αv‐Integrin isoform expression in primary human tumors and brain metastases

To determine whether metastasis to brain is associated with altered expression patterns of integrins, we investigated the expression of αvβ3, αvβ5, αvβ6 and αvβ8 integrins in primary malignancies and metastases to brain of breast, lung and renal carcinomas and in malignant melanoma. Inhibitors of αv integrins are currently in clinical trials for glioblastoma. The role of integrins in the process of brain metastasis from other human tumors is unknown. Immunohistochemistry with novel integrin subtype specific rabbit monoclonal antibodies was performed on tissue microarrays of archival material of surgical biopsies taken from primary tumors and brain metastases. Integrin αvβ3 expression was increased in brain metastases compared to primary tumors of breast adenocarcinoma, non‐small cell lung cancer, renal clear cell cancer and malignant cutaneous melanoma (all p < 0.01). Similarly, integrin αvβ8 expression was increased in brain metastases compared to primary tumors of breast cancer (p < 0.0001), lung cancer (p < 0.01) and renal cancer (p < 0.0001), with a similar trend in metastatic melanoma. Integrin αvβ5 was expressed in most primary tumors (98% breast cancer; 67% lung cancer; 90% renal cancer; 89% melanoma) and showed a stronger expression in brain metastases compared to primary tumors from lung cancer and melanoma (p < 0.05). Also integrin αvβ6 expression was increased in brain metastases compared to primary breast cancer (p < 0.001). Conclusions: The stronger αv‐integrin expression in brain metastases, especially of αvβ3 and αvβ8 integrins, suggests that certain αv integrin are involved in the process of brain metastasis. αv Integrins may be therapeutic targets for patients with metastatic cancer in brain.     

Modified heparins inhibit integrin αIIbβ3 mediated adhesion of melanoma cells to platelets in vitro and in vivo

The adhesion of tumor cells with platelets is important in the process of tumor metastasis. A huge work has indicated that anti‐adhesion is an effective strategy for metastasis inhibition. In this article, we assess the role of platelet integrin α_IIbβ₃ in adhesion of melanoma cells to platelets and the effects of heparin and modified heparins on the adhesion in vitro and in vivo. We show that platelet integrin α_IIbβ₃ is involved in the interaction of human melanoma A375 cells with platelets, and the high affinity epitope resides on the α_IIb subunit rather than β₃ subunit. Heparin sulfate‐like proteoglycans on tumor cell surface are implicated in the adhesion of A375 cells to integrin α_IIbβ₃. We also show that RO‐heparin, CR‐heparin, N‐2,3‐DS‐heparin and 2,3‐O‐DS‐heparin can significantly inhibit A375 cells binding to the CHO cells expressing integrin α_IIbβ₃ under static and flow conditions, and remarkably inhibit the adhesion of A375 cells to the immobilized platelet layers under flow conditions. We find that A375 cells and B16F10 cells are arrested in the pulmonary vessels and adhered to platelets, and the initial interaction of tumor cells with platelets in lung vessel and long‐term establishment of metastatic foci can be inhibited by heparin as well as CR‐heparin and N‐2,3‐DS‐heparin. These data suggest that modified heparins can inhibit tumor cell‐platelet interaction mediated by platelet integrin α_IIbβ₃ and modified heparins may be a potential substitute for heparin in inhibiting tumor metastasis. © 2009 UICC     

Significance of integrin αvβ5 and erbB3 in enhanced cell migration and liver metastasis of colon carcinomas stimulated by hepatocyte‐derived heregulin

To study the mechanisms of the highly liver‐metastatic character of colon carcinoma cells, we studied the expression pattern of surface integrins on LS‐LM6 (a highly liver‐metastatic human colon cancer cell line) and the effects of hepatocyte‐derived soluble factors on cell migration. LS‐LM6 showed significantly higher expression of integrin αvβ5, a ligand for vitronectin (VN), as compared with its parental cell line (LS174T). A conditioned medium of cultured mouse hepatocytes enhanced VN‐mediated cell migration of LS‐LM6, which was blocked by neutralizing antibody against integrin αvβ5, while the medium did not affect cell adhesion to VN‐coated plastic surfaces. The conditioned medium induced phosphorylation of erbB3 and its heterodimeric partner, erbB2. Heregulin (HRG), a ligand for erbB3, exerted similar effects on VN‐mediated cell migration and phosphorylation of erbB3 and erbB2. The conditioned medium contained HRG, and depletion of HRG from the medium by pre‐absorption with HRG antibody abolished its effects on cell migration. Heregulin (HRG) was expressed in some hepatocytes in the liver with carcinoma cell metastasis. Furthermore, knockdown of integrin αv and erbB3 by small‐interfering RNAs significantly inhibited cell migration induced by HRG as well as liver metastasis in vivo. Finally, we found that HRG‐induced cell migration was associated with marked phosphorylation of Akt and that cell migration was suppressed by treatment with specific inhibitors of phosphatidylinositol 3‐kinase. Our study suggests that hepatocyte‐derived HRG might participate in a highly liver‐metastatic phenotype of LS‐LM6 through enhancement of integrin αvβ5‐mediated cell migration and erbB3/erbB2 signaling. (Cancer Sci 2010)     

Identification of integrins α6 and β7 as c‐Jun‐ and transformation‐relevant genes in highly invasive fibrosarcoma cells

Understanding the mechanisms of tumor cell invasion is essential for our attempts to prevent cancer deaths. We screened by DNAmicroarrays the c‐Jun‐ and transformation‐related gene expression changes in S‐adenosylmethionine decarboxylase (AdoMetDC)‐overexpressing mouse fibroblasts that are highly invasive in vivo, and their derivatives expressing a tetracycline‐inducible dominant‐negative mutant of c‐Jun (TAM67) or c‐Jun shRNA. Among the small set of target genes detected were integrins α6 and β7, cathepsin L and thymosin β4, all upregulated in the AdoMetDC‐transformed cells and downregulated upon reversal of transformation by TAM67 or c‐Jun shRNA. The upregulation of integrin α6 subunit, pairing with integrin β1, endowed the transformed cells with the capability to attach to basement membrane laminin and to spread. Further, inhibition of integrin α6 or β1 function with neutralizing antibodies blocked the invasiveness of AdoMetDC‐transformants and human HT‐1080 fibrosarcoma cells in three‐dimensional Matrigel. Moreover, immunohistochemical analyses showed strong integrin α6 staining in high‐grade human fibrosarcomas. Our data show that c‐Jun can regulate all three key steps of invasion: cell adhesion (integrin α6), basement membrane/extracellular matrix degradation (cathepsin L) and cell migration (thymosin β4). In addition, this is the first study to associate integrin β7, known as a leukocyte‐specific integrin binding to endothelial/epithelial cell adhesion molecules, with the transformed phenotype in cells of nonleukocyte origin. As tumor cell invasion is a prerequisite for metastasis, the observed critical role of integrin α6β1 in fibrosarcoma cell invasion/spreading allures testing antagonists to integrin α6β1, alone or combined with inhibitors of cathepsin L and thymosin β4, as chemotherapeutic agents. © 2009 UICC     

αvβ_3整合素在小细胞肺癌骨转移细胞株SBC-5中的表达及意义

目的：分析αvβ3整合素在特异性小细胞肺癌骨转移细胞株中的表达,探讨肺癌骨转移的机制。方法：RT-PCR、Western-blot和免疫荧光染色检测小细胞肺癌特异性骨转移细胞株SBC-5和非骨转移细胞株SBC-3中αvβ3整合素的表达差异。结果：αvβ3整合素在SBC-5细胞株中的表达显著高于SBC-3细胞株。结论：αvβ3整合素可能与小细胞肺癌骨转移的发生相关,可能促进了小细胞肺癌骨转移的发生。     

Cancer‐associated fibroblast promote transmigration through endothelial brain cells in three‐dimensional in vitro models

Brain metastases are associated with high morbidity as well as with poor prognosis and survival in breast cancer patients. Despite its clinical importance, metastasis of breast cancer cells through the blood‐brain barrier (BBB) is poorly understood. The objective of our study was to investigate whether cancer‐associated fibroblasts (CAFs) play crucial roles in breast cancer brain metastasis. Using a cell adhesion assays, in vitro BBB permeability and transmigration assays and soft agar colony formation assays, we investigated the physical roles of CAFs in breast cancer brain metastasis. We also performed immunofluorescence, flow cytometric analysis, Droplet Digital PCR and Simon? Simple Western System to confirm changes in expression levels. We established two novel three‐dimensional (3D) culture systems using a perpendicular slide chamber and applying 3D embedded culture method to reflect brain metastasis conditions. With a newly developed device, CAFs was proven to promote cell adhesion to human brain microvascular endothelial cells, in vitro BBB permeability and transmigration and colony formation of breast cancer cells. Furthermore, CAFs enhanced the invasive migration of breast cancer cells in two kinds of 3D cultures. These 3D models also reliably recapitulate the initial steps of BBB transmigration, micro‐metastasis and colonization. Expression of integrin α5β1 and αvβ3, c‐MET and α2,6‐siayltransferase was increased in breast cancer cells that migrated through the BBB. In conclusion, based on our in vitro BBB and co‐culture models, our data suggest that CAFs may play a role in breast cancer brain metastasis.     

α5β1 integrin antagonists reduce chemotherapy‐induced premature senescence and facilitate apoptosis in human glioblastoma cells

The α5β1 integrin represent a new therapeutic target for glioblastoma, which are malignant brain tumors difficult to cure with conventional therapies. Glioblastoma are known to be highly resistant to chemotherapy. We, therefore, investigated whether blocking α5β1 integrin with specific nonpeptidic antagonists concomitantly with chemotherapy (ellipticine and temozolomide) may impact the response to chemotherapy of human glioblastoma. Here we show that inhibiting α5β1 integrin with 2 selective ligands (SJ749 and K34c) decreases chemotherapy‐induced premature senescence and facilitates cell apoptosis in a functional p53 background (U87MG cells). When p53 is mutated and inactive (U373 cells), chemotherapy induces p53‐independent cell apoptosis instead of senescence that is not improved by integrin antagonists. Silencing p53 in U87MG cells with siRNA as well as evaluating HCT116 p53+/+ and p53?/? colon carcinoma cell behavior support the hypothesis of an as yet unknown effect of α5β1 integrin antagonists on the control of chemotherapy‐induced premature senescence and apoptosis. α5β1 integrin antagonists modulate the p53 signaling induced by chemotherapy. Our results highlight a new role of the α5β1 integrin in the control of glioblastoma aggressiveness and responsiveness to chemotherapy, which may have a crucial impact in the clinical management of patients suffering from brain tumors.     

Integrin α3β1 can promote adhesion and spreading of metastatic breast carcinoma cells on the lymph node stroma

We have reported that metastatic human melanoma cells utilize the α_vβ₃ integrin to adhere to lymph node vitronectin (VN). In the present study, the adhesion of human and rat breast carcinoma cells to lymph node tissue was analyzed. We have previously shown a correlation between the metastatic potential of breast carcinoma cells and an RGD-mediated adhesion to cryostat sections of peripheral lymph nodes; this adhesion could be blocked by an antibody to the integrin β₁ subunit. Here, we show that the metastatic breast carcinoma cell were significantly more adherent to fibronectin (FN) expressed by lymph node-derived stromal cells than non-metastatic cells. Metastatic cells also spread more rapidly than non-metastatic cells on FN-coated substrates. Using a combination of immunofluorescence microscopy, immunoprecipitation and blocking assays with integrin-specific antibodies, we found (i) that expression of the α₃β₁ integrin on metastatic mammary carcinoma cells was specifically increased in comparison to non-metastatic cells and (ii) that the α₃β₁ receptor was involved in the increased adhesion of metastatic cells to lymph node FN and in cell spreading on FN-coated substrates. Our data also suggest that the α₅β₁ integrin, which is also expressed on the metastatic cells, did not contribute to this increase in adhesion. Our data implicate the α₃β₁ integrin in adhesion to lymph node stromal cell FN and suggest that metastatic cells of different tissue origins (e.g., melanoma and breast carcinoma) may utilize distinct integrin-ligand combinations to colonize the same target organ. © 1996 Wiley-Liss, Inc.     

Tumor‐associated macrophages promote bladder tumor growth through PI3K/AKT signal induced by collagen

The tumor microenvironment is associated with various tumor progressions, including cancer metastasis, immunosuppression, and tumor sustained growth. Tumor‐associated macrophages (TAMs) are considered an indispensable component of the tumor microenvironment, participating in the progression of tumor microenvironment remodeling and creating various compounds to regulate tumor activities. This study aims to observe enriched TAMs in tumor tissues during bladder cancer development, which markedly facilitated the proliferation of bladder cancer cells and promoted tumor growth in vivo. We determined that TAMs regulate tumor sustained growth by secreting type I collagen, which can activate the prosurvival integrin α2β1/PI3K/AKT signaling pathway. Furthermore, traditional chemotherapeutic drugs combined with integrin α2β1 inhibitor showed intensive anticancer effects, revealing an innovative approach in clinical bladder cancer treatment.     

Endometrial cancer invasion depends on cancer‐derived tumor necrosis factor‐α and stromal derived hepatocyte growth factor

Cancer invasion is an outcome of interactions of the cancer and the host cell. It is now becoming increasingly clear that ovarian hormones have a huge influence on such intercommunications in various types of cancers. Estrogen is known to aggravate the aggressiveness of the endometrial cancer whereas progesterone seems to act as a negative factor. Insight into the mode of ovarian hormonal actions could come from the studies of its regulation of the paracrine interactions between the endometrial cancer and the normal stromal cells during the cancer invasion. In this context, we report here that estrogen promotes the endometrial cancer invasion by inducing humoral interactions between the cancer and the stromal cells, i.e., estrogen stimulates tumor necrosis factor‐α expression from the endometrial cancer cells, which, in turn, induces the stromal expression of hepatocyte growth factor (HGF), conferring the enhanced NK4 (HGF‐antagonist/angiogenesis inhibitor)‐sensitive invasion characteristic of the endometrial cancer cells. Additionally, we demonstrate a close correlation of the invasion of endometrial cancer cells with the expression and dimerization of integrin α_vβ₅ as well as the activation of focal adhesion kinase as the consequences of paracrine interactions. Thus, understanding of paracrine interactions of cancer cells with host stromal cells can yield new insight into the architecture and function of cancer invasion and metastasis, leading to a development of a new cancer therapeutic intervention. © 2008 Wiley‐Liss, Inc.     

ATP‐P2Y2‐β‐catenin axis promotes cell invasion in breast cancer cells

Extracellular adenosine 5′‐triphosphate (ATP), secreted by living cancer cells or released by necrotic tumor cells, plays an important role in tumor invasion and metastasis. Our previous study demonstrated that ATP treatment in vitro could promote invasion in human prostate cancer cells via P2Y2, a preferred receptor for ATP, by enhancing EMT process. However, the pro‐invasion mechanisms of ATP and P2Y2 are still poorly studied in breast cancer. In this study, we found that P2Y2 was highly expressed in breast cancer cells and associated with human breast cancer metastasis. ATP could promote the in vitro invasion of breast cancer cells and enhance the expression of β‐catenin as well as its downstream target genes CD44, c‐Myc and cyclin D1, while P2Y2 knockdown attenuated above ATP‐driven events in vitro and in vivo. Furthermore, iCRT14, a β‐catenin/TCF complex inhibitor, could also suppress ATP‐driven migration and invasion in vitro. These results suggest that ATP promoted breast cancer cell invasion via P2Y2‐β‐catenin axis. Thus blockade of the ATP‐P2Y2‐β‐catenin axis could suppress the invasive and metastatic potential of breast cancer cells and may serve as potential targets for therapeutic interventions of breast cancer.     

TNF‐α enhances TGF‐β‐induced endothelial‐to‐mesenchymal transition via TGF‐β signal augmentation

The tumor microenvironment (TME) consists of various components including cancer cells, tumor vessels, cancer‐associated fibroblasts (CAFs), and inflammatory cells. These components interact with each other via various cytokines, which often induce tumor progression. Thus, a greater understanding of TME networks is crucial for the development of novel cancer therapies. Many cancer types express high levels of TGF‐β, which induces endothelial‐to‐mesenchymal transition (EndMT), leading to formation of CAFs. Although we previously reported that CAFs derived from EndMT promoted tumor formation, the molecular mechanisms underlying these interactions remain to be elucidated. Furthermore, tumor‐infiltrating inflammatory cells secrete various cytokines, including TNF‐α. However, the role of TNF‐α in TGF‐β‐induced EndMT has not been fully elucidated. Therefore, this study examined the effect of TNF‐α on TGF‐β‐induced EndMT in human endothelial cells (ECs). Various types of human ECs underwent EndMT in response to TGF‐β and TNF‐α, which was accompanied by increased and decreased expression of mesenchymal cell and EC markers, respectively. In addition, treatment of ECs with TGF‐β and TNF‐α exhibited sustained activation of Smad2/3 signals, which was presumably induced by elevated expression of TGF‐β type I receptor, TGF‐β2, activin A, and integrin αv, suggesting that TNF‐α enhanced TGF‐β‐induced EndMT by augmenting TGF‐β family signals. Furthermore, oral squamous cell carcinoma‐derived cells underwent epithelial‐to‐mesenchymal transition (EMT) in response to humoral factors produced by TGF‐β and TNF‐α‐cultured ECs. This EndMT‐driven EMT was blocked by inhibiting the action of TGF‐βs. Collectively, our findings suggest that TNF‐α enhances TGF‐β‐dependent EndMT, which contributes to tumor progression.     

Roles for GP IIb/IIIa and αvβ3 integrins in MDA-MB-231 cell invasion and shear flow-induced cancer cell mechanotransduction

Adhesion of cancer cell to endothelial cells and the subsequent trans-endothelial migration are key steps in hematogenous metastasis. However, the molecular mechanisms of cancer cell/endothelial cell interaction under hemodynamic shear flow and how shear flow-induced cancer cell mechanotransduction are yet to be fully defined. In this study, we identified that the integrins of both platelet glycoprotein IIb/IIIa (GP IIb/IIIa) and αvβ3 were crucial for hematogenous metastasis of human breast carcinoma MDA-MB-231cells. The cell migration and invasion were studied by using Millicell cell culture insert system. The numbers of invaded MDA-MB-231 cells significantly increased by thrombin-activated platelets and reduced by eptifibatide, a platelet inhibitor. Meanwhile, RGDWE peptides, a specific inhibitor of αvβ3 integrin, also inhibited MDA-MB-231 cell invasion. We further used a parallel-plate flow chamber to investigate MDA-MB-231 cell adhesion under flow conditions. Alike in static condition, the adhesion capability of MDA-MB-231 cells to endothelial monolayer was also significantly affected by GP IIb/IIIa and αvβ3 integrins. The expression of matrix metalloproteinase-2 (MMP-2), MMP-9 and αvβ3 integrin in MDA-MB-231 cells were up-regulated after low shear stress exposure (1.84 dynes/cm², 2 h). Moreover, we also demonstrated that low shear stress induced a sustained activation of p85 (a regulatory subunit of PI3K) and Akt. Pre-treating MDA-MB-231 cells with the specific PI3K inhibitor of LY294002 abolished the shear stress induced-Akt activation, and the expression of MMP-2, MMP-9, vascular endothelial growth factor (VEGF) and αvβ3 integrin were also down-regulated. Immunofluorescence assay showed that low shear stress also induced αvβ3 integrin clustering and nuclear factor-κB (NF-κB) activation. Interestingly, shear stress-induced activation of Akt and NF-κB was attenuated by LM609, a specific antibody of αvβ3 integrin. It suggests that αvβ3 integrin might be as a mechanosensor to trigger both PI3K/Akt and NF-κB signaling pathways. Taken together, these results establish that GP IIb/IIIa and αvβ3 integrins are essential mediators, and provide insight into how shear stress-induced αvβ3 integrin activation and the downstream pathways for contribution to MDA-MB-231 cell adhesion, migration and invasion.     

Migration properties of the human ovarian adenocarcinoma cell line IGROV1: Importance of αvβ3 integrins and vitronectin

Cell migration of ovarian tumoral cells is essential for cell dissemination and for invasion of the submesothelial extracellular matrix (ECM). We have conducted a study of the migratory properties of an ovarian adenocarcinoma cell line (IGROV1) by using 2 distinct methods for the evaluation of cell migration. We found that in a short‐term transfilter migration assay, IGROV1 cells migrated toward vitronectin, fibronectin, type IV collagen and laminin in an integrin‐dependent manner. When migration was evaluated in a wound healing assay, the restitution of the wounded area was stimulated solely by added, exogenous vitronectin and was almost totally dependent on αvβ3 integrin function. Moreover, we demonstrated that αvβ3 was localized in focal contacts restricted to the leading edge of migrating cells, whereas vitronectin notably localized with actin stress fibers and cortical actin. On the other hand, several kinase inhibitors were found to impede migration of IGROV1 induced by vitronectin. It thus appears that αvβ3–vitronectin interactions lead to the activation of multiple signaling pathway including activation of protein kinase C, phosphatidyl‐inositol‐3‐phosphate kinase and protein tyrosine kinase. The “αvβ3–vitronectin system” is therefore essential to the migration of human ovarian carcinoma cells.Int. J. Cancer 80:285–294, 1999. © 1999 Wiley‐Liss, Inc.     

Genetically modified T cells targeting neovasculature efficiently destroy tumor blood vessels,shrink established solid tumors and increase nanoparticle delivery

Converting T cells into tumor cell killers by grafting them with a chimeric antigen receptor (CAR) has shown promise as a cancer immunotherapeutic. However, the inability of these cells to actively migrate and extravasate into tumor parenchyma has limited their effectiveness in vivo. Here we report the construction of a CAR containing an echistatin as its targeting moiety (eCAR). As echistatin has high binding affinity to αvβ3 integrin that is highly expressed on the surface of endothelial cells of tumor neovasculature, T cells engrafted with eCAR (T‐eCAR) can efficiently lyse human umbilical vein endothelial cells and tumor cells that express αvβ3 integrin when tested in vitro. Systemic administration of T‐eCAR led to extensive bleeding in tumor tissues with no evidence of damage to blood vessels in normal tissues. Destruction of tumor blood vessels by T‐eCAR significantly inhibited the growth of established bulky tumors. Moreover, when T‐eCAR was codelivered with nanoparticles in a strategically designed temporal order, it dramatically increased nanoparticle deposition in tumor tissues, pointing to the possibility that it may be used together with nanocarriers to increase their capability to selectively deliver antineoplastic drugs to tumor tissues.     

Targeting nuclear factor‐κB suppresses the negative effect of Toll‐like receptor 4 signaling on antimetastasis therapy based on targeting αvβ3

The targeting of αvβ3 is a promising therapeutic strategy for suppressing tumor metastasis. However, it is unclear whether the therapeutic efficacy could be influenced by metastasis‐promoting factor(s) in vivo. Here we report that Toll‐like receptor 4 (TLR4) ligand released from damaged tumor cells or bacteria had a negative effect on the therapeutic effect of a recombinant CBD‐HepII polypeptide of fibronectin (CH50) that suppresses tumor metastasis by targeting αvβ3. The TLR4 ligand could antagonize the inhibitory effect of CH50 on tumor cell adhesion and invasion by promoting the expression and activity of αvβ3 in tumor cells. The TLR4 ligand also reduced the antimetastasis effect of CH50 by promoting tumor cell survival in circulation. Moreover, TLR4 ligands released by tumor cells in circulation could increase the survival and proliferation capacity of tumor cells after extravasation, resulting in the formation of more metastatic nodules. The effect of TLR4 signaling was mainly mediated by nuclear factor‐κB (NF‐κB). Inhibiting NF‐κB could abrogate the negative effect of TLR4 ligand, and augment the inhibitory effect of CH50 on tumor metastasis. Consistently, the combination of NF‐κB inhibitor and CH50 significantly inhibited metastasis of tumor cells in vivo and prolonged the survival of mice. The findings in this study suggest that the combination of NF‐κB inhibitor and αvβ3 antagonist would be a novel therapeutic option for the prevention of tumor metastasis. (Cancer Sci 2012; 103: 1319–1326)     

Cilengitide downmodulates invasiveness and vasculogenic mimicry of neuropilin 1 expressing melanoma cells through the inhibition of αvβ5 integrin

During melanoma progression, tumour cells show increased adhesiveness to the vascular wall, invade the extracellular matrix (ECM) and frequently form functional channels similar to vascular vessels (vasculogenic mimicry). These properties are mainly mediated by the interaction of integrins with ECM components. Since we had previously identified neuropilin 1 (NRP‐1), a coreceptor of vascular endothelial growth factor A (VEGF‐A), as an important determinant of melanoma aggressiveness, aims of this study were to identify the specific integrins involved in the highly invasive phenotype of NRP‐1 expressing cells and to investigate their role as targets to counteract melanoma progression. Melanoma aggressiveness was evaluated in vitro as cell ability to migrate through an ECM layer and to form tubule‐like structures using transfected cells. Integrins relevant to these processes were identified using specific blocking antibodies. The αvβ5 integrin was found to be responsible for about 80% of the capability of NRP‐1 expressing cells to adhere on vitronectin. In these cells αvβ5 expression level was twice higher than in low‐invasive control cells and contributed to the ability of melanoma cells to form tubule‐like structures on matrigel. Cilengitide, a potent inhibitor of αν integrins activation, reduced ECM invasion, vasculogenic mimicry and secretion of VEGF‐A and metalloproteinase 9 by melanoma cells. In conclusion, we demonstrated that ανβ5 integrin is involved in the highly aggressive phenotype of melanoma cells expressing NRP‐1. Moreover, we identified a novel mechanism that contributes to the antimelanoma activity of the αv integrin inhibitor cilengitide based on the inhibition of vasculogenic mimicry.     

SHON,a novel secreted protein,regulates epithelial–mesenchymal transition through transforming growth factor‐β signaling in human breast cancer cells

The epithelial–mesenchymal transition (EMT) is one of the main mechanisms contributing to the onset of cancer metastasis, and has proven to be associated with breast cancer progression. SHON is a novel secreted hominoid‐specific protein we have previously identified; it is specifically expressed in all human cancer cell lines tested and is oncogenic for human mammary carcinoma cells. Here, we show that ectopic overexpression of SHON in immortalized human mammary epithelial cells is sufficient for cells to acquire the mesenchymal traits, as well as the enhanced cell migration and invasion, along with the epithelial stem cell properties characterized by increased CD44^high/CD24^low subpopulation and mammosphere‐forming ability. Moreover, we demonstrate that SHON positively activates the autocrine transforming growth factor‐β (TGF‐β) pathway to contribute to EMT, while SHON itself is induced by TGF‐β in mammary epithelial cells. These data are in favor of a SHON‐TGFβ‐SHON‐positive feedback loop that regulates EMT program in breast cancer progression. Finally, examination of the human clinic breast cancer specimens reveals that tumor cells may extracellularly release SHON protein to promote the cancerization of surrounding cells. Together, our findings define an important function of SHON in regulation of EMT via TGF‐β signaling, which is closely associated with the invasive subtypes of human breast cancer.