Takatsugu Ishimoto

CD44 Variant Regulates Redox Status in Cancer Cells by Stabilizing the xCT Subunit of System xc− and Thereby Promotes Tumor Growth

CD44 is an adhesion molecule expressed in cancer stem-like cells. Here, we show that a CD44 variant (CD44v) interacts with xCT, a glutamate-cystine transporter, and controls the intracellular level of reduced glutathione (GSH). Human gastrointestinal cancer cells with a high level of CD44 expression showed an enhanced capacity for GSH synthesis and defense against reactive oxygen species (ROS). Ablation of CD44 induced loss of xCT from the cell surface and suppressed tumor growth in a transgenic mouse model of gastric cancer. It also induced activation of p38(MAPK), a downstream target of ROS, and expression of the gene for the cell cycle inhibitor p21(CIP1/WAF1). These findings establish a function for CD44v in regulation of ROS defense and tumor growth.

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).

Alternative splicing of CD44 mRNA by ESRP1 enhances lung colonization of metastatic cancer cell

In cancer metastasis, various environmental stressors attack the disseminating cells. The successful colonization of cancer cells in secondary sites therefore requires the ability of the cells to avoid the consequences of such exposure to the stressors. Here we show that orthotopic transplantation of a CD44 variant isoform-expressing (CD44v(+)) subpopulation of 4T1 breast cancer cells, but not that of a CD44v(-) subpopulation, in mice results in efficient lung metastasis accompanied by expansion of stem-like cancer cells. Such metastasis is dependent on the activity of the cystine transporter xCT, and the stability of this protein is controlled by CD44v. We find that epithelial splicing regulatory protein 1 regulates the expression of CD44v, and knockdown of epithelial splicing regulatory protein 1 in CD44v(+) cells results in an isoform switch from CD44v to CD44 standard (CD44s), leading to reduced cell surface expression of xCT and suppression of lung colonization. The epithelial splicing regulatory protein 1-CD44v-xCT axis is thus a potential therapeutic target for the prevention of metastasis.

Modulation of glucose metabolism by CD44 contributes to antioxidant status and drug resistance in cancer cells

An increased glycolytic flux accompanied by activation of the pentose phosphate pathway (PPP) is implicated in chemoresistance of cancer cells. In this study, we found that CD44, a cell surface marker for cancer stem cells, interacts with pyruvate kinase M2 (PKM2) and thereby enhances the glycolytic phenotype of cancer cells that are either deficient in p53 or exposed to hypoxia. CD44 ablation by RNA interference increased metabolic flux to mitochondrial respiration and concomitantly inhibited entry into glycolysis and the PPP. Such metabolic changes induced by CD44 ablation resulted in marked depletion of cellular reduced glutathione (GSH) and increased the intracellular level of reactive oxygen species in glycolytic cancer cells. Furthermore, CD44 ablation enhanced the effect of chemotherapeutic drugs in p53-deficient or hypoxic cancer cells. Taken together, our findings suggest that metabolic modulation by CD44 is a potential therapeutic target for glycolytic cancer cells that manifest drug resistance.

Tumor Necrosis Factor-α Regulates Transforming Growth Factor-β-dependent Epithelial-Mesenchymal Transition by Promoting Hyaluronan-CD44-Moesin Interaction

Aberrant epithelial-mesenchymal transition (EMT) is involved in development of fibrotic disorders and cancer invasion. Alterations of cell-extracellular matrix interaction also contribute to those pathological conditions. However, the functional interplay between EMT and cell-extracellular matrix interactions remains poorly understood. We now show that the inflammatory mediator tumor necrosis factor-α (TNF-α) induces the formation of fibrotic foci by cultured retinal pigment epithelial cells through activation of transforming growth factor-β (TGF-β) signaling in a manner dependent on hyaluronan-CD44-moesin interaction. TNF-α promoted CD44 expression and moesin phosphorylation by protein kinase C, leading to the pericellular interaction of hyaluronan and CD44. Formation of the hyaluronan-CD44-moesin complex resulted in both cell-cell dissociation and increased cellular motility through actin remodeling. Furthermore, this complex was found to be associated with TGF-β receptor II and clathrin at actin microdomains, leading to activation of TGF-β signaling. We established an in vivo model of TNF-α-induced fibrosis in the mouse eye, and such ocular fibrosis was attenuated in CD44-null mice. The production of hyaluronan and its interaction with CD44, thus, play an essential role in TNF-α-induced EMT and are potential therapeutic targets in fibrotic disorders.

CD44s regulates the TGF-β-mediated mesenchymal phenotype and is associated with poor prognosis in patients with hepatocellular carcinoma

The prognosis for individuals diagnosed with hepatocellular carcinoma (HCC) remains poor because of the high frequency of invasive tumor growth, intrahepatic spread, and extrahepatic metastasis. Here, we investigated the role of the standard isoform of CD44 (CD44s), a major adhesion molecule of the extracellular matrix and a cancer stem cell marker, in the TGF-β-mediated mesenchymal phenotype of HCC. We found that CD44s was the dominant form of CD44 mRNA expressed in HCC cells. Overexpression of CD44s promoted tumor invasiveness and increased the expression of vimentin, a mesenchymal marker, in HCC cells. Loss of CD44s abrogated these changes. Also in the setting of CD44s overexpression, treatment with TGF-β1 induced the mesenchymal phenotype of HCC cells, which was characterized by low E-cadherin and high vimentin expression. Loss of CD44s inhibited TGF-β-mediated vimentin expression, mesenchymal spindle-like morphology, and tumor invasiveness. Clinically, overexpression of CD44s was associated with low expression of E-cadherin, high expression of vimentin, a high percentage of phospho-Smad2-positive nuclei, and poor prognosis in HCC patients, including reduced disease-free and overall survival. Together, our findings suggest that CD44s plays a critical role in the TGF-β-mediated mesenchymal phenotype and therefore represents a potential therapeutic target for HCC.

CD44+ slow‐cycling tumor cell expansion is triggered by cooperative actions of Wnt and prostaglandin E2 in gastric tumorigenesis

(Cancer Sci 2010; 101: 673–678)

xCT inhibition depletes CD44v-expressing tumor cells that are resistant to EGFR-targeted therapy in head and neck squamous cell carcinoma

The targeting of antioxidant systems that allow stem-like cancer cells to avoid the adverse consequences of oxidative stress might be expected to improve the efficacy of cancer treatment. Here, we show that head and neck squamous cell carcinoma (HNSCC) cells that express variant isoforms of CD44 (CD44v) rely on the activity of the cystine transporter subunit xCT for control of their redox status. xCT inhibition selectively induces apoptosis in CD44v-expressing tumor cells without affecting CD44v-negative differentiated cells in the same tumor. In contrast to CD44v-expressing undifferentiated cells, CD44v-negative differentiated cells manifest EGF receptor (EGFR) activation and rely on EGFR activity for their survival. Combined treatment with inhibitors of xCT-dependent cystine transport and of EGFR resulted in a synergistic reduction of EGFR-expressing HNSCC tumor growth. Thus, xCT-targeted therapy may deplete CD44v-expressing undifferentiated HNSCC cells and concurrently sensitize the remaining differentiating cells to available treatments including EGFR-targeted therapy.

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.

LINE-1 hypomethylation is associated with a poor prognosis among patients with curatively resected esophageal squamous cell carcinoma.

Objective: To investigate the relationship between the long interspersed nucleotide element-1 (L1/LINE-1) methylation level and the disease-free survival and cancer-specific survival in patients with esophageal squamous cell carcinoma (ESCC). Background: Cancer cells exhibit 2 types of deoxyribonucleic acid (DNA) methylation alterations: global DNA hypomethylation and site-specific CpG island promoter hypermethylation. Global DNA hypomethylation plays a role in genomic instability and carcinogenesis. DNA methylation in the LINE-1 repetitive element is a good indicator of the global DNA methylation level. Although the LINE-1 methylation level is attracting interest as a useful marker for predicting cancer prognosis, the prognostic significance of LINE-1 hypomethylaiton in ESCC remains unclear. Methods: Using 217 curatively resected ESCC specimens, we quantified the LINE-1 methylation by utilizing the bisulfite pyrosequencing technology. Promoter methylation levels of MGMT and MLH1 were also evaluated by pyrosequencing. Results: ESCC showed significantly lower LINE-1 methylation levels in comparison with matched normal esophageal mucosa (P < 0.0001; N = 50). LINE-1 hypomethylation was significantly associated with disease-free survival [log-rank P = 0.0008; univariate hazard ratio (HR): 2.32, 95% confidence interval (CI): 1.38–3.84, P = 0.0017; multivariate HR: 1.81, 95% CI: 1.06–3.05, P = 0.031] and cancer-specific survival (log-rank P = 0.0020; univariate HR: 2.21, 95% CI: 1.33–3.60, P = 0.0026; multivariate HR: 1.87, 95% CI: 1.12–3.08, P = 0.018]. MGMT and MLH1 hypermethylation were not associated with patient prognosis. Conclusions: LINE-1 hypomethylation in ESCC is associated with a shorter survival, thus suggesting that it has potential for use as a prognostic biomarker.