Hee-Jung Byun

Homophilic Interactions of Tetraspanin CD151 Up-regulate Motility and Matrix Metalloproteinase-9 Expression of Human Melanoma Cells through Adhesion-dependent c-Jun Activation Signaling Pathways

The tetraspanin membrane protein CD151 has been suggested to regulate cancer invasion and metastasis by initiating signaling events. The CD151-mediated signaling pathways involved in this regulation remain to be revealed. In this study, we found that stable transfection of CD151 into MelJuSo human melanoma cells lacking CD151 expression significantly increased cell motility, matrix metalloproteinase-9 (MMP-9) expression, and invasiveness. The enhancement of cell motility and MMP-9 expression by CD151 overexpression was abrogated by inhibitors and small interfering RNAs targeted to focal adhesion kinase (FAK), Src, p38 MAPK, and JNK, suggesting an essential role of these signaling components in CD151 signaling pathways. Also, CD151-induced MMP-9 expression was shown to be mediated by c-Jun binding to AP-1 sites in the MMP-9 gene promoter, indicating AP-1 activation by CD151 signaling pathways. Meanwhile, CD151 was found to be associated with α3β1 and α6β1 integrins in MelJuSo cells, and activation of associated integrins was a prerequisite for CD151-stimulated MMP-9 expression and activation of FAK, Src, p38 MAPK, JNK, and c-Jun. Furthermore, CD151 on one cell was shown to bind to neighboring cells expressing CD151, suggesting that CD151 is a homophilic interacting protein. The homophilic interactions of CD151 increased motility and MMP-9 expression of CD151-transfected MelJuSo cells, along with FAK-, Src-, p38 MAPK-, and JNK-mediated activation of c-Jun in an adhesion-dependent manner. Furthermore, C8161 melanoma cells with endogenous CD151 were also shown to respond to homophilic CD151 interactions for the induction of adhesion-dependent activation of FAK, Src, and c-Jun. These results suggest that homophilic interactions of CD151 stimulate integrin-dependent signaling to c-Jun through FAK-Src-MAPKs pathways in human melanoma cells, leading to enhanced cell motility and MMP-9 expression.

A Splice Variant of CD99 Increases Motility and MMP-9 Expression of Human Breast Cancer Cells through the AKT-, ERK-, and JNK-dependent AP-1 Activation Signaling Pathways

The CD99 gene encodes two distinct transmembrane proteins by alternative splicing of its transcript. To examine the effects of two CD99 isoforms on the invasive phenotypes of breast cancer cells, MDA-MB-231 and MCF-7 human breast cancer cell lines were stably transfected with CD99 cDNAs encoding the major wild-type form (type I) or a minor splice variant (type II). As a result, expression of CD99 type II, but not type I, markedly elevated the motility, binding to fibronectin, MMP-9 expression, and invasiveness of MDA-MB-231 and MCF-7 breast cancer cells. In MDA-MB-435 breast cancer cells expressing both CD99 type I and type II, invasion-related cellular activities were inhibited by the transfection of small interfering RNA (siRNA) targeted to CD99 type II. Meanwhile, CD99 type II-induced MMP-9 expression in MDA-MB-231 cells was shown to be mediated by the binding of AP-1 factors to the MMP-9 gene promoter. Gel shift assay revealed that ligation of CD99 type II with antibody resulted in the binding of JunD to the AP-1 site of the MMP-9 promoter region. Initiation of CD99 type II signaling by antibody ligation increased expression of JunD and FosB AP-1 factors, along with phosphorylation of Src, Akt, p38 MAPK, ERK, and JNK. Knockdown of JunD and FosB by siRNA transfection abolished the positive effects of CD99 type II on the motility and MMP-9 expression of MDA-MB-231 cells. Increased expression of JunD and FosB as well as elevated cell motility and MMP-9 expression by CD99 type II ligation were also abrogated by inhibitors, dominant-negative forms, and siRNAs for Akt1, ERK1/2, and JNK1 but not for p38 MAPK. These results suggest that expression of a splice variant of CD99 contributes to the invasive ability of human breast cancer cells by up-regulating AP-1-mediated gene expression through the Akt-dependent ERK and JNK signaling pathways.

Fibronectin and vitronectin induce AP-1-mediated matrix metalloproteinase-9 expression through integrin α5β1/αvβ3-dependent Akt, ERK and JNK signaling pathways in human umbilical vein endothelial cells

The activity of matrix metalloproteinases (MMPs), which selectively degrades the extracellular matrix (ECM), is critical in angiogenesis. Conversely, changes in ECM composition/structure alter the expression and activity of MMPs in various cell types. In the present study, we examined whether changes in ECM composition affect MMPs expression/activity of endothelial cells and thereby alter the surrounding ECM structure. Among the ECM molecules examined, fibronectin (FN) and vitronectin (VN) increased the expression and activity of MMP-9 in human umbilical vein endothelial cells (HUVECs). Both α(5)β(1) and α(v)β(3) integrins were involved in FN-induced MMP-9 expression. Also, FN-induced MMP-9 expression was found to be mediated by AP-1 transcription factors, including c-Jun, JunB, and JunD. Inhibitors or siRNAs specific to AP-1 activating signal transducers, including FAK-Src, PI3K/Akt, ERK, and JNK, abolished both FN-induced AP-1 activation and MMP-9 expression. VN-induced AP-1 activation and MMP-9 expression were also mediated by these AP-1 activating signal transducers in addition to p38 MAPK. Moreover, treatment with FN or VN resulted in increased degradation of collagen on HUVEC culture plates. Taken together, our data suggest that both fibronectin and vitronectin induce MMP-9 expression via the AP-1-activating signaling pathways in endothelial cells, and thereby stimulate degradation of surrounding collagen, leading to alterations in ECM structure and potentially the promotion of angiogenesis.

The cancer/testis antigen cage with oncogenic potential stimulates cell proliferation by up-regulating cyclins D1 and E in an AP-1- and E2F-dependent manner

A cancer/testis antigen, CAGE, is widely expressed in various cancer tissues and cancer cell lines but not in normal tissues except the testis. In the present study, ectopic expression of CAGE in fibroblast cells resulted in foci formation, suggesting its cell-transforming ability. Using stable HeLa transfectant clones with the tetracycline-inducible CAGE gene, we found that CAGE overexpression stimulated both anchorage-dependent and -independent cell growth in vitro and promoted tumor growth in a xenograft mouse model. Cell cycle analysis showed that CAGE augments the levels of cyclin D1 and E, thereby activating cyclin-associated cyclin-dependent kinases and subsequently accelerating the G1 to S progression. Moreover, increased cyclin D1 and E levels in CAGE-overexpressing cells were observed even in a growth arrested state, indicating a direct effect of CAGE on G1 cyclin expression. CAGE-induced expression of cyclins D1 and E was found to be mediated by AP-1 and E2F-1 transcription factors, and among the AP-1 members, c-Jun and JunD appeared to participate in CAGE-mediated up-regulation of cyclin D1. CAGE overexpression also enhanced retinoblastoma phosphorylation and subsequent E2F-1 nuclear translocation. In contrast, small interfering RNA-mediated knockdown of CAGE suppressed the expression of G1 cyclins, activation of AP-1 and E2F-1, and cell proliferation in both HeLa cervical cancer cells and Malme-3M melanoma cells. These results suggest that the cancer/testis antigen CAGE possesses oncogenic potential and promotes cell cycle progression by inducing AP-1- and E2F-dependent expression of cyclins D1 and E.

Metastasis Suppressor KAI1/CD82 Attenuates the Matrix Adhesion of Human Prostate Cancer Cells by Suppressing Fibronectin Expression and β 1 Integrin Activation

KAI1/CD82, a tetraspanin membrane protein functions as a metastasis suppressor in many types of human cancers and has been shown to regulate cell adhesion properties. In the present study, we investigated the underlying mechanism of KAI1/CD82-mediated changes in cell adhesion to the extracellular matrix using human prostate cancer cells. We found that high KAI1/CD82 expression attenuated short-term cell adhesion to uncoated- or fibronectin-coated plates. Moreover, high KAI1/CD82 expression generated an extracellular environment unfavorable for cell adhesion as compared to low KAI1/CD82 expression, suggesting KAI1/CD82-dependent regulation of extracellular matrix (ECM) molecule(s) expression and/or secretion. Among ECM components examined, fibronectin exhibited decreased expression and secretion in high KAI1/CD82-expressing cells. Furthermore, high KAI1/CD82 expression interfered with the activation of β 1 integrin at the cell surface while total β 1 integrin levels remained unchanged, concomitant with reduced formation of focal adhesion complex and decreased bundling of actin filaments. Finally, high KAI1/CD82 expression significantly retarded cell motility in a scratch wound assay. Taken together, our results strongly suggest that KAI1/CD82 attenuates the activation of β 1 integrin, and thereby down-regulates outside-in signaling of β 1 integrin, leading to the reduction of focal adhesion formation and fibronectin expression/secretion, which subsequently interferes with cell adhesion properties and motility.

The tetraspanin CD81 protein increases melanoma cell motility by up-regulating metalloproteinase MT1-MMP expression through the pro-oncogenic Akt-dependent Sp1 activation signaling pathways.

Background: CD81-associated tetraspanins influence the invasive and metastatic processes of various cancer cell types. Results: CD81-Akt signaling induces Sp1-mediated MT1-MMP expression, which enhances melanoma cell motility and invasiveness. Conclusion: CD81 functions as an inducer of MT1-MMP that plays a role in melanoma invasive processes. Significance: This study provides the first evidence that CD81 contributes to cancer malignant progression and elucidates the underlying mechanism. Despite the importance of multiple tetraspanin proteins in cancer invasion and metastasis, little is known about the role and significance of tetraspanin CD81 in these processes. In the present study, we examined CD81 effects on melanoma cell invasiveness and metastasis. Transfection of CD81 into melanoma cells lacking endogenous CD81 expression significantly enhanced the migrating, invasive, and metastatic abilities of melanoma cells. Interestingly, membrane type 1 matrix metalloproteinase (MT1-MMP) expression was found in CD81-expressing melanoma cells but not in CD81-deficient cells. siRNA knockdown of CD81 in melanoma cells with endogenous CD81 demonstrated decreased MT1-MMP levels and cell motility. Notably, CD81-induced cell migration was abrogated by antibody blocking and siRNA knockdown of MT1-MMP, indicating that MT1-MMP is responsible for CD81-stimulated melanoma cell migration. Promoter analysis revealed an essential role of the Sp1 transcription factor in CD81-induced MT1-MMP transcription. We also demonstrate that the Sp1-activating Akt pathway is involved in adhesion-dependent CD81 signaling to induce MT1-MMP expression and cell motility. Importantly, human skin cancer tissue specimens displayed a positive correlation of CD81 with MT1-MMP expression levels and a close association of CD81 with malignant melanomas. Taken together, these results strongly suggest that CD81 stimulates melanoma cell motility by inducing MT1-MMP expression through the Akt-dependent Sp1 activation signaling pathway, leading to increased melanoma invasion and metastasis.

The metastasis suppressor CD82/KAI1 inhibits fibronectin adhesion-induced epithelial-to-mesenchymal transition in prostate cancer cells by repressing the associated integrin signaling

The transmembrane protein CD82/KAI1 suppresses the metastatic potential of various cancer cell types. Moreover, decrease or loss of CD82 expression is closely associated with malignancy and poor prognosis in many human cancers including prostate cancer. Despite intense scrutiny, the mechanisms underlying the metastasis-suppressing role of CD82 are still not fully understood. Here, we found that a fibronectin matrix induced mesenchymal phenotypes in human prostate cancer cells with no or low CD82 expression levels. However, high CD82 expression rendered prostate cancer cells to have intensified epithelial characteristics upon fibronectin engagement, along with decreased cell motility and invasiveness. The CD82 function of inhibiting fibronectin-induced epithelial-to-mesenchymal transition (EMT) was dependent not only on CD82 interactions with fibronectin-binding α3β1/α5β1 integrins but also on the integrin-mediated intracellular signaling events. Notably, CD82 attenuated the FAK-Src and ILK pathways downstream of the fibronectin-receptor integrins. Immunofluorescence staining of human prostate cancer tissue specimens illustrated a negative association of CD82 with EMT-related gene expression as well as prostate malignancy. Altogether, these results suggest that CD82 suppresses EMT in prostate cancer cells adhered to the fibronectin matrix by repressing adhesion signaling through lateral interactions with the associated α3β1 and α5β1 integrins, leading to reduced cell migration and invasive capacities.

Tetraspanin CD82 represses Sp1-mediated Snail expression and the resultant E-cadherin expression interrupts nuclear signaling of β-catenin by increasing its membrane localization

Tetraspanin membrane proteins form physical complexes with signaling molecules and have been suggested to influence the signaling events of associated molecules. Of the tetraspanin proteins, CD82 has been shown to promote homotypic cell-cell adhesion, which partially accounts for its role in suppressing cancer invasion and metastasis. We found here that CD82-induced cell-cell adhesion is attributed to increased E-cadherin expression through CD82-mediated downregulation of the E-cadherin repressor Snail. The Snail repression by CD82 resulted from the reduced binding of the Sp1 transcription factor to the Snail gene promoter. Notably, high CD82 expression did not allow the fibronectin matrix to induce Sp1 phosphorylation, implicating CD82 inhibition of the fibronectin-integrin signaling-dependent Sp1 activation. Meanwhile, E-cadherin upregulated by CD82 pulled β-catenin up to the membrane region, and consequently reduced the amount of cytoplasmic β-catenin that was able to move into to the nucleus. The Wnt signal-induced nuclear translocation of β-catenin was also inhibited by the CD82 function of upregulating E-cadherin. Overall, high CD82 expression was likely to suppress fibronectin adhesion-induced Sp1 activation signaling for Snail expression, resulting in continuous E-cadherin expression, which contributed not only to the maintenance of strong cell-cell adhesion but also to the blockage of nuclear β-catenin signaling.

Abstract 1051: Metastasis suppressor CD82 functions as a negative regulator in the adhesion-dependent epithelial-to-mesenchymal transition in prostate cancer cells

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Tetraspanin CD82 suppresses cancer metastasis by inhibiting cell motility and invasiveness. In an effect to reveal the mechanism underlying the metastasis-suppressing role of CD82, we here examined the effect of CD82 on epithelial-mesenchymal transition (EMT), a critical event of cancer cells that promotes migration and invasion. In human prostate cancer cell lines, an increase in CD82 expression levels by exogenous gene delivery elevated E-cadherin levels, but decreased the levels of mesenchymal cell proteins including Snail, Twist, vimentin, N-cadhherin, and α-smooth muscle actin, suggesting EMT-suppressing role of CD82. Also, increased CD82 expression resulted in decreased motility and invasiveness of prostate cancer cells. In contrast, CD82 knockdown decreased E-cadherin levels, but increased the levels of mesenchymal cell proteins, together with cell morphology change to fibroblast-like shape. CD82 also interfered with TGF-β1- and Wnt-induced EMT. Additionally, CD82 decreased expression of β-catenin target genes such as c-myc and cyclin D1 by inhibiting nuclear translocation of β-catenin. Notably, the negative effect of CD82 on EMT was apparent on cells adhered to fibronectin. Fibronectin-binding α3β1/α5β1 integrins were involved in CD82-mediated inhibition of EMT. Importantly, human prostate cancer tissue specimens displayed a positive correlation of CD82 with E-cadherin expression levels, along with a negative correlation of CD82 with vimentin levels. Moreover, both CD82 and E-cadherin levels were inversely correlated with the malignant progression stages of human prostate cancers. Taken together, these results strongly suggest that CD82 suppresses motility and invasiveness of prostate cancer cells by inhibiting EMT in an α3β1/α5β1 integrin-dependent manner. Citation Format: Hee-Jung Byun, Yong-Sun Lee, Young-June Jin, Jae-Sub Lee, Young-Myeong Kim, Hansoo Lee. Metastasis suppressor CD82 functions as a negative regulator in the adhesion-dependent epithelial-to-mesenchymal transition in prostate cancer cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1051. doi:10.1158/1538-7445.AM2014-1051

Abstract 3124: Tetraspanin CD151-mediated signaling network between cell-matrix and cell-cell adhesions

CD151 has been suggested to promote cancer invasion and metastasis by regulating adhesion-dependent signaling events through its association with laminin-binding α3β1/α6β1 integrins. Previously, we have demonstrated that homophilic interactions of CD151 stimulate integrin-dependent signaling to c-Jun through the FAK-Src-MAPKs pathways in human melanoma cells. In this study, we found that CD151 plays a role in recruiting Ras, Rac1, and Cdc42, but not Rho, to the membrane region, leading to formation of α3β1/α6β1 integrins-CD151-small GTPases complexes. Adhesion receptor complexes-associated small GTPases were found to be activated by β1 integrins-CD151 complexes-stimulating adhesion events such as interactions of integrins with laminin and homophilic interactions of CD151 on two contacting cells, implicating CD151-mediated signaling network between cell-matrix and cell-cell adhesions. Adhesion-dependent activation of small GTPases appeared to be mediated by the FAK-Src pathways. Meanwhile, EGF and phorbol ester treatment further enhanced CD151-β1 integrin complexes-induced cell motility and MMP-9 expression, along with activation of p38 MAPK and JNK, indicating a positive signaling cross-talk between CD151-β1 integrin adhesion receptor, EGF receptor, and PKC. Using siRNAs and dominant-inhibitory mutant expression constructs for various intracellular signaling mediators, we found that integrin-linked kinase (ILK), PAK1-interacting exchange factor beta (β-PIX), and p21-activated protein kinase 1 (PAK1) were involved in CD151-β1 integrin adhesion receptor complex signaling pathways. Also, MEK3/6 and MEK7 were found to participate in CD151-β1 integrin signaling cascades, upstream of p38 MAPK and JNK, respectively. Taken together, our data strongly suggest that β1 integrin-CD151 adhesion receptor complexes activate c-Jun AP-1 factor via the signaling cascades involving the FAK-Src, ILK-β-Pix, small GTPases-PAK1, MEK3/6-p38 MAPK, and MEK7-JNK pathways, leading to increased cell motility and MMP-9 expression in human melanoma cells. Key words: tetraspanin, CD151, integrin, adhesion receptor, cell signaling Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3124. doi:10.1158/1538-7445.AM2011-3124