377) of the adenomas and 66% (190/289) of the adenocarcinomas, respectively. The incidence of strongly positive cases was significantly higher in the adenocarcinomas (27%) than in the adenomas (18%) (P < 0.05). The incidence of cases with strong p21WAF1/CIP1 expression was higher in stages 0, 1 and 2 carcinomas than in stages 3 and 4 carcinomas (P < 0.05). A decrease in the incidence of cases with strong expression was detected in carcinomas invading deeper than muscularis propria. The incidence of strongly positive cases was significantly lower in carcinomas with lymph node metastasis than those without metastasis (P < 0.05). The expression of p21 as well as p53 detected by western blotting was compatible with the results of immunohistochemistry in most cases examined. However, there was no significant correlation between the expression of p21WAF1/CIP1 and the abnormal accumulation of p53. These findings overall suggest that: (i) the physiological expression of p21WAF1/CIP1 may be associated with cellular senescence of colorectal mucosa; (ii) reduced expression of p21WAF1/CIP1 may participate in the progression of colorectal carcinoma; and (iii) p53-independent pathway may be considerably involved in the induction of p21WAF1/CIP1.

Expression of cyclin-dependent kinase inhibitor p21WAF1/CIP1 in non-neoplastic mucosa and neoplasia of the stomach: relationship with p53 status and proliferative activity

The expression of the p53-inducible cyclin-dependent kinase inhibitor p21WAF1/CIP1 in non-neoplastic mucosa, adenoma, and adenocarcinoma of the stomach was examined immunohistochemically and its relationship with p53 expression and proliferative activity was analysed. In normal gastric mucosa as well as in intestinal metaplasia the epithelial cells at the surface which showed no proliferative activity expressed p21WAF1/CIP1, whereas the cells in the deep area of the glands expressing Ki-67 did not. In the neoplastic lesions, the expression of p21WAF1/CIP1 was detected in 78 per cent (112/144) of the adenomas and 76 per cent (262/343) of the adenocarcinomas. The incidence of p21WAF1/CIP1 expression did not differ among histological types of gastric carcinoma. The strong expression of p21WAF1/CIP1 was more frequently observed in carcinomas invading into submucosa or in cases of stages 2, 3, and 4 than in carcinomas limited to the mucosa or in stage 1 cases. The incidence of strongly positive cases was higher in carcinomas with lymph node metastasis than in those without metastasis. There was no apparent correlation between the expression of p21WAF1/CIP1 and the abnormal accumulation of p53 or with proliferative activity measured by Ki-67 expression. These findings overall suggest that p21WAF1/CIP1 might be associated with the senescence of non-neoplastic gastric epithelial cells; that a p53-independent pathway might be substantially involved in the induction of p21WAF1/CIP1 in gastric neoplasia; and that the proliferative activity of gastric cancer might not be solely dependent on control of the cell cycle by p21WAF1/CIP1.