Diagnostic potential and limitation of imaging cancer cells in cytological samples using telomerase-specific replicative adenovirus.

Cytological cancer screening that targets genetic or epigenetic abnormalities may be a viable alternative to morphological screening. Detecting cancer cells by specific genetic markers helps their easy detection in cytological samples. We recently established the telomerase-specific replication-selective adenovirus OBP-401, in which the human telomerase reverse transcriptase (hTERT) gene promoter has been inserted upstream of the E1 genes, and in which the green fluorescent protein (GFP) gene is driven by the CMV promoter. This virus selectively replicates only in telomerase-positive cells, expressing GFP, and therefore may be a tool for cancer screening. In the present study, we first confirmed that cytological samples can easily be infected with OBP-401, allowing visualization of GFP-positive cells under fluorescent microscopy 24 h after infection. After 32 cytological samples from patients with cervical, endometrial or ovarian cancers were infected with OBP-401, GFP signals were detected in 31 (96%) of the samples. However, some normal endometrial scrapings exhibited GFP-signals, possibly due to endometrial glandular cells with constitutive telomerase activity. The ability of OBP-401 to enrich cancer cells was then tested. Cytological samples containing cervical or endometrial cancer cells were infected with OBP-401, and GFP-positive cells were sorted by flow cytometry; DNA was extracted from the GFP-positive cells. Direct DNA sequencing or methylation-specific PCR identified cancer-derived mutations or hypermethylations of tumor suppressor genes more efficiently than analyses using crude cytological samples. Thus, OBP-401-based sorting of GFP-positive cells successfully enriched cancer cells, allowing efficient detection of genetic or epigenetic abnormalities in cytological samples.

Role of menin in the regulation of telomerase activity in normal and cancer cells.

Transcriptional activation of human telomerase reverse transcriptase (hTERT) is critical for telomerase expression, a major step for cellular immortality and carcinogenesis. Although several transcriptional activators have been identified, factors responsible for repressing the hTERT promoter are largely unknown. Gene screening that employed enhanced retroviral mutagenesis has identified potential hTERT repressors. Among these, menin, which is a tumor suppressor and a gene product of MEN1, has been reported to play a critical role. In the present study, we further analyzed menin's role in the transcriptional regulation of hTERT in normal and cancer cells. Luciferase reporter assays that use the hTERT promoter have demonstrated that an overexpression of menin decreases the transcriptional activity of the hTERT gene in a cell-type specific manner. Mutation and deletion analyses of the hTERT promoter demonstrated that there was no specific site on the promoter that was responsible for the menin-mediated transcriptional inhibition. An electrophoretic mobility shift assay using recombinant menin protein generated the binding complexes with the hTERT promoter, which was completely diminished by the addition of poly-dI-dC. This indicates that there is a sequence-independent binding of menin. RT-PCR assays have revealed that overexpression of menin inhibits hTERT mRNA expression in some cell types, although this inhibition does not lead to a significant down-regulation of telomerase activity. In cancer cell lines and in normal cells, the siRNA-based inhibition of MEN1 does not lead to the up-regulation of hTERT mRNA expression. No significant correlation has been found between menin and hTERT mRNA expressions in a variety of cancer cell lines and clinical tissue samples. Thus, while menin appears to have some inhibitory effects on the hTERT promoter, possibly via the sequence-independent binding to the promoter, the present study does not support the hypothesis that menin has a crucial role in the determination of telomerase activity in normal and cancer cells.

Concomitant activation of AKT with extracellular-regulated kinase 1/2 occurs independently of PTEN or PIK3CA mutations in endometrial cancer and may be associated with favorable prognosiss.

Deregulated signaling via the phosphatidylinositol 3-kinase (PI3K) pathway is common in many types of cancer, but its clinicopathological significance in endometrial cancer remains unclear. In the present study, we examined the status of the PI3K signaling pathway, especially in relation to PTEN and PIK3CA status, in endometrioid-type endometrial cancer. The immunohistochemical analysis revealed a high level of phosphorylated (p)-AKT expression, which is a hallmark of activated PI3K signaling, in approximately 60% of endometrial cancers. There was no correlation between p-AKT expression and clinicopathological characteristics, such as International Federation of Gynecology and Obstetrics stage, tumor grade, and myometrial invasion. Unexpectedly, a high level of p-AKT expression occurred independently of the presence of PTEN or PIK3CA mutations. Furthermore, p-AKT expression did not correlate with the expression of potential downstream targets, including p-mTOR and p-FOXO1/3a. In turn, p-AKT expression was strongly associated with extracellular-regulated kinase 1/2 expression (P = 0.0031), which is representative of the activated RAS-MAP kinase pathway. Kaplan-Meier analysis suggested that low p-AKT expression was associated with low rates of relapse-free survival, although the difference was not statistically significant, indicating that AKT activation does not confer worse prognosis. The present study demonstrates the presence of complex signaling pathways that might mask the conventional tumorigenic PTEN-PI3K-AKT-mTOR pathway, and strongly suggests a close association between the extracellular-regulated kinase and PI3K pathways in this tumor type.

High Twist expression is involved in infiltrative endometrial cancer and affects patient survival.

Epithelial-mesenchymal transition (EMT) is critical not only for morphogenesis during embryonic development but also the conversion of early-stage tumors into infiltrative phenotypes. The present study examines the expression of Twist, a highly conserved bHLH transcription factor that is known to promote EMT, and evaluated its prognostic significance in endometrial cancers. Tissue specimens from 70 patients with endometrial cancer who underwent primary surgery were immunohistochemically evaluated for Twist expression. A semiquantitative scoring system was developed based on the intensity and extent of cancer cells with Twist expression. Thirty-six patients (51%) exhibited high Twist expression and 34 (49%) had low expression. Most cases exhibited both cytoplasmic and nuclear staining mainly observed in cancer foci and, preferentially, at the margin but, in some cases, the stromal cells located adjacent to cancer foci as well. Among various clinical variables, high Twist expression was significantly associated with deep myometrial invasion (>1/2) (P = .012) and concurrent with decreased E-cadherin expression (P < .001), a hallmark of EMT. In univariate survival analyses, both myometrial invasion and Twist expression influenced overall survival, but Cox multivariate analyses revealed that only Twist was an independent predictor of patient survival (hazard ratio, 5.12; P = .023). Thus, our data implies that high Twist expression is a potential novel prognostic factor for disease survival of endometrial cancer. Furthermore, the present study implicates Twist as a potential therapeutic target for this tumor type.

Analysis of telomeric single-strand overhang length in human endometrial cancers.

The 3' single-strand telomeric overhang (3'-OH) is a key component of telomere structure. Although telomere length has been well analyzed in a variety of human cancers, no information is available on the 3'-OH length in cancers. In the present study, we examined the 3'-OH length in normal and malignant endometria using telomere-oligonucleotide ligation assay. Although 3'-OH lengths varied among patients, 3'-OH length observed in endometrial cancers was significantly shorter than that found in samples derived from normal endometria (P < 0.001: Student's t-test), suggesting that erosion of 3'-OH length induces impaired telomeric integrity and genomic instability, leading to carcinogenesis. Interestingly, we found that the most aggressive subtypes of endometrial cancers harbored significantly longer 3'-OH length than those with non-aggressive subtypes (P < 0.001: Sheffe's test), suggesting that cancer cells with long 3'-OH length have growth advantage due to their stabilized telomere ends. In contrast, we failed to observe an association between overall telomere length and any clinicopathological characteristics of endometrial cancers. These findings suggest that erosion of 3'-OH length, rather than overall telomere length, play roles in endometrial carcinogenesis. Furthermore, long 3'-OH may serve as a molecular marker for aggressive phenotype of tumors.

Association of mismatch repair deficiency with PTEN frameshift mutations in endometrial cancers and the precursors in a Japanese population.

We studied mismatch repair deficiency and PTEN (phosphatase and tensin homologue deleted on chromosome 10) mutations in endometrial cancers and hyperplasias in a Japanese population. Methylation-sensitive restriction enzyme polymerase chain reaction revealed MLH1 hypermethylation in 21 (38%) of 56 endometrial cancers. Sequencing analysis revealed PTEN mutations in 22 patients with cancer (39%) in exons 5 and 8. A PTEN frameshift mutation was associated significantly with MLH1 hypermethylation (P = .01) and a highly positive phenotype with microsatellite instability (P < .001) but not with a PTEN missense mutation. In hyperplasia, MLH1 hypermethylation was similarly observed (11/27 [41%]), but the PTEN mutation was less frequent (5/27 [19%]), observed only in atypical hyperplasias; among the 5 patients with a PTEN mutation, the 2 patients with frameshift mutations had MLH1 hypermethylation, but the 3 patients with missense mutations had unmethylated MLH1. These findings indicate that MLH1 hypermethylation is an early event frequently occurring in hyperplasia without atypia, whereas the PTEN mutation occurs later, mostly in atypical hyperplasia, possibly caused by MLH1 hypermethylation.

Forkhead transcription factor FOXO1 is a direct target of progestin to inhibit endometrial epithelial cell growth.

PURPOSE AND EXPERIMENTAL DESIGN: Despite the therapeutic utility of progestin in invasive and preinvasive endometrial neoplasias, the molecular mechanisms through which it exerts inhibitory effects on endometrial epithelial growth are largely unknown. The aim of the study was to clarify the molecular mechanisms of progestin action to endometrial epithelial cells using originally established in vitro and in vivo treatment models for immortalized and transformed endometrial epithelial cell lines that express progesterone receptor. RESULTS: In this model, progestin effectively inhibited the cell growth, inducing G0/G1 arrest rather than apoptosis without p21/WAF-1 induction. Using DNA microarray analysis, we identified 24 genes whose expression increased more than 10-fold on progestin treatment. Of these genes, we paid special attention to forkhead box transcription factor FOXO1, known as a key gene for endometrial decidualization. Progestin markedly induced FOXO1 gene expression mainly in the nuclei in vitro and in vivo. This induction was not due to the canonical activation of FOXO1 via protein dephosphorylation but due to FOXO1 promoter activation and mRNA induction. siRNA inhibition of FOXO1 significantly attenuated the effects of progestin to inhibit endometrial epithelial cell growth. Disrupting Akt activity by the introduction of the dominant negative form of Akt increased nuclear FOXO1 accumulation and enhanced the effect of progestin. CONCLUSION: These findings suggest that FOXO1 is a direct target of progestin, implicating novel molecular mechanisms of progestin to eradicate endometrial neoplasia.

Activation of ERK1/2 occurs independently of KRAS or BRAF status in endometrial cancer and is associated with favorable prognosis.

The extracellular-regulated kinase (ERK) signaling pathway plays important roles in regulating the malignant potential of cancer cells in vitro. However, the effect of ERK signaling on the prognosis of human tumors is not clearly understood. The present study examined the expression of phosphorylated ERK1/2 (p-ERK1/2) as a hallmark of ERK activation, in relation to KRAS and BRAF mutations, in 63 endometrial cancer specimens with endometrioid-subtype, in order to clarify the prognostic value of p-ERK1/2 expression. Immmunohistochemical analysis revealed that 40 tumors (63%) expressed p-ERK1/2, with varying levels of expression. Total ERK1/2 expression was also evaluated in a subset of tumors; most cases expressed ERK1/2 constitutively but no correlation was observed with p-ERK expression, indicating that p-ERK1/2 staining was not due to ERK overexpression but to hyperactivation of ERK1/2. There was no statistically significant correlation between p-ERK1/2 expression and clinicopathological features, including patient age, International Federation of Gynecology and Obstetrics stage, pathological grade, myometrial invasion and lymph node metastasis. Sequencing analysis indicated that 23% of patients had a mutation in exon 1 of KRAS, whereas none of the patients had a mutation in exons 11 or 15 of BRAF, which are reportedly hot spots for mutation in many tumor types. There was no significant correlation between KRAS or BRAF status and p-ERK1/2 expression. Unexpectedly, patients with low p-ERK1/2 expression had significantly lower relapse-free survival (P = 0.041) and overall survival (P = 0.020). Multivariate Cox regression analysis indicated that p-ERK1/2 expression was an independent prognostic indicator for overall survival (P = 0.047). These findings suggest that ERK activation occurs in a KRAS- and BRAF-independent manner in endometrial cancer, and is associated with favorable prognosis.

Aberrant expression and mutations of TGF-beta receptor type II gene in endometrial cancer.

OBJECTIVE: Transforming growth factor beta (TGF-beta) is a multifunctional cytokine that strongly inhibits epithelial cell growth. Disabling of TGF-beta signaling is thought to be involved in development of a variety of tumors in which abnormal expression or function of TGF-beta receptor plays critical roles. In the present study, we examined aberrant expression and mutation of the gene TGF-beta receptor type II (TbetaRII) in endometrial cancers of endometrioid subtype. METHODS AND RESULTS: Real-time PCR analysis using surgical tissue specimens of 27 endometrial cancers and 24 normal endometria revealed that endometrial cancers had significantly decreased levels of TbetaRII mRNA expression (mean level 2.44 +/- 2.65), compared to normal endometria (mean level 7.23 +/- 6.07) (P < 0.001). Methylation status of TbetaRII promoter containing 30 CpGs was examined by bisulfite sequencing analysis, and 98% (51/52) of the patients were found to have unmethylated TbetaRII promoter, indicating that promoter hypermethylation is not the major cause of decreased expression of TbetaRII in endometrial cancers. Mutational analysis revealed that 15.1% (8/53) of endometrial cancers had frameshift mutations at polyadenine repeats in exon 3 of the TbetaRII gene. Notably, these mutations were preferentially accumulated in patients with MSI-H phenotype (7/19:37%) (P < 0.001) or with those with methylated MLH1 promoters (6/16:38%) (P < 0.01). Thus, it appears that the TbetaRII gene is a target of mismatch repair deficiency. CONCLUSION: Taken together, we found that the decreased expression of TbetaRII as well as frameshift mutation of TbetaRII via mismatch repair deficiency frequently occurs in this tumor type, possibly causing loss of receptor function and unresponsiveness of TGF-beta signaling that may lead to endometrial carcinogenesis.