Tetraspan TM4SF5-dependent direct activation of FAK and metastatic potential of hepatocarcinoma cells

Isoxazole-based molecules restore NK cell immune surveillance in hepatocarcinogenesis by targeting TM4SF5 and SLAMF7 linkage

Dynamic communication between hepatocytes and the environment is critical in hepatocellular carcinoma (HCC) development. Clinical immunotherapy against HCC is currently unsatisfactory and needs more systemic considerations, including the identification of new biomarkers and immune checkpoints. Transmembrane 4 L six family member 5 (TM4SF5) is known to promote HCC, but it remains unclear how cancerous hepatocytes avoid immune surveillance and whether avoidance can be blocked. We investigated how TM4SF5-mediated hepatic tumorigenesis avoids surveillance by natural killer (NK) cells, which are prevalent in the liver, and whether the avoidance can be blocked by anti-TM4SF5 agents. We used comprehensive structure activity relationship analysis to identify TM4SF5-specific isoxazole (TSI)-based small molecules that inhibit TM4SF5-mediated effects. TM4SF5 expressed by hepatocytes reduced NK cell cytotoxicity by downregulating stimulatory ligands/receptors, including signaling lymphocytic activation molecule family member 7 (SLAMF7). TM4SF5 bound SLAMF7 depending on N-glycosylation and caused intracellular trafficking of SLAMF7 from the plasma membrane to lysosomes for degradation. TSI treatments in cell lines and animal models of HCC blocked this binding, intracellular trafficking, and downregulation, resulting in higher levels of stimulatory NK cell ligands. In mouse xenograft models, TSI treatment abrogated HCC development by increasing the abundance and dispersion of Slamf7-positive cells in liver tissues, recapitulating the phenotype of Tm4sf5-knockout mice and indicating TSI-mediated restoration of NK cell surveillance. These findings suggest that TSIs can inhibit TM4SF5-mediated liver carcinogenesis by increasing NK cell surveillance.

MFAP2 upregulation promotes ESCC metastasis via FAK-AKT signaling pathway

Metastasis is the leading cause of mortality from esophageal squamous cell carcinoma (ESCC). By the time of diagnosis, most ESCC tumors have already invaded the lymph nodes or distant organs; however, it has been challenging to identify and confirm genes with a crucial role in ESCC metastasis. The microfibrillar-associated protein 2 (MFAP2) is upregulated in human ESCC, and its expression level was positively associated with poor overall and disease-free survival. Consistently, upregulation of MFAP2 promoted the metastasis and invasion of ESCC cells in vitro and in vivo. Conversely, these processes were reduced by MFAP2 knockdown. Mechanistically, MFAP2 was shown to bind to the FERM domain of focal adhesion kinase (FAK) and to alleviate FAK intramolecular inhibition, resulting in the enhanced binding affinity between FAK and integrin beta 4 (ITGB4) and activation of the FAK-AKT signaling pathway. Treatment of ESCC cells with the FAK inhibitor PND-1186 reduced MFAP2, induced the activation of the FAK-AKT pathway in vitro, and suppressed lung metastasis in a mouse model of ESCC. These findings support a major role for MFAP2 in promoting ESCC metastasis, in part via the activation of FAK-AKT signaling, and highlight the potential of MFAP2 as a promising therapeutic target for ESCC.

Biomechanical Effects of Mechanical Stress on Cells Involved in Fracture Healing

Fracture healing is a complex staged repair process in which the mechanical environment plays a key role. Bone tissue is very sensitive to mechanical stress stimuli, and the literature suggests that appropriate stress can promote fracture healing by altering cellular function. However, fracture healing is a coupled process involving multiple cell types that balance and limit each other to ensure proper fracture healing. The main cells that function during different stages of fracture healing are different, and the types and molecular mechanisms of stress required are also different. Most previous studies have used a single mechanical stimulus on individual mechanosensitive cells, and there is no relatively uniform standard for the size and frequency of the mechanical stress. Analyzing the mechanisms underlying the effects of mechanical stimulation on the metabolic regulation of signaling pathways in cells such as in bone marrow mesenchymal stem cells (BMSCs), osteoblasts, chondrocytes, and osteoclasts is currently a challenging research hotspot. Grasping how stress affects the function of different cells at the molecular biology level can contribute to the refined management of fracture healing. Therefore, in this review, we summarize the relevant literature and describe the effects of mechanical stress on cells associated with fracture healing, and their possible signaling pathways, for the treatment of fractures and the further development of regenerative medicine.

miR-373 promotes invasion and metastasis of colorectal cancer cells via activating ERK/MAPK pathway

To explore the relationship between miR-373 and the occurrence and development of colorectal cancer. Additionally, it aims to predict the potential cellular signaling pathways and regulatory mechanisms in which miR-373 may be involved and provides a theoretical basis and experimental evidence for the clinical application of miR-373 as a potential biomarker, molecular target, and prognostic indicator in colorectal cancer. Real-time quantitative PCR is used to analyze the expression of miR-373 in human colorectal cancer cell lines and normal human colonic epithelial cells. Further validation of the differential expression of miR-373 in colorectal cancer cell lines is being performed. Biological functions such as cell proliferation, invasion and apoptosis are being detected by MTT, CCK-8, transwell, cell cycle analysis, and flow cytometry experiments to verify the changes in the biological behavior of colon cancer cells after overexpression and interference of miR-373 in SW-480 cells and to explore the effects of miR-373 on cell proliferation, invasion, and apoptosis in colon cancer cells. Proteomic analysis is being conducted on proteins extracted from miR-373 overexpressing SW480 cells, and mass spectrometry is used for protein identification. GO, KEGG, and enrichment analysis are being employed to analyze the significantly differentially expressed proteins. The expression levels of pathway-related proteins are being verified using Western blot. Overexpression of miR-373 increased the invasive and metastatic ability of SW-480 cells; knockdown of miR-373 decreased the invasive and metastatic ability of SW-480 cells. However, there was no statistically significant effect on cell proliferation and apoptosis in SW-480 cells. Proteomic analysis identified 78 differentially expressed proteins based on fold change (FC) > 1.2 and P < 0.05. Annotation of differentially changed proteins revealed that the MAPK signaling pathway, PI3K-Akt signaling pathway, and FAK signaling pathway may play crucial roles in the migration and invasion of colorectal cancer. Western blot analysis showed that overexpression of miR-373 significantly increased the levels of p-ERK1/2 in SW480 cells. miR-373 may activate the ERK/MAPK signaling pathway to promote the invasion and migration of colorectal cancer cells.

Focal adhesion kinase: from biological functions to therapeutic strategies

Focal adhesion kinase (FAK), a nonreceptor cytoplasmic tyrosine kinase, is a vital participant in primary cellular functions, such as proliferation, survival, migration, and invasion. In addition, FAK regulates cancer stem cell activities and contributes to the formation of the tumor microenvironment (TME). Importantly, increased FAK expression and activity are strongly associated with unfavorable clinical outcomes and metastatic characteristics in numerous tumors. In vitro and in vivo studies have demonstrated that modulating FAK activity by application of FAK inhibitors alone or in combination treatment regimens could be effective for cancer therapy. Based on these findings, several agents targeting FAK have been exploited in diverse preclinical tumor models. This article briefly describes the structure and function of FAK, as well as research progress on FAK inhibitors in combination therapies. We also discuss the challenges and future directions regarding anti-FAK combination therapies.

Three Members of Transmembrane-4-Superfamily, TM4SF1, TM4SF4, and TM4SF5, as Emerging Anticancer Molecular Targets against Cancer Phenotypes and Chemoresistance

There are six members of the transmembrane 4 superfamily (TM4SF) that have similar topology and sequence homology. Physiologically, they regulate tissue differentiation, signal transduction pathways, cellular activation, proliferation, motility, adhesion, and angiogenesis. Accumulating evidence has demonstrated, among six TM4SF members, the regulatory roles of transmembrane 4 L6 domain family members, particularly TM4SF1, TM4SF4, and TM4SF5, in cancer angiogenesis, progression, and chemoresistance. Hence, targeting derailed TM4SF for cancer therapy has become an emerging research area. As compared to others, this review aimed to present a focused insight and update on the biological roles of TM4SF1, TM4SF4, and TM4SF5 in the progression, metastasis, and chemoresistance of various cancers. Additionally, the mechanistic pathways, diagnostic and prognostic values, and the potential and efficacy of current anti-TM4SF antibody treatment were also deciphered. It also recommended the exploration of other interactive molecules to be implicated in cancer progression and chemoresistance, as well as potential therapeutic agents targeting TM4SF as future perspectives. Generally, these three TM4SF members interact with different integrins and receptors to significantly induce intracellular signaling and regulate the proliferation, migration, and invasion of cancer cells. Intriguingly, gene silencing or anti-TM4SF antibody could reverse their regulatory roles deciphered in different preclinical models. They also have prognostic and diagnostic value as their high expression was detected in clinical tissues and cells of various cancers. Hence, TM4SF1, TM4SF4, and TM4SF5 are promising therapeutic targets for different cancer types preclinically and deserve further investigation.

Liver-originated small extracellular vesicles with TM4SF5 target brown adipose tissue for homeostatic glucose clearance

Transmembrane 4 L six family member 5 (TM4SF5) is involved in chronic liver disease, although its role in glucose homeostasis remains unknown. TM4SF5 deficiency caused age-dependent glucose (in)tolerance with no link to insulin sensitivity. Further, hepatic TM4SF5 binding to GLUT1 promoted glucose uptake and glycolysis. Excessive glucose repletion caused hepatocytes to secrete small extracellular vesicles (sEVs) loaded with TM4SF5 (hep-sEVTm4sf5 ), suggesting a role for sEVTm4sf5 in glucose metabolism and homeostasis. Hep-sEVTm4sf5 were smaller than sEVControl and recruit proteins for efficient organ tropism. Liver-derived sEVs, via a liver-closed vein circuit (LCVC) using hepatic TM4SF5-overexpressing (Alb-Tm4sf5 TG) mice (liv-sEVTm4sf5 ), improved glucose tolerance in Tm4sf5-/- KO mice and targeted brown adipose tissues (BATs), possibly allowing the clearance of blood glucose as heat independent of UCP1. Taken together, hep-sEVTm4sf5 might clear high extracellular glucose levels more efficiently by targeting BAT compared with hep-sEVControl , suggesting an insulin-like role for sEV™4SF5 in affecting age-related metabolic status and thus body weight (BW).

TM4SF5-Mediated Regulation of Hepatocyte Transporters during Metabolic Liver Diseases

Nonalcoholic fatty liver disease (NAFLD) is found in up to 30% of the world’s population and can lead to hepatocellular carcinoma (HCC), which has a poor 5-year relative survival rate of less than 40%. Clinical therapeutic strategies are not very successful. The co-occurrence of metabolic disorders and inflammatory environments during the development of steatohepatitis thus needs to be more specifically diagnosed and treated to prevent fatal HCC development. To improve diagnostic and therapeutic strategies, the identification of molecules and/or pathways responsible for the initiation and progression of chronic liver disease has been explored in many studies, but further study is still required. Transmembrane 4 L six family member 5 (TM4SF5) has been observed to play roles in the regulation of metabolic functions and activities in hepatocytes using in vitro cell and in vivo animal models without or with TM4SF5 expression in addition to clinical liver tissue samples. TM4SF5 is present on the membranes of different organelles or vesicles and cooperates with transporters for fatty acids, amino acids, and monocarbohydrates, thus regulating nutrient uptake into hepatocytes and metabolism and leading to phenotypes of chronic liver diseases. In addition, TM4SF5 can remodel the immune environment by interacting with immune cells during TM4SF5-mediated chronic liver diseases. Because TM4SF5 may act as an NAFLD biomarker, this review summarizes crosstalk between TM4SF5 and nutrient transporters in hepatocytes, which is related to chronic liver diseases.

The PH Domain and C-Terminal polyD Motif of Phafin2 Exhibit a Unique Concurrence in Animals

Phafin2, a member of the Phafin family of proteins, contributes to a plethora of cellular activities including autophagy, endosomal cargo transportation, and macropinocytosis. The PH and FYVE domains of Phafin2 play key roles in membrane binding, whereas the C-terminal poly aspartic acid (polyD) motif specifically autoinhibits the PH domain binding to the membrane phosphatidylinositol 3-phosphate (PtdIns3P). Since the Phafin2 FYVE domain also binds PtdIns3P, the role of the polyD motif remains unclear. In this study, bioinformatics tools and resources were employed to determine the concurrence of the PH-FYVE module with the polyD motif among Phafin2 and PH-, FYVE-, or polyD-containing proteins from bacteria to humans. FYVE was found to be an ancient domain of Phafin2 and is related to proteins that are present in both prokaryotes and eukaryotes. Interestingly, the polyD motif only evolved in Phafin2 and PH- or both PH-FYVE-containing proteins in animals. PolyD motifs are absent in PH domain-free FYVE-containing proteins, which usually display cellular trafficking or autophagic functions. Moreover, the prediction of the Phafin2-interacting network indicates that Phafin2 primarily cross-talks with proteins involved in autophagy, protein trafficking, and neuronal function. Taken together, the concurrence of the polyD motif with the PH domain may be associated with complex cellular functions that evolved specifically in animals.

FAK in Cancer: From Mechanisms to Therapeutic Strategies

Focal adhesion kinase (FAK), a non-receptor tyrosine kinase, is overexpressed and activated in many cancer types. FAK regulates diverse cellular processes, including growth factor signaling, cell cycle progression, cell survival, cell motility, angiogenesis, and the establishment of immunosuppressive tumor microenvironments through kinase-dependent and kinase-independent scaffolding functions in the cytoplasm and nucleus. Mounting evidence has indicated that targeting FAK, either alone or in combination with other agents, may represent a promising therapeutic strategy for various cancers. In this review, we summarize the mechanisms underlying FAK-mediated signaling networks during tumor development. We also summarize the recent progress of FAK-targeted small-molecule compounds for anticancer activity from preclinical and clinical evidence.

TM4SF5-mediated liver malignancy involves NK cell exhaustion-like phenotypes

Aberrant extracellular matrix and immune cell alterations within the tumor microenvironment promote the pathological progression of liver carcinogenesis. Although transmembrane 4 L six family member 5 (TM4SF5) is involved in liver fibrosis and cancer, its mechanism avoiding immune surveillance during carcinogenesis remains unknown. We investigated how TM4SF5-mediated signaling caused immune evasion using in vitro primary cells and in vivo liver tissues from genetic or chemically induced mouse models. TM4SF5-transgenic and diethylnitrosamine (DEN)-induced liver cancer mouse models exhibited fibrotic and cancerous livers, respectively, with enhanced TM4SF5, pY⁷⁰⁵STAT3, collagen I, and laminin γ2 levels. These TM4SF5-mediated effects were abolished by TM4SF5 inhibitor, 4'-(p-toluenesulfonylamido)-4-hydroxychalcone (TSAHC). TM4SF5-dependent tumorigenesis involved natural killer (NK) cell exhaustion-like phenotypes including the reduction of NK cell number or function, which were blocked with TSAHC treatment. TM4SF5 expression in cancer cells downregulated stimulatory ligands and receptors for NK cell cytotoxicity, including SLAMF6, SLAMF7, MICA/B, and others. TM4SF5 suppression or inhibition reduced STAT3 signaling activity and recovered the receptor levels and NK cell surveillance, leading to reduced fibrotic and cancerous phenotypes, and longer survival. Altogether, these findings suggest that TM4SF5-mediated STAT3 activity for extracellular matrix modulation is involved in the progression of liver disease to HCC and that TM4SF5 appears to suppress NK cells during liver carcinogenesis.

N-terminus-independent activation of c-Src via binding to a tetraspan(in) TM4SF5 in hepatocellular carcinoma is abolished by the TM4SF5 C-terminal peptide application

Active c-Src non-receptor tyrosine kinase localizes to the plasma membrane via N-terminal lipid modification. Membranous c-Src causes cancer initiation and progression. Even though transmembrane 4 L six family member 5 (TM4SF5), a tetraspan(in), can be involved in this mechanism, the molecular and structural influence of TM4SF5 on c-Src remains unknown. Methods: Here, we investigated molecular and structural details by which TM4SF5 regulated c-Src devoid of its N-terminus and how cell-penetrating peptides were able to interrupt c-Src activation via interference of c-Src-TM4SF5 interaction in hepatocellular carcinoma models. Results: The TM4SF5 C-terminus efficiently bound the c-Src SH1 kinase domain, efficiently to the inactively-closed form. The complex involved protein tyrosine phosphatase 1B able to dephosphorylate Tyr530. The c-Src SH1 domain alone, even in a closed form, bound TM4SF5 to cause c-Src Tyr419 and FAK Y861 phosphorylation. Homology modeling and molecular dynamics simulation studies predicted the directly interfacing residues, which were further validated by mutational studies. Cell penetration of TM4SF5 C-terminal peptides blocked the interaction of TM4SF5 with c-Src and prevented c-Src-dependent tumor initiation and progression in vivo. Conclusions: Collectively, these data demonstrate that binding of the TM4SF5 C-terminus to the kinase domain of inactive c-Src leads to its activation. Because this binding can be abolished by cell-penetrating peptides containing the TM4SF5 C-terminus, targeting this direct interaction may be an effective strategy for developing therapeutics that block the development and progression of hepatocellular carcinoma.

SLAC2B-dependent microtubule acetylation regulates extracellular matrix-mediated intracellular TM4SF5 traffic to the plasma membranes

Transmembrane 4 L six family member 5 (TM4SF5) translocates intracellularly and promotes cell migration, but how subcellular TM4SF5 traffic is regulated to guide cellular migration is unknown. We investigated the influences of the extracellular environment and intracellular signaling on the TM4SF5 traffic with regard to migration directionality. Cell adhesion to fibronectin (FN) but not poly-l-lysine enhanced the traffic velocity and straightness of the TM4SF5_WT (but not palmitoylation-deficient mutant TM4SF5 Pal - ) toward the leading edges, depending on tubulin acetylation. Acetylated-microtubules in SLAC2B-positive cells reached mostly the juxtanuclear regions, but reached-out toward the leading edges upon SLAC2B suppression. TM4SF5 expression caused SLAC2B not to be localized at the leading edges. TM4SF5 colocalization with HDAC6 depended on paxillin expression. The trimeric complex consisting of TM4SF5, HDAC6, and SLAC2B might, thus, be enriched at the perinuclear cytosols toward the leading edges. More TM4SF5_WT translocation to the leading edges was possible when acetylated-microtubules reached the frontal edges following HDAC6 inhibition by paxillin presumably at new cell-FN adhesions, leading to persistent cell migration. Collectively, this study revealed that cell-FN adhesion and microtubule acetylation could control intracellular traffic of TM4SF5 vesicles to the leading edges via coordinated actions of paxillin, SLAC2B, and HDAC6, leading to TM4SF5-dependent cell migration.

Involvement of the FAK Network in Pathologies Related to Altered Mechanotransduction

Mechanotransduction is a physiological process in which external mechanical stimulations are perceived, interpreted, and translated by cells into biochemical signals. Mechanical stimulations exerted by extracellular matrix stiffness and cell–cell contacts are continuously applied to living cells, thus representing a key pivotal trigger for cell homeostasis, survival, and function, as well as an essential factor for proper organ development and metabolism. Indeed, a deregulation of the mechanotransduction process consequent to gene mutations or altered functions of proteins involved in perceiving cellular and extracellular mechanics can lead to a broad range of diseases, from muscular dystrophies and cardiomyopathies to cancer development and metastatization. Here, we recapitulate the involvement of focal adhesion kinase (FAK) in the cellular conditions deriving from altered mechanotransduction processes.

Role of Transmembrane 4 L Six Family 1 in the Development and Progression of Cancer

Transmembrane 4 L six family 1 (TM4SF1) is a protein with four transmembrane domains that belongs to the transmembrane 4 L six family members (TM4SFs). Structurally, TM4SF1 consists of four transmembrane domains (TM1-4), N- and C-terminal intracellular domains, two extracellular domains, a smaller domain between TM1 and TM2, and a larger domain between TM3 and TM4. Within the cell, TM4SF1 is located at the cell surface where it transmits extracellular signals into the cytoplasm. TM4SF1 interacts with tetraspanins, integrin, receptor tyrosine kinases, and other proteins to form tetraspanin-enriched microdomains. This interaction affects the pro-migratory activity of the cells, and thus it plays important roles in the development and progression of cancer. TM4SF1 has been shown to be overexpressed in many malignant tumors, including gliomas; malignant melanomas; and liver, prostate, breast, pancreatic, bladder, colon, lung, gastric, ovarian, and thyroid cancers. TM4SF1 promotes the migration and invasion of cancer cells by inducing epithelial-mesenchymal transition, self-renewal ability, tumor angiogenesis, invadopodia formation, and regulating the related signaling pathway. TM4SF1 is an independent prognostic indicator and biomarker in several cancers. It also promotes drug resistance, which is a major cause of therapeutic failure. These characteristics make TM4SF1 an attractive target for antibody-based immunotherapy. Here, we review the many functions of TM4SF1 in malignant tumors, with the aim to understand the interaction between its expression and the biological behaviors of cancer and to supply a basis for exploring new therapeutic targets.

A peptide-CpG-DNA-liposome complex vaccine targeting TM4SF5 suppresses growth of pancreatic cancer in a mouse allograft model

Background

Patients with pancreatic cancer have a poor prognosis and are usually diagnosed at a late stage. Because TM4SF5 is known to be overexpressed in hepatocellular carcinoma, colon cancer, and pancreatic cancer, it is considered as one of the candidate molecular targets for an anticancer strategies.

Purpose

The purpose of this study was to evaluate possible utility of TM4SF5 to treat pancreatic cancer using a mouse allograft model.

Materials and methods

We analyzed expression of TM4SF5 in pancreatic cancer tissues using immunohistochemistry. We established a mouse pancreatic cancer cell line stably expressing TM4SF5 and identified the effect of TM4SF5 expression in vitro. We used the CpG-DNA-peptide-liposome complex as a peptide vaccine and investigated antitumor effects of the vaccine in a mouse model with TM4SF5 expressing pancreatic cells. To investigate the function of produced antibody, we evaluated effects of the anti-TM4SF5 monoclonal antibody in vitro in terms of cell growth and migration properties.

Results

Immunohistochemical analysis showed that 36.4% of pancreatic cancer tissue samples expressed TM4SF5. Expression of TM4SF5 induced increased cell proliferation and motility in vitro. Injection of the TM4SF5 peptide vaccine induced the production of anti-hTM4SF5 antibodies and reduced the growth of pancreatic tumors in mice established by subcutaneous injection of the TM4SF5-expressing mouse pancreatic cancer cell line. The treatment of TM4SF5-expressing cells with the anti-hTM4SF5 monoclonal antibody reduced cell growth, modulated the expression of the epithelial–mesenchymal transition markers Vimentin and E-cadherin, and decreased cell motility in vitro.

Conclusion

Our results showed that the TM4SF5 peptide vaccine had a protective effect against pancreatic tumors expressing TM4SF5, and this effect was mediated, at least in part, by the production and suppressive function of the anti-TM4SF5 antibodies. Therefore, we suggest that targeting TM4SF5 could be a novel strategy to prevent or treat pancreatic cancer.

CD133-induced TM4SF5 expression promotes sphere growth via recruitment and blocking of protein tyrosine phosphatase receptor type F (PTPRF)

CD133 is a surface marker of liver cancer stem cells. Transmembrane 4 L six family member 5 (TM4SF5) promotes sphere growth and circulation. However, it is unknown how CD133 and TM4SF5 cross-talk with each other for cancer stem cell properties. Here, we investigated the significance of inter-relationships between CD133, TM4SF5, CD44, and protein tyrosine phosphatase receptor type F (PTPRF) in a three-dimensional (3D) sphere growth system. We found that CD133 upregulated TM4SF5 and CD44, whereas TM4SF5 and CD44 did not affect CD133 expression. Signaling activity following CD133 phosphorylation caused TM4SF5 expression and sphere growth. TM4SF5 bound to CD133 and promoted c-Src activity for CD133 phosphorylation as a positive feedback loop, leading to CD133-mediated sphere growth that was inhibited by TM4SF5 inhibition or suppression. TM4SF5 also bound PTPRF and promoted paxillin phosphorylation. Decreased sphere growth upon CD133 suppression was recovered by TM4SF5 expression and partially by PTPRF suppression. TM4SF5 inhibition enhanced PTPRF levels and abolished PTPRF suppression-mediated sphere growth. Altogether, CD133-induced TM4SF5 expression and function were important for liver cancer sphere growth and may be a promising target to block metastasis.

Targeting Focal Adhesion Kinase Using Inhibitors of Protein-Protein Interactions

Focal adhesion kinase (FAK) is a cytoplasmic non-receptor protein tyrosine kinase that is overexpressed and activated in many human cancers. FAK transmits signals to a wide range of targets through both kinase-dependant and independent mechanism thereby playing essential roles in cell survival, proliferation, migration and invasion. In the past years, small molecules that inhibit FAK kinase function have been developed and show reduced cancer progression and metastasis in several preclinical models. Clinical trials have been conducted and these molecules display limited adverse effect in patients. FAK contain multiple functional domains and thus exhibit both important scaffolding functions. In this review, we describe the major FAK interactions relevant in cancer signalling and discuss how such knowledge provide rational for the development of Protein-Protein Interactions (PPI) inhibitors.

Cellular Mechanotransduction: From Tension to Function

Living cells are constantly exposed to mechanical stimuli arising from the surrounding extracellular matrix (ECM) or from neighboring cells. The intracellular molecular processes through which such physical cues are transformed into a biological response are collectively dubbed as mechanotransduction and are of fundamental importance to help the cell timely adapt to the continuous dynamic modifications of the microenvironment. Local changes in ECM composition and mechanics are driven by a feed forward interplay between the cell and the matrix itself, with the first depositing ECM proteins that in turn will impact on the surrounding cells. As such, these changes occur regularly during tissue development and are a hallmark of the pathologies of aging. Only lately, though, the importance of mechanical cues in controlling cell function (e.g., proliferation, differentiation, migration) has been acknowledged. Here we provide a critical review of the recent insights into the molecular basis of cellular mechanotransduction, by analyzing how mechanical stimuli get transformed into a given biological response through the activation of a peculiar genetic program. Specifically, by recapitulating the processes involved in the interpretation of ECM remodeling by Focal Adhesions at cell-matrix interphase, we revise the role of cytoskeleton tension as the second messenger of the mechanotransduction process and the action of mechano-responsive shuttling proteins converging on stage and cell-specific transcription factors. Finally, we give few paradigmatic examples highlighting the emerging role of malfunctions in cell mechanosensing apparatus in the onset and progression of pathologies.

Production of an anti-TM4SF5 monoclonal antibody and its application in the detection of TM4SF5 as a possible marker of a poor prognosis in colorectal cancer

The cell surface transmembrane 4 superfamily member 5 protein (TM4SF5) has been implicated in various human cancers. Immunization with a peptide vaccine targeting human TM4SF5 has been shown to exert prophylactic and therapeutic effects against the development of hepatocellular carcinoma and colon cancer in mouse models. In this study, we developed a novel monoclonal antibody (mEC2‑CF) targeting a cyclic epitope of TM4SF5 and evaluated its reactivity to TM4SF5 in colorectal cancer (CRC) cells and cancer tissues. The isotype of mEC2‑CF was IgG2a and the antibody specifically recognized the cyclic peptide, based on ELISA. The antibody recognized recombinant TM4SF5 overexpressed in 293F cells, irrespective of N‑glycosidase F treatment. The antibody was internalized into the cytosol after binding to the surface of TM4SF5‑expressing CRC cells, suggesting that this antibody may be useful in therapeutics. In addition, we evaluated TM4SF5 expression in the tissues of patients with CRC patients to determine its prognostic significance. TM4SF5 expression was assessed by immunohistochemistry using mEC2‑CF and tissue microarray blocks of 204 primary CRC samples. The overall rate of TM4SF5 overexpression in the samples (immunohistochemical score >4) was 27.0% (55 of 204). The increased expression of TM4SF5 was significantly associated with a shorter survival rate (P=0.0014) and a worse disease‑free survival (P=0.0483) of patients with CRC. No association was observed between TM4SF5 expression and clinicopathological characteristics, apart from tumor depth of invasion (P=0.027). These results suggest that our novel antibody can be used to detect endogenous and recombinant TM4SF5, and that TM4SF5 may be a possible marker for the poor prognosis of patients with CRC.

Osteopontin production by TM4SF4 signaling drives a positive feedback autocrine loop with the STAT3 pathway to maintain cancer stem cell-like properties in lung cancer cells

Transmembrane 4 L6 family proteins have been known to promote cancer. In this study, we demonstrated that transmembrane 4 L6 family member 4 (TM4SF4), which is induced by γ-radiation in non-small cell lung cancer (NSCLC) cells, is involved in epithelial-to-mesenchymal transition (EMT) and cancer stem cell (CSC) properties of NSCLC through the regulation of osteopontin (OPN). Forced TM4SF4 overexpression in A549 cells increased the secretion of OPN, which activates CD44 or integrin signaling and thus maintains EMT-associated CSC-like properties. OPN, known as a downstream target of β-catenin/T-cell factor 4 (TCF-4), was induced by up-regulated β-catenin via TM4SF4-driven phosphorylation of glycogen synthase kinase 3b (GSK3β). TCF4 complexed to promoter regions of OPN in TM4SF4-overexpressing A549 cells was also confirmed by chromatin immunoprecipitation. Knockout of either β-catenin or TCF4-suppressed OPN expression, demonstrating that both factors are essential for OPN expression in NSCLC cells. OPN secreted by TM4SF4/GSK3β/β-catenin signaling activated the JAK2/STAT3 or FAK/STAT3 pathway, which also up-regulates OPN expression in an autocrine manner and consequently maintains the self-renewal and metastatic capacity of cancer cells. Neutralizing antibody to OPN blocked the autocrine activation of OPN expression, consequently weakened the metastatic and self-renewal capacity of cancer cells. Collectively, our findings indicate that TM4SF4-triggered OPN expression is involved in the persistent reinforcement of EMT or cancer stemness by creating a positive feedback autocrine loop with JAK2/STAT3 or FAK/STAT3 pathways.

Differential regulation of cellular functions by the C-termini of transmembrane 4 L six family proteins in 2- or 3-dimensional environment

The transmembrane 4 L six family proteins TM4SF1, TM4SF4, and TM4SF5 share 40-50% overall sequence identity, but their C-terminus identity is limited. It may be likely that the C-termini of the members are important and unique for own regulatory functions. We thus examined how the TM4SF5 C-terminus affected cellular functions differentially from other family members. Using colon cancer cells expressing wildtype (WT), C-terminus-deleted, or chimeric mutants, diverse cellular functions were explored in 2-dimensional (2D) and 3-dimensional (3D) condition. The C-termini of the proteins were relatively comparable with respect to 2D cell proliferation, although each C-terminal-deletion mutant exhibited increased proliferation relative to the WT. Using chimeric constructs, we found that the TM4SF5 C-terminus was critical for regulating the diverse metastatic functions of TM4SF5, and could positively replace the C-termini of other family members. Replacement of the TM4SF1 or TM4SF4 C-terminus with that of TM4SF5 increased spheroids growth, transwell migration, and invasive dissemination from spheroids in 3D collagen gels. TM4SF5-mediated effects required its extracellular loop 2 linked to the C-terminus via the transmembrane domain 4, with causing c-Src activation. Altogether, the C-terminus of TM4SF5 appears to mediate pro-migratory roles, depending on a structural relay from the second extracellular loop to the C-terminus.

TM4SF5 promotes metastatic behavior of cells in 3D extracellular matrix gels by reducing dependency on environmental cues

Transmembrane 4 L six family member 5 (TM4SF5) is highly expressed in hepatocellular carcinoma tissues and enhances migration in two-dimensional environments. Here, we investigated how TM4SF5 is involved in diverse pro-metastatic phenotypes in in vivo-like three-dimensional (3D) extracellular matrix gels. TM4SF5-positive cells aggressively formed invasive foci in 3D Matrigel, depending on TM4SF5-mediated signaling activity, cytoskeletal organization, and matrix metallopeptidase (MMP) 2-mediated extracellular remodeling, whereas TM4SF5-null cells did not. The TM4SF5-null cells did, however, form invasive foci in 3D Matrigel following inhibition of Rho-associated protein kinase or addition of collagen I, suggesting that collagen I compensated for TM4SF5 expression. Similarly, TM4SF5-positive cells expressing vascular endothelial-cadherin formed network-like vasculogenic mimicry in 3D Matrigel and collagen I mixture gels, whereas TM4SF5-negative cells in the mixture gels displayed the network structures only upon further treatment with epidermal growth factor. The foci formation also required MMP2-mediated remodeling of the extracellular matrix. Co-cultures exhibited TM4SF5-positive or cancer-associated fibroblasts at the outward edges of TM4SF5-null cell clusters. Compared with TM4SF5-null cells, TM4SF5-positive cells in 3D collagen gels showed a more invasive outgrowth with dramatic invadopodia. These observations suggest that TM4SF5 plays roles in the promotion of diverse metastatic properties with fewer environmental requirements than TM4SF5-negative cells.

TM4SF5-Mediated Roles in the Development of Fibrotic Phenotypes

Transmembrane 4 L six family member 5 (TM4SF5) can form tetraspanin-enriched microdomains (TERMs) on the cell's surface. TERMs contain protein-protein complexes comprised of tetraspanins, growth factor receptors, and integrins. These complexes regulate communication between extracellular and intracellular spaces to control diverse cellular functions. TM4SF5 influences the epithelial-mesenchymal transition (EMT), aberrant multilayer cellular growth, drug resistance, enhanced migration and invasion, circulation through the bloodstream, tumor-initiation property, metastasis, and muscle development in zebrafish. Here, current data on TM4SF5's roles in the development of fibrotic phenotypes are reviewed. TM4SF5 is induced by transforming growth factor β1 (TGFβ1) signaling via a collaboration with epidermal growth factor receptor (EGFR) activation. TM4SF5, by itself or in concert with other receptors, transduces signals intracellularly. In hepatocytes, TM4SF5 expression regulates cell cycle progression, migration, and expression of extracellular matrix components. In CCl₄-treated mice, TM4SF5, α-smooth muscle actin (α-SMA), and collagen I expression are observed together along the fibrotic septa regions of the liver. These fibrotic phenotypes are diminished by anti-TM4SF5 reagents, such as a specific small compound [TSAHC, 4'-(p-toluenesulfonylamido)-4-hydroxychalcone] or a chimeric antibody. This review discusses the antifibrotic strategies that target TM4SF5 and its associated protein networks that regulate the intracellular signaling necessary for fibrotic functions of hepatocytes.

Tetraspanins Function as Regulators of Cellular Signaling

Tetraspanins are molecular scaffolds that distribute proteins into highly organized microdomains consisting of adhesion, signaling, and adaptor proteins. Many reports have identified interactions between tetraspanins and signaling molecules, finding unique downstream cellular consequences. In this review, we will explore these interactions as well as the specific cellular responses to signal activation, focusing on tetraspanin regulation of adhesion-mediated (integrins/FAK), receptor-mediated (EGFR, TNF-α, c-Met, c-Kit), and intracellular signaling (PKC, PI4K, β-catenin). Additionally, we will summarize our current understanding for how tetraspanin post-translational modifications (palmitoylation, N-linked glycosylation, and ubiquitination) can regulate signal propagation. Many of the studies outlined in this review suggest that tetraspanins offer a potential therapeutic target to modulate aberrant signal transduction pathways that directly impact a host of cellular behaviors and disease states.

Focal adhesion kinase signaling in unexpected places

Focal adhesion kinase (FAK) is a cytoplasmic protein-tyrosine kinase first identified at extracellular matrix and integrin receptor cell adhesion sites and is a key regulator of cell movement. FAK is activated by a variety of stimuli. Herein, we discuss advances in conformational-associated FAK activation and dimerization mechanisms. Additionally, new roles have emerged for FAK signaling at cell adhesions, adherens junctions, endosomes, and the nucleus. In light of these new findings, we review how FAK activation at these sites is connected to the regulation of integrin recycling-activation, vascular permeability, cell survival, and transcriptional regulation, respectively. Studies uncovering FAK signaling connections in unexpected places within cells have yielded important new regulatory insights in cell biology.

Dynamic and coordinated single-molecular interactions at TM4SF5-enriched microdomains guide invasive behaviors in 2- and 3-dimensional environments

Membrane proteins sense extracellular cues and transduce intracellular signaling to coordinate directionality and speed during cellular migration. They are often localized to specific regions, as with lipid rafts or tetraspanin-enriched microdomains; however, the dynamic interactions of tetraspanins with diverse receptors within tetraspanin-enriched microdomains on cellular surfaces remain largely unexplored. Here, we investigated effects of tetraspan(in) TM4SF5 (transmembrane 4 L6 family member 5)-enriched microdomains (T₅ERMs) on the directionality of cell migration. Physical association of TM4SF5 with epidermal growth factor receptor (EGFR) and integrin α5 was visualized by live fluorescence cross-correlation spectroscopy and higher-resolution microscopy at the leading edge of migratory cells, presumably forming TM4SF5-enriched microdomains. Whereas TM4SF5 and EGFR colocalized at the migrating leading region more than at the rear, TM4SF5 and integrin α5 colocalized evenly throughout cells. Cholesterol depletion and disruption in TM4SF5 post-translational modifications, including N-glycosylation and palmitoylation, altered TM4SF5 interactions and cellular localization, which led to less cellular migration speed and directionality in 2- or 3-dimensional conditions. TM4SF5 controlled directional cell migration and invasion, and importantly, these TM4SF5 functions were dependent on cholesterol, TM4SF5 post-translational modifications, and EGFR and integrin α5 activity. Altogether, we showed that TM4SF5 dynamically interacted with EGFR and integrin α5 in migratory cells to control directionality and invasion.-Kim, H.-J., Kwon, S., Nam, S. H., Jung, J. W., Kang, M., Ryu, J., Kim, J. E., Cheong, J.-G., Cho, C. Y., Kim, S., Song, D.-G., Kim, Y.-N., Kim, T. Y., Jung, M.-K., Lee, K.-M., Pack, C.-G., Lee, J. W. Dynamic and coordinated single-molecular interactions at TM4SF5-enriched microdomains guide invasive behaviors in 2- and 3-dimensional environments.

Anti-metastatic effect of the TM4SF5-specific peptide vaccine and humanized monoclonal antibody on colon cancer in a mouse lung metastasis model

Transmembrane 4 superfamily member 5 protein (TM4SF5) is a potential therapeutic target for hepatocellular carcinoma (HCC) and colon cancer. In a previous study, we demonstrated the prophylactic and therapeutic effects of a TM4SF5-specific peptide vaccine and monoclonal antibody in HCC and colon cancer in a mouse model. Here, we designed a cyclic peptide targeting TM4SF5. Cyclic peptide-specific antibodies were produced in mice after immunization with a complex of the peptide, CpG-DNA, and liposomes. Intravenous injection of the CT-26 mouse colon cancer cell line into mice induced tumors in the lung. Immunization with the peptide vaccine improved the survival rate and reduced the growth of lung tumors. We established a monoclonal antibody specific to the cyclic TM4SF5-based peptide and humanized the antibody sequence by complementarity determining region-grafting. The humanized antibody was reactive to the cyclic peptide and TM4SF5 protein. Treatment of CT-26 cells with the humanized antibody reduced cell motility in vitro. Furthermore, direct injection of the humanized anti-TM4SF5 antibody in vivo reduced growth of lung tumors in mouse metastasis model. Therefore, we conclude that the immunization with the cyclic peptide vaccine and injection of the TM4SF5-specifc humanized antibody have an anti-metastatic effect against colon cancer in mice. Importantly, the humanized antibody may serve as a starting platf.

β-Arrestin1 and Signal-transducing Adaptor Molecule 1 (STAM1) Cooperate to Promote Focal Adhesion Kinase Autophosphorylation and Chemotaxis via the Chemokine Receptor CXCR4

The chemokine receptor CXCR4 and its chemokine ligand CXCL12 mediate directed cell migration during organogenesis, immune responses, and metastatic disease. However, the mechanisms governing CXCL12/CXCR4-dependent chemotaxis remain poorly understood. Here, we show that the β-arrestin1·signal-transducing adaptor molecule 1 (STAM1) complex, initially identified to govern lysosomal trafficking of CXCR4, also mediates CXCR4-dependent chemotaxis. Expression of minigene fragments from β-arrestin1 or STAM1, known to disrupt the β-arrestin1·STAM1 complex, and RNAi against β-arrestin1 or STAM1, attenuates CXCL12-induced chemotaxis. The β-arrestin1·STAM1 complex is necessary for promoting autophosphorylation of focal adhesion kinase (FAK). FAK is necessary for CXCL12-induced chemotaxis and associates with and localizes with β-arrestin1 and STAM1 in a CXCL12-dependent manner. Our data reveal previously unknown roles in CXCR4-dependent chemotaxis for β-arrestin1 and STAM1, which we propose act in concert to regulate FAK signaling. The β-arrestin1·STAM1 complex is a promising target for blocking CXCR4-promoted FAK autophosphorylation and chemotaxis.

Noncanonical roles of membranous lysyl-tRNA synthetase in transducing cell-substrate signaling for invasive dissemination of colon cancer spheroids in 3D collagen I gels

The adhesion properties of cells are involved in tumor metastasis. Although KRS at the plasma membrane is shown important for cancer metastasis, additionally to canonical roles of cytosolic KRS in protein translation, how KRS and its downstream effectors promote the metastatic migration remains unexplored. Disseminative behaviors (an earlier metastatic process) of colon cancer cell spheroids embedded in 3D collagen gels were studied with regards to cell adhesion properties, and relevance in KRS^−/+ knocked-down animal and clinical colon cancer tissues. Time-lapse imaging revealed KRS-dependent cell dissemination from the spheroids, whereas KRS-suppressed spheroids remained static due to the absence of outbound movements supported by cell-extracellular matrix (ECM) adhesion. While keeping E-cadherin at the outward disseminative cells, KRS caused integrin-involved intracellular signaling for ERK/c-Jun, paxillin, and cell-ECM adhesion-mediated signaling to modulate traction force for crawling movement. KRS-suppressed spheroids became disseminative following ERK or paxillin re-expression. The KRS-dependent intracellular signaling activities correlated with the invasiveness in clinical colon tumor tissues and in KRS^−/+ knocked-down mice tissues. Collectively, these observations indicate that KRS at the plasma membrane plays new roles in metastatic migration as a signaling inducer, and causes intracellular signaling for cancer dissemination, involving cell-cell and cell-ECM adhesion, during KRS-mediated metastasis.

Suppression of lysyl-tRNA synthetase, KRS, causes incomplete epithelial-mesenchymal transition and ineffective cell‑extracellular matrix adhesion for migration

The cell-adhesion properties of cancer cells can be targeted to block cancer metastasis. Although cytosolic lysyl-tRNA synthetase (KRS) functions in protein synthesis, KRS on the plasma membrane is involved in cancer metastasis. We hypothesized that KRS is involved in cell adhesion-related signal transduction for cellular migration. To test this hypothesis, colon cancer cells with modulated KRS protein levels were analyzed for cell-cell contact and cell-substrate adhesion properties and cellular behavior. Although KRS suppression decreased expression of cell-cell adhesion molecules, cells still formed colonies without being scattered, supporting an incomplete epithelial mesenchymal transition. Noteworthy, KRS-suppressed cells still exhibited focal adhesions on laminin, with Tyr397-phopshorylated focal adhesion kinase (FAK), but they lacked laminin-adhesion-mediated extracellular signal-regulated kinase (ERK) and paxillin activation. KRS, p67LR and integrin α6β1 were found to interact, presumably to activate ERK for paxillin expression and Tyr118 phosphorylation even without involvement of FAK, so that specific inhibition of ERK or KRS in parental HCT116 cells blocked cell-cell adhesion and cell-substrate properties for focal adhesion formation and signaling activity. Together, these results indicate that KRS can promote cell-cell and cell-ECM adhesion for migration.

Transmembrane 4 L Six Family Member 5 (TM4SF5)-Mediated Epithelial-Mesenchymal Transition in Liver Diseases

The membrane protein TM4SF5, a member of the transmembrane 4L six family, forms a tetraspanin-enriched microdomain (TEM) on the cell surface, where many different membrane proteins and receptors form a massive protein-protein complex to regulate cellular functions including transdifferentiation, migration, and invasion. We recently reported that TM4SF5 causes epithelial-mesenchymal transition (EMT), eventually contributing to aberrant multilayer cellular growth, drug resistance, enhanced migration, invasion, its circulation in the blood, tumor initiation for successful metastasis, and muscle development in zebrafish. In this review, I summarize the information on the role of TM4SF5 in EMT-related functions at TM4SF5-enriched microdomain (T5EM) on cell surface, where proteins such as TM4SF5, CD151, CD44, integrins, and epidermal growth factor receptor (EGFR) can form numerous protein complexes. TM4SF5-mediated EMT contributes to diverse cellular functions, leading to fibrotic phenotypes and initiating and maintaining tumors in primary and/or metastatic regions, in addition to its role in muscle development in zebrafish. Anti-TM4SF5 strategies for addressing the protein networks can lead to regulation of the fibrotic, tumorigenic, and tumor-maintaining functions of TM4SF5-positive hepatic cells. This review is for us to (re)consider the antifibrotic or antitumorigenic (i.e., anti-EMT-related diseases) strategies of dealing with protein networks that would be involved in cross-talks to regulate various cellular functions during TM4SF5-dependent progression from fibrotic to cancerous hepatic cells.

Interaction of tetraspan(in) TM4SF5 with CD44 promotes self-renewal and circulating capacities of hepatocarcinoma cells

Tumor metastasis involves circulating and tumor-initiating capacities of metastatic cancer cells. Epithelial-mesenchymal transition (EMT) is related to self-renewal capacity and circulating tumor cell (CTC) characteristics for tumor metastasis. Although tumor metastasis is a life-threatening, complicated process that occurs through circulation of tumor cells, mechanistic aspects of self-renewal and circulating capacities have been largely unknown. Hepatic transmembrane 4 L six family member 5 (TM4SF5) promotes EMT for malignant growth and migration, so it was rationalized that TM4SF5, as a hepatocellular carcinoma (HCC) biomarker, might be important for metastatic potential. Here, self-renewal capacity by TM4SF5 was mechanistically explored using hepatocarcinoma cells with or without TM4SF5 expression, and we explored whether they became CTCs using mouse liver-orthotopic model systems. We found that TM4SF5-dependent sphere growth correlated with CD24(-) , aldehyde dehydrogenase (ALDH) activity, as well as a physical association between CD44 and TM4SF5. Interaction between TM4SF5 and CD44 was through their extracellular domains with N-glycosylation modifications. TM4SF5/CD44 interaction activated proto-oncogene tyrosine-protein kinase Src (c-Src)/signal transducer and activator of transcription 3 (STAT3)/Twist-related protein 1 (Twist1)/B-cell-specific Moloney murine leukemia virus integration site 1 (Bmi1) signaling for spheroid formation, whereas disturbing the interaction, expression, or activity of any component in this signaling pathway inhibited spheroid formation. In serial xenografts using 200∼5,000 cells per injection, TM4SF5-positive tumors exhibited subpopulations with locally increased CD44 expressions, supporting for tumor cell differentiation. TM4SF5-positive, but not TM4SF5- or CD44-knocked-down, cells were identified circulating in blood 4-6 weeks after orthotopic liver injection using in vivo laser scanning endomicroscopy. Anti-TM4SF5 reagent blocked their metastasis to distal intestinal organs.

CONCLUSION

TM4SF5 promotes self-renewal and CTC properties supported by TM4SF5(+) /CD44(+(TM4SF5-bound)) /ALDH(+) /CD24(-) markers during HCC metastasis.

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.

Hanging on for the ride: adhesion to the extracellular matrix mediates cellular responses in skeletal muscle morphogenesis and disease

Skeletal muscle specification and morphogenesis during early development are critical for normal physiology. In addition to mediating locomotion, skeletal muscle is a secretory organ that contributes to metabolic homeostasis. Muscle is a highly adaptable tissue, as evidenced by the ability to increase muscle cell size and/or number in response to weight bearing exercise. Conversely, muscle wasting can occur during aging (sarcopenia), cancer (cancer cachexia), extended hospital stays (disuse atrophy), and in many genetic diseases collectively known as the muscular dystrophies and myopathies. It is therefore of great interest to understand the cellular and molecular mechanisms that mediate skeletal muscle development and adaptation. Muscle morphogenesis transforms short muscle precursor cells into long, multinucleate myotubes that anchor to tendons via the myotendinous junction. This process requires carefully orchestrated interactions between cells and their extracellular matrix microenvironment. These interactions are dynamic, allowing muscle cells to sense biophysical, structural, organizational, and/or signaling changes within their microenvironment and respond appropriately. In many musculoskeletal diseases, these cell adhesion interactions are disrupted to such a degree that normal cellular adaptive responses are not sufficient to compensate for accumulating damage. Thus, one major focus of current research is to identify the cell adhesion mechanisms that drive muscle morphogenesis, with the hope that understanding how muscle cell adhesion promotes the intrinsic adaptability of muscle tissue during development may provide insight into potential therapeutic approaches for muscle diseases. Our objectives in this review are to highlight recent studies suggesting conserved roles for cell-extracellular matrix adhesion in vertebrate muscle morphogenesis and cellular adaptive responses in animal models of muscle diseases.

Regulation of FAK Activity by Tetraspan Proteins: Potential Clinical Implications in Cancer

Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase that regulates multiple cell signaling pathways in both physiological and pathological conditions. Overexpression and activation of FAK is associated with many advanced stage cancers through promoting cancer cell tumorigenicity and progression as well as by regulating the tumor microenvironment. FAK has multiple binding partners through which FAK exerts its functions including RhoGEF, Src family, talin, cortactin, and paxilin. Over the last few years, it has been proposed that a novel group of four transmembrane proteins can interact with FAK and regulate its activity. These include select tetraspanins such as CD151 and CD9 as well as the GAS3 family members epithelial membrane protein-2 (EMP2) and peripheral myelin protein-22 (PMP22). In this review, we discuss the current knowledge of the interaction between FAK and tetraspan proteins in physiological and pathological conditions, with an emphasis on the potential of tetraspan family members as therapeutic targets in cancer.

FAK in cancer: mechanistic findings and clinical applications

Focal adhesion kinase (FAK) is a cytoplasmic protein tyrosine kinase that is overexpressed and activated in several advanced-stage solid cancers. FAK promotes tumour progression and metastasis through effects on cancer cells, as well as stromal cells of the tumour microenvironment. The kinase-dependent and kinase-independent functions of FAK control cell movement, invasion, survival, gene expression and cancer stem cell self-renewal. Small molecule FAK inhibitors decrease tumour growth and metastasis in several preclinical models and have initial clinical activity in patients with limited adverse events. In this Review, we discuss FAK signalling effects on both tumour and stromal cell biology that provide rationale and support for future therapeutic opportunities.

TM4SF5 suppression disturbs integrin α5-related signalling and muscle development in zebrafish

TM4SF5 suppression in zebrafish causes abnormal trunk morphology with aberrant translocation and organization of muscle cells, via altered fibronectin/integrin α5/FAK/vinculin/actin signalling. TM4SF5 controls muscle differentiation via alteration in integrin α5-related signalling.

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.

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.

Membrane Proteins Involved in Epithelial-Mesenchymal Transition and Tumor Invasion: Studies on TMPRSS4 and TM4SF5

The epithelial-mesenchymal transition (EMT) is one mechanism by which cells with mesenchymal features can be generated and is a fundamental event in morphogenesis. Recently, invasion and metastasis of cancer cells from the primary tumor are now thought to be initiated by the developmental process termed the EMT, whereby epithelial cells lose cell polarity and cell-cell interactions, and gain mesenchymal phenotypes with increased migratory and invasive properties. The EMT is believed to be an important step in metastasis and is implicated in cancer progression, although the influence of the EMT in clinical specimens has been debated. This review presents the recent results of two cell surface proteins, the functions and underlying mechanisms of which have recently begun to be demonstrated, as novel regulators of the molecular networks that induce the EMT and cancer progression.

The clinical significance of Psoriasin for non-small cell lung cancer patients and its biological impact on lung cancer cell functions

BACKGROUND

Psoriasin (S100A7) is a member of the S100 gene family. Alteration of Psoriasin expression has previously been reported to play an important role in cancer aggressive behaviour. The current study sought to investigate the level of Psoriasin expression at the mRNA level in a cohort of patients with non-small cell lung cancer (NSCLC), the association with clinical implication and outcomes, and the molecular and cellular impact of the protein on lung cancer cells.

METHODS

Fresh frozen NSCLC cell carcinoma tissues, along with matched normal tissues were obtained from 83 NSCLC patients who received curative resection from January 2003 to December 2011. The expression of Psoriasin in the NSCLC specimens was assessed using both quantitative real time PCR (QPCR) and immunochemical staining. Knockdown and forced expression of Psoriasin in NSCLC cell lines were carried out using constructed plasmid vectors carrying either ribozyme transgenes targeting human Psoriasin or full-length coding sequence, respectively. The effect of Psoriasin on the functions of NSCLC cells was determined using a variety of in vitro cell function assays.

RESULTS

Higher mRNA levels of Psoriasin were observed in tumour tissues when compared to both the paired normal background tissues and none paired normal tissues (p = 0.0251 and 0.0195). The mRNA level of Psoriasin was found to be higher in the squamous carcinoma (P=0.035). Higher Psoriasin expression is associated with poor prognosis. The cell function tests had supportive results to the clinical findings. Over-expression of Posriasin in lung cancer cells (SK-MES-1) resulted in an increase in in vitro growth and invasiveness. In contrast, Psoriasin knockdown suppressed cell growth and invasion (P<0.05), but increased cell adhesion (P<0.05).

CONCLUSIONS

Psoriasin expression is increased in lung cancer, more specifically in lung squamous carcinoma compared with adenocarcinoma, and is associated with poor prognosis. Psoriasin plays crucial roles in regulating the growth and invasion of lung cancer cells.