Ichiro Ota

EZH2 is a marker of aggressive breast cancer and promotes neoplastic transformation of breast epithelial cells

The Polycomb Group Protein EZH2 is a transcriptional repressor involved in controlling cellular memory and has been linked to aggressive prostate cancer. Here we investigate the functional role of EZH2 in cancer cell invasion and breast cancer progression. EZH2 transcript and protein were consistently elevated in invasive breast carcinoma compared with normal breast epithelia. Tissue microarray analysis, which included 917 samples from 280 patients, demonstrated that EZH2 protein levels were strongly associated with breast cancer aggressiveness. Overexpression of EZH2 in immortalized human mammary epithelial cell lines promotes anchorage-independent growth and cell invasion. EZH2-mediated cell invasion required an intact SET domain and histone deacetylase activity. This study provides compelling evidence for a functional link between dysregulated cellular memory, transcriptional repression, and neoplastic transformation.

Tumor cell traffic through the extracellular matrix is controlled by the membrane-anchored collagenase MT1-MMP

As cancer cells traverse collagen-rich extracellular matrix (ECM) barriers and intravasate, they adopt a fibroblast-like phenotype and engage undefined proteolytic cascades that mediate invasive activity. Herein, we find that fibroblasts and cancer cells express an indistinguishable pericellular collagenolytic activity that allows them to traverse the ECM. Using fibroblasts isolated from gene-targeted mice, a matrix metalloproteinase (MMP)–dependent activity is identified that drives invasion independently of plasminogen, the gelatinase A/TIMP-2 axis, gelatinase B, collagenase-3, collagenase-2, or stromelysin-1. In contrast, deleting or suppressing expression of the membrane-tethered MMP, MT1-MMP, in fibroblasts or tumor cells results in a loss of collagenolytic and invasive activity in vitro or in vivo. Thus, MT1-MMP serves as the major cell-associated proteinase necessary to confer normal or neoplastic cells with invasive activity.

A Wnt–Axin2–GSK3β cascade regulates Snail1 activity in breast cancer cells

Accumulating evidence indicates that hyperactive Wnt signalling occurs in association with the development and progression of human breast cancer. As a consequence of engaging the canonical Wnt pathway, a β-catenin–T-cell factor (TCF) transcriptional complex is generated, which has been postulated to trigger the epithelial–mesenchymal transition (EMT) that characterizes the tissue-invasive phenotype. However, the molecular mechanisms by which the β-catenin–TCF complex induces EMT-like programmes remain undefined. Here, we demonstrate that canonical Wnt signalling engages tumour cell dedifferentiation and tissue-invasive activity through an Axin2-dependent pathway that stabilizes the Snail1 zinc-transcription factor, a key regulator of normal and neoplastic EMT programmes. Axin2 regulates EMT by acting as a nucleocytoplasmic chaperone for GSK3β, the dominant kinase responsible for controlling Snail1 protein turnover and activity. As dysregulated Wnt signalling marks a diverse array of cancerous tissue types, the identification of a β-catenin–TCF-regulated Axin2–GSK3β–Snail1 axis provides new mechanistic insights into cancer-associated EMT programmes.

MT1-MMP-dependent neovessel formation within the confines of the three-dimensional extracellular matrix.

During angiogenesis, endothelial cells initiate a tissue-invasive program within an interstitial matrix comprised largely of type I collagen. Extracellular matrix–degradative enzymes, including the matrix metalloproteinases (MMPs) MMP-2 and MMP-9, are thought to play key roles in angiogenesis by binding to docking sites on the cell surface after activation by plasmin- and/or membrane-type (MT) 1-MMP–dependent processes. To identify proteinases critical to neovessel formation, an ex vivo model of angiogenesis has been established wherein tissue explants from gene-targeted mice are embedded within a three-dimensional, type I collagen matrix. Unexpectedly, neither MMP-2, MMP-9, their cognate cell-surface receptors (i.e., β3 integrin and CD44), nor plasminogen are essential for collagenolytic activity, endothelial cell invasion, or neovessel formation. Instead, the membrane-anchored MMP, MT1-MMP, confers endothelial cells with the ability to express invasive and tubulogenic activity in a collagen-rich milieu, in vitro or in vivo, where it plays an indispensable role in driving neovessel formation.

Induction of a MT1-MMP and MT2-MMP-dependent basement membrane transmigration program in cancer cells by Snail1

The ability of carcinoma cells arising at primary sites to cross their underlying basement membrane (BM), a specialized form of extracellular matrix that subtends all epithelial cells, and to access the host vasculature are central features of the malignant phenotype. The initiation of the invasive phenotype has been linked to the aberrant expression of zinc-finger transcriptional repressors, like Snail1, which act by triggering an epithelial-mesenchymal cell-like transformation (EMT-like) via the regulation of largely undefined, downstream effectors. Herein, we find that Snail1 induces cancer cells to (i) degrade and perforate BM barriers, (ii) initiate angiogenesis, and (iii) and intravasate vascular networks in vivo via a matrix metalloproteinase (MMP)-dependent process. Unexpectedly, the complete Snail1 invasion program can be recapitulated by expressing directly either of the membrane-anchored metalloproteinases, MT1-MMP or MT2-MMP. The pro-invasive, angiogenic, and metastatic activities of MT1-MMP and MT2-MMP are unique relative to all other metalloproteinase family members and cannot be mimicked in vivo by the secreted MMPs, MMP-1, MMP-2, MMP-3, MMP-7, MMP-9, or MMP-13. Further, siRNA-specific silencing of MT1-MMP and MT2-MMP ablates completely the ability of Snail1 to drive cancer cell BM invasion, induce angiogenesis, or trigger intravasation. Taken together, these data demonstrate that MT1-MMP and MT2-MMP cooperatively function as direct-acting, pro-invasive factors that confer Snail1-triggered cells with the key activities most frequently linked to morbidity and mortality in cancer.

Gene expression analysis of preinvasive and invasive cervical squamous cell carcinomas identifies HOXC10 as a key mediator of invasion

If left untreated, a subset of high-grade squamous intraepithelial lesions (HSIL) of the cervix will progress to invasive squamous cell carcinomas (SCC). To identify genes whose differential expression is linked to cervical cancer progression, we compared gene expression in microdissected squamous epithelial samples from 10 normal cervices, 7 HSILs, and 21 SCCs using high-density oligonucleotide microarrays. We identified 171 distinct genes at least 1.5-fold up-regulated (and P < 0.001) in the SCCs relative to HSILs and normal cervix samples. Differential expression of a subset of these genes was confirmed by quantitative reverse transcription-PCR and immunohistochemical staining of cervical tissue samples. One of the genes up-regulated during progression, HOXC10, was selected for functional studies aimed at assessing its role in mediating invasive behavior of neoplastic squamous epithelial cells. Elevated HOXC10 expression was associated with increased invasiveness of human papillomavirus-immortalized keratinocytes and cervical cancer-derived cell lines in both in vitro and in vivo assays. Cervical cancer cells with high endogenous levels of HOXC10 were less invasive after short hairpin RNA-mediated knockdown of HOXC10 expression. Our findings support a key role for the HOXC10 homeobox protein in cervical cancer progression. Other genes with differential expression in invasive SCC versus HSIL may contribute to tumor progression or may be useful as markers for cancer diagnosis or progression risk.

Molecular Dissection of the Structural Machinery Underlying the Tissue-invasive Activity of Membrane Type-1 Matrix Metalloproteinase

Membrane type-1 matrix metalloproteinase (MT1-MMP) drives cell invasion through three-dimensional (3-D) extracellular matrix (ECM) barriers dominated by type I collagen or fibrin. Based largely on analyses of its impact on cell function under two-dimensional culture conditions, MT1-MMP is categorized as a multifunctional molecule with 1) a structurally distinct, N-terminal catalytic domain; 2) a C-terminal hemopexin domain that regulates substrate recognition as well as conformation; and 3) a type I transmembrane domain whose cytosolic tail controls protease trafficking and signaling cascades. The MT1-MMP domains that subserve cell trafficking through 3-D ECM barriers in vitro or in vivo, however, remain largely undefined. Herein, we demonstrate that collagen-invasive activity is not confined strictly to the catalytic, hemopexin, transmembrane, or cytosolic domain sequences of MT1-MMP. Indeed, even a secreted collagenase supports invasion when tethered to the cell surface in the absence of the MT1-MMP hemopexin, transmembrane, and cytosolic tail domains. By contrast, the ability of MT1-MMP to support fibrin-invasive activity diverges from collagenolytic potential, and alternatively, it requires the specific participation of MT-MMP catalytic and hemopexin domains. Hence, the tissue-invasive properties of MT1-MMP are unexpectedly embedded within distinct, but parsimonious, sequences that serve to tether the requisite matrix-degradative activity to the surface of migrating cells.

Snail1 is stabilized by O-GlcNAc modification in hyperglycaemic condition.

Protein O‐phosphorylation often occurs reciprocally with O‐GlcNAc modification and represents a regulatory principle for proteins. O‐phosphorylation of serine by glycogen synthase kinase‐3β on Snail1, a transcriptional repressor of E‐cadherin and a key regulator of the epithelial–mesenchymal transition (EMT) programme, results in its proteasomal degradation. We show that by suppressing O‐phosphorylation‐mediated degradation, O‐GlcNAc at serine112 stabilizes Snail1 and thus increases its repressor function, which in turn attenuates E‐cadherin mRNA expression. Hyperglycaemic condition enhances O‐GlcNAc modification and initiates EMT by transcriptional suppression of E‐cadherin through Snail1. Thus, dynamic reciprocal O‐phosphorylation and O‐GlcNAc modification of Snail1 constitute a molecular link between cellular glucose metabolism and the control of EMT.

Transfection with mutant p53 gene inhibits heat-induced apoptosis in a head and neck cell line of human squamous cell carcinoma

PURPOSE To confirm that human cancer cells show p53-dependent heat sensitivity through an apoptosis-related mechanism, we examined the heat sensitivity and Bax-mediated apoptosis after heating in a human squamous cell carcinoma cell line, SAS, with identical genetic backgrounds except for the p53 status. MATERIALS AND METHODS We performed colony formation assay, Western blotting and analyses of apoptosis, using the SAS cells transfected with pC53-248 vector with mutant p53 gene (SAS/Trp248 cells) or the cells transfected with pCMV-Neo-Bam vector (SAS/neo cells) as a control. RESULTS SAS/Trp248 cells showed heat resistance due to the dominant negative nature of mp53, compared with SAS/neo cells. The incidence of DNA ladders and apoptotic bodies increased markedly after heating in SAS/neo cells, but increased very little in SAS/Trp248 cells. CONCLUSION These results suggest that heat resistance brought by mp53-transfection is p53-dependent and closely correlates with the induction of apoptosis in human squamous cell carcinomas.

p53-dependent thermal enhancement of cellular sensitivity in human squamous cell carcinomas in relation to LET

Purpose : To investigate the dependence on p53 gene status of the thermal enhancement of cellular sensitivity against different levels of linear energy transfer (LET) from X-rays or carbon-ion (C-) beams. Materials and methods : Two kinds of human squamous cell carcinoma cell lines were used with an identical genotype except for the p53 gene. SAS/m p53 cells were established by transfection with mutated p53 (m p53) gene to SAS cells having functional wild-type p53 (wtp53). As the control, a neo vector was transfected to the SAS cells (SAS/ neo cells). Both cells were exposed to X-rays or accelerated C-beams (30-150 KeV w m -1) followed by heating at 44°;C. Cellular sensitivity was determined by colony-forming activity. Induction of apoptosis was analysed by Hoechst 33342 staining of apoptotic bodies and agarose-gel electrophoresis for the formation of DNA ladders. Results : It was found that (1) there was no significant difference in cellular sensitivity between SAS/ neo and SAS/m p53 cells to LET radiation of >30 KeV w m -1, although the radiosensitivity of SAS/ neo cells to X-rays was higher (1.2-fold) than that of SAS/m p53 cells; (2) there was an interactive thermal enhancement of radiosensitivity below an LET of 70 KeV w m -1 in SAS/ neo cells, although only additive thermal enhancement was observed in SAS/m p53 cells through all LET levels examined; (3) low-LET radiation induced apoptosis only in SAS/ neo cells; (4) high-LET radiation at an isosurvival dose-induced apoptosis of SAS/ neo cells at a higher frequency compared with that with low-LET radiation; (5) high-LET radiation-induced p53-independent apoptosis in SAS/m p53 cells; and (6) thermal enhancement of cellular sensitivity to X-rays was due to induction of p53-dependent apoptosis. Conclusions : The findings suggest that thermal enhancement of radiosensitivity may result from p53-dependent apoptosis induced by inhibition of p53-dependent cell survival system(s) through either regulation of the cell cycle or induction of DNA repair. It is also suggested that the analysis of p53 gene status of cancer cells may predict response to combined therapies with low-LET radiation and hyperthermia.