Kuo-Tai Hua

H3K9 histone methyltransferase G9a promotes lung cancer invasion and metastasis by silencing the cell adhesion molecule Ep-CAM

G9a is a mammalian histone methyltransferase that contributes to the epigenetic silencing of tumor suppressor genes. Emerging evidence suggests that G9a is required to maintain the malignant phenotype, but the role of G9a function in mediating tumor metastasis has not been explored. Here, we show that G9a is expressed in aggressive lung cancer cells, and its elevated expression correlates with poor prognosis. RNAi-mediated knockdown of G9a in highly invasive lung cancer cells inhibited cell migration and invasion in vitro and metastasis in vivo. Conversely, ectopic G9a expression in weakly invasive lung cancer cells increased motility and metastasis. Mechanistic investigations suggested that repression of the cell adhesion molecule Ep-CAM mediated the effects of G9a. First, RNAi-mediated knockdown of Ep-CAM partially relieved metastasis suppression imposed by G9a suppression. Second, an inverse correlation between G9a and Ep-CAM expression existed in primary lung cancer. Third, Ep-CAM repression was associated with promoter methylation and an enrichment for dimethylated histone H3K9. G9a knockdown reduced the levels of H3K9 dimethylation and decreased the recruitment of the transcriptional cofactors HP1, DNMT1, and HDAC1 to the Ep-CAM promoter. Our findings establish a functional contribution of G9a overexpression with concomitant dysregulation of epigenetic pathways in lung cancer progression.

CTGF enhances the motility of breast cancer cells via an integrin-αvβ3–ERK1/2-dependent S100A4-upregulated pathway

Connective tissue growth factor (CTGF) expression is elevated in advanced stages of breast cancer, but the regulatory role of CTGF in invasive breast cancer cell phenotypes is unclear. Presently, overexpression of CTGF in MCF-7 cells (MCF-7/CTGF cells) enhanced cellular migratory ability and spindle-like morphological alterations, as evidenced by actin polymerization and focal-adhesion-complex aggregation. Reducing the CTGF level in MDA-MB-231 (MDA231) cells by antisense CTGF cDNA (MDA231/AS cells) impaired cellular migration and promoted a change to an epithelial-like morphology. A neutralizing antibody against integrin αvβ3 significantly attenuated CTGF-mediated ERK1/2 activation and cellular migration, indicating that the integrin-αvβ3–ERK1/2 signaling pathway is crucial in mediating CTGF function. Moreover, the cDNA microarray analysis revealed CTGF-mediated regulation of the prometastatic gene S100A4. Transfection of MCF-7/CTGF cells with AS-S100A4 reversed the CTGF-induced cellular migratory ability, whereas overexpression of S100A4 in MDA231/AS cells restored their high migratory ability. Genetic and pharmacological manipulations suggested that the CTGF-mediated S100A4 upregulation was dependent on ERK1/2 activation, with expression levels of CTGF and S100A4 being closely correlated with human breast tumors. We conclude that CTGF plays a crucial role in migratory/invasive processes in human breast cancer by a mechanism involving activation of the integrin-αvβ3–ERK1/2–S100A4 pathway.

miR-107 promotes tumor progression by targeting the let-7 microRNA in mice and humans

MicroRNAs (miRNAs) influence many biological processes, including cancer. They do so by posttranscriptionally repressing target mRNAs to which they have sequence complementarity. Although it has been postulated that miRNAs can regulate other miRNAs, this has never been shown experimentally to our knowledge. Here, we demonstrate that miR-107 negatively regulates the tumor suppressor miRNA let-7 via a direct interaction. miR-107 was found to be highly expressed in malignant tissue from patients with advanced breast cancer, and its expression was inversely correlated with let-7 expression in tumors and in cancer cell lines. Ectopic expression of miR-107 in human cancer cell lines led to destabilization of mature let-7, increased expression of let-7 targets, and increased malignant phenotypes. In contrast, depletion of endogenous miR-107 dramatically increased the stability of mature let-7 and led to downregulation of let-7 targets. Accordingly, miR-107 expression increased the tumorigenic and metastatic potential of a human breast cancer cell line in mice via inhibition of let-7 and upregulation of let-7 targets. By mutating individual sites within miR-107 and let-7, we found that miR-107 directly interacts with let-7 and that the internal loop of the let-7/miR-107 duplex is critical for repression of let-7 expression. Altogether, we have identified an oncogenic role for miR-107 and provide evidence of a transregulational interaction among miRNAs in human cancer development.

N-α-Acetyltransferase 10 Protein Suppresses Cancer Cell Metastasis by Binding PIX Proteins and Inhibiting Cdc42/Rac1 Activity

N-α-acetyltransferase 10 protein, Naa10p, is an N-acetyltransferase known to be involved in cell cycle control. We found that Naa10p was expressed lower in varieties of malignancies with lymph node metastasis compared with non-lymph node metastasis. Higher Naa10p expression correlates the survival of lung cancer patients. Naa10p significantly suppressed migration, tumor growth, and metastasis independent of its enzymatic activity. Instead, Naa10p binds to the GIT-binding domain of PIX, thereby preventing the formation of the GIT-PIX-Paxillin complex, resulting in reduced intrinsic Cdc42/Rac1 activity and decreased cell migration. Forced expression of PIX in Naa10-transfected tumor cells restored the migration and metastasis ability. We suggest that Naa10p functions as a tumor metastasis suppressor by disrupting the migratory complex, PIX-GIT- Paxillin, in cancer cells.

The H3K9 methyltransferase G9a is a marker of aggressive ovarian cancer that promotes peritoneal metastasis

BackgroundOvarian cancer (OCa) peritoneal metastasis is the leading cause of cancer–related deaths in women with limited therapeutic options available for treating it and poor prognosis, as the underlying mechanism is not fully understood.MethodThe clinicopathological correlation of G9a expression was assessed in tumor specimens of ovarian cancer patients. Knockdown or overexpression of G9a in ovarian cancer cell lines was analysed with regard to its effect on adhesion, migration, invasion and anoikis-resistance. In vivo biological functions of G9a were tested by i.p. xenograft ovarian cancer models. Microarray and quantitative RT-PCR were used to analyze G9a-regulated downstream target genes.ResultsWe found that the expression of histone methyltransferase G9a was highly correlated with late stage, high grade, and serous-type OCa. Higher G9a expression predicted a shorter survival in ovarian cancer patients. Furthermore, G9a expression was higher in metastatic lesions compared with their corresponding ovarian primary tumors. Knockdown of G9a expression suppressed prometastatic cellular activities including adhesion, migration, invasion and anoikis-resistance of ovarian cancer cell lines, while G9a over-expression promoted these cellular properties. G9a depletion significantly attenuated the development of ascites and tumor nodules in a peritoneal dissemination model. Importantly, microarray and quantitative RT-PCR analysis revealed that G9a regulates a cohort of tumor suppressor genes including CDH1, DUSP5, SPRY4, and PPP1R15A in ovarian cancer. Expression of these genes was also inversely correlated with G9a expression in OCa specimens.ConclusionWe propose that G9a contributes to multiple steps of ovarian cancer metastasis and represents a novel target to combat this deadly disease.

Annexin A1 is associated with gastric cancer survival and promotes gastric cancer cell invasiveness through the formyl peptide receptor/extracellular signal‐regulated kinase/integrin beta‐1‐binding protein 1 pathway

Annexin A1 (AnxA1) has been well‐known as a glucocorticoid‐regulated anti‐inflammatory protein, and it is implicated in tumorigenesis in a tumor type–specific pattern. However, the role of AnxA1 in gastric cancer (GC) is indeterminate, and the underlying mechanism is not clear. The purpose of this study was to evaluate the prognostic significance and associated mechanism of AnxA1 in GC.

FOXO3a-Dependent Mechanism of E1A-Induced Chemosensitization

Gene therapy trials in human breast, ovarian, and head and neck tumors indicate that adenovirus E1A can sensitize cancer cells to the cytotoxic effects of paclitaxel in vitro and in vivo. Resistance to paclitaxel has been reported to occur in cells expressing low levels of the Forkhead transcription factor FOXO3a. In this article, we report that FOXO3a is critical for E1A-mediated chemosensitization to paclitaxel. RNA interference-mediated knockdown of FOXO3a abolished E1A-induced sensitivity to paclitaxel. Mechanistic investigations indicated that E1A indirectly stabilized FOXO3a by acting at an intermediate step to inhibit a ubiquitin-dependent proteolysis pathway involving the E3 ligase βTrCP and the FOXO3a inhibitory kinase IKKβ. E1A derepressed this inhibitory pathway by stimulating expression of the protein phosphatase 2A (PP2A)/C protein phosphatases, which by binding to the TGF-β-activated kinase TAK1, inhibited its ability to activate IKKβ and, thereby, to suppress βTrCP-mediated degradation of FOXO3a. Thus, by stimulating PP2A/C expression, E1A triggers a signaling cascade that stabilizes FOXO3a and mediates chemosensitization. Our findings provide a leap forward in understanding paclitaxel chemosensitization by E1A, and offer a mechanistic rational to apply E1A gene therapy as an adjuvant for improving therapeutic outcomes in patients receiving paclitaxel treatment.

Inhibition of G9a induces DUSP4-dependent autophagic cell death in head and neck squamous cell carcinoma

BackgroundHead and neck squamous cell carcinoma (HNSCC) is a common cancer worldwide. Emerging evidence indicates that alteration of epigenetics might be a key event in HNSCC progression. Abnormal expression of histone methyltransferase G9a, which contributes to transcriptional repression of tumor suppressors, has been implicated in promoting cancerous malignancies. However, its role in HNSCC has not been previously characterized. In this study, we elucidate the function of G9a and its downstream mechanism in HNSCC.MethodsWe investigated the clinical relevance of G9a in HNSCC using immunohistochemistry (IHC) staining. In vitro cell proliferation and tumorigenesis ability of G9a-manipulated HNSCC cells were examined with MTT assays, clonogenic assays, and soft agar assays. We examined different routes of cell death in HNSCC cells induced by G9a-depletion or enzymatic inhibition by immunoblot, flow cytometry, fluorescent and transmission electron microscopy analysis. Specific targets of G9a were identified by affymetrix microarray and quantitative reverse transcription-polymerase chain reaction (qRT-PCR). Lastly, functions of G9a in vivo were confirmed with a xenograft tumor model.ResultsG9a expression is positively correlated to proliferation marker Ki-67 and to poor prognosis in HNSCC patients. Genetic or pharmacological inhibition of G9a reduced cell proliferation without inducing necrosis or apoptosis. Instead, autophagic cell death was the major consequence, and our investigation of mechanisms suggested it is mediated via the dual specificity phosphatase-4 (DUSP4) dependent ERK inactivation pathway. An orthotopic tumor model further confirmed the growth inhibiting effect and induction of autophagy that followed suppression of G9a.ConclusionsIn this study, we provide evidence that G9a confers the survival advantage of HNSCC. Genetic or pharmacological inhibition of G9a induces autophagic cell death; this finding provides a basis for new therapeutic targets for treating HNSCC.

Pentagalloylglucose inhibits estrogen receptor α by lysosome‐dependent depletion and modulates ErbB/PI3K/Akt pathway in human breast cancer MCF‐7 cells

Estrogens and estrogen receptors (ER) play important roles in estrogen‐dependent and ER‐positive breast cancer development. Inhibitors against estrogen biosynthesis or anti‐estrogens have been used in breast cancer treatment for many years. The aim of this study was to determine whether pentagalloylglucose (5GG) has inhibitory effects on ER function. In the present study, we found that 5GG significantly reduced the growth of estrogen‐responsive human breast cancer MCF‐7 cells, and suppressed the phosphorylation and protein level of estrogen receptor α (ERα). Interestingly, 5GG decreased ERα protein levels by promoting the degradation of ERα protein in the lysosome. The ERα can be activated through a ligand‐dependent and/or a ligand‐independent pathway. The activated Akt kinase was shown to directly phosphorylate ERα at its serine residues and cause ligand independent activation. Our results showed that 5GG might inhibit the phosphatidylinositol 3‐kinase (PI3K)/Akt pathway either through directly inhibiting Akt kinase activity or through inhibiting phosphorylation of the upstream receptor tyrosine kinases. The depletion of ErbB family receptors, including epidermal growth factor receptor (EGFR), ErbB2, and ErbB3, was also observed. 5GG treatment also led to a dose‐dependent decrease in the expression of the estrogen‐activated cyclin D1 expression. These findings suggested that 5GG might be a useful chemopreventive or therapeutic agent for hormone‐dependent breast cancer through suppressing the functions of ERα by lysosome‐dependent depletion and modulating the ErbB/PI3K/Akt pathway.

Hispolon induces apoptosis through JNK1/2-mediated activation of a caspase-8, -9, and -3-dependent pathway in acute myeloid leukemia (AML) cells and inhibits AML xenograft tumor growth in vivo.

Hispolon is an active phenolic compound of Phellinus igniarius, a mushroom that was recently shown to have antioxidant and anticancer activities in various solid tumors. Here, the molecular mechanisms by which hispolon exerts anticancer effects in acute myeloid leukemia (AML) cells was investigated. The results showed that hispolon suppressed cell proliferation in the various AML cell lines. Furthermore, hispolon effectively induced apoptosis of HL-60 AML cells through caspases-8, -9, and -3 activations and PARP cleavage. Moreover, treatment of HL-60 cells with hispolon induced sustained activation of JNK1/2, and inhibition of JNK by JNK1/2 inhibitor or JNK1/2-specific siRNA significantly abolished the hispolon-induced activation of the caspase-8/-9/-3. In vivo, hispolon significantly reduced tumor growth in mice with HL-60 tumor xenografts. In hispolon-treated tumors, activation of caspase-3 and a decrease in Ki67-positive cells were observed. Our results indicated that hispolon may have the potential to serve as a therapeutic tool to treat AML.