Effect of Fibulin-5 on cell proliferation and invasion in human gastric cancer patients

Cancer-associated fibroblast-derived fibulin-5 promotes epithelial-mesenchymal transition in diffuse-type gastric cancer via cAMP response element-binding protein pathway, showing poor prognosis

Diffuse-type gastric cancer (DGC), characterized by poorly cohesive cells within fibrotic stroma, is associated with advanced disease and poor prognosis. Here, to identify distinct biomarkers for DGC compared with intestinal-type gastric cancer, we constructed a comprehensive large-scale signaling network using RNA-sequencing data from three genomic databases (The Cancer Genome Atlas, GSE62254 and GSE26253), developed a mathematical model and conducted simulation analyses. For validation, we used tissue microarray blocks of gastric cancers with immunohistochemical staining, single-cell RNA sequencing, primary cultures of cancer-associated fibroblasts (CAFs) and organoids, and a co-culture system involving CAFs and cancer cells. Signaling network analysis identified six differentially activated signaling components across the database, including BIRC5, TTK, NEK2, FHL1, NR2F1 and FBLN5. Among the differentially activated signaling components, high tumoral expression of fibulin-5 protein encoded by FBLN5 correlated with poor overall and disease-specific survival rates in patients with DGC, even after adjusting for the tumor, node, metastases (TNM) stage. Fibulin-5, derived from CAFs within DGC stroma, promoted organoid growth and epithelial-mesenchymal transition (EMT) in DGC cell lines via the cAMP response element-binding protein (CREB) pathway in a CAF co-culture system. FBLN5 knockdown in CAFs reduced the aggressive phenotype of co-cultured DGC cells, while CREB inhibitors reversed EMT. Furthermore, levels of secreted FBLN5 in patient blood samples correlated with its expression in primary tumors. In summary, fibulin-5 secreted by CAFs and interacted with DGC cells promotes EMT and is clinically associated with poor patient outcomes. These findings suggest fibulin-5 as a potential prognostic marker and therapeutic target in patients with DGC.

Loss of NDUFS1 promotes gastric cancer progression by activating the mitochondrial ROS-HIF1α-FBLN5 signaling pathway

BACKGROUND

Recent studies suggested that NDUFS1 has an important role in human cancers; however, the effects of NDUFS1 on gastric cancer (GC) are still not fully understood.

METHODS

We confirmed that NDUFS1 is downregulated in GC cells through western blot immunohistochemistry and bioinformation analysis. The effect of NDUFS1 on GC was studied by CCK-8, colony formation, transwell assay in vitro and Mouse xenograft assay in vivo. Expression and subcellular localization of NDUFS1 and the content of mitochondrial reactive oxygen species (mROS) was observed by confocal reflectance microscopy.

RESULTS

Reduced expression of NDUFS1 was found in GC tissues and cell lines. Also, NDUFS1 overexpression inhibited GC cell proliferation, migration, and invasion in vitro as well as growth and metastasis in vivo. Mechanistically, NDUFS1 reduction led to the activation of the mROS-hypoxia-inducible factor 1α (HIF1α) signaling pathway. We further clarified that NDUFS1 reduction upregulated the expression of fibulin 5 (FBLN5), a transcriptional target of HIF1α, through activation of mROS-HIF1α signaling in GC cells.

CONCLUSIONS

The results of this study indicate that NDUFS1 downregulation promotes GC progression by activating an mROS-HIF1α-FBLN5 signaling pathway.

De novo variants in an extracellular matrix protein coding gene, fibulin-5 (FBLN5) are associated with pseudoexfoliation

Fibulin-5 (FBLN5), an extracellular scaffold protein, plays a crucial role in the activation of Lysyl oxidase like-1 (LOXL1), a tropoelastin crosslinking enzyme, and subsequent deposition of elastin in the extracellular matrix. Following study identifies polymorphisms within FBLN5 gene as risk factors and its aberrant expression in the pathogenesis of an ocular disorder, pseudoexfoliation (PEX). Exons and exon-intron boundaries within FBLN5 gene were scanned through fluorescence-based capillary electrophoresis for polymorphisms as risk factors for PEX pathogenesis in recruited study subjects with Indian ethnicity. mRNA and protein expression of FBLN5 was checked in lens capsule of study subjects through qRT-PCR and western blotting, respectively. In vitro functional analysis of risk variants was done through luciferase reporter assays. Thirty study subjects from control and PEX affected groups were scanned for potential risk variants. Putative polymorphisms identified by scanning were further evaluated for genetic association in a larger sample size comprising of 338 control and 375 PEX affected subjects. Two noncoding polymorphisms, hg38 chr14:g.91947643G>A (rs7149187:G>A) and hg38 chr14:g.91870431T>C (rs929608:T>C) within FBLN5 gene are found to be significantly associated with PEX as risk factors with a p-value of 0.005 and 0.004, respectively. Molecular assays showed a decreased expression of FBLN5 at both mRNA and protein level in lens capsule of pseudoexfoliation syndrome (PEXS) affected subjects than control. This study unravels two novel risk variants within FBLN5 gene in the pathogenesis of PEX. Further, a decreased expression of FBLN5 in PEXS affected lens capsules implicates a pathogenic link between extracellular matrix maintenance and onset of PEX.

Fibulin-5 contributes to colorectal cancer cell apoptosis via the ROS/MAPK and Akt signal pathways by downregulating transient receptor potential cation channel subfamily V member 1

Fibulin-5, a multifunctional extracellular matrix (ECM) protein, is secreted into the ECM, regulating metastasis and invasion in many malignant tumors. However, its role in colorectal cancer (CRC) has not been reported. In this study, we detected the expression of fibulin-5 in 56 CRC patients and eight CRC cell lines, revealing that fibulin-5 was expressed lower in CRC tumor tissues than in peritumor tissues. Furthermore, our study verified that fibulin-5 promoted cell apoptosis and reactive oxygen species (ROS) production by inhibiting transient receptor potential cation channel subfamily V member 1 (TRPV1) in CRC cells. Moreover, NAC (the scavenger of ROS), SB203580 (the inhibitor of p38), PD98059 (the inhibitor of ERK), and SC79 (the activator of Akt) were used to uncover that fibulin-5 induced apoptosis through the ROS/mitogen-activated protein kinase and Akt signal pathways by downregulating TRPV1. Together, these results suggest that fibulin-5 might serve as a novel drug target for the treatment of CRC patients.

Identification of the matricellular protein Fibulin-5 as a target molecule of glucokinase-mediated calcineurin/NFAT signaling in pancreatic islets

Glucokinase-mediated glucose signaling induces insulin secretion, proliferation, and apoptosis in pancreatic β-cells. However, the precise molecular mechanisms underlying these processes are not clearly understood. Here, we demonstrated that glucokinase activation using a glucokinase activator (GKA) significantly upregulated the expression of Fibulin-5 (Fbln5), a matricellular protein involved in matrix-cell signaling, in isolated mouse islets. The islet Fbln5 expression was induced by ambient glucose in a time- and dose-dependent manner and further enhanced by high-fat diet or the deletion of insulin receptor substrate 2 (IRS-2), whereas the GKA-induced increase in Fbln5 expression was diminished in Irs-2-deficient islets. GKA-induced Fbln5 upregulation in the islets was blunted by a glucokinase inhibitor, K_ATP channel opener, Ca²⁺ channel blocker and calcineurin inhibitor, while it was augmented by harmine, a dual-specificity tyrosine phosphorylation-regulated kinase (DYRK) 1 A inhibitor. Although deletion of Fbln5 in mice had no significant effects on the glucose tolerance or β-cell functions, adenovirus-mediated Fbln5 overexpression increased glucose-stimulated insulin secretion in INS-1 rat insulinoma cells. Since the islet Fbln5 expression is regulated through a glucokinase/K_ATP channel/calcineurin/nuclear factor of activated T cells (NFAT) pathway crucial for the maintenance of β-cell functions, further investigation of Fbln5 functions in the islets is warranted.

Identification of specific biomarkers for gastric adenocarcinoma by ITRAQ proteomic approach

The aim of this study was to identify biomarkers for gastric cancer (GC) by iTRAQ. Using proteins extracted from a panel of 4 pairs of gastric adenocarcinoma samples (stage III-IV, Her-2 negative), we identified 10 up regulated and 9 down regulated proteins in all four pairs of GC samples compared to adjacent normal gastric tissue. The up regulated proteins are mainly involved in cell motility, while the down regulated proteins are mitochondrial enzymes involved in energy metabolism. The expression of three up regulated proteins (ANXA1, NNMT, fibulin-5) and one of the down regulated proteins (UQCRC1) was validated by Western Blot in 97 GC samples. ANXA1 was up regulated in 61.36% of stage I/II GC samples compared to matched adjacent normal gastric tissue, and its expression increased further in stage III/IV samples. Knockdown of ANXA1 by siRNA significantly inhibited GC cell migration and invasion, whereas over expression of ANXA1 promoted migration and invasion. We found decreased expression of UQCRC1 in all stages of GC samples. Our data suggest that increased cell motility and decreased mitochondrial energy metabolism are important hallmarks during the development of GC.

Hypoxia and Transforming Growth Factor β Cooperate to Induce Fibulin-5 Expression in Pancreatic Cancer

The deposition of extracellular matrix (ECM) is a defining feature of pancreatic ductal adenocarcinoma (PDA), where ECM signaling can promote cancer cell survival and epithelial plasticity programs. However, ECM signaling can also limit PDA tumor growth by producing cytotoxic levels of reactive oxygen species. For example, excess fibronectin stimulation of α5β1 integrin on stromal cells in PDA results in reduced angiogenesis and increased tumor cell apoptosis because of oxidative stress. Fibulin-5 (Fbln5) is a matricellular protein that blocks fibronectin-integrin interaction and thus directly limits ECM-driven reactive oxygen species production and supports PDA progression. Compared with normal pancreatic tissue, Fbln5 is expressed abundantly in the stroma of PDA; however, the mechanisms underlying the stimulation of Fbln5 expression in PDA are undefined. Using in vitro and in vivo approaches, we report that hypoxia triggers Fbln5 expression in a TGF-β- and PI3K-dependent manner. Pharmacologic inhibition of TGF-β receptor, PI3K, or protein kinase B (AKT) was found to block hypoxia-induced Fbln5 expression in mouse embryonic fibroblasts and 3T3 fibroblasts. Moreover, tumor-associated fibroblasts from mouse PDA were also responsive to TGF-β receptor and PI3K/AKT inhibition with regard to suppression of Fbln5. In genetically engineered mouse models of PDA, therapy-induced hypoxia elevated Fbln5 expression, whereas pharmacologic inhibition of TGF-β signaling reduced Fbln5 expression. These findings offer insight into the signaling axis that induces Fbln5 expression in PDA and a potential strategy to block its production.