Hepatocyte growth factor signaling in intrapancreatic ductal cells drives pancreatic morphogenesis. PLoS Genet. 2013;9:e1003650. [PMID: 23935514 PMCID: PMC3723531 DOI: 10.1371/journal.pgen.1003650]

Genetically encoded tension heterogeneity sculpts cardiac trabeculation

The myocardial wall arises from a single layer of cardiomyocytes, some delaminate to create trabeculae while others remain in the compact layer. However, the mechanisms governing cardiomyocyte fate decisions remain unclear. Using single-cell RNA sequencing, genetically encoded biosensors, and in toto live imaging, we observe intrinsic variations in erbb2 expression and its association with trabecular fate. Specifically, erbb2 promotes PI3K activity and recruits the Arp2/3 complex, inducing a polarized accumulation of the actomyosin network to drive cell delamination. Subsequently, the lineage-committed nascent trabeculae trigger Notch activity in neighboring cardiomyocytes to suppress erbb2 expression and reduce cell tension, thereby confining them to the compact layer. Overall, this genetic and cellular interplay governs compact and trabecular cell fate determination to orchestrate myocardial pattern formation.

Implementation of the UNRES/SUGRES-1P Coarse-Grained Model of Heparin for Simulating Protein/Heparin Interactions

Heparin is a natural highly sulfated unbranched periodic polysaccharide that plays a critical role in regulating various cellular events through interactions with its protein targets such as growth factors and cytokines. Although all-atom simulations of heparin-containing systems provide valuable insights into their structural and dynamical properties, long chains of heparin participate in many biologically relevant processes at much bigger scales and longer times than the ones which all-atom MD is able to effectively deal with. Among these processes is the establishment of chemokine gradients, amyloidogenesis, or collagen network organization. To address this limitation, coarse-grained models simplify these systems by reducing the number of degrees of freedom, allowing for the efficient exploration of structural changes within protein/heparin complexes. We introduce and validate the accuracy of a new coarse-grained physics-based model designed for studying protein/heparin interactions, which has been incorporated into the UNRES software package. The effective energy functions from UNRES and SUGRES-1P have been employed for the protein and heparin components, respectively. A good agreement between the obtained coarse-grained simulation results and experimental data confirms the suitability of the combined coarse-grained UNRES and SUGRES-1P model for in silico analysis of complex biological phenomena involving heparin, spanning time scales and molecular system sizes not attainable by conventional atomistic molecular dynamics simulations.

Deficiency of the HGF/Met pathway leads to thyroid dysgenesis by impeding late thyroid expansion

The mechanisms of bifurcation, a key step in thyroid development, are largely unknown. Here we find three zebrafish lines from a forward genetic screening with similar thyroid dysgenesis phenotypes and identify a stop-gain mutation in hgfa and two missense mutations in met by positional cloning from these zebrafish lines. The elongation of the thyroid primordium along the pharyngeal midline was dramatically disrupted in these zebrafish lines carrying a mutation in hgfa or met. Further studies show that MAPK inhibitor U0126 could mimic thyroid dysgenesis in zebrafish, and the phenotypes are rescued by overexpression of constitutively active MEK or Snail, downstream molecules of the HGF/Met pathway, in thyrocytes. Moreover, HGF promotes thyrocyte migration, which is probably mediated by downregulation of E-cadherin expression. The delayed bifurcation of the thyroid primordium is also observed in thyroid-specific Met knockout mice. Together, our findings reveal that HGF/Met is indispensable for the bifurcation of the thyroid primordium during thyroid development mediated by downregulation of E-cadherin in thyrocytes via MAPK-snail pathway.

Acinar-ductal cell rearrangement drives branching morphogenesis of the murine pancreas in an IGF/PI3K-dependent manner

During organ formation, progenitor cells need to acquire different cell identities and organize themselves into distinct structural units. How these processes are coordinated and how tissue architecture(s) is preserved despite the dramatic cell rearrangements occurring in developing organs remain unclear. Here, we identified cellular rearrangements between acinar and ductal progenitors as a mechanism to drive branching morphogenesis in the pancreas while preserving the integrity of the acinar-ductal functional unit. Using ex vivo and in vivo mouse models, we found that pancreatic ductal cells form clefts by protruding and pulling on the acinar basement membrane, which leads to acini splitting. Newly formed acini remain connected to the bifurcated branches generated by ductal cell rearrangement. Insulin growth factor (IGF)/phosphatidylinositol 3-kinase (PI3K) pathway finely regulates this process by controlling pancreatic ductal tissue fluidity, with a simultaneous impact on branching and cell fate acquisition. Together, our results explain how acinar structure multiplication and branch bifurcation are synchronized during pancreas organogenesis.

Roles of MET in human cancer

The MET proto-oncogene was first identified in osteosarcoma cells exposed to carcinogens. Although expressed in many normal cells, MET is overexpressed in many human cancers. MET is involved in the initiation and development of various human cancers and mediates proliferation, migration and invasion. Accordingly, MET has been successfully used as a biomarker for diagnosis and prognosis, survival, post-operative recurrence, risk assessment and pathologic grading, as well as a therapeutic target. In addition, recent work indicates that inhibition of MET expression and function has potential clinical benefit. This review summarizes the role, mechanism, and clinical significance of MET in the formation and development of human cancer.

Progranulin A Promotes Compensatory Hepatocyte Proliferation via HGF/c-Met Signaling after Partial Hepatectomy in Zebrafish

Compensatory hepatocyte proliferation and other liver regenerative processes are activated to sustain normal physiological function after liver injury. A major mitogen for liver regeneration is hepatocyte growth factor (HGF), and a previous study indicated that progranulin could modulate c-met, the receptor for HGF, to initiate hepatic outgrowth from hepatoblasts during embryonic development. However, a role for progranulin in compensatory hepatocyte proliferation has not been shown previously. Therefore, this study was undertaken to clarify whether progranulin plays a regulatory role during liver regeneration. To this end, we established a partial hepatectomy regeneration model in adult zebrafish that express a liver-specific fluorescent reporter. Using this model, we found that loss of progranulin A (GrnA) function by intraperitoneal-injection of a Vivo-Morpholino impaired and delayed liver regeneration after partial hepatectomy. Furthermore, transcriptome analysis and confirmatory quantitative real-time PCR suggested that cell cycle progression and cell proliferation was not as active in the morphants as controls, which may have been the result of comparative downregulation of the HGF/c-met axis by 36 h after partial hepatectomy. Finally, liver-specific overexpression of GrnA in transgenic zebrafish caused more abundant cell proliferation after partial hepatectomy compared to wild types. Thus, we conclude that GrnA positively regulates HGF/c-met signaling to promote hepatocyte proliferation during liver regeneration.

Identification of zebrafish ortholog for human coagulation factor IX and its age-dependent expression

BACKGROUND

Coagulation factor IX (FIX) is a serine protease zymogen involved in the intrinsic blood coagulation pathway, and its deficiency causes hemophilia B. Zebrafish has three f9 genes, and the ortholog to human F9 is unknown.

OBJECTIVE

To identify the zebrafish ortholog to F9 using sequence analysis and piggyback knockdown technology.

METHODS

Gene and protein sequence analysis for three f9 genes, f9a, f9b, and f9l, present in the zebrafish genome was performed. In vivo and in vitro assays after knockdown of each gene and immunodepletion using specific antibodies were carried out.

RESULTS

Sequence analysis revealed that f9a and f9b are similar to human F9, whereas f9l is similar to human F10. RNA analysis showed an age-dependent increase in expression of all three genes. Zebrafish f9a gene knockdown and Fixa immunodepletion prolonged kinetic partial thromboplastin time (kPTT), whereas f9l knockdown and Fixl immunodepletion prolonged kPTT, kinetic prothrombin time, and kinetic Russell viper venom activation time. Laser-assisted venous thrombosis increased time to occlusion after f9a and f9l knockdown and antibody inhibition of Fixa and Fixl. Further, analysis of plasma proteins by mass spectrometry and immunohistochemistry detected all three proteins.

CONCLUSIONS

Our findings suggest that zebrafish f9a has functional activity similar to human F9. Fixl is functionally similar to Fx. The age-dependent increases of these factors are comparable to those observed in mice and humans. Thus, the zebrafish model could be used to study factors involved in increasing f9a expression during aging. It could also be used to test whether normal human Factor IX and Factor IX Leyden promoter work in zebrafish background.

Targeting polyamine biosynthesis to stimulate beta cell regeneration in zebrafish

Type 1 diabetes (T1D) is a disease characterized by destruction of the insulin-producing beta cells. Currently, there remains a critical gap in our understanding of how to reverse or prevent beta cell loss in individuals with T1D. Previous studies in mice discovered that pharmacologically inhibiting polyamine biosynthesis using difluoromethylornithine (DFMO) resulted in preserved beta cell function and mass. Similarly, treatment of non-obese diabetic mice with the tyrosine kinase inhibitor Imatinib mesylate reversed diabetes. The promising findings from these animal studies resulted in the initiation of two separate clinical trials that would repurpose either DFMO (NCT02384889) or Imatinib (NCT01781975) and determine effects on diabetes outcomes; however, whether these drugs directly stimulated beta cell growth remained unknown. To address this, we used the zebrafish model system to determine pharmacological impact on beta cell regeneration. After induction of beta cell death, zebrafish embryos were treated with either DFMO or Imatinib. Neither drug altered whole-body growth or exocrine pancreas length. Embryos treated with Imatinib showed no effect on beta cell regeneration; however, excitingly, DFMO enhanced beta cell regeneration. These data suggest that pharmacological inhibition of polyamine biosynthesis may be a promising therapeutic option to stimulate beta cell regeneration in the setting of diabetes.

Retinoic Acid Organizes the Zebrafish Vagus Motor Topographic Map via Spatiotemporal Coordination of Hgf/Met Signaling

Information flow through neural circuits often requires their organization into topographic maps in which the positions of cell bodies and synaptic targets correspond. To understand how topographic map development is controlled, we examine the mechanism underlying targeting of vagus motor axons to the pharyngeal arches in zebrafish. We reveal that retinoic acid organizes topography by specifying anterior-posterior identity in vagus motor neurons. We then show that chemoattractant signaling between Hgf and Met is required for vagus innervation of the pharyngeal arches. Finally, we find that retinoic acid controls the spatiotemporal dynamics of Hgf/Met signaling to coordinate axon targeting with the developmental progression of the pharyngeal arches and show that experimentally altering the timing of Hgf/Met signaling is sufficient to redirect axon targeting and disrupt the topographic map. These findings establish a mechanism of topographic map development in which the regulation of chemoattractant signaling in space and time guides axon targeting.

Mutual inhibitions between epidermal growth factor receptor signaling and miR-124a control pancreatic progenitor proliferation

Pancreatic stem/progenitor cells convert from a proliferative to a differentiated fate passing through proliferation cease to a resting state. However, the molecular mechanisms of cell cycle arrest are poorly understood. In this study, we demonstrated that the microRNA-124a (miR-124a) inhibited the proliferation of pancreatic progenitor cells both in vitro and ex vivo and promoted a quiescent state. The miR-124a directly targeted SOS Ras/Rac guanine nucleotide exchange factor 1 (SOS1), IQ motif-containing GTPase-activating protein 1 (IQGAP1), signal transducer and activator of transcription 3 (STAT3), and cyclin D2 (CCND2), thereby inactivating epidermal growth factor receptor (EGFR) downstream signaling pathways including mitogen-activated protein kinase/extracellular signal-regulated kinase (MEK/ERK), phosphatidylinositol 3-kinase-protein kinase B (PI3K/AKT) and Janus kinase (JAK)/STAT3. miR-124a blocked cell proliferation mainly through targeting STAT3 to inhibit PI3K/AKT and JAK/STAT3 signaling. Moreover, miR-124a expression was negatively regulated by EGFR downstream PI3K/AKT signaling. These results indicated that miR-124a and EGFR signaling mutually interact to form a regulating circuit that determines the proliferation of pancreatic progenitor cells.

Stepwise participation of HGF/MET signaling in the development of migratory muscle precursors during vertebrate evolution

BACKGROUND

The skeletal musculature of gnathostomes, which is derived from embryonic somites, consists of epaxial and hypaxial portions. Some hypaxial muscles, such as tongue and limb muscles, undergo de-epithelialization and migration during development. Delamination and migration of these myoblasts, or migratory muscle precursors (MMPs), is generally thought to be regulated by hepatocyte growth factor (HGF) and receptor tyrosine kinase (MET) signaling. However, the prevalence of this mechanism and the expression patterns of the genes involved in MMP development across different vertebrate species remain elusive.

RESULTS

We performed a comparative analysis of Hgf and Met gene expression in several vertebrates, including mouse, chicken, dogfish (Scyliorhinus torazame), and lamprey (Lethenteron camtschaticum). While both Hgf and Met were expressed during development in the mouse tongue muscle, and in limb muscle formation in the mouse and chicken, we found no clear evidence for the involvement of HGF/MET signaling in MMP development in shark or lamprey embryos.

CONCLUSIONS

Our results indicate that the expressions and functions of both Hgf and Met genes do not represent shared features of vertebrate MMPs, suggesting a stepwise participation of HGF/MET signaling in MMP development during vertebrate evolution.

The molecular and morphogenetic basis of pancreas organogenesis

The pancreas is an essential endoderm-derived organ that ensures nutrient metabolism via its endocrine and exocrine functions. Here we review the essential processes governing the embryonic and early postnatal development of the pancreas discussing both the mechanisms and molecules controlling progenitor specification, expansion and differentiation. We elaborate on how these processes are orchestrated in space and coordinated with morphogenesis. We draw mainly from experiments conducted in the mouse model but also from investigations in other model organisms, complementing a recent comprehensive review of human pancreas development (Jennings et al., 2015) [1]. The understanding of pancreas development in model organisms provides a framework to interpret how human mutations lead to neonatal diabetes and may contribute to other forms of diabetes and to guide the production of desired pancreatic cell types from pluripotent stem cells for therapeutic purposes.

ARF1 and ARF6 regulate recycling of GRASP/Tamalin and the Rac1-GEF Dock180 during HGF-induced Rac1 activation

Hepatocyte growth factor (HGF) is a potent signaling factor that acts on epithelial cells, causing them to dissociate and scatter. This migration is coordinated by a number of small GTPases, such as ARF6 and Rac1. Active ARF6 is required for HGF-stimulated migration and intracellular levels of ARF6-GTP and Rac1-GTP increase following HGF treatment. During migration, cross talk between ARF6 and Rac1 occurs through formation of a multi-protein complex containing the ARF-GEF cytohesin-2, the scaffolding protein GRASP/Tamalin, and the Rac1-GEF Dock180. Previously, the role of ARF6 in this process was unclear. We have now found that ARF6 and ARF1 regulate trafficking of GRASP and Dock180 to the plasma membrane following HGF treatment. Trafficking of GRASP and Dock180 is impaired by blocking ARF6-mediated recycling pathways and is required for HGF-stimulated Rac1 activation. Finally, HGF treatment stimulates association of GRASP and Dock180. Inhibition of ARF6 trafficking pathways traps GRASP and Dock180 as a complex in the cell.

Coordinating cardiomyocyte interactions to direct ventricular chamber morphogenesis

Many organs are composed of complex tissue walls that are structurally organized to optimize organ function. In particular, the ventricular myocardial wall of the heart is comprised of an outer compact layer that concentrically encircles the ridge-like inner trabecular layer. Although disruption in the morphogenesis of this myocardial wall can lead to various forms of congenital heart disease (CHD)¹ and non-compaction cardiomyopathies², it remains unclear how embryonic cardiomyocytes assemble to form ventricular wall layers of appropriate spatial dimensions and myocardial mass. Here, we utilize advanced genetic and imaging tools in zebrafish to reveal an interplay between myocardial Notch and Erbb2 signaling that directs the spatial allocation of myocardial cells to their proper morphologic positions in the ventricular wall. Although previous studies have shown that endocardial Notch signaling non-cell-autonomously promotes myocardial trabeculation through Erbb2 and BMP signaling³, we discover that distinct ventricular cardiomyocyte clusters exhibit myocardial Notch activity that cell-autonomously inhibits Erbb2 signaling and prevents cardiomyocyte sprouting and trabeculation. Myocardial-specific Notch inactivation leads to ventricles of reduced size and increased wall thickness due to excessive trabeculae, whereas widespread myocardial Notch activity results in ventricles of increased size with a single-cell thick wall but no trabeculae. Notably, this myocardial Notch signaling is activated non-cell-autonomously by neighboring Erbb2-activated cardiomyocytes that sprout and form nascent trabeculae. Thus, these findings support an interactive cellular feedback process that guides the assembly of cardiomyocytes to morphologically create the ventricular myocardial wall and more broadly provides insight into the cellular dynamics of how diverse cell lineages organize to create form.

An insulin signaling feedback loop regulates pancreas progenitor cell differentiation during islet development and regeneration

As one of the key nutrient sensors, insulin signaling plays an important role in integrating environmental energy cues with organism growth. In adult organisms, relative insufficiency of insulin signaling induces compensatory expansion of insulin-secreting pancreatic beta (β) cells. However, little is known about how insulin signaling feedback might influence neogenesis of β cells during embryonic development. Using genetic approaches and a unique cell transplantation system in developing zebrafish, we have uncovered a novel role for insulin signaling in the negative regulation of pancreatic progenitor cell differentiation. Blocking insulin signaling in the pancreatic progenitors hastened the expression of the essential β cell genes insulin and pdx1, and promoted β cell fate at the expense of alpha cell fate. In addition, loss of insulin signaling promoted β cell regeneration and destabilization of alpha cell character. These data indicate that insulin signaling constitutes a tunable mechanism for β cell compensatory plasticity during early development. Moreover, using a novel blastomere-to-larva transplantation strategy, we found that loss of insulin signaling in endoderm-committed blastomeres drove their differentiation into β cells. Furthermore, the extent of this differentiation was dependent on the function of the β cell mass in the host. Altogether, our results indicate that modulation of insulin signaling will be crucial for the development of β cell restoration therapies for diabetics; further clarification of the mechanisms of insulin signaling in β cell progenitors will reveal therapeutic targets for both in vivo and in vitro β cell generation.

Hepatocyte Growth Factor from a Clinical Perspective: A Pancreatic Cancer Challenge

Pancreatic cancer is the fourth leading cause of cancer-related deaths in the United States and incidence rates are rising. Both detection and treatment options for pancreatic cancer are limited, providing a less than 5% five-year survival advantage. The need for new biomarkers for early detection and treatment of pancreatic cancer demands the efficient translation of bench knowledge to provide clinical benefit. One source of therapeutic resistance is the pancreatic tumor microenvironment, which is characterized by desmoplasia and hypoxia making it less conducive to current therapies. A major factor regulating desmoplasia and subsequently promoting chemoresistance in pancreatic cancer is hepatocyte growth factor (HGF), the sole ligand for c-MET (mesenchymal-epithelial transition), an epithelial tyrosine kinase receptor. Binding of HGF to c-MET leads to receptor dimerization and autophosphorylation resulting in the activation of multiple cellular processes that support cancer progression. Inhibiting activation of c-MET in cancer cells, in combination with other approaches for reducing desmoplasia in the tumor microenvironment, might significantly improve the success of chemotherapy. Therefore, HGF makes a potent novel target for developing therapeutic strategies in combination with existing drugs for treating pancreatic adenocarcinoma. This review provides a comprehensive analysis of HGF and its promising potential as a chemotherapeutic target for pancreatic cancer.

A mutation of MET, encoding hepatocyte growth factor receptor, is associated with human DFNB97 hearing loss

BACKGROUND

Hearing loss is a heterogeneous neurosensory disorder. Mutations of 56 genes are reported to cause recessively inherited non-syndromic deafness.

OBJECTIVE

We sought to identify the genetic lesion causing hearing loss segregating in a large consanguineous Pakistani family.

METHODS AND RESULTS

Mutations of GJB2 and all other genes reported to underlie recessive deafness were ruled out as the cause of the phenotype in the affected members of the participating family. Homozygosity mapping with a dense array of one million SNP markers allowed us to map the gene for recessively inherited severe hearing loss to chromosome 7q31.2, defining a new deafness locus designated DFNB97 (maximum logarithm of the odds score of 4.8). Whole-exome sequencing revealed a novel missense mutation c.2521T>G (p.F841V) in MET (mesenchymal epithelial transition factor), which encodes the receptor for hepatocyte growth factor. The mutation cosegregated with the hearing loss phenotype in the family and was absent from 800 chromosomes of ethnically matched control individuals as well as from 136 602 chromosomes in public databases of nucleotide variants. Analyses by multiple prediction programmes indicated that p.F841V likely damages MET function.

CONCLUSIONS

We identified a missense mutation of MET, encoding the hepatocyte growth factor receptor, as a likely cause of hearing loss in humans.

c-Met signaling in the development of tumorigenesis and chemoresistance: Potential applications in pancreatic cancer

Pancreatic ductal adenocarcinoma is the 4^th leading cause of cancer deaths in the United States. The majority of patients are candidates only for palliative chemotherapy, which has proven largely ineffective in halting tumor progression. One proposed mechanism of chemoresistance involves signaling via the mesenchymal-epithelial transition factor protein (MET), a previously established pathway critical to cell proliferation and migration. Here, we review the literature to characterize the role of MET in the development of tumorigenesis, metastasis and chemoresistance, highlighting the potential of MET as a therapeutic target in pancreatic cancer. In this review, we characterize the role of c-Met in the development of tumorigenesis, metastasis and chemoresistance, highlighting the potential of c-Met as a therapeutic target in pancreatic cancer.

MET inhibitor PHA-665752 suppresses the hepatocyte growth factor-induced cell proliferation and radioresistance in nasopharyngeal carcinoma cells

Although ionizing radiation (IR) has provided considerable improvements in nasopharyngeal carcinoma (NPC), in subsets of patients, radioresistance is still a major problem in the treatment. In this study, we demonstrated that irradiation induced MET overexpression and activation, and the aberrant MET signal mediated by hepatocyte growth factor (HGF) induced radioresistance. We also found that MET inhibitor PHA-665752 effectively suppressed HGF induced cell proliferation and radioresistance in NPC cells. Further investigation indicated that PHA-665752 suppressed the phosphorylation of the Akt, ERK1/2, and STAT3 proteins in a dose-dependent manner. Our data indicated that the combination of IR with a MET inhibitor, such as PHA-665752, might be a promising therapeutic strategy for NPC.