Pancreatic cancer stem cell-derived exosomal miR-210 mediates macrophage M2 polarization and promotes gemcitabine resistance by targeting FGFRL1.

Pancreatic cancer (PC) is a serious threat to human health, with most patients diagnosed at the advanced stages of the disease. Treatment with gemcitabine (GEM) leads to PC GEM resistance. In addition, cancer stem cell (CSC)-derived exosomes play an important role in cancer progression. We aimed to investigate the role and mechanism of action of PC stem cell-derived exosomes in PC drug resistance and progression. CSC-derived exosomes increased the proportion of F4/80+/CD86 + cells and levels of M2 polarization factors. miR-210 is expressed in CSC-derived exosomes. Thus, following co-culture, miR-210 was taken up by macrophages. Transfection or the addition of miR-210 mimics increased the proportion of F4/80+/CD206 + cells and levels of M2 polarization factors. Further, the miR-210 targets inhibited the levels of FGFRL1. The FGFRL1 overexpression plasmid also inhibited miR-210-mediated M2 polarization. After co-culture of THP-M2 cells with PC cells and treatment with GEM, the survival rate, migration rate, and levels of MDR, YB-1, BCRP, p-PI3K, p-AKT, and p-mTOR in PC cells increased. And THP-M2 increased the tumor volume and MDR, YB-1, BCRP, p-PI3K, p-AKT, and p-mTOR levels. Overall, miR-210 from PC stem cell-derived exosome targets and inhibits FGFRL1 to promote macrophage M2 polarization, which activates the p-PI3K/p-AKT/p-mTOR pathway and increases GEM resistance.

Aberrant Expression of FGFRL1 in Esophageal Cancer and Its Regulation by miR-107.

BACKGROUND: Fibroblast growth factor receptors are growth factor receptor tyrosine kinases, exerting their roles in embryogenesis, tissue homeostasis, and development of cancer. However, little is known about the expression and function of FGFRL1 in esophageal cancer (EC). METHODS: We systematically evaluated the expression of FGFRL1 in TCGA and GETex datasets followed by expression analysis in EC cell lines and clinical specimens using immunofluorescence (IF) and immunohistochemistry (IHC) respectively. RESULTS: GEPIA analysis on TCGA and GETex datasets identified significant upregulation of FGFRL1 in EC patients (n=182) compared to normal controls (n=286, p<0.05). IHC analysis showed significantly higher FGFRL1 expression in EC tissues as compared to the distant matched non-malignant tissues (p<0.001).  Immunoflourescence in EC cells suggested increased expression of FGFRL1 from WDSCC (KYSE30) to MDSCC (KYSE140) and finally to PDSCC (KYSE410). In-silico tools predicted miR-107 as most significant miRNA regulating FGFRL1 expression. qRT-PCR revealed miR-107 expression to be significantly and inversely correlated with FGFRL1 expression in 73% (22/30) EC tissues (p=0.015) and over-expression of miR-107 resulted in significantly decreased expression of FGFRL1 at mRNA (fold change=0.11, p=0.0016) as well as protein level in miR-107 versus NC treated cells. Luciferase reporter assay using FGFRL1-3'UTR further confirmed it to be a direct target of miR-107. CONCLUSION: Our results herein document clinical as well as functional relevance of FGFRL1 in EC and its regulation by miR-107.

Downregulation of miR-210-3p Attenuates High Glucose-Induced Angiogenesis of Vascular Endothelial Cells via Targeting FGFRL1.

INTRODUCTION: Vascular endothelial cell injury and angiogenesis induced by hyperglycemia are the main pathological basis of vascular complications in diabetes mellitus. Our study aimed to investigate the role and mechanism of miR-210-3p in high glucose (HG)-induced angiogenesis. METHODS: Human umbilical vein endothelial cells (HUVECs) were treated with HG to mimic the pathological process of hyperglycemia. HUVECs were divided into the control group, HG group, HG+inhibitor-NC group, and HG+miR-210-3p inhibitor group. Proliferation and migration were tested by wound healing assay, tube formation, and Transwell assay. Quantitation real-time PCR and Western blots were performed to determine the expression of miR-210-3p and relative proteins, respectively. RESULTS: The level of miR-210-3p significantly increased in HUVECs treated by HG. The knockdown of miR-210-3p attenuated the tube formation, proliferation, and migration of cultured HUVECs in vitro to inhibit angiogenesis by increasing the expression of fibroblast growth factor receptor-like 1 (FGFRL1) and then attenuating the phosphorylation of signal transducer and activator of transcription 3 (STAT3), extracellular regulated protein kinases, and protein kinase B (Akt). CONCLUSION: Our study revealed that miR-210-3p might be a promising target for treating diabetic-associated vascular injury.

FGFRL1 and FGF genes are associated with height, hypertension, and osteoporosis.

Hypertension and osteoporosis are two major disorders, which interact with each other. Specific genetic signals involving the fibroblast growth factor receptor-like 1 (FGFRL1) gene are related to high blood pressure and bone growth in giraffes. FGFRL1 is associated with cardiovascular system and bone formation. We performed an association study to investigate the role of FGFRL1 in hypertension, osteoporosis, and height determination in humans. In addition, we identified three kinds of phenotypes in fibroblast growth factor (FGF) genes and examined their association with the FGFRL1 gene. We identified 42 SNPs in the FGFRL1 gene associated with each trait. We then analyzed the potential functional annotation of each SNP. The FGFRL1 gene was found to be associated with height, hypertension, and osteoporosis, consistent with the results of a previous study. In addition, the FGF2, FGF4, FGF10, FGF18, and FGF22 genes were found to interact with the FGFRL1 gene. Our study suggests that both FGFRL1 and FGFRL1-related genes may determine the height and the prevalence of osteoporosis and hypertension in the Korean population.

Lung CSC-derived exosomal miR-210-3p contributes to a pro-metastatic phenotype in lung cancer by targeting FGFRL1.

Lung cancer has the highest mortality rate among human cancers, and the majority of deaths can be attributed to metastatic spread. Lung cancer stem cells (CSCs) are a component of the tumour microenvironment that contributes to this process. Exosomes are small membrane vesicles secreted by all types of cells that mediate cell interactions, including cancer metastasis. Here, we show that lung CSC-derived exosomes promote the migration and invasion of lung cancer cells, up-regulate expression levels of N-cadherin, vimentin, MMP-9 and MMP-1, and down-regulate E-cadherin expression. Moreover, we verified that these exosomes contribute to a pro-metastatic phenotype in lung cancer cells via miR-210-3p transfer. The results of bioinformatics analysis and dual-luciferase reporter assays further indicated that miR-210-3p may bind to fibroblast growth factor receptor-like 1 (FGFRL1); silencing FGFRL1 enhanced the metastatic ability of lung cancer cells, whereas overexpressing FGFRL1 suppressed metastasis. Taken together, our results provide new insights into a potential molecular mechanism whereby lung CSC-derived exosomal miR-210-3p targets FGFRL1 to promote lung cancer metastasis. FGFRL1 may be a promising therapeutic target in lung cancer.

Fibroblast growth factor receptor-like-1: a new therapeutic target and unfavorable prognostic indicator for rectal adenocarcinoma.

Fibroblast growth factor receptor-like-1 (FGFRL1) is important to cell motility and links with tumorigenic potential in various types of cancers. To investigate the biological function and underlying mechanism of FGFRL1 in rectal adenocarcinoma, we conducted this study. TCGA and Oncomine databases were used to analyze FGFRL1 expression and its association with clinical characteristics or overall survival (OS) in rectal adenocarcinoma patients. siRNA strategy was implemented to knockdown FGFRL1 expression in rectal adenocarcinoma cells. CCK8, colony formation, wound healing, and transwell assays were implemented to measure cell behaviors. qRT-PCR and western blot were utilized to identify mRNA and protein expression levels. FGFRL1 was significantly increased in rectal adenocarcinoma tissue samples, either colon or rectum. High-regulation of FGFRL1 expression induced poorer outcome of rectal adenocarcinoma patients. Downregulation of FGFRL1 inhibited the proliferation, colony formation, migration, and invasion of SW837 cells. The MAPK pathway-related proteins, phosphorylation of MEK and ERK, were also decreased after si-FGFRL1 transfection. These findings demonstrated that FGFRL1, acting as a potential inducator, may promote the progression of rectal adenocarcinoma via activating the MAPK signaling pathway.

FGFRL1 affects chemoresistance of small-cell lung cancer by modulating the PI3K/Akt pathway via ENO1.

Fibroblast growth factor receptor-like 1 (FGFRL1), a member of the FGFR family, has been demonstrated to play important roles in various cancers. However, the role of FGFRL1 in small-cell lung cancer (SCLC) remains unclear. Our study aimed to investigate the role of FGFRL1 in chemoresistance of SCLC and elucidate the possible molecular mechanism. We found that FGFRL1 levels are significantly up-regulated in multidrug-resistant SCLC cells (H69AR and H446DDP) compared with the sensitive parental cells (H69 and H446). In addition, clinical samples showed that FGFRL1 was overexpressed in SCLC tissues, and high FGFRL1 expression was associated with the clinical stage, chemotherapy response and survival time of SCLC patients. Knockdown of FGFRL1 in chemoresistant SCLC cells increased chemosensitivity by increasing cell apoptosis and cell cycle arrest, whereas overexpression of FGFRL1 in chemosensitive SCLC cells produced the opposite results. Mechanistic investigations showed that FGFRL1 interacts with ENO1, and FGFRL1 was found to regulate the expression of ENO1 and its downstream signalling pathway (the PI3K/Akt pathway) in SCLC cells. In brief, our study demonstrated that FGFRL1 modulates chemoresistance of SCLC by regulating the ENO1-PI3K/Akt pathway. FGFRL1 may be a predictor and a potential therapeutic target for chemoresistance in SCLC.

Long non-coding RNA FGD5-AS1 promotes non-small cell lung cancer cell proliferation through sponging hsa-miR-107 to up-regulate FGFRL1.

Long non-coding RNA (lncRNA) FYVE, RhoGEF and PH domain containing 5 antisense RNA 1 (FGD5-AS1) has been reported as an oncogene in colorectal cancer, promoting its tumorgenesis. The present paper focused on searching the potential function of FGD5-AS1 in non-small cell lung carcinoma (NSCLC). There are connections between the expression of lncRNA FGD5-AS1 and human NSCLC tumor growth and progression. Also, the relationships between FGD5-AS1, hsa-miR-107 and mRNA fibroblast growth factor receptor like 1 (FGFRL1) are going to test their interaction in NSCLC cell lines, which may cause a series of biological behaviors of NSCLC cells. qRT-PCR analysis was conducted to test the expression of RNAs in different situation. CCK-8 experiment and clone formation assay were performed to assess proliferation of NSCLC cells. Also, connection between FGD5-AS1 and hsa-miR-107 were investigated by luciferase reporter assay and RNA pull-down assay. Rescue experiments were performed to verify the modulating relationship between FGD5-AS1, hsa-miR-107 and FGFRL1. High-level expression of FGD5-AS1 was found in NSCLC. FGD5-AS1 may promote the proliferation of NSCLC cells. Also, the combination between hsa-miR-107, FGD5-AS1 and NSCLC have been proved, which means they can play an interaction function in NSCLC cells. Thence, we concluded that lncRNA FGD5-AS1 promotes non-small cell lung cancer cell proliferation through sponging hsa-miR-107 to up-regulate FGFRL1.

Functional domains of the FgfrL1 receptor.

FgfrL1 is a novel growth factor receptor that is primarily expressed in musculoskeletal tissues and the kidney. FgfrL1-deficient mice have a malformed diaphragm and no kidneys. Such animals die immediately after birth because they are not able to inflate their lungs. The FgfrL1 molecule is composed of three extracellular Ig domains, a transmembrane helix and a short intracellular domain. To investigate the contribution of each of these domains to the function of the novel receptor, we generated mice with deletions of the individual domains. Mice lacking the intracellular domain are viable and phenotypically normal. Mice lacking the first (N-terminal) Ig domain are also viable and normal, but have a reduced life span. Mice lacking the Ig2 or the Ig3 domain are born alive, but die within 24 â€‹h after birth. Ig2-deficient animals exhibit substantially smaller kidneys than wild-type littermates and contain a lower number of glomeruli. Ig3-deficient mice completely lack metanephric kidneys. Interestingly, both the Ig2 and the Ig3-deficient animals show only minor alterations in the diaphragm, which still enables them to inflate their lungs after birth. Our results demonstrate that the principal function of the FgfrL1 receptor is to control the growth of the metanephric kidneys by regulating nephrogenesis. It appears that this function is primarily accomplished by the Ig3 domain with some contribution of the Ig2 domain. It is conceivable that the two domains interact with an Fgf ligand and another molecule from the surface of neighboring cells to induce condensation of the metanephric mesenchyme to renal epithelia and glomeruli.

The Genetic Basis of Scale-Loss Phenotype in the Rapid Radiation of Takifugu Fishes.

Rapid radiation associated with phenotypic divergence and convergence provides an opportunity to study the genetic mechanisms of evolution. Here we investigate the genus Takifugu that has undergone explosive radiation relatively recently and contains a subset of closely-related species with a scale-loss phenotype. By using observations during development and genetic mapping approaches, we show that the scale-loss phenotype of two Takifugu species, T. pardalis Temminck & Schlegel and T. snyderi Abe, is largely controlled by an overlapping genomic segment (QTL). A search for candidate genes underlying the scale-loss phenotype revealed that the QTL region contains no known genes responsible for the evolution of scale-loss phenotype in other fishes. These results suggest that the genes used for the scale-loss phenotypes in the two Takifugu are likely the same, but the genes used for the similar phenotype in Takifugu and distantly related fishes are not the same. Meanwhile, Fgfrl1, a gene predicted to function in a pathway known to regulate bone/scale development was identified in the QTL region. Since Fgfr1a1, another memebr of the Fgf signaling pathway, has been implicated in scale loss/scale shape in fish distantly related to Takifugu, our results suggest that the convergence of the scale-loss phenotype may be constrained by signaling modules with conserved roles in scale development.

FGFRL1 Promotes Ovarian Cancer Progression by Crosstalk with Hedgehog Signaling.

Fibroblast growth factor receptor-like-1 (FGFRL1) has been identified as the fifth fibroblast growth factor receptor. So far, little is known about its biological functions, particularly in cancer development. Here, for the first time, we demonstrated the roles of FGFRL1 in ovarian carcinoma (OC). An array and existing databases were used to investigate the expression profile of FGFRL1 and the relationship between FGFRL1 expression and clinicopathological parameters. FGFRL1 was significantly upregulated in OC patients, and high FGFRL1 expression was correlated with poor prognosis. In vitro cell proliferation, apoptosis and migration assays, and in vivo subcutaneous xenograft tumor models were used to determine the role of FGFRL1. Loss of function of FGFRL1 significantly influenced cell proliferation, apoptosis, and migration of OC cells in vitro and tumor growth in vivo. Chromatin immunoprecipitation PCR analysis and microarray hybridization were performed to uncover the mechanism. FGFRL1 expression could be induced by hypoxia through hypoxia-inducible factor 1α, which directly binds to the promoter elements of FGFRL1. FGFRL1 promoted tumor progression by crosstalk with Hedgehog (Hh) signaling. Taken together, FGFRL1 is a potential predictor and plays an important role in tumor growth and Hh signaling which could serve as potential therapeutic targets for the treatment of OC.

Role of fibroblast growth factor receptors (FGFR) and FGFR like-1 (FGFRL1) in mesenchymal stromal cell differentiation to osteoblasts and adipocytes.

Fibroblast growth factors (FGF) and their receptors (FGFRs) regulate many developmental processes including differentiation of mesenchymal stromal cells (MSC). We developed two MSC lines capable of differentiating to osteoblasts and adipocytes and studied the role of FGFRs in this process. We identified FGFR2 and fibroblast growth factor receptor like-1 (FGFRL1) as possible actors in MSC differentiation with gene microarray and qRT-PCR. FGFR2 and FGFRL1 mRNA expression strongly increased during MSC differentiation to osteoblasts. FGF2 treatment, resulting in downregulation of FGFR2, or silencing FGFR2 expression with siRNAs inhibited osteoblast differentiation. During adipocyte differentiation expression of FGFR1 and FGFRL1 increased and was down-regulated by FGF2. FGFR1 knockdown inhibited adipocyte differentiation. Silencing FGFR2 and FGFR1 in MSCs was associated with decreased FGFRL1 expression in osteoblasts and adipocytes, respectively. Our results suggest that FGFR1 and FGFR2 regulate FGFRL1 expression. FGFRL1 may mediate or modulate FGFR regulation of MSC differentiation together with FGFR2 in osteoblastic and FGFR1 in adipocytic lineage.

Evolution of the fusogenic activity of the receptor FGFRL1.

FGFRL1 is a transmembrane receptor that can induce the fusion of CHO cells to multinucleated syncytia. This cell fusion activity has been attributed to the extracellular Ig3 domain of the receptor. We investigated how the fusogenic activity evolved during the evolution of animals. We found that the Ig3 domain from humans, mice, chicken and fish stimulates fusion of CHO cells, while the Ig3 domain from lancelet and sea urchin does not. It is therefore conceivable that the fusogenic activity of FGFRL1 developed during the evolution of vertebrates. Bony fish contain two copies of the FGFRL1 gene because they have undergone a whole-genome duplication. One of the corresponding proteins (FGFRL1a) induces cell-cell fusion, while the other (FGFRL1b) does not. Analysis of chimeric constructs and in vitro mutagenesis suggested that FGFRL1b has lost its fusogenic activity after duplication. A rescue experiment supported this conclusion. When four amino acids were changed, the Ig3 domain of FGFRL1b was converted into an active, fusogenic protein comparable to FGFRL1a. The four amino acids are located in a hydrophobic pocket of the Ig3 domain. It is likely that this hydrophobic pocket interacts with a target molecule on the membrane of adjacent cells to induce cell-cell fusion.

Receptor FGFRL1 does not promote cell proliferation but induces cell adhesion.

Fibroblast growth factor receptor (FGFR)-like protein 1 (FGFRL1) is the most recently discovered member of the FGFR family. Owing to the fact that it interacts with FGF ligands, but lacks the intracellular tyrosine kinase domain, several researchers have speculated that it may function as a decoy receptor and exert a negative effect on cell proliferation. In this study, we performed overexpression experiments with TetOn­inducible cell clones and downregulation experiments with siRNA oligonucleotides, and found that FGFRL1 had absolutely no effect on cell growth and proliferation. Likewise, we did not observe any influence of FGFRL1 on ERK1/2 activation and on the phosphorylation of 250 other signaling proteins analyzed by the Kinexus antibody microarray. On the other hand, with bacterial petri dishes, we observed a clear effect of FGFRL1 on cell adhesion during the initial hours after cell seeding. Our results suggest that FGFRL1 is a cell adhesion protein similar to the nectins rather than a signaling receptor similar to FGFR1-FGFR4.

Glucose tolerance in obese men is associated with dysregulation of some angiogenesis-related gene expressions in subcutaneous adipose tissue.

Obesity and its metabolic complications are one of the most profound public health problems and result from interactions between genes and environmental. The development of obesity is tightly connected with dysregulation of intrinsic gene expression mechanisms controlling majority of metabolic processes, which are essential for regulation many physiological functions, including insulin sensitivity, cellular proliferation and angiogenesis. Our objective was to evaluate if expression of angiogenesis related genes VEGF-A, CYR61, PDGFC, FGF1, FGF2, FGFR2, FGFRL1, E2F8, BAI2, HIF1A, and EPAS1 at mRNA level in adipose tissue could participate in the development of obesity and metabolic complications. We have shown that expression level of VEGF-A, PDGFC, FGF2, and FGFRL1 genes is decreased in adipose tissue of obese men with normal glucose tolerance (NGT) versus a group of control subjects. At the same time, in this group of obese individuals a significant up-regulation of CYR61, FGF1, FGFR2, E2F8, BAI2, and HIF1A gene expressions was observed. Impaired glucose tolerance (IGT) in obese patients associates with down-regulation of CYR61 and FGFR2 mRNA and up-regulations of E2F8, FGF1, FGF2, VEGF-A and its splice variant 189 mRNA expressions in adipose tissue versus obese (NGT) individuals. Thus, our data demonstrate that the expression of almost all studied genes is affected in subcutaneous adipose tissue of obese individuals with NGT and that glucose intolerance is associated with gene-specific changes in the expression of E2F8, FGF1, FGF2, VEGF-A, CYR61 and FGFR2 mRNAs. The data presented here provides evidence that VEGF-A, CYR61, PDGFC, FGF1, FGF2, FGFR2, FGFRL1, E2F8, BAI2, and HIF1A genes are possibly involved in the development of obesity and its complications.

Cell-cell fusion induced by the Ig3 domain of receptor FGFRL1 in CHO cells.

FGFRL1 is a single-pass transmembrane protein with three extracellular Ig domains. When overexpressed in CHO cells or related cell types, it induces cell-cell fusion and formation of large, multinucleated syncytia. For this fusion-promoting activity, only the membrane-proximal Ig domain (Ig3) and the transmembrane domain are required. It does not matter whether the transmembrane domain is derived from FGFRL1 or from another receptor, but the distance of the Ig3 domain to the membrane is crucial. Fusion can be inhibited with soluble recombinant proteins comprising the Ig1-Ig2-Ig3 or the Ig2-Ig3 domains as well as with monoclonal antibodies directed against Ig3. Mutational analysis reveals a hydrophobic site in Ig3 that is required for fusion. If a single amino acid from this site is mutated, fusion is abolished. The site is located on a ß-sheet, which is part of a larger ß-barrel, as predicted by computer modeling of the 3D structure of FGFRL1. It is possible that this site interacts with a target protein of neighboring cells to trigger cell-cell fusion.

Targeted disruption of the intracellular domain of receptor FgfrL1 in mice.

FgfrL1 is the fifth member of the fibroblast growth factor receptor (Fgfr) family. Studies with FgfrL1 deficient mice have demonstrated that the gene plays an important role during embryonic development. FgfrL1 knock-out mice die at birth as they have a malformed diaphragm and lack metanephric kidneys. Similar to the classical Fgfrs, the FgfrL1 protein contains an extracellular part composed of three Ig-like domains that interact with Fgf ligands and heparin. However, the intracellular part of FgfrL1 is not related to the classical receptors and does not possess any tyrosine kinase activity. Curiously enough, the amino acid sequence of this domain is barely conserved among different species, with the exception of three motifs, namely a dileucine peptide, a tandem tyrosine-based motif YXXΦ and a histidine-rich sequence. To investigate the function of the intracellular domain of FgfrL1, we have prepared genetically modified mice that lack the three conserved sequence motifs, but instead contain a GFP cassette (FgfrL1ΔC-GFP). To our surprise, homozygous FgfrL1ΔC-GFP knock-in mice are viable, fertile and phenotypically normal. They do not exhibit any alterations in the diaphragm or the kidney, except for a slight reduction in the number of glomeruli that does not appear to affect life expectancy. In addition, the pancreas of both FgfrL1ΔC-GFP knock-in and FgfrL1 knock-out mice do not show any disturbances in the production of insulin, in contrast to what has been suggested by recent studies. Thus, the conserved motifs of the intracellular FgfrL1 domain are dispensable for organogenesis and normal life. We conclude that the extracellular domain of the protein must conduct the vital functions of FgfrL1.

The FgfrL1 receptor is required for development of slow muscle fibers.

FgfrL1, which interacts with Fgf ligands and heparin, is a member of the fibroblast growth factor receptor (Fgfr) family. FgfrL1-deficient mice show two significant alterations when compared to wildtype mice: They die at birth due to a malformed diaphragm and they lack metanephric kidneys. Utilizing gene arrays, qPCR and in situ hybridization we show here that the diaphragm of FgfrL1 knockout animals lacks any slow muscle fibers at E18.5 as indicated by the absence of slow fiber markers Myh7, Myl2 and Myl3. Similar lesions are also found in other skeletal muscles that contain a high proportion of slow fibers at birth, such as the extraocular muscles. In contrast to the slow fibers, fast fibers do not appear to be affected as shown by expression of fast fiber markers Myh3, Myh8, Myl1 and MylPF. At early developmental stages (E10.5, E15.5), FgfrL1-deficient animals express slow fiber genes at normal levels. The loss of slow fibers cannot be attributed to the lack of kidneys, since Wnt4 knockout mice, which also lack metanephric kidneys, show normal expression of Myh7, Myl2 and Myl3. Thus, FgfrL1 is specifically required for embryonic development of slow muscle fibers.

Evidence that the novel receptor FGFRL1 signals indirectly via FGFR1.

Fibroblast growth factor (FGF) receptor-like protein 1 (FGFRL1) is a recently discovered member of the FGF receptor (FGFR) family. Similar to the classical FGFRs, it contains three extracellular immunoglobulin-like domains and interacts with FGF ligands. However, in contrast to the classical receptors, it does not contain any intracellular tyrosine kinase domain and consequently cannot signal by transphosphorylation. In mouse kidneys, FgfrL1 is expressed primarily at embryonic stages E14-E15 in regions where nascent nephrons develop. In this study, we used whole-mount in situ hybridization to show the spatial pattern of five different Fgfrs in the developing mouse kidney. We compared the expression pattern of FgfrL1 with that of other Fgfrs. The expression pattern of FgfrL1 closely resembled that of Fgfr1, but clearly differed from that of Fgfr2­Fgfr4. It is therefore conceivable that FgfrL1 signals indirectly via Fgfr1. The mechanisms by which FgfrL1 affects the activity of Fgfr1 remain to be elucidated.

Fibroblast growth factor receptor like-1 (FGFRL1) interacts with SHP-1 phosphatase at insulin secretory granules and induces beta-cell ERK1/2 protein activation.

FGFRL1 is a newly identified member of the fibroblast growth factor receptor (FGFR) family expressed in adult pancreas. Unlike canonical FGFRs that initiate signaling via tyrosine kinase domains, the short intracellular sequence of FGFRL1 consists of a putative Src homology domain-2 (SH2)-binding motif adjacent to a histidine-rich C terminus. As a consequence of nonexistent kinase domains, FGFRL1 has been postulated to act as a decoy receptor to inhibit canonical FGFR ligand-induced signaling. In pancreatic islet beta-cells, canonical FGFR1 signaling affects metabolism and insulin processing. This study determined beta-cell expression of FGFRL1 as well as consequent effects on FGFR1 signaling and biological responses. We confirmed FGFRL1 expression at the plasma membrane and within distinct intracellular granules of both primary beta-cells and ßTC3 cells. Fluorescent protein-tagged FGFRL1 (RL1) induced a significant ligand-independent increase in MAPK signaling. Removal of the histidine-rich domain (RL1-ΔHis) or entire intracellular sequence (RL1-ΔC) resulted in greater retention at the plasma membrane and significantly reduced ligand-independent ERK1/2 responses. The SHP-1 phosphatase was identified as an RL1-binding substrate. Point mutation of the SH2-binding motif reduced the ability of FGFRL1 to bind SHP-1 and activate ERK1/2 but did not affect receptor localization to insulin secretory granules. Finally, overexpression of RL1 increased cellular insulin content and matrix adhesion. Overall, these data suggest that FGFRL1 does not function as a decoy receptor in beta-cells, but rather it enhances ERK1/2 signaling through association of SHP-1 with the receptor's intracellular SH2-binding motif.