Regulation of TM4SF5-mediated tumorigenesis through induction of cell detachment and death by tiarellic acid

Immune-related gene TM4SF18 could promote the metastasis of gastric cancer cells and predict the prognosis of gastric cancer patients

Gastric cancer (GC) is one of the most common malignancies in the world, and the search for better markers has become one of the challenges today. It has been found that the L6 superfamily regulates the biological functions of numerous tumors, but transmembrane 4 L six family member 18 (TM4SF18) has been rarely reported. We found that TM4SF18 expression is upregulated in GC tissues and cells, which can be effectively diagnosed and dynamically monitored to assess the prognosis of GC patients. Furthermore, knockdown of TM4SF18 effectively inhibited proliferation, migration, and invasion of GC cells, and affected the epithelial-mesenchymal transition process. TM4SF18 was found to be an independent prognostic factor for GC by univariate and multifactorial Cox analyses as well as by establishing nomogram plots. In addition, in TM4SF18 and immune correlation analysis, TM4SF18 expression levels were found to be negatively correlated with most immune cell marker genes and associated with numerous immune cells and immune pathways, resulting in less benefit from treatment with immune checkpoint inhibitors. In summary, we found that TM4SF18 is a promising GC biomarker that promotes the proliferation, migration, and invasion abilities of GC cells, and is associated with immune response.

Tetraspanin TM4SF5 in hepatocytes negatively modulates SLC27A transporters during acute fatty acid supply

Transmembrane 4 L six family member 5 (TM4SF5) is involved in nonalcoholic steatosis and further aggravation of liver disease. However, its mechanism for regulating FA accumulation is unknown. We investigated how TM4SF5 in hepatocytes affected FA accumulation during acute FA supply. TM4SF5-expressing hepatocytes and mouse livers accumulated less FAs, compared with those of TM4SF5 deficiency or inactivation. Binding of TM4SF5 to SLC27A2 increased gradually upon acute FA treatment, whereas TM4SF5 constitutively bound SLC27A5. Suppression of either SLC27A2 or SLC27A5 in hepatocytes expressing TM4SF5 differentially modulated initial and maximal FA uptake levels for a fast turnover of fatty acid. Altogether, TM4SF5 negatively modulates FA accumulation into hepatocytes via association with the transporters for an energy homeostasis, when FA are supplied acutely.

TM4SF18 is aberrantly expressed in pancreatic cancer and regulates cell growth

Current therapies for pancreatic ductal adenocarcinoma (PDAC) only modestly impact survival and can be highly toxic. A greater understanding of the molecules regulating this disease is critical for identifying new drug targets and developing more effective therapies. The L6 family of proteins are known to be positive regulators of tumor growth and metastasis among various cancers. However, little is known about the L6 family member TM4SF18. We investigated the expression and localization of the TM4SF18 protein in normal human pancreas and in PDAC tissue. Utilizing immunohistochemistry (IHC) and western blot analysis, our studies for the first time demonstrate that TM4SF18 is highly expressed in PDAC tumor epithelium. Furthermore, we identified TM4SF18 to be expressed in normal acinar tissue and weakly expressed in normal ducts. Although there is minimal expression in normal ducts, we observed increased TM4SF18 levels in preneoplastic ducts and tumor epithelium. To investigate a functional role of TM4SF18 in PDAC we developed stably-expressing inducible shRNA pancreatic cancer cell lines. Knockdown of the TM4SF18 protein led to a significant decrease in Capan-1 cell growth as measured by the MTT assay, demonstrating this molecule to be a novel regulator of PDAC. Uniquely there is no ortholog of the TM4SF18 gene in mouse or rat prompting us to seek other in vivo experimental models. Using IHC and western blot analysis, expression of TM4SF18 was confirmed in the porcine PDAC model, thus we establish an alternative model to investigate this gene. TM4SF18 represents a promising novel biomarker and therapeutic target for pancreatic cancer.

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.

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

Transmembrane 4 L six family member 5 (TM4SF5) plays an important role in cell migration, and focal adhesion kinase (FAK) activity is essential for homeostatic and pathological migration of adherent cells. However, it is unclear how TM4SF5 signaling mediates the activation of cellular migration machinery, and how FAK is activated during cell adhesion. Here, we showed that direct and adhesion-dependent binding of TM4SF5 to FAK causes a structural alteration that may release the inhibitory intramolecular interaction in FAK. In turn, this may activate FAK at the cell's leading edge, to promote migration/invasion and in vivo metastasis. TM4SF5-mediated FAK activation occurred during integrin-mediated cell adhesion. TM4SF5 was localized at the leading edge of the cells, together with FAK and actin-organizing molecules, indicating a signaling link between TM4SF5/FAK and actin reorganization machinery. Impaired interactions between TM4SF5 and FAK resulted in an attenuated FAK phosphorylation (the signaling link to actin organization machinery) and the metastatic potential. Our findings demonstrate that TM4SF5 directly binds to and activates FAK in an adhesion-dependent manner, to regulate cell migration and invasion, suggesting that TM4SF5 is a promising target in the treatment of metastatic cancer.

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.

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.

Cytotoxic triterpenoids from the rhizomes of Astilbe chinensis

Six new triterpenoids (1-6) with a carboxylic acid functionality at C-27 were isolated from the rhizomes of a Korean native perennial herb, Astilbe chinensis, along with nine known triterpenoids. The structures of 1-6 were elucidated on the basis of spectroscopic data interpretation. All compounds isolated were evaluated for cytotoxic effects against a small panel of human cancer lines.

Cooperation between integrin alpha5 and tetraspan TM4SF5 regulates VEGF-mediated angiogenic activity

Tetraspan TM4SF5 is highly expressed in a diverse number of tumor types. Here we explore the mechanistic roles of TM4SF5 in angiogenesis. We found that TM4SF5 overexpression correlates with vascular endothelial growth factor (VEGF) expression in SNU449 hepatocytes and with vessel formation in clinical hepatocarcinoma samples. Conditioned media from TM4SF5-expressing cells enhanced viability and tube formation of primary human umbilical vein endothelial cells, and outgrowth of endothelial cells from aorta ring segments, which was abolished by treatment with an anti-VEGF antibody. TM4SF5 retained integrin alpha(5) on the cell surface for VEGF induction, and preincubation with anti-integrin alpha(5) antibody abolished TM4SF5-mediated VEGF expression and secretion. TM4SF5-mediated effects required integrin alpha(5), c-Src, and signal transducer and activator of transcription 3 (STAT3). In addition, tumors from nude mice injected with TM4SF5-expressing cells and from clinical human hepatocarcinoma tissues showed enhanced integrin alpha(5) expression, vessel formation, and signaling activity, which were inhibited by administration of anti-integrin alpha(5) or -VEGF antibody. This study suggests that TM4SF5 facilitates angiogenesis of neighboring endothelial cells through VEGF induction, mediated by cooperation between TM4SF5 and integrin alpha(5) of epithelial cells.