Specificity for fibroblast growth factors determined by heparan sulfate in a binary complex with the receptor kinase

Liver organoid culture methods

Organoids, three-dimensional structures cultured in vitro, can recapitulate the microenvironment, complex architecture, and cellular functions of in vivo organs or tissues. In recent decades, liver organoids have been developed rapidly, and their applications in biomedicine, such as drug screening, disease modeling, and regenerative medicine, have been widely recognized. However, the lack of repeatability and consistency, including the lack of standardized culture conditions, has been a major obstacle to the development and clinical application of liver organoids. It is time-consuming for researchers to identify an appropriate medium component scheme, and the usage of some ingredients remains controversial. In this review, we summarized and compared different methods for liver organoid cultivation that have been published in recent years, focusing on controversial medium components and discussing their advantages and drawbacks. We aimed to provide an effective reference for the development and standardization of liver organoid cultivation.

Fibroblast growth factor 23, klotho and heparin

PURPOSE OF REVIEW

Fibroblast growth factor (FGF) 23 is a bone-derived hormone that regulates phosphate and vitamin D metabolism by targeting the kidney. When highly elevated, such as in chronic kidney disease (CKD), FGF23 can also target the heart and induce pathologic remodeling. Here we discuss the mechanisms that underlie the physiologic and pathologic actions of FGF23, with focus on its FGF receptors (FGFR) and co-receptors.

RECENT FINDINGS

Klotho is a transmembrane protein that acts as an FGFR co-receptor for FGF23 on physiologic target cells. Klotho also exists as a circulating variant, and recent studies suggested that soluble klotho (sKL) can mediate FGF23 effects in cells that do not express klotho. Furthermore, it has been assumed that the actions of FGF23 do not require heparan sulfate (HS), a proteoglycan that acts as a co-receptor for other FGF isoforms. However, recent studies revealed that HS can be part of the FGF23:FGFR signaling complex and modulate FGF23-induced effects.

SUMMARY

sKL and HS have appeared as circulating FGFR co-receptors that modulate the actions of FGF23. Experimental studies suggest that sKL protects from and HS accelerates CKD-associated heart injury. However, the in vivo relevance of these findings is still speculative.

Alterations in heparan sulfate proteoglycan synthesis and sulfation and the impact on vascular endothelial function

The glycocalyx attached to the apical surface of vascular endothelial cells is a rich network of proteoglycans, glycosaminoglycans, and glycoproteins with instrumental roles in vascular homeostasis. Given their molecular complexity and ability to interact with the intra- and extracellular environment, heparan sulfate proteoglycans uniquely contribute to the glycocalyx's role in regulating endothelial permeability, mechanosignaling, and ligand recognition by cognate cell surface receptors. Much attention has recently been devoted to the enzymatic shedding of heparan sulfate proteoglycans from the endothelial glycocalyx and its impact on vascular function. However, other molecular modifications to heparan sulfate proteoglycans are possible and may have equal or complementary clinical significance. In this narrative review, we focus on putative mechanisms driving non-proteolytic changes in heparan sulfate proteoglycan expression and alterations in the sulfation of heparan sulfate side chains within the endothelial glycocalyx. We then discuss how these specific changes to the endothelial glycocalyx impact endothelial cell function and highlight therapeutic strategies to target or potentially reverse these pathologic changes.

FGF21: A Novel Regulator of Glucose and Lipid Metabolism and Whole-Body Energy Balance

Fibroblast growth factor (FGF) 21 is a recently recognized metabolic regulator that evokes interest due to its beneficial action of maintaining whole-body energy balance and protecting the liver from excessive triglyceride production and storage. Together with FGF19 and FGF23, FGF21 belongs to the FGF family with hormone-like activity. Serum FGF21 is generated primarily in the liver under nutritional stress stimuli like prolonged fasting or the lipotoxic diet, but also during increased mitochondrial and endoplasmic reticulum stress. FGF21 exerts its endocrine action in the central nervous system and adipose tissue. Acting in the ventromedial hypothalamus, FGF21 diminishes simple sugar intake. In adipose tissue, FGF21 promotes glucose utilization and increases energy expenditure by enhancing adipose tissue insulin sensitivity and brown adipose tissue thermogenesis. Therefore, FGF21 favors glucose consumption for heat production instead of energy storage. Furthermore, FGF21 specifically acts in the liver, where it protects hepatocytes from metabolic stress caused by lipid overload. FGF21 stimulates hepatic fatty acid oxidation and reduces lipid flux into the liver by increasing peripheral lipoprotein catabolism and reducing adipocyte lipolysis. Paradoxically, and despite its beneficial action, FGF21 is elevated in insulin resistance states, that is, fatty liver, obesity, and type 2 diabetes.

The Role of Fibroblast Growth Factor (FGF) Signaling in Tissue Repair and Regeneration

Fibroblast growth factors (FGFs) are a large family of secretory molecules that act through tyrosine kinase receptors known as FGF receptors. They play crucial roles in a wide variety of cellular functions, including cell proliferation, survival, metabolism, morphogenesis, and differentiation, as well as in tissue repair and regeneration. The signaling pathways regulated by FGFs include RAS/mitogen-activated protein kinase (MAPK), phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K)–protein kinase B (AKT), phospholipase C gamma (PLCγ), and signal transducer and activator of transcription (STAT). To date, 22 FGFs have been discovered, involved in different functions in the body. Several FGFs directly or indirectly interfere with repair during tissue regeneration, in addition to their critical functions in the maintenance of pluripotency and dedifferentiation of stem cells. In this review, we summarize the roles of FGFs in diverse cellular processes and shed light on the importance of FGF signaling in mechanisms of tissue repair and regeneration.

Role of fibroblast growth factor signalling in hepatic fibrosis

Fibrotic remodelling is a highly conserved protective response to tissue injury and it is essential for the maintenance of structural and functional tissue integrity. Also hepatic fibrosis can be considered as a wound-healing response to liver injury, reflecting a balance between liver repair and scar formation. In contrast, pathological fibrosis corresponds to impaired wound healing. Usually, the liver regenerates after acute injury. However, if the damaging mechanisms persist, the liver reacts with progressive and uncontrolled accumulation of extracellular matrix proteins. Eventually, excessive fibrosis can lead to cirrhosis and hepatic failure. Furthermore, cirrhosis is the major risk factor for the development of hepatocellular cancer (HCC). Therefore, hepatic fibrosis is the most critical pathological factor that determines the morbidity and mortality of patients with chronic liver disease. Still, no effective anti-fibrogenic therapies exist, despite the very high medical need. The regulation of fibroblast growth factor (FGF) signalling is a prerequisite for adequate wound healing, repair and homeostasis in various tissues and organs. The FGF family comprises 22 proteins that can be classified into paracrine, intracrine and endocrine factors. Most FGFs signal through transmembrane tyrosine kinase FGF receptors (FGFRs). Although FGFRs are promising targets for the treatment of HCC, the expression and function of FGFR-ligands in hepatic fibrosis is still poorly understood. This review summarizes the latest advances in our understanding of FGF signalling in hepatic fibrosis. Furthermore, the potential of FGFs as targets for the treatment of hepatic fibrosis and remaining challenges for the field are discussed.

Metabolic Messengers: FGF21

As a non-canonical fibroblast growth factor, fibroblast growth factor 21 (FGF21) functions as an endocrine hormone that signals to distinct targets throughout the body. Interest in therapeutic applications for FGF21 was initially sparked by its ability to correct metabolic dysfunction and decrease body weight associated with diabetes and obesity. More recently, new functions for FGF21 signalling have emerged, thus indicating that FGF21 is a dynamic molecule capable of regulating macronutrient preference and energy balance. Here, we highlight the major physiological and pharmacological effects of FGF21 related to nutrient and energy homeostasis and summarize current knowledge regarding FGF21’s pharmacodynamic properties. In addition, we provide new perspectives and highlight critical unanswered questions surrounding this unique metabolic messenger.

Hepatokines and adipokines in NASH-related hepatocellular carcinoma

The incidence of hepatocellular carcinoma (HCC) is increasing in industrialised societies; this is likely secondary to the increasing burden of non-alcoholic fatty liver disease (NAFLD), its progressive form non-alcoholic steatohepatitis (NASH), and the metabolic syndrome. Cumulative studies suggest that NAFLD-related HCC may also develop in non-cirrhotic livers. However, prognosis and survival do not differ between NAFLD- or virus-associated HCC. Thus, research has increasingly focused on NAFLD-related risk factors to better understand the biology of hepatocarcinogenesis and to develop new diagnostic, preventive, and therapeutic strategies. One important aspect thereof is the role of hepatokines and adipokines in NAFLD/NASH-related HCC. In this review, we compile current data supporting the use of hepatokines and adipokines as potential markers of disease progression in NAFLD or as early markers of NAFLD-related HCC. While much work must be done to elucidate the mechanisms and interactions underlying alterations to hepatokines and adipokines, current data support the possible utility of these factors - in particular, angiopoietin-like proteins, fibroblast growth factors, and apelin - for detection or even as therapeutic targets in NAFLD-related HCC.

Interactions of fibroblast growth factors with sulfated galactofucan from Saccharina japonica

A total 68 types of marine algae oligosaccharides and polysaccharides were prepared and used to study the structure-activity relationship of oligosaccharides and polysaccharides in their interactions with fibroblast growth factors (FGF) 1 and 2. Factors considered include different types of algae, extraction methods, molecular weight, sulfate content and fractions. In the case of low molecular weight polysaccharide (SJ-D) from Saccharina japonica and its fractions eluting from anion exchange column, both 1.0 M NaCl fraction (SJ-D-I) and 2.0 M NaCl fraction (SJ-D-S) had stronger binding affinity than the parent SJ-D, suggesting that sulfated galactofucans represented the major tight binding component. Nuclear magnetic resonance showed that SJ-D-I was a typical sulfated galactofucan, composed of four units: 1, 3-linked 4-sulfated α-L-fucose (Fuc); 1, 3-linked 2, 4-disulfated α-L-Fuc; 1, 6-linked 4-sulfated β-D-Gal and/or 1, 6-linked 3, 4-sulfated β-D-Gal. Modification by autohydrolysis to oligosaccharides and desulfation decreased the FGF binding affinity while oversulfation increased the affinity. The solution-based affinities of SJ-D-I to FGF1 and FGF2 were 69 nM and 3.9 nM, suggesting that SJ-D-I showed better preferentially binding to FGF1 than a natural ligand, heparin, suggesting that sulfated galactofucan might represent a good regulator of FGF1.

FGFR4: A promising therapeutic target for breast cancer and other solid tumors

The fibroblast growth factor receptor (FGFR) signaling pathway has long been known to cancer researchers because of its role in cell survival, proliferation, migration, and angiogenesis. Dysregulation of FGFR signaling is frequently reported in cancer studies, but most of these studies focus on FGFR1-3. However, there is growing evidence implicating an important and unique role of FGFR4 in oncogenesis, tumor progression, and resistance to anti-tumor therapy in multiple types of cancer. Importantly, there are several novel FGFR4-specific inhibitors in clinical trials, making FGFR4 an attractive target for further research. In this review, we focus on assessing the role of FGFR4 in cancer, with an emphasis on breast cancer. First, the structure, physiological functions and downstream signaling pathways of FGFR4 are introduced. Next, different mechanisms reported to cause aberrant FGFR4 activation and their functions in cancer are discussed, including FGFR4 overexpression, FGF ligand overexpression, FGFR4 somatic hotspot mutations, and the FGFR4 G388R single nucleotide polymorphism. Finally, ongoing and recently completed clinical trials targeting FGFRs in cancer are reviewed, highlighting the therapeutic potential of FGFR4 inhibition for the treatment of breast cancer.

The Role of Fibroblast Growth Factor 23 in Inflammation and Anemia

In patients with chronic kidney disease (CKD), adverse outcomes such as systemic inflammation and anemia are contributing pathologies which increase the risks for cardiovascular mortality. Amongst these complications, abnormalities in mineral metabolism and the metabolic milieu are associated with chronic inflammation and iron dysregulation, and fibroblast growth factor 23 (FGF23) is a risk factor in this context. FGF23 is a bone-derived hormone that is essential for regulating vitamin D and phosphate homeostasis. In the early stages of CKD, serum FGF23 levels rise 1000-fold above normal values in an attempt to maintain normal phosphate levels. Despite this compensatory action, clinical CKD studies have demonstrated powerful and dose-dependent associations between FGF23 levels and higher risks for mortality. A prospective pathomechanism coupling elevated serum FGF23 levels with CKD-associated anemia and cardiovascular injury is its strong association with chronic inflammation. In this review, we will examine the current experimental and clinical evidence regarding the role of FGF23 in renal physiology as well as in the pathophysiology of CKD with an emphasis on chronic inflammation and anemia.

Basement Membranes in Development and Disease

The basement membrane is a thin but dense, sheet-like specialized type of extracellular matrix that has remarkably diverse functions tailored to individual tissues and organs. Tightly controlled spatial and temporal changes in its composition and structure contribute to the diversity of basement membrane functions. These different basement membranes undergo dynamic transformations throughout animal life, most notably during development. Numerous developmental mechanisms are regulated or mediated by basement membranes, often by a combination of molecular and mechanical processes. A particularly important process involves cell transmigration through a basement membrane because of its link to cell invasion in disease. While developmental and disease processes share some similarities, what clearly distinguishes the two is dysregulation of cells and extracellular matrices in disease. With its relevance to many developmental and disease processes, the basement membrane is a vitally important area of research that may provide novel insights into biological mechanisms and development of innovative therapeutic approaches. Here we present a review of developmental and disease dynamics of basement membranes in Caenorhabditis elegans, Drosophila, and vertebrates.

Cardiac actions of fibroblast growth factor 23

Fibroblast growth factors (FGF) are mitogenic signal mediators that induce cell proliferation and survival. Although cardiac myocytes are post-mitotic, they have been shown to be able to respond to local and circulating FGFs. While precise molecular mechanisms are not well characterized, some FGF family members have been shown to induce cardiac remodeling under physiologic conditions by mediating hypertrophic growth in cardiac myocytes and by promoting angiogenesis, both events leading to increased cardiac function and output. This FGF-mediated physiologic scenario might transition into a pathologic situation involving cardiac cell death, fibrosis and inflammation, and eventually cardiac dysfunction and heart failure. As discussed here, cardiac actions of FGFs - with the majority of studies focusing on FGF2, FGF21 and FGF23 - and their specific FGF receptors (FGFR) and precise target cell types within the heart, are currently under experimental investigation. Especially cardiac effects of endocrine FGFs entered center stage over the past five years, as they might provide communication routes that couple metabolic mechanisms, such as bone-regulated phosphate homeostasis, or metabolic stress, such as hyperphosphatemia associated with kidney injury, with changes in cardiac structure and function. In this context, it has been shown that elevated serum FGF23 can directly tackle cardiac myocytes via FGFR4 thereby contributing to cardiac hypertrophy in models of chronic kidney disease, also called uremic cardiomyopathy. Precise characterization of FGFs and their origin and regulation of expression, and even more importantly, the identification of the FGFR isoforms that mediate their cardiac actions should help to develop novel pharmacological interventions for heart failure, such as FGFR4 inhibition to tackle uremic cardiomyopathy.

Heparanase Inhibitors Facilitate the Assembly of the Basement Membrane in Artificial Skin

Recent research suggests that the basement membrane at the dermal-epidermal junction of the skin plays an important role in maintaining a healthy epidermis and dermis, and repeated damage to the skin can destabilize the skin and accelerate the aging process. Skin-equivalent models are suitable for studying the reconstruction of the basement membrane and its contribution to epidermal homeostasis because they lack the basement membrane and show abnormal expression of epidermal differentiation markers. By using these models, it has been shown that reconstruction of the basement membrane is enhanced not only by supplying basement membrane components, but also by inhibiting proteinases such as urokinase and matrix metalloproteinase. Although matrix metalloproteinase inhibitors assist in the reconstruction of the basement membrane structure, their action is not sufficient to promote its functional recovery. However, heparanase inhibitors stabilize the heparan sulfate chains of perlecan (a heparan sulfate proteoglycan) and promote the regulation of heparan sulfate binding growth factors in the basement membrane. Heparan sulfate promotes effective protein-protein interactions, thereby facilitating the assembly of type VII collagen anchoring fibrils and elastin-associated microfibrils. Using both matrix metalloproteinase inhibitors and heparanase inhibitors, the basement membrane in a skin-equivalent model comes close to recapitulating the structure and function of an in vivo basement membrane. Therefore, by using an appropriate dermis model and suitable protease inhibitors, it may be possible to produce skin-equivalent models that are more similar to natural skin

Fibroblast growth factor 23 directly targets hepatocytes to promote inflammation in chronic kidney disease

Patients with chronic kidney disease (CKD) develop increased levels of the phosphate-regulating hormone, fibroblast growth factor (FGF) 23, that are associated with a higher risk of mortality. Increases in inflammatory markers are another common feature that predicts poor clinical outcomes. Elevated FGF23 is associated with higher circulating levels of inflammatory cytokines in CKD, which can stimulate osteocyte production of FGF23. Here, we studied whether FGF23 can directly stimulate hepatic production of inflammatory cytokines in the absence of α-klotho, an FGF23 coreceptor in the kidney that is not expressed by hepatocytes. By activating FGF receptor isoform 4 (FGFR4), FGF23 stimulated calcineurin signaling in cultured hepatocytes, which increased the expression and secretion of inflammatory cytokines, including C-reactive protein. Elevating serum FGF23 levels increased hepatic and circulating levels of C-reactive protein in wild-type mice, but not in FGFR4 knockout mice. Administration of an isoform-specific FGFR4 blocking antibody reduced hepatic and circulating levels of C-reactive protein in the 5/6 nephrectomy rat model of CKD. Thus, FGF23 can directly stimulate hepatic secretion of inflammatory cytokines. Our findings indicate a novel mechanism of chronic inflammation in patients with CKD and suggest that FGFR4 blockade might have therapeutic anti-inflammatory effects in CKD.

Personalized Clinical Trials in Hepatocellular Carcinoma Based on Biomarker Selection

BACKGROUND

Since the approval of sorafenib there have been numerous failures of new agents in Phase III studies for treatment of advanced hepatocellular carcinoma (HCC). These studies have generally ignored the molecular heterogeneity of HCC and they have not enrolled patients based on predictive markers of response. The development of molecular targeted therapeutics in HCC needs to model the approach that has been taken with great success in other solid tumors, to decrease the likelihood of failure in future studies.

SUMMARY

Here we review the paradigm taken with novel targeted agents in other solid tumors and highlight ongoing studies in HCC that are incorporating biomarkers in clinical development.

KEY MESSAGES

With the appreciation of the molecular diversity of HCC, clinical development of new agents in HCC will need to be targeted towards those patients who are most likely to benefit. This strategy, based on biomarkers for patient selection, is more likely to yield positive results and mitigate the risk of continued negative Phase III studies.

Fibroblast growth factors, old kids on the new block

The fibroblast growth factors (FGFs) are a family of cell intrinsic regulatory peptides that control a broad spectrum of cellular activities. The family includes canonic FGFs that elicit their activities by activating the FGF receptor (FGFR) tyrosine kinase and non-canonic members that elicit their activities intracellularly and via FGFR-independent mechanisms. The FGF signaling axis is highly complex due to the existence of multiple isoforms of both ligands and receptors, as well as cofactors that include the chemically heterogeneous heparan sulfate (HS) cofactors, and in the case of endocrine FGFs, the Klotho coreceptors. Resident FGF signaling controls embryonic development, maintains tissue homeostasis, promotes wound healing and tissue regeneration, and regulates functions of multiple organs. However, ectopic or aberrant FGF signaling is a culprit for various diseases, including congenital birth defects, metabolic disorder, and cancer. The molecular mechanisms by which the specificity of FGF signaling is achieved remain incompletely understood. Since its application as a druggable target has been gradually recognized by pharmaceutical companies and translational researchers, understanding the determinants of FGF signaling specificity has become even more important in order to get into the position to selectively suppress a particular pathway without affecting others to minimize side effects.

Targeting FGF19/FGFR4 Pathway: A Novel Therapeutic Strategy for Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is a lethal cancer with limited systemic therapeutic options. Liver carcinogenesis is a complex procedure and various pathways have been found to be deregulated which are potential targets for novel treatments. Aberrant signalling through FGF19 and its receptor FGFR4 seems to be the oncogenic driver for a subset of HCCs and is associated with poor prognosis. Inhibition of the pathway in preclinical models has shown antitumour activity and has triggered further evaluation of this strategy to in vivo models. This review aims to describe the role of the FGF19/FGFR4 pathway in hepatocellular carcinoma and its role as a potential predictive biomarker for novel targeted agents against FGF19/FGFR4 signalling.

Is fibroblast growth factor receptor 4 a suitable target of cancer therapy?

Fibroblast growth factors (FGF) and their tyrosine kinase receptors (FGFR) support cell proliferation, survival and migration during embryonic development, organogenesis and tissue maintenance and their deregulation is frequently observed in cancer development and progression. Consequently, increasing efforts are focusing on the development of strategies to target FGF/FGFR signaling for cancer therapy. Among the FGFRs the family member FGFR4 is least well understood and differs from FGFRs1-3 in several aspects. Importantly, FGFR4 deletion does not lead to an embryonic lethal phenotype suggesting the possibility that its inhibition in cancer therapy might not cause grave adverse effects. In addition, the FGFR4 kinase domain differs sufficiently from those of FGFRs1-3 to permit development of highly specific inhibitors. The oncogenic impact of FGFR4, however, is not undisputed, as the FGFR4-mediated hormonal effects of several FGF ligands may also constitute a tissue-protective tumor suppressor activity especially in the liver. Therefore it is the purpose of this review to summarize all relevant aspects of FGFR4 physiology and pathophysiology and discuss the options of targeting this receptor for cancer therapy.

Fibroblast growth factor receptor 4 polymorphism is associated with liver cirrhosis in hepatocarcinoma

Background

Fibroblast growth factor receptor 4 (FGFR4) polymorphisms are positively correlated with tumor progression in numerous malignant tumors. However, the association between FGFR4 genetic variants and the risk of hepatocellular carcinoma (HCC) has not yet been determined. In this study, we investigated the potential associations of FGFR4 single nucleotide polymorphisms (SNPs) with HCC susceptibility and its clinicopathological characteristics.

Methodology/Principal Findings

Four SNPs in FGFR4 (rs1966265, rs351855, rs2011077, and rs7708357) were analyzed among 884 participants, including 595 controls and 289 patients with HCC. The samples were further analyzed to clarify the associations between these gene polymorphisms and the risk of HCC, and the impact of these SNPs on the susceptibility and clinicopathological characteristics of HCC. After adjusting for other covariants, HCC patients who carrying at least one A genotype (GA and AA) at rs351855 were observed to have a higher risk of liver cirrhosis compared with those carrying the wild-type genotype (GG) (OR: 2.113, 95% CI: 1.188–3.831). Moreover, the patients with at least one A genotype were particularly showed a high level of alpha-fetoprotein (AFP).

Conclusions

Our findings suggest that genetic polymorphism in FGFR4 rs351855 may be associated with the risk of HCC coupled with liver cirrhosis and may markedly increase the AFP level in Taiwanese patients with HCC. In addition, this is the first study that evaluated the risk factors associated with FGFR4 polymorphism variants in Taiwanese patients with HCC.

Fibroblast growth factor receptor isotype expression and its association with overall survival in patients with hepatocellular carcinoma

Background/Aims

Fibroblast growth factor signaling is involved in hepatocarcinogenesis. The aim of this study was to determine the fibroblast growth factor receptor (FGFR) isotype expression in hepatocellular carcinoma (HCC) and neighboring nonneoplastic liver tissue, and elucidate its prognostic implications.

Methods

Immunohistochemical staining of FGFR1, -2, -3, and -4 was performed in the HCCs and paired neighboring nonneoplastic liver tissue of 870 HCC patients who underwent hepatic resection. Of these, clinical data for 153 patients who underwent curative resection as a primary therapy were reviewed, and the relationship between FGFR isotype expression and overall survival was evaluated (development set). This association was also validated in 73 independent samples (validation set) by Western blot analysis.

Results

FGFR1, -2, -3, and -4 were expressed in 5.3%, 11.1%, 3.8%, and 52.7% of HCCs, respectively. Among the development set of 153 patients, FGFR2 positivity in HCC was associated with a significantly shorter overall survival (5-year survival rate, 35.3% vs. 61.8%; P=0.02). FGFR2 expression in HCC was an independent predictor of a poor postsurgical prognosis (hazard ratio, 2.10; P=0.02) in the development set. However, the corresponding findings were not statistically significant in the validation set.

Conclusions

FGFR2 expression in HCC could be a prognostic indicator of postsurgical survival.

Activation of FGF receptor signaling promotes invasion of non-small-cell lung cancer

The molecular regulation of metastasis of non-small-cell lung cancer (NSCLC) remains not completely defined. Here we showed significant higher MMP26 in the resected NSCLC than adjacent healthy tissue from the patients. Moreover, a strong correlation between MMP26 and the phosphorylated fibroblast growth factor receptor 1 (FGFR1) was detected. To examine the causal relationship between activated FGFR signaling and MMP26, we studied a human NSCLC cell line, A549. We found that FGF1-induced FGFR1 phosphorylation in A549 cells activated MMP26, resulting in an increase in cancer invasiveness. Inhibition of FGFR1 phosphorylation abolished FGF1-stimulated MMP26 activation, suggesting that activation of FGFR signaling pathway in NSCLC promotes cancer metastasis through MMP26. To define the signal transduction cascades downstream of FGFR1 activation for MMP26 activation, we used specific inhibitors for PI3K, ERK/MAPK, and JNK, respectively, to the FGF1-stimulated A549 cells. We found that only inhibition of JNK significantly decreased the activation of MMP26 in response to FGF1 stimulation, suggesting that activation of FGFR1 signaling may activate JNK to activate MMP26 in NSCLC. Our study thus highlights FGFR signaling pathway and MMP26 as novel therapeutic targets for NSCLC therapy.

Targeting fibroblast growth factor 19 in liver disease: a potential biomarker and therapeutic target

INTRODUCTION

Fibroblast growth factor 19 (FGF19) is a member of the hormone-like FGF family and has activity as an ileum-derived postprandial hormone. It shares high binding affinity with β-Klotho and together with the FGF receptor (FGFR) 4, is predominantly targeted to the liver. The main function of FGF19 in metabolism is the negative control of bile acid synthesis, promotion of glycogen synthesis, lipid metabolism and protein synthesis.

AREAS COVERED

Drawing on in vitro and in vivo studies, this review discusses FGF19 and some underlying mechanisms of action of FGF19 as an endocrine hormone in several liver diseases. The molecular pathway of the FGF19-FGFR4 axis in non-alcoholic liver disease and hepatocellular carcinoma are discussed. Furthermore, definition of function and pharmacological effects of FGF19 for liver disease are also presented.

EXPERT OPINION

A series of studies have highlighted a crucial role of FGF19 in liver disease. However, the conclusions of these studies are partly paradoxical and controversial. An understanding of the underlying biological mechanisms which may explain inconsistent findings is especially important for consideration of potential biomarker strategies and an exploration of the putative therapeutic efficacy of FGF19 for human liver disease.

Heparin and liver heparan sulfate can rescue hepatoma cells from topotecan action

Topotecan (TpT) is a major inhibitory compound of topoisomerase (topo) I that plays important roles in gene transcription and cell division. We have previously reported that heparin and heparan sulfate (HS) might be transported to the cell nucleus and they can interact with topoisomerase I. We hypothesized that heparin and HS might interfere with the action of TpT. To test this hypothesis we isolated topoisomerase I containing cell nuclear protein fractions from normal liver, liver cancer tissues, and hepatoma cell lines. The enzymatic activity of these extracts was measured in the presence of heparin, liver HS, and liver cancer HS. In addition, topo I activity, cell viability, and apoptosis of HepG2 and Hep3B cells were investigated after heparin and TpT treatments. Liver cancer HS inhibited topo I activity in vitro. Heparin treatment abrogated topo I enzyme activity in Hep3B cells, but not in HepG2 cells, where the basal activity was higher. Heparin protected the two hepatoma cell lines from TpT actions and decreased the rate of TpT induced S phase block and cell death. These results suggest that heparin and HS might interfere with the function of TpT in liver and liver cancer.

Inhibition of fibroblast growth factor receptor signaling impairs metastasis of hepatocellular carcinoma

The molecular mechanism underlying metastasis of hepatocellular carcinoma (HCC) remains elusive. Here, we showed that matrix metalloproteinase (MMP) 7 and MMP26 levels are significantly higher in the resected HCC than in the adjacent healthy hepatic cells from the patients. Moreover, a strong correlation of the levels of MMP7 or MMP26 with the phosphorylated fibroblast growth factor receptor 2 (FGFR2) was detected. To prove a causal link between the activation of FGFR signaling pathway and expression of MMP7 and MMP26, we used two human HCC lines, HepG2 and HuH-7, to study the underlying molecular basis. We found that FGF1-induced FGFR2 phosphorylation in either line resulted in significant activation of MMP7 and MMP26 and consequently an increase in cancer invasiveness. Inhibition of FGFR2 phosphorylation in HCC abolished FGF1-stimulated MMP7 and MMP26 expression, suggesting that activation of the FGFR signaling pathway in HCC may promote cancer metastasis by inducing MMP7 and MMP26 expression. To define the signal transduction cascades downstream of FGFR2 activation for MMP7 and MMP26 activation, we applied specific inhibitors for phosphatidylinositol-3 kinase (PI3K), extracellular signal-related kinase/mitogen-activated protein kinase (ERK/MAPK), and Jun N-terminal kinase (JNK), respectively, to the FGF1-stimulated HCC cells. We found that only inhibition of JNK significantly decreased the activation of MMP26 in response to FGF1 stimulation, and only inhibition of PI3K significantly decreased the activation of MMP7 in response to FGF1 stimulation, suggesting that the activation of the FGFR2 signaling may activate PI3K to activate MMP7 and activate JNK to activate MMP26, in HCC. Our study thus highlights the FGFR2 signaling pathway and MMP7 and MMP26 as novel therapeutic targets for HCC.

Targeted inhibition of the FGF19-FGFR4 pathway in hepatocellular carcinoma; translational safety considerations

Hepatocellular carcinoma (HCC) is a leading cause of cancer-related death and new therapies are urgently required to treat this disease. Recent data suggest that the FGF19-FGFR4 axis may be a key driver in certain forms of HCC, making the pathway an interesting, emerging molecular target for potential therapeutic intervention. A complication is that, outside of malignant disease, FGFR4 plays an important physiological role in the regulation of hepatic bile acid (BA) synthesis. FGF19 signalling via FGFR4 suppresses de novo BA production in the liver, tightly maintaining hepatic and systemic levels of these detergent-like molecules at a physiological threshold and preventing pathological complications of raised BA levels, such as cholestatic liver injury and bile acid diarrhoea. In some cases of HCC, the malignant disease causes bile duct obstruction, preventing BA secretion from the liver and resulting in cholestasis. Here, the role of FGFR4 signalling in both HCC and BA homoeostasis is discussed. The potential effects of therapeutic FGF19-FGFR4 inhibition on human hepatobiliary/gastrointestinal physiology are considered along with the potential safety implications of FGF19-FGFR4 blockade in patients with HCC.

Regulation of metastasis of pediatric multiple myeloma by MMP13

The molecular mechanism underlying metastasis of pediatric multiple myeloma (MM) remains elusive. Here, we showed that the levels of MMP13 are significantly higher in MM from young patients than those from adult patients. Moreover, a strong correlation of the MMP13 and phosphorylated fibroblast growth factor receptor 4 (FGFR4) levels was detected in MM from young patients. To prove a causal link between activation of fibroblast growth factor receptors (FGFR) signaling pathway and MMP13 expression, we used a human MM line, RPMI-8226 (8226), to study the underlying molecular basis. We found that FGF1-induced FGFR4 phosphorylation in 8,226 cells resulted in significant activation of MMP13, and consequently, an increase in cancer invasiveness. FGFR4 inhibition in 8,226 cells abolished FGF1-stimulated MMP13 expression, suggesting that activation of FGFR signaling pathway in MM may promote cancer metastasis by inducing MMP13 expression. To define the signaling cascades downstream of FGFR4 activation for MMP13 activation, we applied specific inhibitors for PI3K, Jun N-terminal kinase (JNK), and ERK/MAPK, respectively, to the FGF1-stimulated 8,226 cells. We found that only inhibition of ERK1/2 significantly decreased the activation of MMP13 in response to FGF stimulation, suggesting that activation of FGFR signaling may activate ERK/MAPK, rather than JNK or PI3K pathway to activate MMP13 expression in 8,226 cells. Our study thus highlights FGFR4 signaling pathway and MMP13 as novel therapeutic targets for MM.

Fibroblast growth factor family as a potential target in the treatment of hepatocellular carcinoma

Hepatocellular cancer (HCC) is currently the third leading cause of cancer death worldwide. The prognosis of patients diagnosed with late-stage disease is dismal due to high resistance to conventional systemic therapies. The introduction of sorafenib, despite its limited efficacy, as the standard systemic therapy for advanced HCC has paved a way for targeted molecular therapies for HCC. Fibroblast growth factor (FGF) signaling plays an important role in the developing embryo and the adult. The FGF signaling pathway is often hijacked by cancer cells, including HCC. Several alterations in FGF signaling correlate with poor outcome in HCC patients, suggesting that this family of signaling molecules plays an important role in the development of HCC. Multikinase inhibitors targeting FGF signaling are currently under investigation in clinical trials. This review discusses the current understanding of the biological and clinical implications of aberrant FGF signaling in the prognosis, diagnosis, and treatment of HCC.

Deficiency of metabolic regulator FGFR4 delays breast cancer progression through systemic and microenvironmental metabolic alterations

BACKGROUND

Endocrine FGF21 and FGF19 target adipocytes and hepatocytes through betaKlotho (KLB) and FGFR tyrosine kinases effecting glucose, lipid and energy metabolism. Both factors alleviate obesity and metabolic abnormalities which are contributing factors to breast tumor progression. Genomic manipulation of hepatic FGFR4 has uncovered roles of endocrine FGF signaling in both metabolic and cellular homeostasis. Here we determined whether systemic and microenvironmental metabolic alterations caused by the FGFR4 deficiency affect tumorigenesis in breast where FGFR4 is negligible. Breast tumors were induced in the bigenic mice with ablation of FGFR4 and overexpression of TGFα that activates Her2 in the ductal and lobular epithelium surrounded by adipocytes. Mammary tumorigenesis and alterations in systemic and breast microenvironmental metabolic parameters and regulatory pathways were analyzed.

RESULTS

Ablation of FGFR4 had no effect on cellular homeostasis and Her2 activity of normal breast tissue. However, the absence of FGFR4 reduced TGFα-driven breast tumor incidence and progression and improved host survival. Notable increases in hepatic and serum FGF21, ileal FGF15/19, adiponectin and adipsin, and decreases in systemic Fetuin A, IGF-1, IGFBP-1, RBP4 and TIMP1 were observed. The ablation affected adipogenesis and secretory function of adipocytes as well as lipogenesis, glycolysis and energy homeostasis associated with the functions of mitochondria, ER and peroxisomes in the breast and tumor foci. Treatment with a chemical inhibitor of NAMPT involved in the pathways inhibited the growth and survival of breast tumor cells and tumor-initiating cell-containing spheres. The FGFR4 ablation also caused elevation of inflammatory factors in the breast.

CONCLUSIONS

Although the primary role of FGFR4 in metabolism occurs in hepatocytes, its ablation results in a net inhibitory effect on mammary tumor progression. We suggest that the tumor-delaying effect of FGFR4 deficiency may be in large part due to elevated anti-obesogenic FGF21 that triggers tumor-suppressing signals from both peripheral and breast adipocytes. The predominant changes in metabolic pathways suggested roles of metabolic effects from both peripheral and breast adipocytes on metabolic reprogramming in breast epithelial cells that contribute to the suppression of tumor progression. These results provide new insights into the contribution of systemic and microenvironmental metabolic effects controlled by endocrine FGF signaling to breast carcinogenesis.

βKlotho suppresses tumor growth in hepatocellular carcinoma by regulating Akt/GSK-3β/cyclin D1 signaling pathway

βKlotho is a regulator in multiple metabolic processes, while its role in cancer remains unclear. We found the expression of βKlotho was down-regulated in human hepatocellular carcinoma tissues compared with that in paired adjacent non-tumourous liver tissues. Hepatoma cells also showed decreased expression of βKlotho compared with normal hepatocyte cells. Reintroduction of βKlotho into hepatoma cells inhibited their proliferation. The anti-proliferative effect of βKlotho might be linked with G1 to S phase arrest, which was mediated by Akt/GSK-3β/cyclin D1 signaling, since forced expression βKlotho reduced the phosphorylation level of Akt and GSK-3β and induced down-regulation of cyclin D1. Furthermore, βKlotho overexpression could inhibit tumorgenesis, while constitutively activated Akt could override the suppressive effects of βKlotho in vivo. These data suggest βKlotho suppresses tumor growth in hepatocellular carcinoma.

Differential sulfation remodelling of heparan sulfate by extracellular 6-O-sulfatases regulates fibroblast growth factor-induced boundary formation by glial cells: implications for glial cell transplantation

Previously, it has been shown that rat Schwann cells (SCs), but not olfactory ensheathing cells (OECs), form a boundary with astrocytes, due to a SC-specific secreted factor. Here, we identify highly sulfated heparan sulfates (HSs) and fibroblast growth factors (FGFs) 1 and 9 as possible determinants of boundary formation induced by rat SCs. Disaccharide analysis of HS in SC-conditioned and rat OEC-conditioned media showed that SCs secrete more highly sulfated HS than OECs. The dependence of the boundary-forming activity on high levels of sulfation was confirmed using a panel of semisynthetic modified heparins with variable levels of sulfation. Furthermore, extracellular HS 6-O-endosulfatase enzymes, Sulf 1 and Sulf 2, were expressed at a significantly lower level by SCs compared with OECs, and siRNA reduction of Sulfs in OECs was, in itself, sufficient to induce boundary formation. This demonstrates a key role for remodelling (reduction) of HS 6-O-sulfation by OECs, compared with SCs, to suppress boundary formation. Furthermore, specific anti-FGF1 and anti-FGF9 antibodies disrupted SC-astrocyte boundary formation, supporting a role for an HS sulfation-dependent FGF signaling mechanism via FGF receptors on astrocytes. We propose a model in which FGF1 and FGF9 signaling is differentially modulated by patterns of glial cell HS sulfation, dependent on Sulf 1 and Sulf 2 expression, to control FGF receptor 3-IIIb-mediated astrocytic responses. Moreover, these data suggest manipulation of HS sulfation after CNS injury as a potential novel approach for therapeutic intervention in CNS repair.

Identification of FGFR4 as a potential therapeutic target for advanced-stage, high-grade serous ovarian cancer

PURPOSE

To evaluate the prognostic value of fibroblast growth factor receptor 4 (FGFR4) protein expression in patients with advanced-stage, high-grade serous ovarian cancer, delineate the functional role of FGFR4 in ovarian cancer progression, and evaluate the feasibility of targeting FGFR4 in serous ovarian cancer treatment.

EXPERIMENTAL DESIGN

Immunolocalization of FGFR4 was conducted on 183 ovarian tumor samples. The collected FGFR4 expression data were correlated with overall survival using Kaplan-Meier and Cox regression analyses. The effects of FGFR4 silencing on ovarian cancer cell growth, survival, invasiveness, apoptosis, and FGF1-mediated signaling pathway activation were evaluated by transfecting cells with FGFR4-specific siRNAs. An orthotopic mouse model was used to evaluate the effect of injection of FGFR4-specific siRNAs and FGFR4 trap protein encapsulated in nanoliposomes on ovarian tumor growth in vivo.

RESULTS

Overexpression of FGFR4 protein was significantly associated with decreased overall survival durations. FGFR4 silencing significantly decreased the proliferation, survival, and invasiveness and increased apoptosis of ovarian cancer cells. Also, downregulation of FGFR4 significantly abrogated the mitogen-activated protein kinase (MAPK), nuclear factor-κB (NF-κB), and WNT signaling pathways, which are activated by FGF1. Targeting FGFR4 with the FGFR4-specific siRNAs and FGFR4 trap protein significantly decreased ovarian tumor growth in vivo.

CONCLUSIONS

FGFR4 is a prognostic marker for advanced-stage, high-grade serous ovarian carcinoma. Silencing FGFR4 and inhibiting ligand-receptor binding significantly decrease ovarian tumor growth both in vitro and in vivo, suggesting that targeting ovarian cancer cells with high levels of FGFR4 protein expression is a new therapeutic modality for this disease and will improve survival of it.

FGFR4 and TGF-β1 expression in hepatocellular carcinoma: correlation with clinicopathological features and prognosis

OBJECTIVE

To investigate the expression and correlation of transforming growth factor-β1 (TGF-β1) and fibroblast growth factor receptor 4 (FGFR4) in human hepatocellular carcinoma (HCC) and the relationship with clinicopathological features and prognosis.

MATERIALS AND METHODS

The expression of TGF-β1 and FGFR4 in 126 HCC samples was detected immunohistochemically. Combined with clinical postoperative follow-up data, the expression of TGF-β1 and FGFR4 in HCC and the relationship with the prognosis of patients were analyzed by statistically.

RESULTS

The positive expression rate of TGF-β1 was 84.1% (106/126) in tumors, and that in peritumoral liver tissues was 64.3% (81/126); the positive expression rate of FGFR4 in tumors was 74.6% (94/126) and that in peritumoral liver tissues was 57.1% (72/126). The expression of TGF-β1 and FGFR4 in the carcinoma tissues was significantly higher than that in peritumoral liver tissues (p < 0.05). Intratumoral TGF-β1 and FGFR4 expression was associated with TNM stage (p < 0.05). TGF-β1 and FGFR4 expression levels didn't significantly correlate with other clinicopathological parameters, including age, sex, tumor size, serum AFP level, tumor differentiation, lymph node metastasis, etc. (p > 0.05). TGF-β1 expression was positively correlated with FGFR4 expression (r = 0.595, p < 0.05). Patients with positive FGFR4 or TGF-β1 expression had shorter overall survival compared with negative expression (p < 0.05).

CONCLUSIONS

The expression of TGF-β1 and FGFR4 could make synergy on the occurrence and progression of HCC, and may be used as prognosis indicators for HCC patients.

Signals and cells involved in regulating liver regeneration

Liver regeneration is a complex phenomenon aimed at maintaining a constant liver mass in the event of injury resulting in loss of hepatic parenchyma. Partial hepatectomy is followed by a series of events involving multiple signaling pathways controlled by mitogenic growth factors (HGF, EGF) and their receptors (MET and EGFR). In addition multiple cytokines and other signaling molecules contribute to the orchestration of a signal which drives hepatocytes into DNA synthesis. The other cell types of the liver receive and transmit to hepatocytes complex signals so that, in the end of the regenerative process, complete hepatic tissue is assembled and regeneration is terminated at the proper time and at the right liver size. If hepatocytes fail to participate in this process, the biliary compartment is mobilized to generate populations of progenitor cells which transdifferentiate into hepatocytes and restore liver size.

Structural basis of heparan sulfate-specific degradation by heparinase III

Heparinase III (HepIII) is a 73-kDa polysaccharide lyase (PL) that degrades the heparan sulfate (HS) polysaccharides at sulfate-rare regions, which are important co-factors for a vast array of functional distinct proteins including the well-characterized antithrombin and the FGF/FGFR signal transduction system. It functions in cleaving metazoan heparan sulfate (HS) and providing carbon, nitrogen and sulfate sources for host microorganisms. It has long been used to deduce the structure of HS and heparin motifs; however, the structure of its own is unknown. Here we report the crystal structure of the HepIII from Bacteroides thetaiotaomicron at a resolution of 1.6 Å. The overall architecture of HepIII belongs to the (α/α)₅ toroid subclass with an N-terminal toroid-like domain and a C-terminal β-sandwich domain. Analysis of this high-resolution structure allows us to identify a potential HS substrate binding site in a tunnel between the two domains. A tetrasaccharide substrate bound model suggests an elimination mechanism in the HS degradation. Asn260 and His464 neutralize the carboxylic group, whereas Tyr314 serves both as a general base in C-5 proton abstraction, and a general acid in a proton donation to reconstitute the terminal hydroxyl group, respectively. The structure of HepIII and the proposed reaction model provide a molecular basis for its potential practical utilization and the mechanism of its eliminative degradation for HS polysaccarides.

Endothelial heparan sulfate 6-O-sulfation levels regulate angiogenic responses of endothelial cells to fibroblast growth factor 2 and vascular endothelial growth factor

Fibroblast growth factor 2 (FGF2) and vascular endothelial growth factor 165 (VEGF(165)) are potent pro-angiogenic growth factors that play a pivotal role in tumor angiogenesis. The activity of these growth factors is regulated by heparan sulfate (HS), which is essential for the formation of FGF2/FGF receptor (FGFR) and VEGF(165)/VEGF receptor signaling complexes. However, the structural characteristics of HS that determine activation or inhibition of such complexes are only partially defined. Here we show that ovarian tumor endothelium displays high levels of HS sequences that harbor glucosamine 6-O-sulfates when compared with normal ovarian vasculature where these sequences are also detected in perivascular area. Reduced HS 6-O-sulfotransferase 1 (HS6ST-1) or 6-O-sulfotransferase 2 (HS6ST-2) expression in endothelial cells impacts upon the prevalence of HS 6-O-sulfate moieties in HS sequences, which consist of repeating short, highly sulfated S domains interspersed by transitional N-acetylated/N-sulfated domains. 1-40% reduction in 6-O-sulfates significantly compromises FGF2- and VEGF(165)-induced endothelial cell sprouting and tube formation in vitro and FGF2-dependent angiogenesis in vivo. Moreover, HS on wild-type neighboring endothelial or smooth muscle cells fails to restore endothelial cell sprouting and tube formation. The affinity of FGF2 for HS with reduced 6-O-sulfation is preserved, although FGFR1 activation is inhibited correlating with reduced receptor internalization. These data show that 6-O-sulfate moieties in endothelial HS are of major importance in regulating FGF2- and VEGF(165)-dependent endothelial cell functions in vitro and in vivo and highlight HS6ST-1 and HS6ST-2 as potential targets of novel antiangiogenic agents.

Targeting FGFR4 inhibits hepatocellular carcinoma in preclinical mouse models

The fibroblast growth factor (FGF)-FGF receptor (FGFR) signaling system plays critical roles in a variety of normal developmental and physiological processes. It is also well documented that dysregulation of FGF-FGFR signaling may have important roles in tumor development and progression. The FGFR4-FGF19 signaling axis has been implicated in the development of hepatocellular carcinomas (HCCs) in mice, and potentially in humans. In this study, we demonstrate that FGFR4 is required for hepatocarcinogenesis; the progeny of FGF19 transgenic mice, which have previously been shown to develop HCCs, bred with FGFR4 knockout mice fail to develop liver tumors. To further test the importance of FGFR4 in HCC, we developed a blocking anti-FGFR4 monoclonal antibody (LD1). LD1 inhibited: 1) FGF1 and FGF19 binding to FGFR4, 2) FGFR4-mediated signaling, colony formation, and proliferation in vitro, and 3) tumor growth in a preclinical model of liver cancer in vivo. Finally, we show that FGFR4 expression is elevated in several types of cancer, including liver cancer, as compared to normal tissues. These findings suggest a modulatory role for FGFR4 in the development and progression of hepatocellular carcinoma and that FGFR4 may be an important and novel therapeutic target in treating this disease.

Klotho-beta overexpression as a novel target for suppressing proliferation and fibroblast growth factor receptor-4 signaling in hepatocellular carcinoma

Background

We had previously demonstrated overexpression of fibroblast growth factor receptor-4 (FGFR4) in hepatocellular carcinoma (HCC). However, additional molecular mechanisms resulting in amplified FGFR4 signaling in HCC remain under-studied. Here, we studied the mechanistic role of its co-receptor klotho-beta (KLB) in driving elevated FGFR4 activity in HCC progression.

Results

Quantitative real-time PCR analysis identified frequent elevation of KLB gene expression in HCC tumors relative to matched non-tumor tissue, with a more than two-fold increase correlating with development of multiple tumors in patients. KLB-silencing in Huh7 cells decreased cell proliferation and suppressed FGFR4 downstream signaling. While transient repression of KLB-FGFR4 signaling decreased protein expression of alpha-fetoprotein (AFP), a HCC diagnostic marker, prolonged inhibition enriched for resistant HCC cells exhibiting increased liver stemness.

Conclusions

Elevated KLB expression in HCC tissues provides further credence to the oncogenic role of increased FGFR4 signaling in HCC progression and represents a novel biomarker to identify additional patients amenable to anti-FGFR4 therapy. The restricted tissue expression profile of KLB, together with the anti-proliferative effect observed with KLB-silencing, also qualifies it as a specific and potent therapeutic target for HCC patients. The enrichment of a liver stem cell-like population in response to extended KLB-FGFR4 repression necessitates further investigation to target the development of drug resistance.

Differential specificity of endocrine FGF19 and FGF21 to FGFR1 and FGFR4 in complex with KLB

BACKGROUND

Recent studies suggest that betaKlotho (KLB) and endocrine FGF19 and FGF21 redirect FGFR signaling to regulation of metabolic homeostasis and suppression of obesity and diabetes. However, the identity of the predominant metabolic tissue in which a major FGFR-KLB resides that critically mediates the differential actions and metabolism effects of FGF19 and FGF21 remain unclear.

METHODOLOGY/PRINCIPAL FINDINGS

We determined the receptor and tissue specificity of FGF21 in comparison to FGF19 by using direct, sensitive and quantitative binding kinetics, and downstream signal transduction and expression of early response gene upon administration of FGF19 and FGF21 in mice. We found that FGF21 binds FGFR1 with much higher affinity than FGFR4 in presence of KLB; while FGF19 binds both FGFR1 and FGFR4 in presence of KLB with comparable affinity. The interaction of FGF21 with FGFR4-KLB is very weak even at high concentration and could be negligible at physiological concentration. Both FGF19 and FGF21 but not FGF1 exhibit binding affinity to KLB. The binding of FGF1 is dependent on where FGFRs are present. Both FGF19 and FGF21 are unable to displace the FGF1 binding, and conversely FGF1 cannot displace FGF19 and FGF21 binding. These results indicate that KLB is an indispensable mediator for the binding of FGF19 and FGF21 to FGFRs that is not required for FGF1. Although FGF19 can predominantly activate the responses of the liver and to a less extent the adipose tissue, FGF21 can do so significantly only in the adipose tissue and adipocytes. Among several metabolic and endocrine tissues, the response of adipose tissue to FGF21 is predominant, and can be blunted by the ablation of KLB or FGFR1.

CONCLUSIONS

Our results indicate that unlike FGF19, FGF21 is unable to bind FGFR4-KLB complex with affinity comparable to FGFR1-KLB, and therefore, at physiological concentration less likely to directly and significantly target the liver where FGFR4-KLB predominantly resides. However, both FGF21 and FGF19 have the potential to activate responses of primarily the adipose tissue where FGFR1-KLB resides.

Review: The skeletal muscle extracellular matrix: Possible roles in the regulation of muscle development and growth

Velleman, S. G., Shin, J., Li, X. and Song, Y. 2012. Review: The skeletal muscle extracellular matrix: Possible roles in the regulation of muscle development and growth. Can. J. Anim. Sci. 92: 1–10. Skeletal muscle fibers are surrounded by an extrinsic extracellular matrix environment. The extracellular matrix is composed of collagens, proteoglycans, glycoproteins, growth factors, and cytokines. How the extracellular matrix influences skeletal muscle development and growth is an area that is not completely understood at this time. Studies on myogenesis have largely been directed toward the cellular components and overlooked that muscle cells secrete a complex extracellular matrix network. The extracellular matrix modulates muscle development by acting as a substrate for muscle cell migration, growth factor regulation, signal transduction of information from the extracellular matrix to the intrinsic cellular environment, and provides a cellular structural architecture framework necessary for tissue function. This paper reviews extracellular matrix regulation of muscle growth with a focus on secreted proteoglycans, cell surface proteoglycans, growth factors and cytokines, and the dynamic nature of the skeletal muscle extracellular matrix, because of its impact on the regulation of muscle cell proliferation and differentiation during myogenesis.

Physiology of FGF15/19

This chapter will review the various biological actions of the mouse fibroblast growth factor 15 (Fgf15) and human fibroblast growth factor 19 (FGF19). Unlike other members of the fibroblast growth factor (FGF) family, the Fgf15 and FGF19 orthologs do not share a high degree of sequence identity. Fgf15 and FGF19 are members of an atypical subfamily of FGFs that function as hormones. Due to subtle changes in tertiary structure, these FGFs have low heparin binding affinity enabling them to diffuse away from their site of secretion and signal to distant cells. FGF signaling through the FGF receptors is also different for this sub-family, requiring klotho protein cofactors rather than heparin sulfate proteoglycan. Mouse Fgf15 and human FGF19 play key roles in enterohepatic signaling, regulation of liver bile acid biosynthesis, gallbladder motility and metabolic homeostasis.

Chlamydia trachomatis co-opts the FGF2 signaling pathway to enhance infection

The molecular details of Chlamydia trachomatis binding, entry, and spread are incompletely understood, but heparan sulfate proteoglycans (HSPGs) play a role in the initial binding steps. As cell surface HSPGs facilitate the interactions of many growth factors with their receptors, we investigated the role of HSPG-dependent growth factors in C. trachomatis infection. Here, we report a novel finding that Fibroblast Growth Factor 2 (FGF2) is necessary and sufficient to enhance C. trachomatis binding to host cells in an HSPG-dependent manner. FGF2 binds directly to elementary bodies (EBs) where it may function as a bridging molecule to facilitate interactions of EBs with the FGF receptor (FGFR) on the cell surface. Upon EB binding, FGFR is activated locally and contributes to bacterial uptake into non-phagocytic cells. We further show that C. trachomatis infection stimulates fgf2 transcription and enhances production and release of FGF2 through a pathway that requires bacterial protein synthesis and activation of the Erk1/2 signaling pathway but that is independent of FGFR activation. Intracellular replication of the bacteria results in host proteosome-mediated degradation of the high molecular weight (HMW) isoforms of FGF2 and increased amounts of the low molecular weight (LMW) isoforms, which are released upon host cell death. Finally, we demonstrate the in vivo relevance of these findings by showing that conditioned medium from C. trachomatis infected cells is enriched for LMW FGF2, accounting for its ability to enhance C. trachomatis infectivity in additional rounds of infection. Together, these results demonstrate that C. trachomatis utilizes multiple mechanisms to co-opt the host cell FGF2 pathway to enhance bacterial infection and spread.

Chlamydia trachomatis is an obligate intracellular bacterium that is an important cause of human disease, including sexually transmitted diseases and acquired blindness in developing countries. The inability to carry out conventional genetic manipulations limits our understanding of the mechanisms of C. trachomatis binding, entry, and spread. Previous studies have shown that heparan sulfate proteoglycans (HSPGs) play a role in early binding events. As cell surface HSPGs facilitate the interactions of many growth factors with their receptors, we investigated whether HSPG-associated growth factors affect C. trachomatis binding or entry. Here, we report the novel finding that Fibroblast Growth Factor 2 (FGF2), a ubiquitously expressed growth factor, enhances C. trachomatis binding to host cells in an HSPG-dependent manner. Furthermore, C. trachomatis infection stimulates production and release of FGF2 through distinct signaling pathways. Released FGF2 is sufficient to enhance the subsequent rounds of infection. Together, these results demonstrate that C. trachomatis utilizes multiple mechanisms to co-opt the host cell FGF2 pathway that sets up a positive feedback loop to enhance bacterial infection and spread.

Sulfated glycosaminoglycans are required for specific and sensitive fibroblast growth factor (FGF) 19 signaling via FGF receptor 4 and betaKlotho

Secreted from intestine, human fibroblast growth factor 19 (hFGF19) is an endocrine metabolic regulator that controls bile acid synthesis in the liver. Earlier studies have suggested that hFGF19 at 10-100 nM levels signals through FGF receptor 4 (FGFR4) in the presence of a co-receptor, betaKlotho, but its activity and receptor specificity at physiological concentrations (picomolar levels) remain unclear. Here we report that hFGF19 at picomolar levels require sulfated glycosaminoglycans (sGAGs), such as heparan sulfate, heparin, and chondroitin sulfates, for its signaling via human FGFR4 in the presence of human betaKlotho. Importantly, sGAGs isolated from liver are highly active in enhancing the picomolar hFGF19 signaling. At nanomolar levels, in contrast, hFGF19 activates all types of human FGFRs, i.e. FGFR1c, FGFR2c, FGFR3c, and FGFR4 in the co-presence of betaKlotho and heparin and activates FGFR4 even in the absence of betaKlotho. These results show that sGAGs play crucial roles in specific and sensitive hFGF19 signaling via FGF receptors and suggest that hepatic sGAGs are involved in the highly potent and specific signaling of picomolar hFGF19 through FGFR4 and betaKlotho. The results further suggest that hFGF19 at pathological concentrations may evoke aberrant signaling through various FGF receptors.

Association between fibroblast growth factor receptor 4 polymorphisms and risk of hepatocellular carcinoma

Human fibroblast growth factor receptor 4 (FGFR4) polymorphisms have recently been shown to be associated with tumor progression of various types of cancer, including cancer of the breast, colon, and prostate and sarcoma. However, their association with hepatocellular carcinoma (HCC) is unknown. We evaluated the association of FGFR4 polymorphisms with risk of HCC in a study population with HCC and with/without hepatitis B virus (HBV) infection in East China. We genotyped four FGFR4 SNPs (rs351855, rs641101, rs376618, and rs31777) in 1,451 Chinese subjects, including 711 patients with HCC, 368 controls with HBV infection and 372 controls without HBV infection, using the TaqMan genotyping assay. Unconditional logistic regression analysis was performed to evaluate associations of genotypes of each SNP with HCC risk. For the rs351855 (Arg388) locus, we observed a reduced HCC risk associated with the T variant genotypes, particularly for those whose tumors with gross portal vein tumor thrombosis (gross PVTT) (OR = 0.66; 95% confidence interval, 95% CI = 0.46-0.95 for CT + TT). Such a protective effect was also observed for those with liver cirrhosis (OR = 0.42; 95% CI = 0.20-0.88 for CT + TT). Clearly the T allele was associated with these conditions. Our findings suggest that genetic polymorphism in FGFR4 may be a marker for risk of HCC with liver cirrhosis and gross PVTT in Chinese populations.