Apurinic/apyrimidinic endonuclease 1 regulates angiogenesis in a transforming growth factor β‐dependent manner in human osteosarcoma

Angiogenesis plays an important role in tumor growth and metastasis and has been reported to be inversely correlated with overall survival of osteosarcoma patients. It has been shown that apurinic/apyrimidinic endonuclease 1 (APE1), a dually functional protein possessing both base excision repair and redox activities, is involved in tumor angiogenesis, although these mechanisms are not fully understood. Our previous study showed that the expression of transforming growth factor β (TGFβ) was significantly reduced in APE1‐deficient osteosarcoma cells. Transforming growth factor β promotes cancer metastasis through various mechanisms including immunosuppression, angiogenesis, and invasion. In the current study, we initially revealed that APE1, TGFβ, and microvessel density (MVD) have pairwise correlation in osteosarcoma tissue samples, whereas TGFβ, tumor size, and MVD were inversely related to the prognosis of the cohort. We found that knocking down APE1 in osteosarcoma cells resulted in TGFβ downregulation. In addition, APE1‐siRNA led to suppression of angiogenesis in vitro based on HUVECs in Transwell and Matrigel tube formation assays. Reduced secretory protein level of TGFβ of culture medium also resulted in decreased phosphorylation of Smad3 of HUVECs. In a mouse xenograft model, siRNA‐mediated silencing of APE1 downregulated TGFβ expression, tumor size, and MVD. Collectively, the current evidence indicates that APE1 regulates angiogenesis in osteosarcoma by controlling the TGFβ pathway, suggesting a novel target for anti‐angiogenesis therapy in human osteosarcoma.     

Transforming growth factor‐β induces CD44 cleavage that promotes migration of MDA‐MB‐435s cells through the up‐regulation of membrane type 1‐matrix metalloproteinase

CD44, a transmembrane receptor for hyaluronic acid, is implicated in various adhesion‐dependent cellular processes, including cell migration, tumor cell metastasis and invasion. Recent studies demonstrated that CD44 expressed in cancer cells can be proteolytically cleaved at the ectodomain by membrane type 1‐matrix metalloproteinase (MT1‐MMP) to form soluble CD44 and that CD44 cleavage plays a critical role in cancer cell migration. Here, we show that transforming growth factor‐β (TGF‐β), a multifunctional cytokine involved in cell proliferation, differentiation, migration and pathological processes, induces MT1‐MMP expression in MDA‐MB‐435s cells. TGF‐β‐induced MT1‐MMP expression was blocked by the specific extracellular regulated kinase‐1/2 (ERK1/2) inhibitor PD98059 and the specific phosphoinositide 3‐OH kinase (PI3K) inhibitor LY294002. In addition, treatment with SP600125, an inhibitor for c‐Jun NH₂‐terminal kinase (JNK), resulted in a significant inhibition of MT1‐MMP production. These data suggest that ERK1/2, PI3K, and JNK likely play a role in TGF‐β‐induced MT1‐MMP expression. Interestingly, treatment of MDA‐MB‐435s cells with TGF‐β resulted in a colocalization of MT1‐MMP and CD44 in the cell membrane and in an increased level of soluble CD44. Using an electric cell‐substrate impedance sensing cell‐electrode system, we demonstrated that TGF‐β treatment promotes MDA‐MB‐435s cell migration, involving MT1‐MMP‐mediated CD44 cleavage. MT1‐MMP siRNA transfection‐inhibited TGF‐β‐induced cancer cell transendothelial migration. Thus, this study contributes to our understanding of molecular mechanisms that play a critical role in tumor cell invasion and metastasis. © 2009 Wiley‐Liss, Inc.     

Kaposi's sarcoma associated herpesvirus G protein-coupled receptor immortalizes human endothelial cells by activation of the VEGF receptor-2/ KDR

The G protein-coupled receptor oncogene (vGPCR) of the Kaposi's sarcoma (KS) associated herpesvirus (KSHV), an oncovirus implicated in angioproliferative neoplasms, induces angiogenesis by VEGF secretion. Accordingly, we found that expression of vGPCR in human umbilical vein endothelial cells (HUVEC) leads to immortalization with constitutive VEGF receptor-2/ KDR expression and activation. vGPCR immortalization was associated with anti-senescence mediated by alternative lengthening of telomeres and an anti-apoptotic response mediated by vGPCR constitutive signaling and KDR autocrine signaling leading to activation of the PI3K/AKT pathway. In the presence of the KS growth factor VEGF, this mechanism can sustain suppression of signaling by the immortalizing gene. We conclude that vGPCR can cause an oncogenic immortalizing event and recapitulate aspects of the KS angiogenic phenotype in human endothelial cells, pointing to this gene as a pathogenic determinant of KSHV.     

Lysophosphatidic acid receptor 2/3-mediated IL-8-dependent angiogenesis in cervical cancer cells

The expression of lysophosphatidic acid (LPA)-specific receptors in cervical cancer has not been clearly defined. In this study, we identified LPA1, LPA2 and LPA3 receptors' mRNA in SiHa, HeLa and CaSki cell lines by RT-PCR. These receptors were not associated with tumor cell proliferation in vitro. We then used a xenograph animal model to evaluate the effects of these receptors on in vivo cervical cancer tumorigenicity. When SiHa cells with different receptor expression patterns were seeded on the backs of SCID mice, the resulting knockout of both LPA2 and LPA3 significantly attenuated tumor growth; this decrease in tumor growth was found to be linked with decreased angiogenesis (microvessel density), suggesting that LPA2 and LPA3 are crucial for in vivo tumor growth through an angiogenic mechanism. We further investigated this mechanism of LPA receptor 2/3-mediated angiogenic capability by analyzing angiogenic factors in protein lysates from receptor knockout tumors, by detecting interleukin (IL-8) mRNA expression after treating with siRNA, by evaluating the biological role of LPA-enhanced IL-8 via endothelial cell tube formation, monolayer permeability, migration and cell growth assays, and by IL-8 knockout xenograft mice modeling. We found that the angiogenesis is mediated through IL-8. Finally, we evaluated the regulation pathways involved in LPA-induced IL-8 expression. We found that LPA receptor 2/3-mediated IL-8 expression occurs through Gi/PI3K/AKT, Gi/PKC and IκB/NF-κB signaling. In conclusion, we propose that LPA2 and LPA3 might play an important role in cervical cancer tumor growth through IL-8-dependent angiogenesis.     

miR‐335 inhibited cell proliferation of lung cancer cells by target Tra2β

Accumulating evidence has suggested that the dysregulation of miRNA is an important factor in the pathogenesis of lung cancer. Here, we demonstrate that miR‐335 expression is reduced in non‐small cell lung cancer (NSCLC) tumors relative to non‐cancerous adjacent tissues, while the expression of Tra2β is increased. In addition, clinical data revealed that the increased Tra2β and decreased miR‐335 expression observed in NSCLC cells was associated with poor patient survival rates. In vitro experimentation showed that the overexpression of miR‐335 inhibited the growth, invasion and migration capabilities of A459 lung cancer cells, by targeting Tra2β. In contrast, inhibition of miR‐335 or overexpression of the Tra2β target gene stimulated the growth, invasion and migratory capabilities of A459 lung cancer cells in vitro. Furthermore, overexpression of miR‐335 or inhibition of Tra2β decreased the phosphorylation of Rb‐S780 and Rb‐AKT. Overall, these findings suggest that the downregulation of miR‐335 in A459 lung cancer cells promoted cell proliferation through upregulation of Tra2β, mediated via activation of the AKT/mTOR signaling pathway, and suggest that miR‐335 may have potential as a novel therapeutic target for NSCLC.     

Lymphotoxin‐β receptor activation by lymphotoxin‐α1β2 and LIGHT promotes tumor growth in an NFκB‐dependent manner

Lymphotoxin beta receptor (LTβR) activation on mouse fibrosarcoma cells (BFS‐1) results in enhanced solid tumor growth paralleled by increased angiogenesis induced by the expression of pro‐angiogenic CXCL2. In our study, we demonstrate that both functional ligands of the LTβR, namely LTα₁β₂ and LIGHT, are involved in the activation of LTβR in solid fibrosarcomas. To identify whether the lymphocyte population is involved in the activation of LTβR in these fibrosarcoma tumors, we used conditional LTβ‐deficient mice that specifically lack LTβ expression either on T cells (T‐LTβ^?/?) or on B cells (B‐LTβ^?/?). Solid tumor growth was reduced in both mouse strains when compared to tumor growth in wild‐type mice, indicating the participation of both T and B host lymphocytes in the activation of LTβR in these tumors. Tumor growth was also reduced in LIGHT‐deficient mice, suggesting a contribution of this ligand to the activation of LTβR in BFS‐1 fibrosarcomas. LTβR signaling can involve IκBα and/or NFκB‐inducing kinase (NIK) for subsequent NFκB activation in different types of cells. Expression of a dominant negative form of IκBα or of a dominant negative mutant of NIK resulted in decreased activation of NFκB signaling and reduced expression of pro‐angiogenic CXCL2 in vitro. Moreover, expression of dominant negative form of NIK or an IκBα repressor in these fibrosarcoma cells resulted in reduced solid tumor growth in vivo, suggesting that both IκBα and NIK are involved in pro‐angiogenic signaling after LTβR activation. Our data support the idea that the ablation of LTβR signaling should be considered for cancer treatment.     

Exogenous introduction of tissue inhibitor of metalloproteinase 2 reduces accelerated growth of TGF‐β‐disrupted diffuse‐type gastric carcinoma

Diffuse‐type gastric carcinoma is characterized by rapid progression and poor prognosis. High expression of transforming growth factor (TGF)‐β and thick stromal fibrosis are observed in this type of gastric carcinoma. We have previously shown that disruption of TGF‐β signaling via introduction of a dominant negative form of the TGF‐β type II receptor (dnTβRII) into diffuse‐type gastric cancer cell lines, including OCUM‐2MLN, caused accelerated tumor growth through induction of tumor angiogenesis in vivo. In the present study, we show that TGF‐β induces upregulation of expression of tissue inhibitor of metalloproteinase 2 (TIMP2) in the OCUM‐2MLN cell line in vitro, and that expression of TIMP2 is repressed by dnTβRII expression in vivo. Transplantation of the OCUM‐2MLN cells to nude mice exhibited accelerated tumor growth in response to dnTβRII expression, which was completely abolished when TIMP2 was coexpressed with dnTβRII. Although the blood vessel density of TIMP2‐expressing tumors was only slightly decreased, the degree of hypoxia in tumor tissues was significantly increased and pericytes covering tumor vasculature were decreased by TIMP2 expression in OCUM‐2MLN cells, suggesting that the function of tumor vasculatures was repressed by TIMP2 and consequently tumor growth was reduced. These findings provide evidence that one of the mechanisms of the increase in angiogenesis in diffuse‐type gastric carcinoma is the downregulation of the anti‐angiogenic protein TIMP2. (Cancer Sci 2010; 101: 2398–2403)     

Tetraspanin CD63 acts as a pro‐metastatic factor via β‐catenin stabilization

The tetraspanin CD63 is implicated in pro‐metastatic signaling pathways but, so far, it is unclear, how CD63 levels affect the tumor cell phenotype. Here, we investigated the effect of CD63 modulation in different metastatic tumor cell lines. In vitro, knock down of CD63 induced a more epithelial‐like phenotype concomitant with increased E‐cadherin expression, downregulation of its repressors Slug and Zeb1, and decreased N‐cadherin. In addition, β‐catenin protein was markedly reduced, negatively affecting expression of the target genes MMP‐2 and PAI‐1. β‐catenin inhibitors mimicked the epithelial phenotype induced by CD63 knock down. Inhibition of β‐catenin upstream regulators PI3K/AKT or GSK3β could rescue the mesenchymal phenotype underlining the importance of the β‐catenin pathway in CD63‐regulated cell plasticity. CD63 knock down‐induced phenotypical changes correlated with a decrease of experimental metastasis whereas CD63 overexpression enhanced the tumor cell‐intrinsic metastatic potential. Taken together, our data show that CD63 is a crucial player in the regulation of the tumor cell‐intrinsic metastatic potential by affecting cell plasticity.     

C/EBPβ promotes angiogenesis through secretion of IL‐6, which is inhibited by genistein,in EGFRvIII‐positive glioblastoma

To study the mechanisms underlying the IL‐6‐promoted angiogenic microenvironment in EGFRvIII‐positive glioblastoma, VEGF expression in EGFRvIII‐positive/negative tumors was determined by optical molecular imaging. Next, the HUVEC tube formation assay, Western blot, qPCR, RNA silencing, chromatin immunoprecipitation, luciferase reporter and ELISA assays were performed to examine the role of IL‐6 and C/EBPβ in the formation of the angiogenic microenvironment in EGFRvIII‐positive tumors. Finally, in vitro and in vivo genistein treatment experiments were conducted to challenge the interaction between the IL‐6 promoter and C/EBPβ. Optical imaging revealed greater VEGF expression in EGFRvIII‐positive tumor‐bearing mice, suggesting an angiogenic microenvironment. In vitro experiments demonstrated that C/EBPβ‐mediated regulation of IL‐6 was indispensable for maintenance of this angiogenic microenvironment. In contrast, genistein‐mediated upregulation of CHOP impeded C/EBPβ interaction with the IL‐6 promoter, thus disturbing the angiogenic microenvironment. This more malignant microenvironment in EGFRvIII glioblastoma is generated, at least in part, by greater VEGF, IL‐6 and C/EBPβ expression. Interaction of C/EBPβ with the IL‐6 promoter maintains this angiogenic microenvironment, while disturbance of this dynamically balanced interaction inhibits EGFRvIII tumor proliferation by reducing both VEGF and IL‐6 expression.     

Inhibition of MK2 suppresses IL‐1β, IL‐6, and TNF‐α‐dependent colorectal cancer growth

Colorectal cancer (CRC) development and progression is associated with chronic inflammation. We have identified the MAPK‐activated protein kinase 2 (MK2) pathway as a primary mediator of inflammation in CRC. MK2 signaling promotes production of proinflammatory cytokines IL‐1β, IL‐6 and TNF‐α. These cytokines have been implicated in tumor growth, invasion and metastasis. For the first time, we investigate whether MK2 inhibition can improve outcome in two mouse models of CRC. In our azoxymethane/dextran sodium sulfate (AOM/DSS) model of colitis‐associated CRC, MK2 inhibitor treatment eliminated murine tumor development. Using the implanted, syngeneic murine CRC cell line CT26, we observe significant tumor volume reduction following MK2 inhibition. Tumor cells treated with MK2 inhibitors produced 80% less IL‐1β, IL‐6 and TNF‐α and demonstrated decreased invasion. Replenishment of downstream proinflammatory MK2‐mediated cytokines (IL‐1β, IL‐6 and TNF‐α) to tumors led to restoration of tumor proliferation and rapid tumor regrowth. These results demonstrate the importance of MK2 in driving proinflammatory cytokine production, its relevance to in vivo tumor proliferation and invasion. Inhibition of MK2 may represent an attractive therapeutic target to suppress tumor growth and progression in patients.     

Effect of VEGF and VEGF Trap on vascular endothelial cell signaling in tumors

Vascular endothelial growth factor (VEGF) A is a major promoter of tumor angiogenesis and a prime target of antiangiogenic cancer therapy. To examine whether endothelial cell signaling might provide histological biomarkers of angiogenesis and VEGF activity in vivo, normal mouse organs and multiple tumor models were studied immunohistochemically for endothelial expression of activated ERK, STAT3, and AKT. Phospho(p)-ERK and p-STAT3 expression was negligible in the endothelia of normal organs but was significantly elevated in tumor endothelium. p-AKT was present at significant and comparable levels in both tumor and normal endothelia. In K1735 tumors induced to express more VEGF, endothelial p-ERK, p-STAT3 and p-AKT increased accompanied by signs of accelerated angiogenesis. Treatment of K1735 and Colo-205 tumors with the VEGF inhibitor, VEGF Trap (aflibercept), decreased tumor endothelial p-ERK, p-STAT3 and p-AKT expression accompanied by signs of antiangiogenic effect. These results show that endothelial p-ERK and p-STAT3 (but not p-AKT) distinguish tumor from normal vessels and that the presence of these two signaling intermediates may be useful indicators of tumor angiogenic activity and angiogenesis inhibition by VEGF antagonist.     

Cancer cells acquire a drug resistant,highly tumorigenic,cancer stem‐like phenotype through modulation of the PI3K/Akt/β‐catenin/CBP pathway

Cancer initiation and progression have been attributed to newly discovered subpopulations of self‐renewing, highly tumorigenic, drug‐resistant tumor cells termed cancer stem cells. Recently, we and others reported a new phenotypic plasticity wherein highly tumorigenic, drug‐resistant cell populations could arise not only from pre‐existing cancer stem‐like populations but also from cancer cells lacking these properties. In the current study, we hypothesized that this newfound phenotypic plasticity may be mediated by PI3K/Akt and Wnt/β‐catenin signaling, pathways previously implicated in carcinogenesis, pluripotency and drug resistance. Using GFP expression, Hoechst dye exclusion and fluorescence activated cell sorting (FACS) of cancer cell lines, we identified and tracked cancer stem‐like side populations (SP) of cancer cells characterized by high tumorigenicity and drug resistance. We found that pharmacological inhibition or genetic depletion of PI3K and AKT markedly reduced the spontaneous conversion of nonside population (NSP) cells into cancer stem‐like SP cells, whereas PI3K/Akt activation conversely enhanced NSP to SP conversion. PI3K/AKT signaling was mediated through downstream phosphorylation of GSK3β, which led to activation and accumulation of β‐catenin. Accordingly, pharmacological or genetic perturbation of GSK3β or β‐catenin dramatically impacted conversion of NSP to SP. Further downstream, β‐catenin's effects on NSP‐SP equilibrium were dependent upon its interaction with CBP, a KAT3 family coactivator. These studies provide a mechanistic model wherein PI3K/Akt/β‐catenin/CBP signaling mediates phenotypic plasticity in and out of a drug‐resistant, highly tumorigenic state. Therefore, targeting this pathway has unique potential for overcoming the therapy resistance and disease progression attributed to the cancer stem‐like phenotype.