TM4SF5-mediated protein-protein networks and tumorigenic roles

Transmembrane 4 L six family member 5 (TM4SF5), as a membrane glycoprotein with 4 transmembrane domains, is similar to the tetraspanins in terms of membrane topology and plays important roles in tumorigenesis and tumor metastasis. Especially, TM4SF5 appears to form a massive protein-protein complex consisting of diverse membrane proteins and/or receptors in addition to cytosolic signaling molecules to regulate their signaling activities during the pathological processes. TM4SF5 is shown to interact with integrins α2, α5, and β1, EGFR, IL6R, CD151, focal adhesion kinase (FAK), and c-Src. This review focuses on the significance of the interactions with regards to TM4SF5-positive tumorigenesis and metastasis. [BMB Reports 2014; 47(9): 483-487]     

Cross Talk between the TM4SF5/Focal Adhesion Kinase and the Interleukin-6/STAT3 Pathways Promotes Immune Escape of Human Liver Cancer Cells

TM4SF5 overexpressed in hepatocellular carcinoma activates focal adhesion kinase (FAK) during tumor cell migration. However, it remains unknown how TM4SF5 in hepatocellular carcinoma cells compromises with immune actions initiated by extracellular cytokines. Normal and cancerous hepatocytes with or without TM4SF5 expression were analyzed for the effects of cytokine signaling activity on TM4SF5/FAK signaling and metastatic potential. We found that interleukin-6 (IL-6) was differentially expressed in hepatocytes depending on cancerous malignancy and TM4SF5 expression. IL-6 treatment activated FAK and STAT3 and enhanced focal adhesion (FA) formation in TM4SF5-null cells, but it decreased TM4SF5-dependent FAK activity and FA formation in SNU761-TM4SF5 cells. STAT3 suppression abolished the IL-6-mediated effects in normal Chang cells, but it did not recover the TM4SF5-dependent FAK activity that was inhibited by IL-6 treatment in cancerous SNU761-TM4SF5 cells. In addition, modulation of FAK activity did not change the IL-6-mediated STAT3 activity in either the Chang or SNU761 cell system. TM4SF5 expression in SNU761 cells caused invasive extracellular matrix degradation negatively depending on IL-6/IL-6 receptor (IL-6R) signaling. Thus, it is likely that hepatic cancer cells adopt TM4SF5-dependent FAK activation and metastatic potential by lowering IL-6 expression and avoiding its immunological action through the IL-6-STAT3 pathway.     

Correlations between Transmembrane 4 L6 Family Member 5 (TM4SF5), CD151, and CD63 in Liver Fibrotic Phenotypes and Hepatic Migration and Invasive Capacities

Transmembrane 4 L6 family member 5 (TM4SF5) is overexpressed during CCl₄-mediated murine liver fibrosis and in human hepatocellular carcinomas. The tetraspanins form tetraspanin-enriched microdomains (TEMs) consisting of large membrane protein complexes on the cell surface. Thus, TM4SF5 may be involved in the signal coordination that controls liver malignancy. We investigated the relationship between TM4SF5-positive TEMs with liver fibrosis and tumorigenesis, using normal Chang hepatocytes that lack TM4SF5 expression and chronically TGFβ1-treated Chang cells that express TM4SF5. TM4SF5 expression is positively correlated with tumorigenic CD151 expression, but is negatively correlated with tumor-suppressive CD63 expression in mouse fibrotic and human hepatic carcinoma tissues, indicating cooperative roles of the tetraspanins in liver malignancies. Although CD151 did not control the expression of TM4SF5, TM4SF5 appeared to control the expression levels of CD151 and CD63. TM4SF5 interacted with CD151, and caused the internalization of CD63 from the cell surface into late lysosomal membranes, presumably leading to terminating the tumor-suppressive functions of CD63. TM4SF5 could overcome the tumorigenic effects of CD151, especially cell migration and extracellular matrix (ECM)-degradation. Taken together, TM4SF5 appears to play a role in liver malignancy by controlling the levels of tetraspanins on the cell surface, and could provide a promising therapeutic target for the treatment of liver malignancies.     

Self-renewal and circulating capacities of metastatic hepatocarcinoma cells required for collaboration between TM4SF5 and CD44

Tumor metastasis involves circulating and tumor-initiating capacities of metastatic cancer cells. Hepatic TM4SF5 promotes EMT for malignant growth and migration. Hepatocellular carcinoma (HCC) biomarkers remain unexplored for metastatic potential throughout metastasis. Here, novel TM4SF5/CD44 interaction-mediated self-renewal and circulating tumor cell (CTC) capacities were mechanistically explored. TM4SF5-dependent sphere growth was correlated with CD133⁺, CD24^-, ALDH activity, and a physical association between CD44 and TM4SF5. The TM4SF5/CD44 interaction activated c-Src/STAT3/ Twist1/ B mi1 signaling for spheroid formation, while disturbing the interaction, expression, or activity of any component in this signaling pathway inhibited spheroid formation. In serial xenografts of less than 5,000 cells/injection, TM4SF5-positive tumors exhibited locally-increased CD44 expression, suggesting tumor cell differentiation. TM4SF5-positive cells were identified circulating in blood 4 to 6 weeks after orthotopic liver-injection. Anti-TM4SF reagents blocked their metastasis to distal intestinal organs. Altogether, our results provide evidence that TM4SF5 promotes self-renewal and CTC properties supported by CD133⁺/TM4SF5⁺/CD44^{+(TM4SF5-bound)}/ALDH⁺/ CD24^- markers during HCC metastasis. [BMB Reports 2015; 48(3): 127-128]     

Proteasome inhibition causes epithelial-mesenchymal transition upon TM4SF5 expression

Transmembrane 4 L six family member 5 (TM4SF5) is highly expressed in hepatocarcinoma and causes epithelial-mesenchymal transition (EMT) of hepatocytes. We found that TM4SF5-expressing cells showed lower mRNA levels but maintained normal protein levels in certain gene cases, indicating that TM4SF5 mediates stabilization of proteins. In this study, we explored whether regulation of proteasome activity and TM4SF5 expression led to EMT. We observed that TM4SF5 expression caused inhibition of proteasome activity and proteasome subunit expression, causing morphological changes and loss of cell-cell contacts. shRNA against TM4SF5 recovered proteasome expression, with leading to blockade of proteasome inactivation and EMT. Altogether, TM4SF5 expression appeared to cause loss of cell-cell adhesions via proteasome suppression and thereby proteasome inhibition, leading to repression of cell-cell adhesion molecules, such as E-cadherin.     

Focal adhesion and actin organization by a cross-talk of TM4SF5 with integrin alpha2 are regulated by serum treatment

The biological functions of transmembrane 4 L6 family member 5 (TM4SF5) homologues to a tumor-associated antigen L6 are unknown, although it is over-expressed in certain forms of cancer. In the present study, the ectopic expression of TM4SF5 in Cos7 cells reduced integrin signaling under serum-containing conditions, but increased integrin signaling upon serum-free replating on substrates. TM4SF5 regulated actin organization and focal contact dynamics via the serum treatment-dependent differential regulation of FAK Tyr925 and paxillin Tyr118 phosphorylations and their localizations on peripheral cell boundaries. Y925F FAK mutation abolished the TM4SF5 effects. TM4SF5 associated with integrin alpha2 subunit, and this association was abolished by serum treatment. Furthermore, functional blocking anti-integrin alpha2 antibody abolished TM4SF5-enhanced signaling activity and caused membrane blebbing with abnormal actin organization. TM4SF5 increased chemotactic but decreased haptotactic migration. Altogether, this study reveals the functions of TM4SF5 collaborative with integrin signaling to alter focal contact dynamics, actin reorganization, and migration. Furthermore, this study suggests a mechanism of cross-talk between TM4SF5 and integrin which is further regulated by growth factor signaling.     

Prevention and therapy of hepatocellular carcinoma by vaccination with TM4SF5 epitope-CpG-DNA-liposome complex without carriers

Although peptide vaccines have been actively studied in various animal models, their efficacy in treatment is limited. To improve the efficacy of peptide vaccines, we previously formulated an efficacious peptide vaccine without carriers using the natural phosphodiester bond CpG-DNA and a special liposome complex (Lipoplex(O)). Here, we show that immunization of mice with a complex consisting of peptide and Lipoplex(O) without carriers significantly induces peptide-specific IgG2a production in a CD4(+) cells- and Th1 differentiation-dependent manner. The transmembrane 4 superfamily member 5 protein (TM4SF5) has gained attention as a target for hepatocellular carcinoma (HCC) therapy because it induces uncontrolled growth of human HCC cells via the loss of contact inhibition. Monoclonal antibodies specific to an epitope of human TM4SF5 (hTM4SF5R2-3) can recognize native mouse TM4SF5 and induce functional effects on mouse cancer cells. Pre-immunization with a complex of the hTM4SF5R2-3 epitope and Lipoplex(O) had prophylactic effects against tumor formation by HCC cells implanted in an mouse tumor model. Furthermore, therapeutic effects were revealed regarding the growth of HCC when the vaccine was injected into mice after tumor formation. These results suggest that our improved peptide vaccine technology provides a novel prophylaxis measure as well as therapy for HCC patients with TM4SF5-positive tumors.     

Transmembrane 4 L six family member 5 (TM4SF5) enhances migration and invasion of hepatocytes for effective metastasis

Overexpression of transmembrane 4 L six family member 5 (TM4SF5), a four‐transmembrane L6 family member, causes aberrant cell proliferation and angiogenesis, but the roles of TM4SF5 in migration, invasion, and tumor metastasis remain unknown. Using in vitro hepatocarcinoma cells that ectopically or endogenously express TM4SF5 and in vivo mouse systems, roles of TM4SF5 in metastatic potentials were examined. We found that TM4SF5 expression facilitated migration, invadopodia formation, MMP activation, invasion, and eventually lung metastasis in nude mice, but suppression of TM4SF5 with its shRNA blocked the effects. Altogether, TM4SF5‐mediated migration and invasion suggest that TM4SF5 may be therapeutically targeted to deal with TM4SF5‐mediated hepatocellular cancers. J. Cell. Biochem. 111: 59–66, 2010. © 2010 Wiley‐Liss, Inc.     

Characterization of integrin-tetraspanin adhesion complexes: role of tetraspanins in integrin signaling.

Tetraspanins (or proteins from the transmembrane 4 superfamily, TM4SF) form membrane complexes with integrin receptors and are implicated in integrin-mediated cell migration. Here we characterized cellular localization, structural composition, and signaling properties of alpha3beta1-TM4SF adhesion complexes. Double-immunofluorescence staining showed that various TM4SF proteins, including CD9, CD63, CD81, CD82, and CD151 are colocalized within dot-like structures that are particularly abundant at the cell periphery. Differential extraction in conjunction with chemical cross-linking indicated that the cell surface fraction of alpha3beta1-TM4SF protein complexes may not be directly linked to the cytoskeleton. However, in cells treated with cytochalasin B alpha3beta1-TM4SF protein complexes are relocated into intracellular vesicles suggesting that actin cytoskeleton plays an important role in the distribution of tetraspanins into adhesion structures. Talin and MARCKS are partially codistributed with TM4SF proteins, whereas vinculin is not detected within the tetraspanin-containing adhesion structures. Attachment of serum-starved cells to the immobilized anti-TM4SF mAbs induced dephosphorylation of focal adhesion kinase (FAK). On the other hand, clustering of tetraspanins in cells attached to collagen enhanced tyrosine phosphorylation of FAK. Furthermore, ectopic expression of CD9 in fibrosarcoma cells affected adhesion-induced tyrosine phosphorylation of FAK, that correlated with the reorganization of the cortical actin cytoskeleton. These results show that tetraspanins can modulate integrin signaling, and point to a mechanism by which TM4SF proteins regulate cell motility.     

Early role of CD4+ Th1 cells and antibodies in HER-2 adenovirus vaccine protection against autochthonous mammary carcinomas

HER-2 is an oncogenic tumor-associated Ag that is overexpressed in several human tumors including breast and ovarian cancer. The efficacy and mechanism of a HER-2-expressing recombinant adenoviral vaccine to protect against tumorigenesis was examined using HER-2 transgenic (BALB-neuT) mice, which develop spontaneous breast tumors in all 10 mammary glands, and also using a transplantable mouse tumor model. Vaccination beginning at 6-8 wk of age (through 19 wk of age) prevented development of spontaneous mammary tumors even after 50 wk, whereas the animals in the control groups had tumors in all mammary glands by 25 wk. Such long-term protection after the last boost has not been achieved previously in this transgenic mouse in which the oncogene is continuously spawning tumorigenesis. Using beta(2)-microglobulin-knockout, IFN-gamma-knockout, and B cell-deficient mice, CD4(+) and CD8(+) cell depletion, and Ab transfer studies, we show that induction of anti-HER-2/neu Abs are both necessary and sufficient for protection, and the IgG2a isotype is most effective. In contrast, CD8(+) T cells are not necessary at all, and CD4(+) T cells are necessary for only 36-48 h after immunization to provide help for B cells but not as effector cells. Equal protection in immunized mice deficient in FcgammaRI/III excluded an FcR-mediated mechanism. Anti-HER-2 serum not only inhibited growth of mammary tumor cell lines expressing HER-2 in vitro but also protected mice from tumors in vivo, suggesting a direct action of Ab on the tumor cells. Such a vaccine may provide Ab-mediated protection against HER-2-expressing breast cancers in humans.     

Abrogation of junctional adhesion molecule-A expression induces cell apoptosis and reduces breast cancer progression

Intercellular junctions promote homotypic cell to cell adhesion and transfer intracellular signals which control cell growth and apoptosis. Junctional adhesion molecule-A (JAM-A) is a transmembrane immunoglobulin located at tight junctions of normal epithelial cells of mammary ducts and glands. In the present paper we show that JAM-A acts as a survival factor for mammary carcinoma cells. JAM-A null mice expressing Polyoma Middle T under MMTV promoter develop significantly smaller mammary tumors than JAM-A positive mice. Angiogenesis and inflammatory or immune infiltrate were not statistically modified in absence of JAM-A but tumor cell apoptosis was significantly increased. Tumor cells isolated from JAM-A null mice or 4T1 cells incubated with JAM-A blocking antibodies showed reduced growth and increased apoptosis which paralleled altered junctional architecture and adhesive function. In a breast cancer clinical data set, tissue microarray data show that JAM-A expression correlates with poor prognosis. Gene expression analysis of mouse tumor samples showed a correlation between genes enriched in human G3 tumors and genes over expressed in JAM-A +/+ mammary tumors. Conversely, genes enriched in G1 human tumors correlate with genes overexpressed in JAM-A-/- tumors. We conclude that down regulation of JAM-A reduces tumor aggressive behavior by increasing cell susceptibility to apoptosis. JAM-A may be considered a negative prognostic factor and a potential therapeutic target.     

Therapeutic effect of a TM4SF5-specific peptide vaccine against colon cancer in a mouse model

Molecular-targeted therapy has gained attention because of its high efficacy and weak side effects. Previously, we confirmed that transmembrane 4 superfamily member 5 protein (TM4SF5) can serve as a molecular target to prevent or treat hepatocellular carcinoma (HCC). We recently extended the application of the peptide vaccine, composed of CpG-DNA, liposome complex, and TM4SF5 peptide, to prevent colon cancer in a mouse model. Here, we first implanted mice with mouse colon cancer cells and then checked therapeutic effects of the vaccine against tumor growth. Immunization with the peptide vaccine resulted in robust production of TM4SF5-specific antibodies, alleviated tumor growth, and reduced survival rate of the tumor-bearing mice. We also found that serum levels of VEGF were markedly reduced in the mice immunized with the peptide vaccine. Therefore, we suggest that the TM4SF5-specific peptide vaccine has a therapeutic effect against colon cancer in a mouse model. [BMB Reports 2014; 47(4): 215-220]     

alpha4beta1 integrin regulates lamellipodia protrusion via a focal complex/focal adhesion-independent mechanism

alpha4beta1 integrin plays an important role in cell migration. We show that when ectopically expressed in Chinese hamster ovary cells, alpha4beta1 is sufficient and required for promoting protrusion of broad lamellipodia in response to scratch-wounding, whereas alpha5beta1 does not have this effect. By time-lapse microscopy of cells expressing an alpha4/green fluorescent protein fusion protein, we show that alpha4beta1 forms transient puncta at the leading edge of cells that begin to protrude lamellipodia in response to scratch-wounding. The cells expressing a mutant alpha4/green fluorescent protein that binds paxillin at a reduced level had a faster response to scratch-wounding, forming alpha4-positive puncta and protruding lamellipodia much earlier. While enhancing lamellipodia protrusion, this mutation reduces random motility of the cells in Transwell assays, indicating that lamellipodia protrusion and random motility are distinct types of motile activities that are differentially regulated by interactions between alpha4beta1 and paxillin. Finally, we show that, at the leading edge, alpha4-positive puncta and paxillin-positive focal complexes/adhesions do not colocalize, but alpha4beta1 and paxillin colocalize partially in ruffles. These findings provide evidence for a specific role of alpha4beta1 in lamellipodia protrusion that is distinct from the motility-promoting functions of alpha5beta1 and other integrins that mediate cell adhesion and signaling events through focal complexes and focal adhesions.     

E2F1 Has Both Oncogenic and Tumor-Suppressive Properties in a Transgenic Model

Using a transgenic mouse model expressing the E2F1 gene under the control of a keratin 5 (K5) promoter, we previously demonstrated that increased E2F1 activity can promote tumorigenesis by cooperating with either a v-Ha-ras transgene to induce benign skin papillomas or p53 deficiency to induce spontaneous skin carcinomas. We now report that as K5 E2F1 transgenic mice age, they are predisposed to develop spontaneous tumors in a variety of K5-expressing tissues, including the skin, vagina, forestomach, and odontogenic epithelium. On the other hand, K5 E2F1 transgenic mice are found to be resistant to skin tumor development following a two-stage carcinogenesis protocol. Additional experiments suggest that this tumor-suppressive effect of E2F1 occurs at the promotion stage and may involve the induction of apoptosis. These findings demonstrate that increased E2F1 activity can either promote or inhibit tumorigenesis, dependent upon the experimental context.     

EphB4 promotes site-specific metastatic tumor cell dissemination by interacting with endothelial cell-expressed ephrinB2

The tyrosine kinase receptor EphB4 interacts with its ephrinB2 ligand to act as a bidirectional signaling system that mediates adhesion, migration, and guidance by controlling attractive and repulsive activities. Recent findings have shown that hematopoietic cells expressing EphB4 exert adhesive functions towards endothelial cells expressing ephrinB2. We therefore hypothesized that EphB4/ephrinB2 interactions may be involved in the preferential adhesion of EphB4-expressing tumor cells to ephrinB2-expressing endothelial cells. Screening of a panel of human tumor cell lines identified EphB4 expression in nearly all analyzed tumor cell lines. Human A375 melanoma cells engineered to express either full-length EphB4 or truncated EphB4 variants which lack the cytoplasmic catalytic domain (ΔC-EphB4) adhered preferentially to ephrinB2-expressing endothelial cells. Force spectroscopy by atomic force microscopy confirmed, on the single cell level, the rapid and direct adhesive interaction between EphB4 and ephrinB2. Tumor cell trafficking experiments in vivo using sensitive luciferase detection techniques revealed significantly more EphB4-expressing A375 cells but not ΔC-EphB4-expressing or mock-transduced control cells in the lungs, the liver, and the kidneys. Correspondingly, ephrinB2 expression was detected in the microvessels of these organs. The specificity of the EphB4-mediated tumor homing phenotype was validated by blocking the EphB4/ephrinB2 interaction with soluble EphB4-Fc. Taken together, these experiments identify adhesive EphB4/ephrinB2 interactions between tumor cells and endothelial cells as a mechanism for the site-specific metastatic dissemination of tumor cells. AACR.     

The Adhesion GPCR CD97/ADGRE5 inhibits apoptosis

The Adhesion G protein-coupled receptor (GPCR) CD97/ADGRE5 is induced, upregulated, and/or biochemically modified in various malignancies, compared to the corresponding normal tissues. As tumor cells are generally more resistant to apoptosis, we here studied the ability of CD97 to regulate tumor cell survival under apoptotic conditions. Stable overexpression of wild-type CD97 reduced serum starvation- and staurosporine-induced intrinsic and tumor necrosis factor (TNF)/cycloheximide-induced extrinsic apoptosis, indicated by an increase in cell viability, a lower percentage of cells within the subG0/G1 phase, expressing annexin V, or having condensed nuclei, and a reduction of DNA laddering. Protection from cell death by CD97 was accompanied by an inhibition of caspase activation and modulation of anti- and pro-apoptotic members of the BCL-2 superfamily. shRNA-mediated knockdown of CD97 and, in part, truncation of the seven-span transmembrane (TM7) region of CD97 increased caspase-mediated apoptosis. Protection from apoptosis required not only the TM7 region but also cleavage of the receptor at its GPCR proteolysis site (GPS), whereas alternative splicing of its extracellular domain had no effect. Together, our data indicate a role of CD97 in tumor cell survival.