Masaaki Iwatsuki

Epithelial–mesenchymal transition in cancer development and its clinical significance

The epithelial–mesenchymal transition (EMT) plays a critical role in embryonic development. EMT is also involved in cancer progression and metastasis and it is probable that a common molecular mechanism is shared by these processes. Cancer cells undergoing EMT can acquire invasive properties and enter the surrounding stroma, resulting in the creation of a favorable microenvironment for cancer progression and metastasis. Furthermore, the acquisition of EMT features has been associated with chemoresistance which could give rise to recurrence and metastasis after standard chemotherapeutic treatment. Thus, EMT could be closely involved in carcinogenesis, invasion, metastasis, recurrence, and chemoresistance. Research into EMT and its role in cancer pathogenesis has progressed rapidly and it is now hypothesized that novel concepts such as cancer stem cells and microRNA could be involved in EMT. However, the involvement of EMT varies greatly among cancer types, and much remains to be learned. In this review, we present recent findings regarding the involvement of EMT in cancer progression and metastasis and provide a perspective from clinical and translational viewpoints. (Cancer Sci 2009)

Clinical impact of serum exosomal microRNA‐21 as a clinical biomarker in human esophageal squamous cell carcinoma

Exosomes are 40‐nm to 100‐nm membrane vesicles that are secreted by various cells, and they play a major role in cell‐cell communication. The objective of this study was to clarify the significance of the levels of microRNA in exosomes extracted from the sera of patients with esophageal squamous cell cancer (ESCC).

Plastin3 Is a Novel Marker for Circulating Tumor Cells Undergoing the Epithelial–Mesenchymal Transition and Is Associated with Colorectal Cancer Prognosis

Circulating tumor cells (CTC) in blood have attracted attention both as potential seeds for metastasis and as biomarkers. However, most CTC detection systems might miss epithelial-mesenchymal transition (EMT)-induced metastatic cells because detection is based on epithelial markers. First, to discover novel markers capable of detecting CTCs in which EMT has not been repressed, microarray analysis of 132 colorectal cancers (CRC) from Japanese patients was conducted, and 2,969 genes were detected that were overexpressed relative to normal colon mucosa. From the detected genes, we selected those that were overexpressed CRC with distant metastasis. Then, we analyzed the CRC metastasis-specific genes (n = 22) to determine whether they were expressed in normal circulation. As a result, PLS3 was discovered as a CTC marker that was expressed in metastatic CRC cells but not in normal circulation. Using fluorescent immunocytochemistry, we validated that PLS3 was expressed in EMT-induced CTC in peripheral blood from patients with CRC with distant metastasis. PLS3-expressing cells were detected in the peripheral blood of approximately one-third of an independent set of 711 Japanese patients with CRC. Multivariate analysis showed that PLS3-positive CTC was independently associated with prognosis in the training set (n = 381) and the validation set [n = 330; HR = 2.17; 95% confidence interval (CI) = 1.38-3.40 and HR = 3.92; 95% CI = 2.27-6.85]. The association between PLS3-positive CTC and prognosis was particularly strong in patients with Dukes B (HR = 4.07; 95% CI = 1.50-11.57) and Dukes C (HR = 2.57; 95% CI = 1.42-4.63). PLS3 is a novel marker for metastatic CRC cells, and it possesses significant prognostic value.

MicroRNA-200b Regulates Cell Proliferation, Invasion, and Migration by Directly Targeting ZEB2 in Gastric Carcinoma

BackgroundThe microRNA-200 (miR-200) family has been reported to induce epithelial differentiation and suppress epithelial–mesenchymal transition (EMT) by inhibiting translation of zinc finger E-box-binding homeobox (ZEB) 1 and 2 mRNAs in several types of cancers. This study aimed to clarify the role of miR-200b in regulating EMT and promoting cellular proliferation, invasion, and migration in gastric cancer.MethodsThe relationships among the expression levels of miR-200b, ZEB1 and ZEB2, and E-cadherin mRNAs were analyzed by quantitative real-time reverse transcription–polymerase chain reaction in frozen tissue samples from 40 gastric cancer patients who underwent gastrectomy from 2008 to 2010. The effects of miR-200b on EMT in gastric cancer cells in vitro were also analyzed.ResultsDiffuse histologic type, depth of tumor, tumor size, lymph node metastasis, and lymphatic invasion were significantly higher in the low-miR-200b expression group compared with the high expression group. There was a strong correlation between the levels of miR-200b, and ZEB2 and E-cadherin mRNAs in gastric cancer patients. Upregulation of miR-200b in gastric cancer cells changed the cell morphology from fibroblast- to epithelial-like, associated with localization of E-cadherin to the plasma membrane. ZEB2 mRNA levels fell, while E-cadherin expression levels increased in gastric cells overexpressing miR-200b, associated with significantly reduced cellular proliferation, and inhibition of cellular migration and invasion.ConclusionsmiR-200b regulates ZEB2 expression and thus controls metastasis in gastric cancer.

Cancer stem cells and chemoradiation resistance

Cancer is a disease of genetic and epigenetic alterations, which are emphasized as the central mechanisms of tumor progression in the multistepwise model. Discovery of rare subpopulations of cancer stem cells (CSCs) has created a new focus in cancer research. The heterogeneity of tumors can be explained with the help of CSCs supported by antiapoptotic signaling. CSCs mimic normal adult stem cells by demonstrating resistance to toxic injuries and chemoradiation therapy. Moreover, they might be responsible for tumor relapse following apparent beneficial treatments. Compared with hematopoietic malignancies, conventional therapy regimes in solid tumors have improved the overall survival marginally, illustrating the profound impact of treatment resistance. This implies that the present therapies, which follow total elimination of rapidly dividing and differentiated tumor cells, need to be modified to target CSCs that repopulate the tumor. In this review article, we report on recent findings regarding the involvement of CSCs in chemoradiation resistance and provide new insights into their therapeutic implications in cancer. (Cancer Sci 2008; 99: 1871–1877)

p53-Altered FBXW7 Expression Determines Poor Prognosis in Gastric Cancer Cases

A molecular target associated with the progression of gastric cancer has not yet been uncovered. FBXW7 is a tumor suppressor gene transcriptionally controlled by p53 that plays a role in the regulation of cell cycle exit and reentry via c-Myc degradation. Few studies have addressed the clinical significance of FBXW7 expression in gastric cancer. Therefore, we examined FBXW7 mRNA expression to determine its clinicopathologic significance in 100 cases of gastric cancer. Low expression levels of FBXW7 in primary gastric cancer contributed to malignant potential, such as lymph node metastasis (P = 0.0012), tumor size (P = 0.0003), and poor prognosis (P = 0.018). In comparison with 52 cases of gastric cancer without the p53 mutation, 29 cases with the mutation exhibited lower expression levels of FBXW7 (P = 0.0034), revealing a significant relationship between p53 mutation and FBXW7 expression. Furthermore, we found that gastric cancer patients who had low FBXW7 expression levels and p53 mutation had a distinctively poor prognosis in comparison with other subgroups (P = 0.0033). In conclusion, we showed a role for p53 in the transcriptional regulation of FBXW7 expression in clinical gastric cancer cases and showed that disruption of both p53 and FBXW7 contributes to poor prognosis.

Overexpression of microRNA-223 regulates the ubiquitin ligase FBXW7 in oesophageal squamous cell carcinoma

Background:F-box and WD repeat domain-containing 7 (FBXW7) is a cell cycle regulatory gene whose protein product ubiquitinates positive cell cycle regulators such as c-Myc, cyclin E, and c-Jun, thereby acting as a tumour-suppressor gene. This study focused on microRNA-223 (miR-223), which is a candidate regulator of FBXW7 mRNA. The aim of this study was to clarify the clinical significance of miR-223 and FBXW7 in oesophageal squamous cell carcinoma (ESCC) patients, and to elucidate the mechanism by which FBXW7 is regulated by miR-223.Methods:The expression levels of miR-223 and the expression of FBXW7 protein was examined using 109 resected specimens to determine the clinicopathological significance. We also investigated the role of miR-223 in the regulation of FBXW7 expression in ESCC cell lines in an in vitro analysis.Results:We found that miR-223 expression was significantly higher in cancerous tissues than in the corresponding normal tissues. There was a significant inverse relationship between the expression levels of miR-223 and FBXW7 protein. Moreover, patients with high miR-223 expression demonstrated a significantly poorer prognosis than those with low expression. On the basis of a series of gain-of-function and loss-of-function studies in vitro, we identified FBXW7 as a functional downstream target of miR-223.Conclusion:Our present study indicates that high expression of miR-223 had a significant adverse impact on the survival of ESCC patients through repression of the function of FBXW7.

Loss of FBXW7, a cell cycle regulating gene, in colorectal cancer: Clinical significance

This study focused on a cell cycle regulatory gene, FBXW7, which ubiquitinates c‐Myc and cyclin E and promotes exit from the cell cycle. We determined the expression level of FBXW7 in colorectal cancer (CRC) cases, correlated those values with clinicopathologic features, and characterized the molecular mechanism of reduced expression of FBXW7 in CRC cells in vitro. FBXW7 mRNA and protein expression were evaluated in 93 CRC cases. Using CGH array, the copy number aberrations of the flanking region of FBXW7 were evaluated in another 130 CRC specimens. In vitro analysis of FBXW7 gene silencing in CRC cells was conducted. FBXW7 mRNA expression was significantly lower in tumor tissues than the corresponding normal tissues. The low FBXW7 expression group showed a significantly poorer prognosis than patients in the high expression group. A concordant relationship was observed between the incidence of FBXW7 repression and the genetic alteration. The incidence of genetic alteration was associated with the stage of disease progression. In vitro, FBXW7‐specific siRNA enhanced expression of c‐MYC and cyclin E proteins and up‐regulated cell proliferation. Genetic alterations in tumors led to the loss of FBXW7 expression and increased cell proliferation. FBXW7 expression provides a prognostic factor for patients with CRC.

Serum microRNA-21 is a novel biomarker in patients with esophageal squamous cell carcinoma

It was recently revealed that microRNAs (miRNAs) can stably exist in serum and may affect the pathogenesis of several diseases. However, there are few reports that have demonstrated the significance of miRNAs in the serum of patients with esophageal squamous cell carcinoma (ESCC). Thus, the aims of this study were to clarify the status of miRNA‐21 in serum of ESCC patients and to reveal the usefulness of this molecule as a biomarker.

PIK3CA Mutation Is Associated with a Favorable Prognosis among Patients with Curatively Resected Esophageal Squamous Cell Carcinoma

Purpose: PIK3CA encodes the catalytic subunit of PI3K, p110α. Mutant PIK3CA stimulates the AKT pathway and promotes cancer cell proliferation. PIK3CA mutations have been associated with poor prognosis in patients with colorectal or lung cancer. In contrast, the relationship between PIK3CA mutations and favorable prognoses has been shown in breast cancer. However, the influence of PIK3CA mutations on the prognosis of patients with esophageal squamous cell carcinoma (ESCC) remains unclear. Experimental Design: Using a nonbiased database of 219 curatively resected ESCCs and eight esophageal cancer cell lines, we evaluated PIK3CA mutational status by pyrosequencing. The expression of p53 and phosphorylated AKT (i.e., AKT activation) was evaluated by immunohistochemistry. Results: PIK3CA mutations in exon 9 and/or 20 were detected in 46 cases (21%). No ESCC cell line harbored PIK3CA mutations. PIK3CA mutations were significantly associated with phosphorylated AKT expression, but not with p53 expression, sex, age at surgery, tobacco use, alcohol use, or histologic grade. Compared with wild-type PIK3CA cases, patients with PIK3CA mutations in exons 9 and/or 20 experienced significantly better disease-free survival [log-rank P = 0.0089; univariate HR: 0.37, 95% confidence interval (CI): 0.15–0.75, P = 0.0042; multivariate HR: 0.34, 95% CI: 0.10–0.86, P = 0.021] and overall survival (log-rank P = 0.012; univariate HR: 0.38, 95% CI: 0.16–0.78, P = 0.0060; multivariate HR: 0.35, 95% CI: 0.10–0.90, P = 0.028). Conclusion: PIK3CA mutations in ESCC are associated with longer survival, suggesting its role as a prognostic biomarker. Future studies are needed to confirm this association and to elucidate the exact mechanisms by which PIK3CA mutations affect tumor behavior. Clin Cancer Res; 19(9); 2451–9. ©2013 AACR.