Expression of the E2F family in human gastrointestinal carcinomas

E2F4 expression is required for cell cycle progression of normal intestinal crypt cells and colorectal cancer cells

The generation of knock-out mice for E2F4 gene expression has suggested a role for this transcription factor in establishing and/or maintaining the intestinal crypt compartment. Having previously demonstrated that E2F4 is cytoplasmic in quiescent-differentiated cells but nuclear in growth factor-stimulated proliferative cells, the present study was aimed at determining the role of E2F4 in the control of human intestinal epithelial proliferation. Results herein demonstrate that lentiviral infection of an shRNA which specifically knocked-down E2F4 expression slowed down G1/S phase transition and the proliferation rate of normal human intestinal epithelial cells (HIEC) and of colon cancer cells. Protein expression of Cdk2, cyclins D1 and A, Cdc25A and c-myc was markedly down-regulated in shE2F4-expressing cells; by contrast, expression of the cell cycle inhibitors p21(Cip/Waf) and p27(Kip1) was increased. In addition, the expression of many genes involved in DNA synthesis was down-regulated in shE2F4-expressing cells, whereas no modulation in E2F1 expression was observed. A decrease in E2F4 in colon cancer cell lines also resulted in a reduction in soft-agar growth capacity. Immunofluorescence experiments in human fetal intestine revealed that cells expressing high nuclear levels of E2F4 also expressed cyclin A protein. Lastly, E2F4 and its target cyclin A were up-regulated and mostly nuclear in human colorectal tumor cells in comparison to the corresponding benign epithelium. These results indicate that nuclear E2F4 may be determinant in the promotion of proliferation of human intestinal epithelial crypt cells and colorectal cancer cells.

E2F1 overexpression correlates with thymidylate synthase and survivin gene expressions and tumor proliferation in non small-cell lung cancer

PURPOSE

We investigated the clinical significance of E2F1 gene expression in relation to its target genes, thymidylate synthase (TS) and Survivin, in case of non-small-cell lung cancer (NSCLC).

EXPERIMENTAL DESIGN

One hundred twenty-seven cases of resected NSCLC were analyzed. Quantitative reverse transcription-PCR was done to evaluate the gene expression of E2F1, TS, and Survivin. Immunohistochemistry was done to investigate the protein expression of E2F1, TS, and Survivin. The Ki-67 proliferation index and the apoptotic index using the terminal deoxyribonucleotidyl transferase-mediated dUTP nick-end labeling method were also evaluated.

RESULTS

E2F1 gene expression significantly correlated with the Ki-67 proliferation index (r = 0.487; P < 0.0001), although no correlation was observed between E2F1 gene expression and the apoptotic index. With regard to E2F1 target genes, E2F1 gene expression significantly correlated with TS gene expression (r = 0.709; P < 0.0001) and Survivin gene expression (r = 0.403; P < 0.0001). The overall survival rate was significantly lower in patients with high-E2F1 tumors than in those with low-E2F1 tumors (P = 0.0027), especially among patients with stage II to III NSCLCs (P = 0.0188). A Cox regression analysis showed that the E2F1 status was a significant prognostic factor for NSCLC patients (hazard ratio, 2.052; P = 0.0261).

CONCLUSIONS

The present study revealed that E2F1 gene expression correlates with TS and Survivin gene expressions and tumor proliferation. During the progression of NSCLC, E2F1 overexpression could produce more aggressive tumors with a high proliferation rate and chemoresistance.

Impact of E2F-1 expression on clinical outcome of gastric adenocarcinoma patients with adjuvant chemoradiation therapy

PURPOSE

There are no reliable prognostic markers that identify gastric cancer patients who may benefit from adjuvant chemoradiation therapy. E2F-1 was shown to be associated with radiosensitivity and chemosensitivity in certain tumor types. Therefore, we analyzed expression and prognostic significance of E2F-1 along with thymidylate synthase (TS) in R(0)-resected gastric adenocarcinoma patients, who underwent adjuvant chemoradiation therapy with 5-fluorouracil (5-FU) and leucovorin.

EXPERIMENTAL DESIGN

The chemosensitivity to 5-FU and radiosensitivity were tested in three E2F-1-overexpressed gastric cancer cell lines in vitro. The expressions of TS and E2F-1 were analyzed in 467 R(0)-resected primary gastric cancer patients, who received adjuvant chemoradiation therapy with 5-FU and leucovorin using tissue microarray.

RESULTS

The E2F-1 immunopositivity rate was 22.2% (103 of 465 samples) with a cutoff value of 5% immunoreactivity, whereas the TS-positive expression occurred in 19.0% of the 463 tumors tested. Using stepwise Cox proportional hazards regression modeling, multivariate analyses showed that the E2F-1 immunopositivity predicted more favorable survival as compared with the E2F-1 immunonegativity with borderline statistical significance [P = 0.050, hazard ratio (HR) = 0.702, 95% confidence interval, 0.487, 1.013]. However, the E2F-1 immunopositivity did not retain its statistical significance at multivariate analysis for predicting disease-free survival (data not shown, P = 0.270), but stage was the only influential factor for disease-free survival in stages IB to IV (M(0)) patients (P < 0.001). TS immunopositivity did not influence survival (P = 0.459) or disease-free survival (P = 0.447).

CONCLUSION

E2F-1 is a potentially novel independent prognostic factor that may identify gastric cancer patients who will likely benefit from adjuvant chemoradiation therapy following curative resection.

p110 CUX1 cooperates with E2F transcription factors in the transcriptional activation of cell cycle-regulated genes

The transcription factor p110 CUX1 was shown to stimulate cell proliferation by accelerating entry into S phase. As p110 CUX1 can function as a transcriptional repressor or activator depending on promoter context, we investigated its mechanism of transcriptional activation using the DNA polymerase alpha gene promoter as a model system. Linker-scanning analysis revealed that a low-affinity E2F binding site is required for transcriptional activation. Moreover, coexpression with a dominant-negative mutant of DP-1 suggested that endogenous E2F factors are indeed needed for p110-mediated activation. Tandem affinity purification, coimmunoprecipitation, chromatin immunoprecipitation, and reporter assays indicated that p110 CUX1 can engage in weak protein-protein interactions with E2F1 and E2F2, stimulate their recruitment to the DNA polymerase alpha gene promoter, and cooperate with these factors in transcriptional activation. On the other hand, in vitro assays suggested that the interaction between CUX1 and E2F1 either is not direct or is regulated by posttranslational modifications. Genome-wide location analysis revealed that targets common to p110 CUX1 and E2F1 included many genes involved in cell cycle, DNA replication, and DNA repair. Comparison of the degree of enrichment for various E2F factors suggested that binding of p110 CUX1 to a promoter will favor the specific recruitment of E2F1, and to a lesser extent E2F2, over E2F3 and E2F4. Reporter assays on a subset of common targets confirmed that p110 CUX1 and E2F1 cooperate in their transcriptional activation. Overall, our results show that p110 CUX1 and E2F1 cooperate in the regulation of many cell cycle genes.

E2F1-regulated microRNAs impair TGFbeta-dependent cell-cycle arrest and apoptosis in gastric cancer

Deregulation of E2F1 activity and resistance to TGFbeta are hallmarks of gastric cancer. MicroRNAs (miRNAs) are small noncoding RNAs frequently misregulated in human malignancies. Here we provide evidence that the miR-106b-25 cluster, upregulated in a subset of human gastric tumors, is activated by E2F1 in parallel with its host gene, Mcm7. In turn, miR-106b and miR-93 regulate E2F1 expression, establishing a miRNA-directed negative feedback loop. Furthermore, upregulation of these miRNAs impairs the TGFbeta tumor suppressor pathway, interfering with the expression of CDKN1A (p21(Waf1/Cip1)) and BCL2L11 (Bim). Together, these results suggest that the miR-106b-25 cluster is involved in E2F1 posttranscriptional regulation and may play a key role in the development of TGFbeta resistance in gastric cancer.

Transcriptional regulation of subtilisin-like proprotein convertase PACE4 by E2F: Possible role of E2F-mediated upregulation of PACE4 in tumor progression

PACE4, a member of the subtilisin-like proprotein convertase (SPC) family, is expressed at high levels in certain tumor cells and plays a role in metastatic progression through activation of matrix metalloproteinases. The mechanism leading to overexpression of PACE4 in tumor cells remains unclear. In this study, we show that the E2F1 transcription factor, which is implicated in carcinoma invasiveness, upregulates the expression of PACE4. HT1080 (highly tumorigenic and invasive) cells expressed much higher levels of PACE4 and E2F family (E2F1 and E2F2) transcripts than IMR90 (normal fibroblast) cells. Expression levels of other SPCs (furin and PC6) remained unchanged in these cells. Promoter analysis indicated that two E2F consensus binding sites (-117/-110 and -86/-79) in the 5'-flanking region of the human PACE4 gene function as positive regulatory elements. Mutation of these sites abolished PACE4 promoter response to E2F1 as well as binding of E2F1 in electrophoretic mobility-shift assays. Other E2F members, E2F2 and E2F3, also activated PACE4 expression, as in the case of E2F1. These results indicate a novel mechanism for E2F family-mediated promotion of carcinoma invasiveness through PACE4.

Deciphering the underlying genetic and epigenetic events leading to gastric carcinogenesis

Gastric cancer is a common aggressive malignancy. Although its incidence shows considerable variation among different countries, gastric cancer is still a major health problem worldwide. The causes of stomach cancer are not completely understood. What is clear is that gastric cancer is a multi-stage process involving genetic and epigenetic factors. This review is an in-depth study of the known genetic and epigenetic processes in the development of this tumor, and delineates possible approaches in gene and epigenetic therapy.

Cellular and molecular aspects of gastric cancer

Gastric cancer remains a global killer with a shifting burden from the developed to the developing world. The cancer develops along a multistage process that is defined by distinct histological and pathophysiological phases. Several genetic and epigenetic alterations mediate the transition from one stage to another and these include mutations in oncogenes, tumour suppressor genes and cell cycle and mismatch repair genes. The most significant advance in the fight against gastric caner came with the recognition of the role of Helicobacter pylori (H pylori) as the most important acquired aetiological agent for this cancer. Recent work has focussed on elucidating the complex host/microbial interactions that underlie the neoplastic process. There is now considerable insight into the pathogenesis of this cancer and the prospect of preventing and eradicating the disease has become a reality. Perhaps more importantly, the study of H pylori-induced gastric carcinogenesis offers a paradigm for understanding more complex human cancers. In this review, we examine the molecular and cellular events that underlie H pylori-induced gastric cancer.

Increased E2F-1 expression via tumour cell proliferation and decreased apoptosis are correlated with adverse prognosis in patients with squamous cell carcinoma of the oesophagus

BACKGROUND

The retinoblastoma (Rb) pathway, which governs cell cycle progression, is frequently genetically altered in cancer, causing deregulated expression of the E2F-1 transcription factor, which promotes DNA synthesis and cell cycle progression. Recent studies show that E2F-1 also participates in apoptosis induction in a p53 dependent or independent manner. Despite its crucial role and paradoxical effects on cell turnover, the function of E2F-1 in human cancer is unclear.

AIMS

To evaluate E2F-1 expression using immunohistochemistry in 43 surgically resected oesophageal squamous cell carcinoma (OSCC) specimens.

METHODS

This study analysed the association of E2F-1 with tumour cell proliferation and apoptosis and the upstream regulators modulating these processes, and its impact on patient outcome. Tumour cell proliferation and apoptosis were assessed as percentage of MIB-1 positive or apoptotic cells (MIB-1 labelling index (MI) and apoptotic index (AI)), respectively.

RESULTS

Entire specimens showed abnormal expression of one or more upstream regulators of pRb/E2F-1. Although E2F-1 positivity was not associated with the expression of upstream regulators, it showed a linear and positive correlation with MI but not AI. Patients with high MI, low AI, or high E2F-1 positivity had significantly shorter recurrence free survival. By multivariate analysis, high MI and low AI were independently associated with recurrence free survival, but E2F-1 was not.

CONCLUSIONS

Increased cell proliferation and decreased apoptosis are associated with adverse prognosis in patients with OSCC. Although E2F-1 remains a controversial prognostic factor, its expression was closely associated with tumour cell proliferation and might influence clinical outcome, mainly via cell cycle progression.

Involvement of E2F transcription factor family in cancer

The E2F family of transcription factors is a central modulator of important cellular events, including cell cycle progression, apoptosis and DNA damage response. The role of E2F family members in various human malignancies is yet unclear and may provide vital clues to the diagnosis, prognosis and therapy of cancer patients. In this review we provide a brief but concise overview of E2F function and its putative role in the most common human tumour types.

Cyclin D1, E2F1 expression levels are associated with characteristics and prognosis of esophageal squamous cell carcinoma

SUMMARY. We performed a multi-institutional analysis of E2F1 and cyclin D1 expression in cases of esophageal squamous cell carcinoma (ESCC). Cyclin D1 and E2F1 are involved in the transition of cell cycle phases and associated with tumor progression. However, no previous studies have concurrently analyzed combined E2F1 and cyclin D1 expression. The purpose of this study was to clarify the relationship of E2F1 and cyclin D1 in ESCC. We studied 122 patients with primary ESCC who underwent surgical tumor resection. Immunohistochemical analyses were performed for E2F1 and cyclin D1. A statistical analysis of immunohistochemistry results, clinicopathological features, and prognosis was performed. E2F1/cyclin D1 (-/-) tumors were present in 31 patients (25.4%) and correlated with reduced tumor progression. In these patients, pT (P=0.0001), pN (P<0.0001), p-Stage (P=0.0019), and survival rates were better than in patients who were positive for either E2F1 or cyclin D1 (P=0.0232). The expression of E2F1 and cyclin D1 is an indicator of tumor progression and prognosis in patients with ESCC. Combined analysis of E2F1 and cyclin D1 expression helps to determine the characteristics and prognosis of ESCC.

Over-expression of E2F-1 in esophageal squamous cell carcinoma correlates with tumor progression

The transcription factor E2F-1, a downstream regulator of the p16-cyclinD-Rb pathway, is required for cell cycle progression. Evidence shows that overexpression of E2F-1 can either promote or inhibit the development of tumors, depending on tissue or experimental conditions. However, the clinical impact of E2F-1 expression on esophageal squamous cell carcinoma (ESCC) remains unknown. To analyze E2F-1 expression in ESCC, we investigated the immunoreactivity of E2F-1 and its correlation with clinicopathological features in 122 patients who underwent surgical resection for ESCC. Positive E2F-1 immunostaining was detected in 73 patients (59.8%). Positive E2F-1 immunostaining correlated positively with pathologic stage (P = 0.0103), p-Grade (P = 0.0014) and pT (P = 0.0192). The overall survival rate was worse in patients with E2F-1-positive tumors than in patients with E2F-1-negative tumors (P = 0.0290). Over-expression of E2F-1 is associated with tumor progression and a worse prognosis after surgery in ESCC.

E2F1 expression is related with the poor survival of lymph node-positive breast cancer patients treated with fluorouracil, doxorubicin and cyclophosphamide

The expressions of E2F1 and retinoblastoma protein (pRB) were analyzed in 165 lymph node-positive breast cancers. All patients underwent adjuvant chemotherapy with fluorouracil, doxorubicin and cyclophosphamide (FAC). E2F1 was expressed in 43.6% and pRB was expressed in 46.1%. E2F1 expression was significantly increased in pRB-expressing tumors and was associated with an S-phase fraction. By univariate survival analyses, E2F1 expression and ER were identified as significant prognostic factors for disease recurrence and patient survival. E2F1 was the only significant prognostic factor of patient outcome after FAC chemotherapy by multivariate analysis.

Overexpression of E2F1 associated with LOH at RB locus and hyperphosphorylation of RB in non-small cell lung carcinoma

PURPOSE

E2F1 plays a critical role in cell proliferation, and its function is controlled by the retinoblastoma (RB) protein. We examined the expression of E2F1 and the aberration of RB gene and protein to elucidate what factors contribute to the overexpression of E2F1 in non-small cell lung carcinomas.

METHODS

The expression level of E2F1 in tissues of non-small cell lung carcinomas was measured by means of quantitative reverse transcription-polymerase chain reaction and immunohistochemistry. For RB, we examined loss of heterozygosity (LOH) by PCR-restriction fragment length polymorphism and a variable number of tandem repeats, and protein expression by immunohistochemistry.

RESULTS

Fifteen cases of carcinoma (46%) showed high transcription levels of E2F1 gene. Immunohistochemically, almost all (14 of 15) cases overexpressing E2F1 mRNA were positive for E2F1 protein. LOH at the RB locus was found in 13 of 30 informative cases. In 13 cases with LOH, ten showed overexpression of E2F1 mRNA and protein. Immunohistochemical positivity for phosphorylated RB protein was also closely correlated with overexpression of E2F1.

CONCLUSIONS

Our results suggest that overexpression of E2F1, induced both by LOH at the RB locus and anomalous phosphorylation of the RB protein, is involved in the development of non-small cell lung carcinoma.

Expression of transcription factor E2F-1 in pancreatic ductal carcinoma: an immunohistochemical study

E2F-1 is a transcriptional factor that mediates cell cycle progression from G1 to S phase, thereby influencing tumor progression. However, only a few clinicopathologic studies have been carried out using surgically removed specimens for defining its role in tumor biology. Therefore, we studied the expression of this cell cycle regulator on surgical specimens at the immunohistochemical level, and examined its possible relationship with proliferative index, assessed by analysis of MIB-1 expression, and clinicopathologic factors in pancreatic ductal carcinomas. E2F-1 and MIB-1 were immunostained on 54 surgically removed specimens, and nuclear reactivity was evaluated. The percentage of E2F-1 positive cells (E2F-1 PI) ranged from 3.8% to 71.4%. We found a statistically significant correlation between E2F-1 PI and the histologic grade of tumor differentiation (p = 0.0133), i.e. E2F-1 PI was higher in less-differentiated carcinomas. Furthermore, there was a positive correlation between E2F-1 PI and the percentage of MIB-1 PI (r = 0.763; p < 0.0001). The patients with higher E2F-1 PI (E2F-1 PI > or = 38.0 = median) showed a significantly shorter disease-associated survival time in R0 resection cases (n = 49, p = 0.015). The present analysis seems to support the theory that E2F-1 is upregulated in cell cycle, and its expression reflects the effector function of G1/S progression as far as pancreatic ductal carcinoma is concerned.

ICBP90 belongs to a new family of proteins with an expression that is deregulated in cancer cells

ICBP90 (Inverted CCAAT box Binding Protein of 90 kDa) is a recently identified nuclear protein that binds to one of the inverted CCAAT boxes of the topoisomerase IIalpha (TopoIIalpha) gene promoter. Here, we show that ICBP90 shares structural homology with several other proteins, including Np95, the human and mouse NIRF, suggesting the emergence of a new family of nuclear proteins. Towards elucidating the functions of this family, we analysed the expression of ICBP90 in various cancer or noncancer cell lines and in normal or breast carcinoma tissues. We found that cancer cell lines express higher levels of ICBP90 and TopoIIalpha than noncancer cell lines. By using cell-cycle phase-blocking drugs, we show that in primary cultured human lung fibroblasts, ICBP90 expression peaks at late G1 and during G2/M phases. In contrast, cancer cell lines such as HeLa, Jurkat and A549 show constant ICBP90 expression throughout the entire cell cycle. The effect of overexpression of E2F-1 is more efficient on ICBP90 and TopoIIalpha expression in noncancer cells (IMR90, WI38) than in cancer cells (U2OS, SaOs). Together, these results show that ICBP90 expression is altered in cancer cell lines and is upregulated by E2F-1 overexpression with an efficiency depending on the cancer status of the cell line.

The phenotype of Hurthle and Warthin-like papillary thyroid carcinomas is distinct from classic papillary carcinoma as to the expression of retinoblastoma protein and E2F-1 transcription factor

Retinoblastoma protein plays an important role in controlling cell cycle progression. The active form of retinoblastoma protein binds to E2F-1 and inhibits transcription of S phase genes. Overexpression of E2F-1 has been suggested as an important factor in carcinogenesis. The Hurthle cell (HPCA) and Warthin-like (WLPCA) variants of papillary carcinoma are two closely related entities that arise in association with Hashimoto's thyroiditis and share the presence of oxyphilic changes in the lining of epithelial cells and the presence of papillary nuclear features. The current study included formalin-fixed, paraffin-embedded tissues from 58 cases of thyroid papillary carcinoma: 20 HPCA, 6 WLPCA, 22 conventional papillary carcinomas (PCA), and 10 follicular variants of papillary carcinoma (FVPCA). The immunohistochemical studies were performed for retinoblastoma (Rb-1) and E2F-1, (KH95) after heat-induced epitope retrieval. None of the PCA or FVPCA cases were in the positive range for Rb-1. All cases of HPCA and WLPCA of the thyroid showed reactivity in 50% or more of the nuclei in the neoplastic cell population. As for E2F-1, all cases of HPCA and WLPCA showed positive reactivity, whereas none of the PCA or FVPCA cases were in the positive range. In conclusion, HPCA and WLPCA are Rb-positive and E2F-1-positive; PCA and FVPCA are Rb-negative and E2F1-negative. Hurthle metaplastic epithelium in Hashimoto's thyroiditis is Rb-positive and E2F-1-negative. This phenotypic difference is also helpful in distinguishing hyperplastic Hurthle cell proliferation in Hashimoto's thyroiditis from HPCA or WLPCA.

Transcription factor E2F-1 acts as a growth-promoting factor and is associated with adverse prognosis in non-small cell lung carcinomas

Numerous upstream stimulatory and inhibitory signals converge to the pRb/E2F pathway, which governs cell-cycle progression, but the information concerning alterations of E2F-1 in primary malignancies is very limited. Several in vitro studies report that E2F-1 can act either as an oncoprotein or as a tumour suppressor protein. In view of this dichotomy in its functions and its critical role in cell cycle control, this study examined the following four aspects of E2F-1 in a panel of 87 non-small cell lung carcinomas (NSCLCs), previously analysed for defects in the pRb-p53-MDM2 network: firstly, the status of E2F-1 at the protein, mRNA and DNA levels; secondly, its relationship with the kinetic parameters and genomic instability of the tumours; thirdly, its association with the status of its transcriptional co-activator CBP, downstream target PCNA and main cell cycle regulatory and E2F-1-interacting molecules pRb, p53 and MDM2; and fourthly, its impact on clinical outcome. The protein levels of E2F-1 and its co-activator CBP were significantly higher in the tumour area than in the corresponding normal epithelium (p<0.001). E2F-1 overexpression was associated with increased E2F-1 mRNA levels in 82% of the cases examined. The latter finding, along with the low frequency of E2F-1 gene amplification observed (9%), suggests that the main mechanism of E2F-1 protein overexpression in NSCLCs is deregulation at the transcriptional level. Mutational analysis revealed only one sample with asomatic mutation at codon 371 (Glu-->Asp) and one carrying a polymorphism at codon 393 (Gly-->Ser). Carcinomas with increased E2F-1 positivity demonstrated a significant increase in their growth indexes (r=0.402, p=0.001) and were associated with adverse prognosis (p=0.033 by Cox regression analysis). The main determinant of the positive association with growth was the parallel increase between E2F-1 staining and proliferation (r=0.746, p<0.001), whereas apoptosis was not influenced by the status of E2F-1. Moreover, correlation with the status of the pRb-p53-MDM2 network showed that the cases with aberrant pRb expression displayed significantly higher E2F-1 indexes (p=0.033), while a similar association was noticed in the group of carcinomas with deregulation of the p53-MDM2 feedback loop. In conclusion, the results suggest that E2F-1 overexpression may contribute to the development of NSCLCs by promoting proliferation and provide evidence that this role is further enhanced in a genetic background with deregulated pRb-p53-MDM2 circuitry.

Immunohistochemical expression of cell cycle proteins E2F-1, Cdk-2, Cyclin E, p27(kip1), and Ki-67 in normal placenta and gestational trophoblastic disease

The role of cell cycle protein expression in gestational trophoblastic disease is poorly understood. In this study we investigated the immunostaining patterns of G(1) restriction point and G(1)-S regulatory proteins E2F-1, Cdk2, cyclin E, p27(kip1), and the proliferation marker Ki-67 on routinely processed sections of 29 hydatidiform moles (10 partial moles and 19 complete moles, including 9 persistent moles), 7 choriocarcinomas, and 7 normal placentas. Ki-67 trophoblast staining decreased with increasing gestational age of the placenta, and showed maximal expression in gestational trophoblastic disease. Cyclin-dependent kinase activity, as reflected by Cdk2 expression patterns, also decreased with placental maturation. E2F-1 was uniquely expressed by trophoblasts of moles and choriocarcinoma. Cyclin E was maximally expressed by complete moles and choriocarcinomas, and showed an inverse relationship with the cyclin-dependent kinase inhibitor p27(kip1). Abnormal trophoblastic proliferations may be mediated through interactions of Cdk-2, E2F-1, cyclin E, and p27(kip1). Overexpression of cyclin E was associated with more aggressive forms of gestational trophoblastic disease. However, we did not find distinguishing features between complete moles that spontaneously resolved after evacuation and persistent moles that required chemotherapy. The different expression patterns of cyclin E and E2F-1 in partial and complete moles may be useful in distinguishing these two entities. Furthermore, loss of p27(kip1) in malignant trophoblast may represent a necessary step in the development of choriocarcinoma.

Expression of E2F-1 and E2F-4 is reduced in primary and metastatic breast carcinomas

The E2F family of transcription factors can induce both cell proliferation and apoptosis. Whether they function as oncogenes or tumor suppressors appears to be tissue specific. Their role in breast carcinogenesis remains unclear. We found a decreased expression of E2F-1 and E2F-4 in 70% (7/10) of primary breast carcinomas and in all (10/10) metastatic nodal tissues when compared with the corresponding normal breast tissue. No tumor-specific mutation was detected, but polymorphisms were identified in E2F-1 exon 5 and in the polyserine tract of E2F-4. The presence of polymorphisms did not correlate with E2F expression. Among the 12 human breast cancer cell lines, one contained a missense mutation in E2F-1 exon 2. Five (42%) cell lines overexpressed E2F-1, while three (25%) expressed low levels of the protein. Our results suggest that not only are the E2Fs likely to function as tumor suppressors in breast cancer, but also that their down-regulation may be important in the development of metastases.

Expression and significance of cell cycle-related proteins Cyclin Dl, CDK4, p27, E2F-l and Ets-1 in chondrosarcoma of the jaws

To elucidate the expression and significance of cell cycle-associated proteins in chondrosarcoma of the jaws, Cyclin Dl, CDK4, p27, E2F-l and Ets-l expressions were examined in chondrosarcoma and osteochondroma of the jaws by immunohistochemical ABC method. The results demonstrated that Cyclin Dl, CDK4, p27, E2F-1 and Ets-1 were positive 75% (15 of 20), 60% (12 of 20), 25% (5 of 20), 65% (13 of 20) and 60% (12 of 20) in chondrosarcoma of the jaws, respectively. There was no remarkable difference in the expression of these proteins among histological grades of the chondrosarcoma (P>0.05). In osteochondroma of the jaws, CDK4 and E2F with an equal positivity of 12.5% (1 of 8), whereas p27 was positive 75% (6 of 8). None of the osteochondroma cases was immunohistochemically positive for Cycin Dl and Ets-1. In addition, the positive rate of Cyclin Dl, CDK4, E2F-l and Ets-1 proteins was significantly higher, whereas p27 was lower in chondrosarcoma than in osteochondroma of the jaws (P<0.05). These data show that the expression of cell cycle regulatory proteins is altered in chondrosarcoma of the jaws: cyclin Dl, CDK4, E2F-1 and Ets-1 are over-expressed and p27 is low-expressed.

Minimal regions of chromosomal imbalance in retinoblastoma detected by comparative genomic hybridization

Mutation of both alleles of the retinoblastoma gene (RB1) initiate oncogenesis in developing human retina, but other common genomic alterations are present in the tumors. In order to sublocalize the altered genomic regions, 50 retinoblastoma tumors were examined by comparative genomic hybridization (CGH). The minimal regions most frequent gained were 1q31 (52%), 6p22 (44%), 2p24-p25 (30%) and 13q32-q34 (12%). The minimal region most frequently lost was 16q22 (14%). The overall total number of gains or losses evident on CGH was significantly greater in those tumors with either or both 6p or 1q gain, than in tumors with neither 6p nor 1q gain suggesting that chromosomal instability may be associated with acquisition of these changes. Genes mapping to 6p22 and 1q31 may be important in tumor development in retina subsequent to the loss of RB1 alleles.

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.

Effect of trichostatin A on cell growth and expression of cell cycle- and apoptosis-related molecules in human gastric and oral carcinoma cell lines

The effect of trichostatin A (TSA), histone deacetylase inhibitor, on cell growth and the mechanism of growth modulation was examined in 8 gastric and 3 oral carcinoma cell lines which included 9-cis-retinoic acid resistant (MKN-7 and Ho-1-N-1) and IFN-beta resistant cell lines (MKN-7, -28 and -45). TSA inhibited growth in all cell lines examined. Apoptotic cell death was confirmed by apoptotic ladder formation and induction of a cleaved form (85 kDa) of poly (ADP-ribose) polymerase (PARP) induction. TSA enhanced the protein expression of p21(WAF1), CREB-binding protein, cyclinE, cyclin A, Bak and Bax, while it reduced the expression of E2F-1, E2F-4, HDAC1, p53 and hyperphosphorylated form of Rb. Furthermore, TSA induced morphological changes, such as elongation of cytoplasm and cell-to-cell detachment, in gastric and oral carcinoma cell lines. These results suggest that TSA may inhibit cell growth and induce apoptosis of gastric and oral carcinoma cells through modulation of the expression of cell cycle regulators and apoptosis-regulating proteins.

Effect of trichostatin A on cell growth and expression of cell cycle- and apoptosis-related molecules in human gastric and oral carcinoma cell lines

The effect of trichostatin A (TSA), histone deacetylase inhibitor, on cell growth and the mechanism of growth modulation was examined in 8 gastric and 3 oral carcinoma cell lines which included 9-cis-retinoic acid resistant (MKN-7 and Ho-1-N-1) and IFN-beta resistant cell lines (MKN-7, -28 and -45). TSA inhibited growth in all cell lines examined. Apoptotic cell death was confirmed by apoptotic ladder formation and induction of a cleaved form (85 kDa) of poly (ADP-ribose) polymerase (PARP) induction. TSA enhanced the protein expression of p21(WAF1), CREB-binding protein, cyclinE, cyclin A, Bak and Bax, while it reduced the expression of E2F-1, E2F-4, HDAC1, p53 and hyperphosphorylated form of Rb. Furthermore, TSA induced morphological changes, such as elongation of cytoplasm and cell-to-cell detachment, in gastric and oral carcinoma cell lines. These results suggest that TSA may inhibit cell growth and induce apoptosis of gastric and oral carcinoma cells through modulation of the expression of cell cycle regulators and apoptosis-regulating proteins.

The E2F transcription factors: key regulators of cell proliferation

Ever since its discovery, the RB-1 gene and the corresponding protein, pRB, have been a focal point of cancer research. The isolation of E2F transcription factors provided the key to our current understanding of RB-1 function in the regulation of the cell cycle and in tumor suppression. It is becoming more and more evident that the regulatory circuits governing the cell cycle are very complex and highly interlinked. Certain aspects of RB-1 function, for instance its role in differentiation, cannot be easily explained by the current models of pRB-E2F interaction. One reason is that pRB has targets different from E2F, molecules like MyoD for instance. Another reason may be that we have not completely understood the full complexity of E2F function, itself. In this review, we will try to illuminate the role of E2F in pRB- and p53-mediated tumor suppression pathways with particular emphasis on the aspect of E2F-mediated transcriptional regulation. We conclude that E2F can mediate transcriptional activation as well as transcriptional repression of E2F target genes. The net effect of E2F on the transcriptional activity of a particular gene may be the result of as yet poorly understood protein-protein interactions of E2F with other components of the transcriptional machinery, as well as it may reflect the readout of the different ways of regulating E2F activity, itself. We will discuss the relevance of a thorough understanding of E2F function for cancer therapy.

Expression of cell-cycle-regulating transcription factor E2F-1 in colorectal carcinomas

The expression of E2F-1 in human colorectal carcinomas was examined immunohistochemically, and the correlation of E2F-1 expression with clinicopathological findings and with the expression of p27(Kip1) was analyzed to elucidate the role of E2F-1 in the development and progression of colorectal carcinomas. In nonneoplastic mucosa, a small number of epithelial cells in the proliferative zone were weakly positive for E2F-1. Weak expression of E2F-1 was detected in many adenoma cells. Most of the colorectal carcinomas expressed E2F-1 at various levels, and strong expression of E2F-1 was detected in 56% (49/88) of the cases. There was no correlation between the expression of E2F-1 and any clinicopathological parameters such as tumor stage, depth of tumor invasion and lymph node metastasis. Reduced expression of p27(Kip1) was confirmed to be significantly correlated with deep tumor invasion and presence of metastasis. No correlation was evident between overexpression of E2F-1 and reduced p27(Kip1) expression.