Knockdown of Latent Transforming Growth Factor-β (TGF-β)-Binding Protein 2 (LTBP2) Inhibits Invasion and Tumorigenesis in Thyroid Carcinoma Cells

HIF-1α/LTBP2 axis activate HSCs to promote liver fibrosis by interacting with LOXL1 via the ERK pathway

Latent Transforming Growth Factor Beta Binding Protein 2 (LTBP2) is a multi-domain exocrine protein located in the extracellular matrix (ECM) and has been implicated in fibrosis across various organs. However, its role in liver fibrosis remains inadequately understood. This study aims to elucidate the function and mechanism of LTBP2 in hepatic stellate cells (HSCs) activation and liver fibrosis. Our findings indicate that LTBP2 expression is positively correlated with liver fibrosis and is significantly elevated in fibrotic liver tissues from both human and murine models. Importantly, AAV6-mediated knockdown of LTBP2 in HSCs markedly alleviates CCl4-induced liver fibrosis by inhibiting the HSCs activation and reducing collagen deposition in mice. Gain-of-function and loss-of-function experiments confirmed that overexpression or knockdown of LTBP2 can enhance or inhibit the activation of HSCs, proliferation, migration and epithelial-mesenchymal transition (EMT) in LX-2 cells. Mechanistically, chromatin immunoprecipitation (ChIP) assays and dual-luciferase reporter gene assays revealed that Hypoxia-inducible Factor 1α (HIF-1α) promotes LTBP2 expression by directly binding to the LTBP2 promoter region. Furthermore, molecular docking and co-immunoprecipitation (Co-IP) experiments demonstrated an interaction between Lysyl Oxidase Like Protein 1 (LOXL1) and LTBP2. Rescue experiments verified that LTBP2 interacts with LOXL1 via the ERK signaling pathway to promote the activation of HSCs and EMT. Our results provide compelling evidence that the HIF-1α/LTBP2 axis facilitates the activation of HSCs and EMT by interacting with LOXL1 through ERK signaling pathway, suggesting that LTBP2 may serve as a potential therapeutic target for liver fibrosis.

LTBP2 silence suppresses glioblastoma proliferation and tumor growth of xenograft tumor mice through modulating JAK2/STAT2 signaling pathway

Glioblastoma is considered the most malignant central nervous system tumor. This study aimed to investigate effects of latent transforming growth factor-β binding protein-2 (LTBP2) on glioblastoma growth and associated mechanisms. LTBP2 gene transcription in glioblastoma was determined using RT-PCR. LTBP2 gene silencing lentiviral vectors were synthesized, and the highest efficient vector was selected to package sh-LTBP2 lentivirus. Xenograft tumor model was constructed by injecting sh-LTBP2-infected U87MG cells into mice, and tumor growth was evaluated. Proliferation, colony formation and migration of U87MG were verified with CCK-8, colony-formation assay and migration assay, and cell cycle was examined. Western blot and immunohistochemistry were performed to examine Janus kinase 2 (JAK2) and signal transducers and activators of transcription 2 (STAT2) phosphorylation. LTBP2 gene transcription in SVGp12 cells was significantly lower compared to U87MG, U251 and T98G cells (P < 0.001). LTBP2 gene silence suppressed U87MG cell proliferation, migration and colony formation compared to U87MG group and sh-NC group (P < 0.05). LTBP2 gene silence regulated phases of cell cycle in U87MG cells. JAK2/STAT2 participated in LTBP2 silence-induced decreased U87MG proliferation. LTBP2 gene silence suppressed tumor growth by modulating JAK2/STAT2 pathway in xenograft tumor mice. In conclusion, LTBP2 silence inhibited proliferation and migration of U87MG cells and tumor growth of xenograft tumor mice through modulating JAK2/STAT2 signaling pathway.

Transcriptional regulators ensuring specific gene expression and decision-making at high TGFβ doses

TGFβ-signaling regulates cancer progression by controlling cell division, migration, and death. These outcomes are mediated by gene expression changes, but the mechanisms of decision-making toward specific fates remain unclear. Here, we combine SMAD transcription factor imaging, genome-wide RNA sequencing, and morphological assays to quantitatively link signaling, gene expression, and fate decisions in mammary epithelial cells. Fitting genome-wide kinetic models to our time-resolved data, we find that most of the TGFβ target genes can be explained as direct targets of SMAD transcription factors, whereas the remainder show signs of complex regulation, involving delayed regulation and strong amplification at high TGFβ doses. Knockdown experiments followed by global RNA sequencing revealed transcription factors interacting with SMADs in feedforward loops to control delayed and dose-discriminating target genes, thereby reinforcing the specific epithelial-to-mesenchymal transition at high TGFβ doses. We identified early repressors, preventing premature activation, and a late activator, boosting gene expression responses for a sufficiently strong TGFβ stimulus. Taken together, we present a global view of TGFβ-dependent gene regulation and describe specificity mechanisms reinforcing cellular decision-making.

Integrated analyses and a novel nomogram for the prediction of significant fibrosis in patients

INTRODUCTION AND OBJECTIVES

This study aimed to explore the key genes involved in the pathophysiological process of liver fibrosis and develop a novel predictive model for noninvasive assessment of significant liver fibrosis patients.

PATIENTS AND METHODS

Differentially expressed genes (DEGs) were identified using the Limma package. The hub genes were explored using the CytoHubba plugin app and validated in GEO datasets and cell models. Furthermore, serum LTBP2 was measured in liver fibrosis (LF) patients with biopsy-proven by ELISA. All patients' clinical characteristics and laboratory results were analyzed. Finally, multivariate logistic regression analysis was used to construct the model for visualization by nomogram. Area under the receiver operating characteristic curve (AUROC) analysis, calibration curves, and decision curve analysis (DCA) certify the accuracy of the nomogram.

RESULTS

RNA sequencing was performed on the liver tissues of 66 biopsy-proven HBV-LF patients. After multiple analyses and in vitro simulation of HSC activation, LTBP2 was found to be the most associated with HSC activation regardless of the causes. Serum LTBP2 expression was measured in 151 patients with biopsy, and LTBP2 was found to increase in parallel with the fibrosis stage. Multivariate logistic regression analysis showed that LTBP2, PLT and AST levels were demonstrated as the independent prediction factors. A nomogram that included the three factors was tabled to evaluate the probability of significant fibrosis occurrence. The AUROC of the nomogram model was 0.8690 in significant fibrosis diagnosis.

CONCLUSIONS

LTBP2 may be a new biomarker for liver fibrosis patients. The nomogram showed better diagnostic performance in patients.

Shotgun proteomics of thyroid carcinoma exosomes - Insight into the role of exosomal proteins in carcinogenesis and thyroid homeostasis

BACKGROUND

Transport of molecules via exosomes is one of the factors involved in thyroid cancer development, and transported molecules may serve as cancer biomarkers. The aim of the study was to characterize protein content of thyroid-derived exosomes and their functional effect exerted on recipient cells.

METHODS

LC-MS/MS proteomics of exosomes released by FTC and 8305C thyroid carcinoma cell lines, and Nthy-ori 3-1 normal thyroid follicular cells was performed, followed by bioinformatic analysis and functional tests (wound healing and Alamar Blue assays).

RESULTS

Exosomes from Nthy-ori 3-1 cells had the highest number of 1504 proteins, while in exosomes from thyroid carcinoma FTC and 8305C cells 730 and 1304 proteins were identified, respectively. For proteins uniquely found in FTC- and 8305C-derived exosomes, enriched cancer-related gene ontology categories included cell adhesion, positive regulation of cell migration, N-glycosylation, drug resistance, and response to NK/T cell cytotoxicity. Furthermore, through label-free quantification (that identified differentially expressed proteins) and comparison with The Human Protein Atlas database several potential diagnostic and/or prognostic biomarkers were indicated. Finally, exosomes from FTC and 8305C cells displayed ability to stimulate migratory properties of recipient Nthy-ori 3-1 cells. Additionally, 8305C-derived exosomes increased recipient cell viability.

CONCLUSIONS

Multiple proteins identified in thyroid cancer-derived exosomes have a direct link to thyroid cancer progression. Also, in functional tests exosomes enhanced growth and dissemination of non-transformed thyroid cells.

GENERAL SIGNIFICANCE

The obtained results expands the knowledge concerning the role of exosomal proteins in thyroid cancer and indicate potential biomarkers for further evaluation in clinical settings.

Case Report: Small intestinal metastatic breast cancer: A case report and literature review

Breast cancer is considered a malignant tumor with the highest incidence among women and is prone to develop distant metastasis. Small intestinal metastasis of breast cancer, however, is relatively rare. This case report describes a 49-year-old Chinese female patient who presented with small intestinal obstruction and was diagnosed with lobular breast cancer with small intestinal and contralateral breast metastasis. Clinical manifestations, clinicopathological features and potential mechanisms of metastasis, along with diagnosis and treatment, are discussed with a review of the relevant literature. Although small intestinal metastasis is rare in breast cancer, we should keep high alert on the possibility of gastrointestinal metastasis when treating lobular breast cancer patients.

Assessment of the TGFB1 gene expression and methylation status of the promoter region in patients with colorectal cancer

The aim of this study was to evaluate the expression of the TGFB1 gene encoding the TGF-β1 cytokine in 64 patients, and then to compare it with clinico-pathological features. The study also investigated whether the regulation of the gene expression is caused by methylation of the promoter region between - 235 and + 22 nucleotide from the start of transcription. The dependence of the relative level of the TGFB1 gene expression on the clinical advancement according to the TNM classifications was shown. Additionally, the individual grades of the T and M features of the TNM classification differed in the relative transcript levels of the TGFB1 gene. Moreover, the higher relative expression level of the studied gene was associated with a lack of vascular invasion by cancer cells and presence of lymphocytes in the neoplastic tissue. The obtained results may indicate a possible impact of the gene on the process of carcinogenesis in colorectal cancer and reduction of its expression level may be one of the factors contributing to progression of the disease.

Elevated latent transforming growth factor beta binding protein 2 in endometriosis promotes endometrial stromal cell invasion and proliferation via the NF-kB signaling pathway

Endometriosis, defined as the abnormal growth of functional endometrium outside the uterus, is characterized by the abnormal phenotype of endometrial cells. This study aimed to investigate the role of latent transforming growth factor beta binding protein 2 (LTBP2), an extracellular matrix protein, in the occurrence and development of endometriosis. Elevated LTBP2 expression levels were observed in endometrial tissues and serum of endometriosis patients and their area under the ROC curve (AUC) values for distinguishing endometriosis were 0.9044 and 0.9534, respectively. Overexpressing-LTBP2 could promote proliferation, migration, and invasion, whereas suppressing apoptosis of endometrial stromal cells (ESCs). Moreover, LTBP2 downregulation induced the opposite effect. The supernatant from ESCs overexpressing LTBP2 promoted the tube formation of human umbilical vein endothelial cells (HUVECs), thus indicating an angiogenic effect. Furthermore, overexpression of LTBP2 facilitated the inflammation and might promote endometriosis progression through the NF-kB signaling pathway. Conclusively, LTBP2 might be a potential target in the diagnosis and treatment of endometriosis.

The prognostic significance of LTBP2 for malignant tumors: Evidence based on 11 observational studies

BACKGROUND AIMS

At present, increasing reports have shown that latent transforming growth factor-β-binding protein 2 (LTBP2) was associated with the prognosis of many types of cancer. We performed rounded analysis to comprehensively analyze and evaluate the prognostic significance of LTBP2 for patients with malignant tumors.

METHODS

We identified relevant studies by searching database including PubMed, Embase, Cochrane Library, and Web of Science. The odds ratio with its 95% confidence interval (CI) was used to assess the correlation between LTBP2 and clinicopathologic features or overall survival of patients with cancer. Hazard ratio with its 95% CI was used to explore the prognostic risk factors. The analysis was performed and assessed using Review Manager 5.2.

RESULTS

A total of 11 studies including 2322 participants were included in this systematic review. Pooled results showed that malignant tissues experienced higher incidence of high LTBP2 expression when compared with adjacent or normal tissues. Patients with high LTBP2 expression experienced significantly lower 1-year, 2-year, 3-year, and 4-year overall survival rate, with the pooled odds ratios being 0.26 (95% CI 0.13-0.53; P = .0002), 0.27 (95% CI 0.14-0.50; P < .0001), 0.26 (95% CI 0.13-0.53; P = .0002), and 0.21 (95% CI 0.06-0.73; P = .01) respectively. Univariate analysis showed high LTBP2 expression, tumor node metastasis stage, T stage, and N stage were prognostic factors of patients with tumors. Multivariate analysis indicated high LTBP2 expression was an independent prognostic factor.

CONCLUSIONS

The present analysis suggested that LTBP2 may have significant association with survival of patients with cancer. High LTBP2 expression was an independent prognostic factor and indicated poor survival.

CircWHSC1 expedites cervical cancer progression via miR-532-3p/LTBP2 axis

Dysregulated circRNAs have potential roles in the progression of various cancer types, including cervical cancer (CaCx). The carcinogenic roles of circRNA Wolf-Hirschhorn syndrome candidate gene-1 (circWHSC1) are described in the development of diverse cancers. The objective of this study was to investigate the expression and the underlying role of circWHSC1 in CaCx. The expression of circWHSC1 was detected by real-time PCR. After the suppression of circWHSC1 expression, the changes in the proliferation, migration, invasion, and apoptosis capacities were detected by CCK-8 assay, colony formation assay, Transwell assays, flow cytometry, and the determination of apoptosis-related proteins. The interplay among circWHSC1, miR-532-3p, and latent transforming growth factor-β binding protein 2 (LTBP2) was confirmed by luciferase reporter and biotinylated RNA pull-down assays. A nude mice xenograft tumor model was established to evaluate the anti-tumorigenic role of circWHSC1 silencing in vivo. CircWHSC1 was overexpressed in CaCx tissues and cell lines and its high expression was inversely associated with the survival rate of patients with CaCx. CircWHSC1 silencing was capable of suppressing the proliferation, metastasis, and invasion of tumor cells and inducing apoptosis. Investigation to its molecular mechanism revealed that circWHSC1 functioned as a competitive endogenous RNA (ceRNA), mediating LTBP2 expression by targeting miR-532-3p. The in vivo experiments further confirmed the inhibition of tumor growth and metastasis by circWHSC1 knockdown. The circWHSC1-mediated miR-532-3p/LTBP2 signaling axis might be a novel therapeutic target for CaCx.

Latent Transforming Growth Factor-β Binding Protein-2 Regulates Lung Fibroblast-to-Myofibroblast Differentiation in Pulmonary Fibrosis via NF-κB Signaling

Despite past extensive studies, the mechanisms underlying pulmonary fibrosis (PF) still remain poorly understood. The aberrantly activated lung myofibroblasts, predominantly emerging through fibroblast-to-myofibroblast differentiation, are considered to be the key cells in PF, resulting in excessive accumulation of extracellular matrix (ECM). Latent transforming growth factor-β (TGFβ) binding protein-2 (LTBP2) has been suggested as playing a critical role in modulating the structural integrity of the ECM. However, its function in PF remains unclear. Here, we demonstrated that lungs originating from different types of patients with PF, including idiopathic PF and rheumatoid arthritis-associated interstitial lung disease, and from mice following bleomycin (BLM)-induced PF were characterized by increased LTBP2 expression in activated lung fibroblasts/myofibroblasts. Moreover, serum LTBP2 was also elevated in patients with COVID-19-related PF. LTBP2 silencing by lentiviral shRNA transfection protected against BLM-induced PF and suppressed fibroblast-to-myofibroblast differentiation in vivo and in vitro. More importantly, LTBP2 overexpression was able to induce differentiation of lung fibroblasts to myofibroblasts in vitro, even in the absence of TGFβ1. By further mechanistic analysis, we demonstrated that LTBP2 silencing prevented fibroblast-to-myofibroblast differentiation and subsequent PF by suppressing the phosphorylation and nuclear translocation of NF-κB signaling. LTBP2 overexpression-induced fibroblast-to-myofibroblast differentiation depended on the activation of NF-κB signaling in vitro. Therefore, our data indicate that intervention to silence LTBP2 may represent a promising therapy for PF.

The circEPSTI1/mir-942-5p/LTBP2 axis regulates the progression of OSCC in the background of OSF via EMT and the PI3K/Akt/mTOR pathway

Oral squamous cell carcinoma (OSCC) in the background of oral submucous fibrosis (OSF) caused by areca nut chewing has a high incidence in Asia-Pacific countries. However, the molecular mechanism remains unclear. Here, we performed circRNA microarray analysis to screen the circRNA expression profiles in OSCC and OSF. We identified circEPSTI1 as a circRNA with consistent, sequential upregulation from normal buccal mucosa (NBM) to OSF to OSCC. Functionally, circEPSTI1 significantly promoted OSCC cell proliferation and invasion, as evidenced by the CCK8, colony formation, wound healing, and transwell assays with circEPSTI1 overexpression and silencing. OSCC patients with circEPSTI1^high status exhibited poor prognoses. CircEPSTI1 sponged miR-942-5p and accelerated epithelial-mesenchymal transition (EMT) to increase LTBP2 expression in OSCC through phosphorylation of PI3K/Akt/mTOR signaling pathway components. Blocking the PI3K/Akt/mTOR signaling pathway with the dual PI3k/mTOR inhibitor BEZ235 reversed OSCC progression induced by overexpression of circEPSTI1 and LTBP2. Collectively, these results indicate that the circEPSTI1/miR-942-5p/LTBP2 axis affects OSCC cell proliferation and invasion via the acceleration of EMT and the phosphorylation of PI3K/Akt/mTOR signaling pathway components. CircEPSTI1 may be an independent diagnostic and prognostic marker and a potential therapeutic target for OSCC patients with OSF.

Expression and clinical significance of latent-transforming growth factor beta-binding protein 2 in primary hepatocellular carcinoma

The present study aimed to explore the expression of latent transforming growth factor β binding protein 2 (LTBP2) in patients with hepatocellular carcinoma (HCC) and their correlation to clinicopathologial features.Serum levels of LTBP2 in 60 patients with HCC, 35 patients with hepatocellular benign tumors, 60 patients with precancerous lesions of HCC, and 60 healthy volunteers were determined by enzyme-linked immunosorbent assay. The expression levels of LTBP2 at messenger RNA (mRNA) and protein levels in 60 cases of HCC and adjacent tissues were detected by quantitative real-time polymerase chain reaction and immunohisochemistry. Statistical analysis was used to analyze the relationship between LTBP2 and clinical characteristics of patients with HCC.The mRNA and protein levels of LTBP2 were significantly upregulated in HCC tissues compared to adjacent tissues. Additionally, higher serum LTBP2 level was also observed in HCC patients relative to normal controls. Further investigation demonstrated that LTBP2 expression was associated with malignant degree of tumor, tumor progression, tumor differentiation, tumor size, tumor stage and hepatitis virus infection, and has prognostic implications in HCC patients.LTBP2 might be served as a potential biomarker in diagnosis and treatment of HCC.

Transcriptome clarifies mechanisms of lesion genesis versus progression in models of Ccm3 cerebral cavernous malformations

Cerebral cavernous malformations (CCMs) are dilated capillaries causing epilepsy and stroke. Inheritance of a heterozygous mutation in CCM3/PDCD10 is responsible for the most aggressive familial form of the disease. Here we studied the differences and commonalities between the transcriptomes of microdissected lesional neurovascular units (NVUs) from acute and chronic in vivo Ccm3/Pdcd10ECKO mice, and cultured brain microvascular endothelial cells (BMECs) Ccm3/Pdcd10ECKO.We identified 2409 differentially expressed genes (DEGs) in acute and 2962 in chronic in vivo NVUs compared to microdissected brain capillaries, as well as 121 in in vitro BMECs with and without Ccm3/Pdcd10 loss (fold change ≥ |2.0|; p < 0.05, false discovery rate corrected). A functional clustered dendrogram generated using the Euclidean distance showed that the DEGs identified only in acute in vivo NVUs were clustered in cellular proliferation gene ontology functions. The DEGs only identified in chronic in vivo NVUs were clustered in inflammation and immune response, permeability, and adhesion functions. In addition, 1225 DEGs were only identified in the in vivo NVUs but not in vitro BMECs, and these clustered within neuronal and glial functions. One miRNA mmu-miR-3472a was differentially expressed (FC = - 5.98; p = 0.07, FDR corrected) in the serum of Ccm3/Pdcd10+/- when compared to wild type mice, and this was functionally related as a putative target to Cand2 (cullin associated and neddylation dissociated 2), a DEG in acute and chronic lesional NVUs and in vitro BMECs. Our results suggest that the acute model is characterized by cell proliferation, while the chronic model showed inflammatory, adhesion and permeability processes. In addition, we highlight the importance of extra-endothelial structures in CCM disease, and potential role of circulating miRNAs as biomarkers of disease, interacting with DEGs. The extensive DEGs library of each model will serve as a validation tool for potential mechanistic, biomarker, and therapeutic targets.

miR-421 promotes apoptosis and suppresses metastasis of osteosarcoma cells via targeting LTBP2

Increasing evidence has confirmed that microRNAs (miRs) are involved in tumor development and progression. A previous study reported that miR-421 could serve as a diagnostic marker in patients with osteosarcoma (OS). The present study explored the potential roles of miR-421 in the regulation of cell proliferation, apoptosis, migration, invasion, and epithelial-mesenchymal transition of OS cells. Our results showed that miR-421 was upregulated in OS tissues and cell lines (MG63, U2OS, HOS, and Saos-2) compared with the corresponding adjacent tissues or human osteoblast cells hFOB1.19, while the latent transforming growth factor β-binding protein 2 (LTBP2) expression was reduced. In MG63 and U2OS cells, CCK8 assay displayed that cell proliferation was repressed by the miR-421 inhibitor, conversely increased by miR-421 mimics. Inhibition of miR-421 promoted cell apoptosis rate, caspase 3 activity, cleaved-caspase 3 (c-caspase 3) expression, and Bax/Bcl-2 ratio, restoration of miR-421 showed the opposite functions. Suppression of miR-421 blocked migration and invasion, whereas miR-421 overexpression promoted the migration and invasion of MG63 and U2OS cells. In addition, real-time polymerase chain reaction and Western blot analysis revealed that miR-421 negatively regulated E-cadherin expression, and positively regulated the expression of N-cadherin and vimentin. The luciferase reporter assay determined that miR-421 could target LTBP2-3'-UTR, and LTBP2 expression was regulated negatively by miR-421 both in mRNA and protein levels. Depletion of LTBP2 partly abolished the biological functions of miR-421 inhibitor in OS. In conclusion, miR-421 plays an oncogenic role in OS via targeting LTBP2, suggesting that miR-421 may be a potential therapeutic target against OS.

High Expression of LTBP2 Contributes to Poor Prognosis in Colorectal Cancer Patients and Correlates with the Mesenchymal Colorectal Cancer Subtype

Colorectal cancer (CRC) is a complex and heterogeneous disease with four consensus molecular subtypes (CMS1-4). LTBP2 is a member of the fibrillin/LTBP super family and plays a critical role in tumorigenesis by activating TGF-β in the CMS4 CRC subtype. So far, the expression and prognostic significance of LTBP2 in CRC remains obscure. In this study, we aimed to analyze the mRNA and protein expression levels of LTBP2 in CRC tissues and then estimate their values as a potential prognostic biomarker. We detected the mRNA expression of LTBP2 in 28 cases of fresh CRC tissues and 4 CRC cell lines and the protein expression of LTBP2 in 483 samples of CRC tissues, matched tumor-adjacent tissues, and benign colorectal diseases. LTBP2 protein expression was then correlated to patients' clinical features and overall survival. Both LTBP2 mRNA and protein expression levels in CRC tissues were remarkably superior to those in adjacent normal colorectal tissues (P = 0.0071 and P < 0.001, respectively), according to TCGA dataset of CRC. High LTBP2 protein expression was correlated with TNM stage (P < 0.001), T stage (P < 0.001), N stage (P < 0.001), and M stage (P < 0.001). High LTBP2 protein expression was related to poor overall survival in CRC patients and was an independent prognostic factor for CRC. LTBP2 mRNA expression was especially higher in the CMS4 subtype (P < 0.001), which was confirmed in CRC cell lines. Our data suggested that LTBP2 may act as an oncogene in the development of colorectal cancer and have important significance in predicting CRC prognosis. LTBP2 could be a novel biomarker and potential therapeutic target for mesenchymal colorectal cancer and can improve the outcome of high-risk CRC.

LTBP2 is secreted from lung myofibroblasts and is a potential biomarker for idiopathic pulmonary fibrosis

Although differentiation of lung fibroblasts into α-smooth muscle actin (αSMA)-positive myofibroblasts is important in the progression of idiopathic pulmonary fibrosis (IPF), few biomarkers reflecting the fibrotic process have been discovered. We performed microarray analyses between FACS-sorted steady-state fibroblasts (lineage (CD45, TER-119, CD324, CD31, LYVE-1, and CD146)-negative and PDGFRα-positive cells) from untreated mouse lungs and myofibroblasts (lineage-negative, Sca-1-negative, and CD49e-positive cells) from bleomycin-treated mouse lungs. Amongst several genes up-regulated in the FACS-sorted myofibroblasts, we focussed on Ltbp2, the gene encoding latent transforming growth factor-β (TGF-β) binding protein-2 (LTBP2), because of the signal similarity to Acta2, which encodes αSMA, in the clustering analysis. The up-regulation was reproduced at the mRNA and protein levels in human lung myofibroblasts induced by TGF-β1. LTBP2 staining in IPF lungs was broadly positive in the fibrotic interstitium, mainly as an extracellular matrix (ECM) protein; however, some of the αSMA-positive myofibroblasts were also stained. Serum LTBP2 concentrations, evaluated using ELISA, in IPF patients were significantly higher than those in healthy volunteers (mean: 21.4 compared with 12.4 ng/ml) and showed a negative correlation with % predicted forced vital capacity (r = -0.369). The Cox hazard model demonstrated that serum LTBP2 could predict the prognosis of IPF patients (hazard ratio for death by respiratory events: 1.040, 95% confidence interval: 1.026-1.054), which was validated using the bootstrap method with 1000-fold replication. LTBP2 is a potential prognostic blood biomarker that may reflect the level of differentiation of lung fibroblasts into myofibroblasts in IPF.

LTBP2 promotes the migration and invasion of gastric cancer cells and predicts poor outcome of patients with gastric cancer

Latent transforming growth factor-β-binding protein (LTBP)2 is a member of the fibrillin/LTBP superfamily of extracellular matrix proteins, and has been demonstrated to exhibit tumor-promoting and tumor-suppressive functions in different types of cancer. However, the function of LTBP2 in gastric cancer (GC) remains unknown. The aim of the present study was to investigate the expression and molecular function of LTBP2 in GC, and to evaluate its prognostic value for patients with GC. The results revealed that the expression of LTBP2 was upregulated in GC tissues and cell lines. Increased LTBP2 expression was associated with poor overall survival in patients with early-stage [tumor-node-metastasis (TNM) I/II] and late-stage (TNM III/IV) GC. Furthermore, silencing of LTBP2 effectively suppressed the proliferation, migration, invasion and epithelial-mesenchymal transition in GC cells. These results suggested that LTBP2 may be considered as a potential therapeutic target and a promising prognostic biomarker for human GC.

LTBP3 promotes early metastatic events during cancer cell dissemination

Latent Transforming Growth Factor β (TGFβ) Binding Proteins (LTBPs) are important for the secretion, activation and function of mature TGFβ, especially so in cancer cell physiology. However, specific roles of the LTBPs remain understudied in the context of the primary tumor microenvironment. Herein, we investigated the role of LTBP-3 in the distinct processes involved in cancer metastasis. By using three human tumor cell lines of different tissue origin (epidermoid HEp-3 and prostate PC-3 carcinomas and HT-1080 fibrosarcoma) and several metastasis models conducted in both mammalian and avian settings, we show that LTBP-3 is involved in the early dissemination of primary cancer cells, namely in the intravasation step of the metastatic cascade. Knockdown of LTBP-3 in all tested cell lines led to significant inhibition of tumor cell intravasation, but did not affect primary tumor growth. LTBP-3 was dispensable in the late steps of carcinoma cell metastasis that follow tumor cell intravasation, including vascular arrest, extravasation and tissue colonization. However, LTBP-3 depletion diminished the angiogenesis-inducing potential of HEp-3 cells in vivo, which was restorable by exogenous delivery of LTBP-3 protein. A similar compensatory approach rescued the dampened intravasation of LTBP-3-deficient HEp-3 cells, suggesting that LTBP-3 regulates the induction of the intravasation-supporting angiogenic vasculature within developing primary tumors. Using our recently developed microtumor model, we confirmed that LTBP-3 loss resulted in the development of intratumoral vessels with an abnormal microarchitecture incompatible with efficient intravasation of HEp-3 carcinoma cells. Collectively, these findings demonstrate that LTBP-3 represents a novel oncotarget that has distinctive functions in the regulation of angiogenesis-dependent tumor cell intravasation, a critical process during early cancer dissemination. Our experimental data are also consistent with the survival prognostic value of LTBP3 expression in early stage head and neck squamous cell carcinomas, further indicating a specific role for LTBP-3 in cancer progression towards metastatic disease.

LTBPs in biology and medicine: LTBP diseases

The latent transforming growth factor (TGF) β binding proteins (LTBP) are crucial mediators of TGFβ function, as they control growth factor secretion, matrix deposition, presentation and activation. Deficiencies in specific LTBP isoforms yield discrete phenotypes representing defects in bone, lung and cardiovascular development mediated by loss of TGFβ signaling. Additional phenotypes represent loss of unique TGFβ-independent features of LTBP effects on elastogenesis and microfibril assembly. Thus, the LTBPs act as sensors for the regulation of both growth factor activity and matrix function.

A Central Bioactive Region of LTBP-2 Stimulates the Expression of TGF-β1 in Fibroblasts via Akt and p38 Signalling Pathways

Latent transforming growth factor-β-1 binding protein-2 (LTBP-2) belongs to the LTBP-fibrillin superfamily of extracellular proteins. Unlike other LTBPs, LTBP-2 does not covalently bind transforming growth factor-β1 (TGF-β1) but appears to be implicated in the regulation of TGF-β1 bioactivity, although the mechanisms are largely unknown. In experiments originally designed to study the displacement of latent TGF-β1 complexes from matrix storage, we found that the addition of exogenous LTBP-2 to cultured human MSU-1.1 fibroblasts caused an increase in TGF-β1 levels in the medium. However, the TGF-β1 increase was due to an upregulation of TGF-β1 expression and secretion rather than a displacement of matrix-stored TGF-β1. The secreted TGF-β1 was mainly in an inactive form, and its concentration peaked around 15 h after addition of LTBP-2. Using a series of recombinant LTBP-2 fragments, the bioactivity was identified to a small region of LTBP-2 consisting of an 8-Cys motif flanked by four epidermal growth factor (EGF)-like repeats. The LTBP-2 stimulation of TGF-β expression involved the phosphorylation of both Akt and p38 mitogen-activated protein kinase (MAPK) signalling proteins, and specific inactivation of each protein individually blocked TGF-β1 increase. The search for the cell surface receptor mediating this LTBP-2 activity proved inconclusive. Inhibitory antibodies to integrins β1 and αVβ5 showed no reduction of LTBP-2 stimulation of TGF-β1. However, TGF-β1 upregulation was partially inhibited by anti-αVβ3 integrin antibodies, suggestive of a direct or indirect role for this integrin. Overall, the study indicates that LTBP-2 can directly upregulate cellular TGF-β1 expression and secretion by interaction with cells via a short central bioactive region. This may be significant in connective tissue disorders involving aberrant TGF-β1 signalling.