Receptor-mediated endocytosis of keratinocyte growth factor

Multivalent protein-drug conjugates - An emerging strategy for the upgraded precision and efficiency of drug delivery to cancer cells

With almost 20 million new cases per year, cancer constitutes one of the most important challenges for public health systems. Unlike traditional chemotherapy, targeted anti-cancer strategies employ sophisticated therapeutics to precisely identify and attack cancer cells, limiting the impact of drugs on healthy cells and thereby minimizing the unwanted side effects of therapy. Protein drug conjugates (PDCs) are a rapidly growing group of targeted therapeutics, composed of a cancer-recognition factor covalently coupled to a cytotoxic drug. Several PDCs, mainly in the form of antibody-drug conjugates (ADCs) that employ monoclonal antibodies as cancer-recognition molecules, are used in the clinic and many PDCs are currently in clinical trials. Highly selective, strong and stable interaction of the PDC with the tumor marker, combined with efficient, rapid endocytosis of the receptor/PDC complex and its subsequent effective delivery to lysosomes, is critical for the efficacy of targeted cancer therapy with PDCs. However, the bivalent architecture of contemporary clinical PDCs is not optimal for tumor receptor recognition or PDCs internalization. In this review, we focus on multivalent PDCs, which represent a rapidly evolving and highly promising therapeutics that overcome most of the limitations of current bivalent PDCs, enhancing the precision and efficiency of drug delivery to cancer cells. We present an expanding set of protein scaffolds used to generate multivalent PDCs that, in addition to folding into well-defined multivalent molecular structures, enable site-specific conjugation of the cytotoxic drug to ensure PDC homogeneity. We provide an overview of the architectures of multivalent PDCs developed to date, emphasizing their efficacy in the targeted treatment of various cancers.

N-glycosylation acts as a switch for FGFR1 trafficking between the plasma membrane and nuclear envelope

Fibroblast growth factor receptor 1 (FGFR1) is a heavily N-glycosylated cell surface receptor tyrosine kinase that transmits signals across the plasma membrane, in response to fibroblast growth factors (FGFs). Balanced FGF/FGFR1 signaling is crucial for the development and homeostasis of the human body, and aberrant FGFR1 is frequently observed in various cancers. In addition to its predominant localization to the plasma membrane, FGFR1 has also been detected inside cells, mainly in the nuclear lumen, where it modulates gene expression. However, the exact mechanism of FGFR1 nuclear transport is still unknown. In this study, we generated a glycosylation-free mutant of FGFR1, FGFR1.GF, and demonstrated that it is localized primarily to the nuclear envelope. We show that reintroducing N-glycans into the D3 domain cannot redirect FGFR1 to the plasma membrane or exclude the receptor from the nuclear envelope. Reestablishment of D2 domain N-glycans largely inhibits FGFR1 accumulation in the nuclear envelope, but the receptor continues to accumulate inside the cell, mainly in the ER. Only the simultaneous presence of N-glycans of the D2 and D3 domains of FGFR1 promotes efficient transport of FGFR1 to the plasma membrane. We demonstrate that while disturbed FGFR1 folding results in partial FGFR1 accumulation in the ER, impaired FGFR1 secretion drives FGFR1 trafficking to the nuclear envelope. Intracellular FGFR1.GF displays a high level of autoactivation, suggesting the presence of nuclear FGFR1 signaling, which is independent of FGF. Using mass spectrometry and proximity ligation assay, we identified novel binding partners of the nuclear envelope-localized FGFR1, providing insights into its cellular functions. Collectively, our data define N-glycosylation of FGFR1 as an important regulator of FGFR1 kinase activity and, most importantly, as a switchable signal for FGFR1 trafficking between the nuclear envelope and plasma membrane, which, due to spatial restrictions, shapes FGFR1 interactome and cellular function. Video Abstract.

Keratinocyte Growth Factor-based Strategies for Wound Re-epithelialization

Wound re-epithelialization is a dynamic process that comprises the formation of new epithelium through an active signaling network between several growth factors and various cell types. The main players are keratinocytes that migrate from the wound edges onto the wound bed, to restore the epidermal barrier. One of the most important molecules involved in the re-epithelialization process is Keratinocyte Growth Factor (KGF), since it is central on promoting both migration and proliferation of keratinocytes. Stromal cells, like dermal fibroblasts, are the main producers of this factor, acting on keratinocytes through paracrine signaling. Multiple therapeutic strategies to delivery KGF have been proposed in order to boost wound healing by targeting re-epithelialization. This has been achieved through a range of different approaches, such as topical application, using controlled release-based methods with different biomaterials (hydrogels, nanoparticles and membranes) and also through gene therapy techniques. Among these strategies, KGF delivery via biomaterials and genetic-based strategies show great effectiveness in sustained KGF levels at the wound site, leading to efficient wound closure. Under this scope, this review aims at highlighting the importance of KGF as one of the key molecules on wound re-epithelialization, as well as to provide a critical overview of the different potential therapeutic strategies exploited so far.

Negative Regulation of FGFR (Fibroblast Growth Factor Receptor) Signaling

FGFR (fibroblast growth factor receptor) signaling controls fundamental processes in embryonic, fetal and adult human life. The magnitude, duration, and location of FGFR signaling must be strictly controlled in order to induce the correct biological response. Uncontrolled receptor signaling has been shown to lead to a variety of diseases, such as skeletal disorders and cancer. Here we review the numerous cellular mechanisms that regulate and turn off FGFR signaling, once the receptor is activated. These mechanisms include endocytosis and endocytic sorting, phosphatase activity, negative regulatory proteins and negative feedback phosphorylation events. The mechanisms act together simultaneously or sequentially, controlling the same or different steps in FGFR signaling. Although more work is needed to fully understand the regulation of FGFR signaling, it is clear that the cells in our body have evolved an extensive repertoire of mechanisms that together keep FGFR signaling tightly controlled and prevent excess FGFR signaling.

Sulfated syndecan 1 is critical to preventing cellular senescence by modulating fibroblast growth factor receptor endocytosis

Cellular senescence can be triggered by various intrinsic and extrinsic stimuli. We previously reported that silencing of 3'-phosphoadenosine 5'-phosphosulfate synthetase 2 (PAPSS2) induces cellular senescence through augmented fibroblast growth factor receptor 1 (FGFR1) signaling. However, the exact molecular mechanism connecting heparan sulfation and cellular senescence remains unclear. Here, we investigated the potential involvement of heparan sulfate proteoglycans (HSPGs) in augmented FGFR1 signaling and cellular senescence. Depletion of several types of HSPGs revealed that cells depleted of syndecan 1 (SDC1) exhibited typical senescence phenotypes, and those depleted of PAPSS2-, SDC1-, or heparan sulfate 2-O sulfotransferase 1 (HS2ST1) showed decreased FGFR1 internalization along with hyperresponsiveness to and prolonged activation of fibroblast growth factor 2 (FGF2)-stimulated FGFR1- v-akt murine thymoma viral oncogene homolog (AKT) signaling. Clathrin- and caveolin-mediated FGFR1 endocytosis contributed to cellular senescence through the FGFR1-AKT-p53-p21 signaling pathway. Dynasore treatment triggered senescence phenotypes, augmented FGFR1-AKT-p53-p21 signaling, and decreased SDC1 expression. Finally, the replicatively and prematurely senescent cells were characterized by decreases of SDC1 expression and FGFR1 internalization, and an increase in FGFR1-AKT-p53-p21 signaling. Together, our results demonstrate that properly sulfated SDC1 plays a critical role in preventing cellular senescence through the regulation of FGFR1 endocytosis.

Targeting Cellular Trafficking of Fibroblast Growth Factor Receptors as a Strategy for Selective Cancer Treatment

Fibroblast growth factor receptors (FGFRs) in response to fibroblast growth factors (FGFs) transmit signals across the cell membrane, regulating important cellular processes, like differentiation, division, motility, and death. The aberrant activity of FGFRs is often observed in various diseases, especially in cancer. The uncontrolled FGFRs' function may result from their overproduction, activating mutations, or generation of FGFRs' fusion proteins. Besides their typical subcellular localization on the cell surface, FGFRs are often found inside the cells, in the nucleus and mitochondria. The intracellular pool of FGFRs utilizes different mechanisms to facilitate cancer cell survival and expansion. In this review, we summarize the current stage of knowledge about the role of FGFRs in oncogenic processes. We focused on the mechanisms of FGFRs' cellular trafficking-internalization, nuclear translocation, and mitochondrial targeting, as well as their role in carcinogenesis. The subcellular sorting of FGFRs constitutes an attractive target for anti-cancer therapies. The blocking of FGFRs' nuclear and mitochondrial translocation can lead to the inhibition of cancer invasion. Moreover, the endocytosis of FGFRs can serve as a tool for the efficient and highly selective delivery of drugs into cancer cells overproducing these receptors. Here, we provide up to date examples how the cellular sorting of FGFRs can be hijacked for selective cancer treatment.

Upregulation of VEGFR1 in a rat model of esophagogastric anastomotic healing

INTRODUCTION

Anastomotic leakage after gastrointestinal surgery is a significant cause of morbidity and mortality. Esophagogastric and colorectal anastomoses are vulnerable to leakage. Extended knowledge of growth factors and their receptors is needed to understand anatomic healing.

METHODS

The expression pattern of vascular growth factor receptor (VEGFR1-3), epidermal growth factor receptor (EGFR), platelet-derived growth factor receptor (PDGFRα/β) and keratinocyte growth factor receptor (KGFR) were analyzed by semiquantitative-PCR in the rat intestinal tract and in esophagogastric anastomosis 5d after surgery.

RESULTS

VEGFR1, VEGFR2, EGFR, KGFR and PDGFRα expression was observed throughout the intestinal tract including esophagus, stomach, small bowl and colon. VEGFR3 was not found in gastric samples and PDGFRβ expression was not detected in the small bowl. Semiquantitative analyses of the VEGFR1, PDGFRα and EGFR expression in esophagogastric anastomotic tissues revealed a 2-fold upregulation of the VEGFR1 in gastric samples, while no change was observed in the esophageal anastomotic side.

CONCLUSION

Our results revealed a distinct expression pattern of the investigated growth factor receptors in rat intestinal tract. Showing higher expression levels of growth factor receptors at the gastric anastomotic tissue at the fifth postoperative day suggests a different contribution of the gastric and the esophageal side to the anastomotic healing.

Retinol encapsulated into amorphous Ca(2+) polyphosphate nanospheres acts synergistically in MC3T3-E1 cells

Both the quality and quantity of collagen, the major structural component of the skin, decrease in aging skin. We succeeded to encapsulate retinol into amorphous inorganic polyphosphate (polyP) nanoparticles together with calcium ions ("aCa-polyP-NP"), under formation of amorphous Ca-polyP/retinol nanospheres ("retinol/aCa-polyP-NS"). The globular nanospheres are not cytotoxic, show an almost uniform size of ≈ 45 nm and have a retinol content of around 25%. Both components of those nanospheres, retinol and the aCa-polyP-NP, if administered together, caused a strong increase in proliferation of mouse calvaria MC3T3 cells. The expressions of collagen types I, II and III genes, but not the expression of collagen type V gene, were significantly enhanced if retinol is added together with aCa-polyP-NP. This synergistic effect was especially pronounced for the expression of the collagen type III gene. We propose that the synergistic effect of the retinol/aCa-polyP-NS on cell growth and collagen type III expression is induced via two routes, first through cellular uptake of the 45 nm nanospheres by clathrin-mediated endocytosis and second through extracellular disintegration of the nanospheres resulting in the release of retinol which is then taken up into the cells after binding to the retinal binding protein receptor.

Interaction between Nm23 and the tumor suppressor VHL

Among the anti-tumor genes (tumor suppressors and metastasis suppressors), the von-Hippel Lindau gene and the Nm23 family of genes are among the more intriguing ones. Both are small (long and short forms of VHL are 30 and 19 kD, respectively, and Nm23 is ~17 kD), and both possess diverse molecular and cellular functions. Despite extensive studies, the entire spectra of functions and the molecular function-phenotype correlation of these two proteins have not been completely elucidated. In this report, we present data showing these two proteins interact physically. We also summarize and confirm the previous studies that demonstrated the endocytic function of these two genes and further show that the endocytic function of VHL is mediated through the activity of Nm23. These functional and molecular interactions are evolutionarily conserved from Drosophila to human.

Endocytosis of Fgf8 is a double-stage process and regulates spreading and signaling

Tightly controlled concentration gradients of morphogens provide positional information and thus regulate tissue differentiation and morphogenesis in multicellular organisms. However, how such morphogenetic fields are formed and maintained remains debated. Here we show that fibroblast growth factor 8 (Fgf8) morphogen gradients in zebrafish embryos are established and maintained by two essential mechanisms. Firstly, Fgf8 is taken up into the cell by clathrin-mediated endocytosis. The speed of the uptake rate defines the range of the morphogenetic gradient of Fgf8. Secondly, our data demonstrate that after endocytosis the routing of Fgf8 from the early endosome to the late endosome shuts down signaling. Therefore, intracellular endocytic transport regulates the intensity and duration of Fgf8 signaling. We show that internalization of Fgf8 into the early endosome and subsequent transport towards the late endosome are two independent processes. Therefore, we hypothesize that Fgf8 receiving cells control both, the propagation width and the signal strength of the morphogen.

Regulation of fibroblast growth factor receptor signalling and trafficking by Src and Eps8

Fibroblast growth factor receptors (FGFRs) mediate a wide spectrum of cellular responses that are crucial for development and wound healing. However, aberrant FGFR activity leads to cancer. Activated growth factor receptors undergo stimulated endocytosis, but can continue to signal along the endocytic pathway. Endocytic trafficking controls the duration and intensity of signalling, and growth factor receptor signalling can lead to modifications of trafficking pathways. We have developed live-cell imaging methods for studying FGFR dynamics to investigate mechanisms that coordinate the interplay between receptor trafficking and signal transduction. Activated FGFR enters the cell following recruitment to pre-formed clathrin-coated pits (CCPs). However, FGFR activation stimulates clathrin-mediated endocytosis; FGF treatment increases the number of CCPs, including those undergoing endocytosis, and this effect is mediated by Src and its phosphorylation target Eps8. Eps8 interacts with the clathrin-mediated endocytosis machinery and depletion of Eps8 inhibits FGFR trafficking and immediate Erk signalling. Once internalized, FGFR passes through peripheral early endosomes en route to recycling and degredative compartments, through an Src- and Eps8-dependent mechanism. Thus Eps8 functions as a key coordinator in the interplay between FGFR signalling and trafficking. This work provides the first detailed mechanistic analysis of growth factor receptor clustering at the cell surface through signal transduction and endocytic trafficking. As we have characterised the Src target Eps8 as a key regulator of FGFR signalling and trafficking, and identified the early endocytic system as the site of Eps8-mediated effects, this work provides novel mechanistic insight into the reciprocal regulation of growth factor receptor signalling and trafficking.

Polarized endocytosis of the keratinocyte growth factor receptor in migrating cells: role of SRC-signaling and cortactin

Cell migration is a physiological process that requires endocytic trafficking and polarization of adhesion molecules and receptor tyrosine kinases (RTKs) to the leading edge. Many growth factors are able to induce motility by binding to specific RTK on target cells. Among them, keratinocyte growth factor (KGF or FGF7) and fibroblast growth factor 10 (FGF10), members of the FGF family, are motogenic for keratinocytes, and exert their action by binding to the keratinocyte growth factor receptor (KGFR), a splicing variant of FGFR2, exclusively expressed on epithelial cells. Here we analyzed the possible role of cortactin, an F-actin binding protein which is tyrosine phosphorylated by Src and is involved in KGFR-mediated cell migration, in the KGFR endocytosis and polarization to the leading edge of migrating cells upon ligand-induced stimulation. Biochemical phosphorylation study revealed that both KGF and FGF10 were able to induce tyrosine phosphorylation of Src and in turn of cortactin, as demonstrated by using the specific pharmacological Src-inhibitor SU6656, although FGF10 effect was delayed with respect to that promoted by KGF. Immunofluorescence analysis demonstrated the polarized localization of KGFR upon ligand stimulation to the leading edge of migrating keratinocytes, process that was regulated by Src. Moreover, we showed that the colocalization of cortactin with KGFR at the plasma membrane protrusions and on early endosomes after KGF and FGF10 treatment was Src-dependent. Further, by using a RNA interference approach through microinjection, we showed that cortactin is required for KGFR endocytosis and that the clathrin-dependent internalization of the receptor is a critical event for its polarization. Finally, KGFR expression and polarization enhanced cell migration in a scratch assay. Our results indicate that both Src and cortactin play a key role in the KGFR endocytosis and polarization at the leading edge of migrating keratinocytes, supporting the crucial involvement of RTK trafficking in cell motility.

Clathrin- and dynamin-independent endocytosis of FGFR3--implications for signalling

Endocytosis of tyrosine kinase receptors can influence both the duration and the specificity of the signal emitted. We have investigated the mechanisms of internalization of fibroblast growth factor receptor 3 (FGFR3) and compared it to that of FGFR1 which is internalized predominantly through clathrin-mediated endocytosis. Interestingly, we observed that FGFR3 was internalized at a slower rate than FGFR1 indicating that it may use a different endocytic mechanism than FGFR1. Indeed, after depletion of cells for clathrin, internalization of FGFR3 was only partly inhibited while endocytosis of FGFR1 was almost completely abolished. Similarly, expression of dominant negative mutants of dynamin resulted in partial inhibition of the endocytosis of FGFR3 whereas internalization of FGFR1 was blocked. Interfering with proposed regulators of clathrin-independent endocytosis such as Arf6, flotillin 1 and 2 and Cdc42 did not affect the endocytosis of FGFR1 or FGFR3. Furthermore, depletion of clathrin decreased the degradation of FGFR1 resulting in sustained signalling. In the case of FGFR3, both the degradation and the signalling were only slightly affected by clathrin depletion. The data indicate that clathrin-mediated endocytosis is required for efficient internalization and downregulation of FGFR1 while FGFR3, however, is internalized by both clathrin-dependent and clathrin-independent mechanisms.

Inhibition of fibroblast growth factor receptor 1 endocytosis promotes axonal branching of adult sensory neurons

Fibroblast growth factors (FGFs) promote axon growth during development and regeneration of the nervous system. Among the four types of FGF receptors (FGFRs), FGFR1 is expressed in adult sensory neurons of dorsal root ganglia (DRG), and overexpression of FGFR1 promotes FGF-2-induced elongative axon growth in vitro. Ligand-induced activation of FGFR1 is followed by endocytosis and lysosomal degradation, which leads to the termination of receptor signaling. We previously reported that the lysosomal inhibitor leupeptin enhances FGF-2-induced elongative axon growth of adult DRG neurons overexpressing FGFR1. To better understand the role of subcellular localization of FGFR1 in axon growth, we analyzed the effects of inhibition of endocytosis of FGFR1 on FGF-2-induced neurite outgrowth in PC12 pheochromocytoma cells and adult DRG neurons. The endocytosis inhibitors methyl-β-cyclodextrin (MβCD) and chlorpromazine enhanced surface localization of FGFR1 in PC12 cells and DRG neurons. Furthermore, MβCD and chlorpromazine increased FGF-2-induced neurite outgrowth of PC12 cells and axonal branching of adult DRG neurons overexpressing FGFR1, whereas MβCD inhibited FGF-2-induced axonal elongation. Analysis of the signaling pathways involved in axon morphology revealed that FGF-2-induced phosphorylation of extracellular signal-regulated kinase (ERK) and Akt was increased by inhibition of FGFR1 endocytosis. Together, our results imply that inhibition of FGFR1 endocytosis by MβCD or chlorpromazine promotes FGF-2-induced axonal branching. The results of this study confirm that internalization of FGFR1 controls axon growth and morphology of adult sensory neurons via selective activation of intracellular signaling pathways.

Expression and signaling of the tyrosine kinase FGFR2b/KGFR regulates phagocytosis and melanosome uptake in human keratinocytes

Membrane and actin cytoskeleton dynamics during phagocytosis can be triggered and amplified by the signal transduction of receptor tyrosine kinases. The epidermal keratinocytes appear to use the phagocytic mechanism of uptake to ingest melanosomes released by the melanocytes and play a pivotal role in the transfer process. We have previously demonstrated that the keratinocyte growth factor KGF/FGF7 promotes the melanosome uptake through activation of its receptor tyrosine kinase FGFR2b/KGFR. The aim of the present study was to investigate the contribution of KGFR expression, activation, and signaling in regulating the phagocytic process and the melanosome transfer. Phagocytosis was analyzed in vitro using fluorescent latex beads on human keratinocytes induced to differentiate. Melanosome transfer was investigated in keratinocyte-melanocyte cocultures. KGFR depletion by small interfering RNA microinjection and overexpression by transfection of wild type or defective mutant KGFR were performed to demonstrate the direct effect of the receptor on phagocytosis and melanosome transfer. Colocalization of the phagocytosed beads with the internalized receptors in phagolysosomes was analyzed by optical sectioning and 3-dimensional reconstruction. KGFR ligands triggered phagocytosis and melanosome transfer in differentiated keratinocytes, and receptor kinase activity and signaling were required for these effects, suggesting that FGFR2b/KGFR expression/activity and PLCγ signaling pathway play crucial roles in phagocytosis.

Ubiquitination of fibroblast growth factor receptor 1 is required for its intracellular sorting but not for its endocytosis

Endocytosis and targeting of growth factor receptors for lysosomal degradation have been associated with ubiquitination of the intracellular part of the receptors. To elucidate the role of receptor ubiquitination in internalization and sorting of fibroblast growth factor receptor (FGFR), we constructed several mutants of FGFR1 in which lysines, potential ubiquitination sites, were substituted for arginines. Substitution of all lysine residues in the intracellular part of FGFR1 resulted in inactivation of the tyrosine kinase domain of the receptor. However, several multilysine FGFR1 mutants, where up to 26 of 29 lysines in the intracellular part of the receptor were mutated, retained tyrosine kinase activity. The active multilysine mutants were poorly ubiquitinated, but internalized normally, indicating that ubiquitination of the receptor is not required for endocytosis. In contrast, degradation of the multilysine mutants was dramatically reduced as the mutants were inefficiently transported to lysosomes but rather sorted to recycling endosomes. The altered sorting resulted in sustained signaling. The duration of FGFR1 signaling seems to be tightly regulated by receptor ubiquitination and subsequent sorting to the lysosomes for degradation.

Translocation of fibroblast growth factor-10 and its receptor into nuclei of human urothelial cells

Fibroblast growth factor-10 (FGF-10), a mitogen for the epithelial cells lining the lower urinary tract, has been identified inside urothelial cells, despite its acknowledged role as an extracellular signaling ligand. Recombinant (r)FGF-10 was determined by fluorescence microscopy optical sectioning to localize strongly to nuclei inside cultured urothelial cells. To clarify the possible role of a nuclear localization signal (NLS) in this translocation, a variant of rFGF-10 was constructed which lacked this sequence. rFGF-10(no NLS) was found in cytoplasm to a far greater degree than rFGF-10, identifying this motif as a possible NLS. Furthermore, this variant displayed poor or non-existent bioactivity compared to the wild-type protein in triggering mitogenesis in quiescent urothelial cells. The presence of rFGF-10(no NLS) in the nucleus suggested that additional interactions were also responsible for the nuclear accumulation of rFGF-10. The FGF-10 receptor was observed in cell nuclei regardless of the presence or concentration of exogenous rFGF-10 ligand. Co-localization studies between rFGF-10 and the FGF-10 receptor revealed a strong intracellular relationship between the two. This co-localization was seen in nuclei for both rFGF-10 and for rFGF-10(no NLS), although the correlation was weaker for rFGF-10(no NLS). These data show that an NLS-like motif of rFGF-10 is a partial determinant of its intracellular distribution and is necessary for its mitogenic activity. These advancements in the understanding of the activity of FGF-10 present an opportunity to engineer the growth factor as a therapeutic agent for the healing of damaged urothelial tissue.

Keratinocyte growth factor receptor ligands target the receptor to different intracellular pathways

The keratinocyte growth factor receptor (KGFR)/fibroblast growth factor receptor 2b is activated by high-affinity-specific interaction with two different ligands, keratinocyte growth factor (KGF)/fibroblast growth factor (FGF)7 and FGF10/KGF2, which are characterized by an opposite requirement of heparan sulfate proteoglycans and heparin for binding to the receptor. We investigated here the possible different endocytic trafficking of KGFR, induced by the two ligands. Immunofluorescence and immunoelectron microscopy analysis showed that KGFR internalization triggered by either KGF or FGF10 occurs through clathrin-coated pits. Immunofluorescence confocal microscopy using endocytic markers as well as tumor susceptibility gene 101 (TSG101) silencing demonstrated that KGF drives KGFR to the degradative pathway, while FGF10 targets the receptor to the recycling endosomes. Biochemical analysis showed that KGFR is ubiquitinated and degraded after KGF treatment but not after FGF10 treatment, and that the alternative fate of KGFR might depend on the different ability of the receptor to phosphorylate the fibroblast growth factor receptor substrate 2 (FRS2) substrate and to recruit the ubiquitin ligase c-Cbl. The recycling endocytic pathway followed by KGFR upon FGF10 stimulation correlates with the higher mitogenic activity exerted by this ligand on epithelial cells compared with KGF, suggesting that the two ligands may play different functional roles through the regulation of the receptor endocytic transport.

Differential regulated expression of keratinocyte growth factor and its receptor in experimental and human liver fibrosis

BACKGROUND AND AIM

Immunomodulatory and protective properties have been identified for the keratinocyte growth factor (KGF). For hepatocytes, pro-proliferative and anti-apoptotic effects of this growth factor have been reported in vitro. This study was designed to characterize a putative role of KGF in observed histomorphological changes in both, human and experimental liver fibrosis.

METHODS

Liver fibrosis and cirrhosis was induced in rats by repetitive exposure to phenobarbitone and increasing doses of carbon tetrachloride. Human samples were obtained from patients undergoing surgery for partial hepatectomy or transplantation. Organ samples were scored for inflammation and morphological changes. Expression of KGF and its receptor (KGFR) mRNA was quantified by real-time RT-PCR. Protein expression and receptor phosphorylation was determined by Western blot analysis. In-situ hybridization and immunohistochemistry were utilized to determine distribution of KGF and KGFR in the liver.

RESULTS

Expression of KGF was significantly increased in damaged liver tissue in correlation to the degree of fibrosis, whereas expression of the receptor was up-regulated in early stages of liver fibrosis and down-regulated in cirrhotic organs. Protein expression of this growth factor and its receptor correlated with the alterations in mRNA. KGF expression was restricted to mesenchymal cells, whereas expression of KGFR was detected on hepatocytes only.

CONCLUSION

The expression of KGF and KGFR is differentially and significantly regulated in damaged liver tissue. This growth factor might therefore not only contribute to morphological alterations but also regeneration of liver parenchyma most likely mediated by indirect mechanisms of action.

Expression and function of fibroblast growth factor 10 and its receptor, fibroblast growth factor receptor 2B, in bovine follicles

Some fibroblast growth factors (FGFs) affect ovarian follicle cell growth and/or differentiation. Whereas many FGFs activate several FGF receptors, FGF7 and FGF10 primarily activate only one, FGFR2B. As FGF7 is produced by bovine theca cells and acts on granulosa cells, we tested the hypothesis that FGF10 may also play a role in folliculogenesis in cattle. Reverse transcription-polymerase chain reaction demonstrated the presence of FGF10 mRNA in the oocytes and theca cells of the antral follicles, as well as in the preantral follicles. FGF10 protein was detected by immunohistochemistry in the oocytes of the preantral and antral follicles, and in the granulosa and theca cells of the antral follicles. FGF10 expression in theca cells changed during follicle development; mRNA abundance decreased with increasing follicular estradiol concentration in healthy follicles, and was lowest in highly atretic follicles. Culturing of granulosa cells in serum-free medium revealed FSH regulation of FGF10 receptor expression. The addition of FGF10 to cultured granulosa cells decreased the level of estradiol but did not alter cell proliferation. These data support a role for FGF10 in signaling to granulosa cells from theca cells and/or the oocyte.

Endocytic pathways and biological effects induced by UVB‐dependent or ligand‐dependent activation of the keratinocyte growth factor receptor

UVB exposure of epidermal cells is known to trigger early and late molecular pathways dependent on receptor tyrosine kinases and reactive oxygen species (ROS). We have recently reported that UVB irradiation induces tyrosine phosphorylation, kinase activation, and internalization of the receptor for the keratinocyte growth factor (KGFR), a paracrine mediator of epithelial growth, differentiation, and survival. Here we analyzed in more detail the UVB-induced endocytic pathway of KGFR and the role of KGFR activation and internalization in regulating UVB-promoted apoptosis and cell cycle arrest. Immunogold electron microscopy and confocal analysis revealed that the UVB-induced endocytosis of KGFR occurs through clathrin-coated pits and that the internalized receptors are sorted to the degradative route and reach the lysosomal compartment with a timing similar to that induced by their ligand KGF. Treatment with the anti-oxidant N-acetylcysteine inhibited KGFR endocytosis, suggesting that the receptor internalization is mediated by the intracellular production of ROS. The ligand-independent KGFR endocytic pathway induced by UVB requires receptor kinase activity and tyrosine phosphorylation and involves transient receptor ubiquitination. Inhibition of KGFR activity reduces both the KGF-mediated proliferative response and the UVB-promoted apoptotic cell death, indicating a different effect of ligand-induced and UVB-induced KGFR triggering. In addition, receptor internalization leads to protection from apoptosis caused by UVB exposure. Finally, we compared directly the behavior of KGFR with that of the epidermal growth factor receptor (EGFR) upon UVB exposure. Surprisingly, biochemical and immunofluorescence analysis showed that EGFR, differently from KGFR, does not undergo UVB-induced tyrosine phosphorylation and internalization. Taken together, our results suggest a differential role of KGFR and EGFR in the response of epidermal cells to UVB possibly because KGFR endocytosis could be crucial for attenuation of survival signals in the suprabasal layers of human skin.

Expression of keratinocyte growth factor and its receptor in adaptive changes of ileorectal pouch mucosa

OBJECTIVE

Total proctocolectomy with formation of an ileo-anal pouch is a well-established surgical procedure for patients with ulcerative colitis (UC) or familiar adenomatous polyposis (FAP). The pouch mucosa undergoes adaptive changes, with inflammation of the ileal reservoir being the most common complication. The aetiology is unknown. The keratinocyte growth factor (KGF) has not only been shown to promote intestinal wound healing and re-epithelialization but also to have some immunomodulatory properties. This study was designed to investigate a putative involvement of KGF in observed histomorphological changes in the pouch mucosa.

MATERIALS AND METHODS

Multiple biopsies were obtained from age-matched and sex-matched patients. Biopsies were stained with H&E and scored for inflammation and morphological changes. mRNA expression levels of KGF and KGF-receptor (KGFR) were determined using competitive RT-PCR, protein expression and phosphorylation was analyzed by Western blotting. KGF and KGFR were localized in tissue samples by immunohistochemistry.

RESULTS

Expression of KGF and KGFR was significantly increased in inflamed and adapting mucosa. Patterns of expression did not significantly differ in pouch mucosa from UC or FAP patients. Protein expression correlated with the mRNA results and KGFR was shown to be activated in adapting pouch mucosa. KGF was detected on subepithelial cells, mainly on fibroblasts, whereas expression of KGFR was restricted to epithelial cells.

CONCLUSION

Expression of KGF and KGFR is significantly increased in the pouch mucosa, suggesting an involvement of this growth factor in tissue repair and adaptive changes. Topical application of KGF might alleviate the inflammatory and promote the adaptive process in the ileo-anal pouch mucosa.

Different intracellular trafficking of FGF1 endocytosed by the four homologous FGF receptors

Many growth factors and cytokines bind to more than one receptor, but in many cases the different roles of the separate receptors in signal transduction are unclear. Intracellular sorting of ligand-receptor complexes may modulate the signalling, and we have here studied the intracellular trafficking of ligand bound to receptors for fibroblast growth factors (FGFs). For this purpose, we transfected HeLa cells with any one of the four tyrosine kinase FGF receptors (FGFR1-4). In cells expressing any one of these receptors, externally added FGF1 was localized to sorting/early endosomes after 15 minutes at 37 degrees C. After longer incubation times, FGF1 internalized in cells expressing FGFR1 was localized mainly to late endosomes/lysosomes, similarly to EGF. By contrast, FGF1 internalized in cells expressing FGFR4 followed largely the same intracellular pathway as the recycling ligand, transferrin. In cells expressing FGFR2 or FGFR3, sorting of FGF1 to lysosomes was somewhat less efficient than that observed for FGFR1. Furthermore, FGF1 was more slowly degraded in cells expressing FGFR4 than in cells expressing FGFR1-3 and in addition, internalized FGFR4 as such was more slowly degraded than the other receptors. The data indicate that after endocytosis, FGFR4 and its bound ligand are sorted mainly to the recycling compartment, whereas FGFR1-3 with ligand are sorted mainly to degradation in the lysosomes. Alignment of the amino acid sequence of the intracellular part of the four FGFRs revealed several lysines conserved in FGFR1-3 but absent in FGFR4. Lysines are potential ubiquitylation sites and could thus target a receptor to lysosomes for degradation. Indeed, we found that FGFR4 is less ubiquitylated than FGFR1, which could be the reason for the different sorting of the receptors.

Raised keratinocyte growth factor-1 expression in oral submucous fibrosis in vivo and upregulated by arecoline in human buccal mucosal fibroblasts in vitro

BACKGROUND

Keratinocyte growth factor-1 (KGF-1) is the seventh member of the fibroblast growth factor family. KGF-1 is produced by mesenchymal cells such as fibroblasts and upregulated in a variety of hyperplastic tissues. Currently, there is limited information about the regulation of KGF-1 expression in areca quid-associated oral submucous fibrosis (OSF). The aim of the study was to compare KGF-1 expression in normal human buccal mucosa and OSF specimens and further to explore the potential mechanism that may lead to induce KGF-1 expression.

METHODS

The expression of KGF-1 from fibroblasts cultured from OSF and normal buccal mucosa were using reverse-transcriptase polymerase chain reaction and enzyme-linked immunosorbent assay. In addition, arecoline, a major areca nut alkaloid, was challenged to normal buccal mucosa fibroblasts (BMFs) to elucidate whether KGF-1 expression could affect by arecoline. Furthermore, 25 OSF specimens and six normal buccal mucosa specimens were examined by immunohistochemistry.

RESULTS

Fibroblasts derived from OSF were found to exhibit higher KGF-1 expression than BMFs both in mRNA and protein levels (P < 0.05). In addition, upregulation of KGF-1 mRNA gene and protein expression were found in BMFs stimulated by arecoline (P < 0.05). From the results of immunohistochemistry, KGF-1 expression was significantly higher in OSF specimens and expressed mainly by fibroblasts, endothelial cells, inflammatory cells, and epithelial cells.

CONCLUSIONS

Taken together, these results suggest that KGF-1 expression is significantly upregulated in OSF tissues from areca quid chewers and arecoline may be responsible for the enhanced KGF-1 expression in vivo.

Prostaglandins differently regulate FGF-2 and FGF receptor expression and induce nuclear translocation in osteoblasts via MAPK kinase

We have previously reported that prostaglandin F(2alpha) (PGF(2alpha)) and its selective agonist fluprostenol increase basic fibroblast growth factor (FGF-2) mRNA and protein production in osteoblastic Py1a cells. The present report extends our previous studies by showing that Py1a cells express FGF receptor-2 (FGFR2) and that treatment with PGF(2alpha) or fluprostenol decreases FGFR2 mRNA. We have used confocal and electron microscopy to show that, under PGF(2alpha) stimulation, FGF-2 and FGFR2 proteins accumulate near the nuclear envelope and colocalize in the nucleus of Py1a cells. Pre-treatment with cycloheximide blocks nuclear labelling for FGF-2 in response to PGF(2alpha). Treatment with SU5402 does not block prostaglandin-mediated nuclear internalization of FGF-2 or FGFR2. Various effectors have been used to investigate the signal transduction pathway. In particular, pre-treatment with phorbol 12-myristate 13-acetate (PMA) prevents the nuclear accumulation of FGF-2 and FGFR2 in response to PGF(2alpha). Similar results are obtained by pre-treatment with the protein kinase C (PKC) inhibitor H-7. In addition, cells treated with PGF(2alpha) exhibit increased nuclear labelling for the mitogen-activated protein kinase (MAPK), p44/ERK2. Pre-treatment with PMA blocks prostaglandin-induced ERK2 nuclear labelling, as confirmed by Western blot analysis. We conclude that PGF(2alpha) stimulates nuclear translocation of FGF-2 and FGFR2 by a PKC-dependent pathway; we also suggest an involvement of MAPK/ERK2 in this process.

Differential response to keratinocyte growth factor receptor and epidermal growth factor receptor ligands of proliferating and differentiating intestinal epithelial cells

The expression of the keratinocyte growth factor receptor (KGFR) has been analyzed on intestinal epithelial Caco-2 cells upon confluence-induced spontaneous differentiation. Western blot and immunofluorescence analysis showed that the expression of functional KGFRs, differently from that of epidermal growth factor receptor (EGFR), was up-modulated in post-confluent differentiated cultures compared with the pre-confluent cells. Confocal microscopy and immunoelectron microscopy revealed that the up-regulated KGFRs displayed a basolateral polarized distribution on the cell surfaces in the monolayer. In vivo immunohistochemical analysis on normal human colon tissue sections showed that KGFRs, differently from EGFRs, were mostly distributed on the more differentiated cells located on the upper portion of the intestinal crypt. Bromodeoxyuridine incorporation assay and Ki67 labeling indicated that the differentiated cells were able to proliferate in response to the two ligands of KGFR, KGF and FGF-10, whereas they were not stimulated by the EGFR ligands TGFalpha and EGF. Western blot and quantitative immunofluorescence analysis of the expression of carcinoembryonic antigen (CEA) in post-confluent cells revealed that incubation with KGF induced an increase of cell differentiation. Taken together these results indicate that up-modulation of KGFR may be required to promote proliferation and differentiation in differentiating cells and that, among the cells componing the intestinal epithelial monolayer, the target cells for KGFR ligands appear to be different during differentiation from those responsive to EGFR ligands.

Uptake and trafficking of DNA in keratinocytes: evidence for DNA-binding proteins

The skin is an interesting organ for human gene therapy due to accessibility, immunologic potential and synthesis capabilities. In this study, we attempted to visualize and measure the uptake of naked FITC-labeled plasmid by FACS analysis detecting up to 15% internalization in a dose- and time-dependent manner. Cycloheximide treatment inhibited the uptake by >90%, suggesting a protein-mediated uptake. The inhibition of different internalization pathways demonstrated that blocking macropinocytosis (by amiloride and N,N-dimethylamylorid) reduced DNA uptake by >85%, while the inhibition of clathrin-coated pits (by chlorpromazine) and caveolae (by nystatin/filipin III) did not limit the uptake. Colocalization studies using confocal laser microscopy revealed a time-dependent accumulation of plasmid DNA in endosomes and lysosomes. When a green fluorescent protein (GFP) expression vector was used, specific GFP-RNA became detectable by reverse transcriptase-PCR, whereas measurable amounts of protein could not be identified in FACS experiments. To detect the potential DNA receptors on the keratinocyte surface, membrane proteins were extracted and subjected to South-Western blotting using digoxigenin-labeled calf thymus and lambda-phage DNA. Two DNA-binding proteins, ezrin and moesin, known as plasma membrane-actin linkers, were identified by one- and two-dimensional-South-Western blots and matrix-assisted laser desorption and ionization-mass spectrometry. Ezrin and moesin are functionally associated with a number of transmembrane receptors such as the EGF, CD44 or ICAM-1 receptor. Taken together, naked plasmid DNA seems to enter human keratinocytes through different pathways, mainly by macropinocytosis. Two DNA-binding proteins were identified that seemed to be involved in binding/trafficking of internalized DNA.

Signaling, internalization, and intracellular activity of fibroblast growth factor

The fibroblast growth factor (FGF) family contains 23 members in mammals including its prototype members FGF-1 and FGF-2. FGFs have been implicated in regulation of many key cellular responses involved in developmental and physiological processes. These includes proliferation, differentiation, migration, apoptosis, angiogenesis, and wound healing. FGFs bind to five related, specific cell surface receptors (FGFRs). Four of these have intrinsic tyrosine kinase activity. Dimerization of the receptor is a prerequisite for receptor transphosphorylation and activation of downstream signaling molecules. All members of the FGF family have a high affinity for heparin and for cell surface heparan sulfate proteoglycans, which participate in formation of stable and active FGF-FGFR complexes. FGF-mediated signaling is an evolutionarily conserved signaling module operative in invertebrates and vertebrates. It seems that some members of the family have a dual mode of action. FGF-1, FGF-2, FGF-3, and FGF-11-14 have been found intranuclearly as endogenous proteins. Exogenous FGF-1 and FGF-2 are internalized by receptor-mediated endocytosis, in a clathrin-dependent and -independent way. Internalized FGF-1 and FGF-2 are able to cross cellular membranes to reach the cytosol and the nuclear compartment. The role of FGF internalization and the intracellular activity of some FGFs are discussed in the context of the known signaling induced by FGF.

Ligand-induced clathrin-mediated endocytosis of the keratinocyte growth factor receptor occurs independently of either phosphorylation or recruitment of eps15

Keratinocyte growth factor receptor (KGFR) is a receptor tyrosine kinase expressed on epithelial cells. Following ligand binding, KGFR is rapidly activated and internalized by clathrin-mediated endocytosis. Among the possible receptor substrates which could be involved in the regulation of KGFR endocytosis and down-modulation, we analyzed here the eps15 protein in view of the proposed general role of eps15 in regulating clathrin-mediated endocytosis as well as that of eps15 tyrosine phosphorylation in the control of regulated endocytosis. Immunoprecipitation and Western blot analysis showed that activated KGFR was not able to phosphorylate eps15, suggesting that eps15 is not a receptor substrate. Double immunofluorescence and confocal microscopy revealed that activated KGFR, differently from epidermal growth factor receptor (EGFR), did not induce recruitment of eps15 to the cell plasma membrane. Microinjection of a monoclonal antibody directed against the C-terminal DPF domain which contains the AP2 binding region of eps15 led to inhibition of both pathways of receptor-mediated endocytosis, the EGFR ligand-induced endocytosis and the transferrin constitutive endocytosis, but did not appear to block the KGFR ligand-induced internalization. Taken together our results indicate that the clathrin-mediated uptake of KGFR is not mediated by eps15.

Repifermin (keratinocyte growth factor-2) reduces the severity of graft-versus-host disease while preserving a graft-versus-leukemia effect

Graft-versus-host disease (GVHD) is the principal complication after allogeneic bone marrow transplantation (BMT). Reductions in systemic GVHD are frequently associated with a corresponding diminishment of the graft-versus-leukemia (GVL) response. In this study, we tested the effects of a novel recombinant human keratinocyte growth factor, repifermin (keratinocyte growth factor-2), on the induction of GVHD in a well-defined murine BMT model (B6 --> B6D2F1). Administration of repifermin (5 mg/kg/d) to allogeneic BMT recipients resulted in a significant decrease in both systemic GVHD and target organ histopathology. Repifermin treatment also reduced serum levels of tumor necrosis factor alpha and lipopolysaccharide compared with control mice. In contrast, repifermin did not affect T-cell proliferation, cytokine production, or cytotoxic responses to host antigens. When 2000 host-derived P815 (H-2(d)) leukemia cells were added to the bone marrow inoculum, repifermin preserved GVL effects and resulted in significantly delayed mortality compared with control-treated allogeneic BMT recipients. Collectively, these data suggest that repifermin administration may represent a novel strategy to separate the toxicity of GVHD from the beneficial GVL effects after allogeneic BMT.

UVB-induced activation and internalization of keratinocyte growth factor receptor

Ultraviolet irradiation of mammalian cells induces several events that include activation of growth factor receptors and triggering of signal transduction pathway. Most of the UV responses are mediated by the production of reactive oxygen species (ROS) and can be blocked by antioxidants. In this study, we analysed the effect of UVB irradiation at physiologic doses and that of the pro-oxidant agent cumene hydroperoxide (CUH) on the activation of the receptor for keratinocyte growth factor (KGF), a key mediator of epithelial growth and differentiation. Exposure to both UVB (30-150 mJ/cm(2)) and CUH (200 microM of NIH3T3 KGFR (KGF receptors) transfectants caused a rapid tyrosine phosphorylation and activation of KGFR similar to that induced by KGF, and internalization of the activated receptor. The KGFR expression appeared unmodified by the treatments. Ultrastructural observations of both UVB- and CUH-treated cells showed a normal morphology of the plasma membranes and intracellular organelles. The antioxidant N-acetylcysteine inhibited UVB-induced receptor phosphorylation. The generation of an intracellular oxidative stress was detected as a decrease of catalase activity and of vitamin E, and reduced glutathione levels, whereas superoxide dismutase activity was not significantly modified. A peroxidation of polyunsaturated fatty acids of cell membranes was observed after both treatments, associated with the intracellular oxidative stress. Similar biochemical events were observed on NIH3T3 untransfected control cells, suggesting that KGFR activation follows intracellular generation of ROS and is not associated with a scavenging effect. Taken together our results demonstrate that exposure to UVB and to oxidant stimuli induces a rapid intracellular production of ROS, which in turn are capable of triggering KGFR activation and internalization, similar to those induced by KGF.

Transport of exogenous growth factors and cytokines to the cytosol and to the nucleus

In recent years a number of growth factors, cytokines, protein hormones, and other proteins have been found in the nucleus after having been added externally to cells. This review evaluates the evidence that translocation takes place and discusses possible mechanisms. As a demonstration of the principle that extracellular proteins can penetrate cellular membranes and reach the cytosol, a brief overview of the penetration mechanism of protein toxins with intracellular sites of action is given. Then problems and pitfalls in attempts to demonstrate the presence of proteins in the cytosol and in the nucleus as opposed to intracellular vesicular compartments are discussed, and some new approaches to study this are described. A detailed overview of the evidence for translocation of fibroblast growth factor, HIV-Tat, interferon-gamma, and other proteins where there is evidence for intracellular action is given, and translocation mechanisms are discussed. It is concluded that although there are many pitfalls, the bulk of the experiments indicate that certain proteins are indeed able to enter the cytosol and nucleus. Possible roles of the internalized proteins are discussed.

Novel system to investigate the effects of inhaled volume and rates of rise in simulated inspiratory air flow on fine particle output from a dry powder inhaler

This study evaluated the effect of inhaled volume and simulated inspiratory flow rate ramps on fine particle output from dry powder inhalers (DPIs). A simple, robust system was developed to account for "rate of rise" (ramp) effects while maintaining a constant air flow through a multi-stage liquid impinger (MSLI), used for sizing the emitted particles. Ramps were programmed to reach 30 and 60 L/min over 100 milliseconds; 500 milliseconds; and 1, 2, and 3 seconds. Rotahaler was chosen as the test DPI. Testing was done with simulated inhalation volumes of 2 L and 4 L. Testing was also carried out using the USP apparatus 4. At 30 L/min, for a 2 L volume, the amount of drug exiting the device in fine particle fraction (FPF) increased from 2.33 microg to 6.04 microg from the 3-second ramp to the 100-millisecond ramp, with 11.64 microg in FPF for the USP (no ramp) method. At the same flow rate, for a 4 L volume, FPF increased from 2.23 microg to 8.45 microg, with 10.25 microg for the USP method. At 60 L/min, similar trends were observed. In general, at both flow rates, an increase in FPF was noted going from the shallowest to the steepest ramp. However, there were no significant differences in FPF when a 2 L inhaled volume was compared with a 4 L volume at each flow rate. Overall, these data suggest that the existing USP apparatus may overestimate FPF at flow rates lower than those recommended by the USP.

rHuKGF ameliorates symptoms in DSS and CD4(+)CD45RB(Hi) T cell transfer mouse models of inflammatory bowel disease

There is an acute need for effective therapy for inflammatory bowel disease (IBD), particularly at the level of repair of the damaged epithelium. We evaluated the efficacy of recombinant human keratinocyte growth factor (rHuKGF) in both the dextran sodium sulfate (DSS) and the CD4(+)CD45RB(Hi) T cell transfer models of IBD. Disease was induced either by the ad libitum administration to normal mice of 4% DSS in the drinking water or by the injection of 4 x 10(5) CD4(+)CD45RB(Hi) T cells into immunodeficient scid/scid mice. rHuKGF was administered by subcutaneous injection at doses of 1.0 or 3.0 mg/kg in both preventative and therapeutic regimens during both studies. rHuKGF significantly improved survival and body weight loss in the DSS model in both preventative and therapeutic dosing regimens. It also improved diarrhea, hematochezia, and hematological parameters, as well as large intestine histopathology. In the T cell transfer model, rHuKGF improved body weight loss, diarrhea, and levels of serum amyloid A, as well as large intestine histopathology. In both models of IBD, the colonic levels of intestinal trefoil factor (ITF) were elevated by the disease state and further elevated by treatment with rHuKGF. These data suggest that rHuKGF may prove useful in the clinical management of IBD and its effects are likely mediated by its ability to locally increase the levels of ITF.

Esophageal ulceration activates keratinocyte growth factor and its receptor in rats: implications for ulcer healing

BACKGROUND & AIMS

Cellular and molecular mechanisms of esophageal ulcer healing remain unexplored. We studied the sequential cellular events and the expression of keratinocyte growth factor (KGF) and its receptor (KGF-R) during the healing of experimental esophageal ulcers.

METHODS

Esophageal ulcers were produced in rats by local application of acetic acid. Studies included (1) ulcer size, (2) quantitative histology, and (3) KGF and KGF-R messenger RNA and protein expression by reverse-transcription polymerase chain reaction, Western blotting, and immunostaining. In separate groups, ulcer size and esophageal epithelial proliferation were evaluated after a single injection of recombinant human KGF (1 mg/kg) around the ulcer.

RESULTS

Ulcers were fully developed 3 days after induction, and 58% of ulcers were re-epithelialized by 9 days. At 3 days, in esophageal tissue bordering the ulcers, KGF messenger RNA and protein were increased by 191% and 151%, respectively, and KGF-R messenger RNA and protein were increased by 357% and 237%, respectively. KGF was expressed in stromal cells, whereas KGF-R was expressed in epithelial cells. At 6 days, epithelial proliferation at the ulcer margin was increased by 216%, and treatment with KGF further enhanced cell proliferation and accelerated ulcer healing.

CONCLUSIONS

KGF is a likely mediator of esophageal epithelial proliferation and ulcer healing.

Upregulation of keratinocyte growth factor in cyclosporin A-induced gingival overgrowth

BACKGROUND

Drug-induced gingival overgrowth (GO) is a frequent and adverse side-effect associated principally with the administration of the immunosuppressive drug cyclosporin A (CsA) and also certain anti-epileptic and anti-hypertensive drugs. It is characterized by a marked increase in the thickness of the epithelial layer and the accumulation of excessive amounts of connective tissue. Although the mechanism by which the drugs cause GO is not yet understood, keratinocyte growth factor (KGF), which is a potent epithelial cell mitogen, has been implicated in other hyperplastic conditions, including mammary and prostatic hyperplasia, and could also be involved in the molecular pathology of GO.

METHODS

Immunohistochemistry was used to examine the expression of KGF in normal gingiva (NG) and GO tissue sections. The relative level of KGF mRNA in GO tissue and cells was compared with that of NG tissue and fibroblast cells using the semi-quantitative reverse transcribed-polymerase chain reaction (RT-PCR) and DNA sequencing was carried out to confirm the identity of the PCR product.

RESULTS

KGF antigen and mRNA were readily detected in the GO tissue immunohistochemically and by RT-PCR, respectively, but were not expressed in the NG tissue. Moreover, KGF transcripts were found to be approximately 2 times higher in the GO than in the NG fibroblasts in vitro, although the difference was not statistically significant.

CONCLUSIONS

This study has shown, for the first time, that the level of KGF is elevated in GO and suggests that KGF may have an important role in the enhanced epithelial proliferation associated with GO.

Epsin 3 is a novel extracellular matrix-induced transcript specific to wounded epithelia

Using an in vitro model of keratinocyte activation by the extracellular matrix following injury, we have identified epsin 3, a novel protein closely related to, but distinct from previously described epsins. Epsin 3 contains a domain structure common to this gene family, yet demonstrates novel differences in its regulation and pattern of expression. Epsin 3 mRNA and protein were undetectable in keratinocytes isolated from unwounded skin, but induced in cells following contact with fibrillar type I collagen. The native triple helical structure of collagen was required to mediate this response as cells failed to express epsin 3 when plated on gelatin. Consistent with the reported function of other epsins, epsin 3 was evident in keratinocytes as punctate vesicles throughout the cytoplasm that partially co-localized with clathrin. In addition, epsin 3 exhibited nuclear accumulation when nuclear export was inhibited. In contrast to other known epsins, epsin 3 was restricted to keratinocytes migrating across collagen and down-regulated following cell differentiation, suggesting that expression was spatially and temporally regulated. Indeed, epsin 3 was localized specifically to migrating keratinocytes in cutaneous wounds, but not found in intact skin. Intriguingly, Northern hybridization and reverse transcriptase-polymerase chain reaction experiments indicated that epsin 3 expression was restricted to epithelial wounds or pathologies exhibiting altered cell-extracellular matrix interactions. Thus, we have identified a novel type I collagen-induced epsin that demonstrates structural and behavioral similarity to this gene family, yet exhibits restricted and regulated expression, suggesting that epsin 3 may serve an important function in activated epithelial cells during tissue morphogenesis.

Fibroblast growth factor 10 induces proliferation and differentiation of human primary cultured keratinocytes

Fibroblast growth factor 10 is a novel member of the fibroblast growth factor family, which is involved in morphogenesis and epithelial proliferation. It is highly homologous to the keratinocyte growth factor (or fibroblast growth factor 7), a key mediator of keratinocyte growth and differentiation. Both fibroblast growth factor 10 and keratinocyte growth factor bind with high affinity to the tyrosine kinase keratinocyte growth factor receptor. Here we analyzed the effect of fibroblast growth factor 10 on primary cultures of human keratinocytes, grown in chemically defined medium, and we compared the proliferative and differentiative cell responses to fibroblast growth factor 10 with those induced by keratinocyte growth factor and epidermal growth factor. Cell counting, 5-bromo-2'-deoxyuridine incorporation, and western blot analysis showed that fibroblast growth factor 10, similarly to keratinocyte growth factor, not only is a potent mitogen for human keratinocytes, but also promotes the expression of both early differentiation markers K1 and K10 and late differentiation marker filaggrin in response to the Ca2+ signal, and seems to sustain the proliferative activity in suprabasal stratified cells. Immunoprecipitation/western blot analysis revealed that fibroblast growth factor 10, similarly to keratinocyte growth factor, is able to induce tyrosine phosphorylation of keratinocyte growth factor receptor and of cellular substrates such as PLCgamma.

Functional characterization of the keratinocyte growth factor system in human fetal gastrointestinal tract

Keratinocyte growth factor (KGF) is a paracrine growth factor whose mRNA has been detected in human adult and rodent gut tissues together with its associated receptor. Our objectives were to assess the presence of immunoreactive KGF ligand and receptor proteins in human fetal gastrointestinal (GI) tract segments and to evaluate the role of exogenous KGF on cell proliferation and intestinal digestive functions. KGF (26-28 kD doublet) was identified in esophagus, stomach, small intestine, and colon by Western blot. Its receptor (135 kD) was ubiquitously detected in proliferative and differentiated epithelial cells of each GI segment by use of indirect immunofluorescence (anti-bek, anti-K-sam). The addition of KGF to explants cultured in serum-free conditions greatly stimulated DNA synthesis in all GI tract tissues. The growth factor up-regulated intestinal sucrase-isomaltase and gamma-glutamyl-transpeptidase activities in jejunal explants, whereas it down-regulated these activities in colon explants. It is suggested that the KGF system likely represents an important paracrine pathway that is able to stimulate cell proliferation in all segments of the human fetal GI tract and to differentially regulate intestinal digestive functions.

Expression of functional mGlu5 metabotropic glutamate receptors in human melanocytes

Cultured human melanocytes express mGlu5 metabotropic glutamate (mGlu) receptors, as shown by RT-PCR, immunocytochemistry, Western blot analysis, and measurement of agonist-stimulated polyphosphoinositide hydrolysis. The mGlu5 receptor agonists (S)-3, 5-dihydroxyphenylglycine and quisqualate increased [(3)H-methyl]thymidine incorporation and melanocyte proliferation in subconfluent cultures, but impaired cell viability in confluent cultures. Both effects were prevented by 2-methyl-6-(2-phenyl-1-ethynyl)-pyridine, a potent and highly selective mGlu5 receptor antagonist. Agonists of other mGlu receptor subtypes (such as the mGlu2/3 receptor agonist, 2S,2'R,3'R-2-2', 3'-dicarboxycyclopropylglycine, or the mGlu4/6/7/8 receptor agonist, L-2-amino-4-phosphonobutanoate) or selective agonists of ionotropic glutamate receptors (N-methyl-D-aspartate, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate, and kainate) did not affect melanocyte proliferation or viability. The presence of a receptor for glutamate, the major excitatory neurotransmitter, in human melanocytes is intriguing. mGlu5 receptors may be involved in the control of melanocyte proliferation (and perhaps in other functions), but harbor a potential toxicity and may therefore contribute to cell damage under pathological conditions.

Keratinocyte growth factor signalling: a mathematical model of dermal-epidermal interaction in epidermal wound healing

A wealth of growth factors are known to regulate the various cell functions involved in the repair process. An understanding of their therapeutic value is essential to achieve improved wound healing. Keratinocyte growth factor (KGF) seems to have a unique role as a mediator of mesenchymal-epithelial interactions: it originates from mesenchymal cells, yet acts exclusively on epithelial cells. In this paper, we study KGF's role in epidermal wound healing, since its production is substantially up-regulated after injury. We begin by modelling the dermal-epidermal signalling mechanism of KGF to investigate how this extra production affects the signal range. We then incorporate the effect of KGF on cell proliferation, and using travelling wave analysis we obtain an approximation for the rate of healing. Our modelling shows that the large up-regulation of KGF post-wounding extends the KGF signal range but is above optimal for the rate of wound closure. We predict that other functions of KGF may be more important than its role as a mitogen for the healing process.

Synergistic growth factors enhance rat liver proliferation and enable retroviral gene transfer via a peripheral vein

BACKGROUND & AIMS

Genetic diseases reflecting abnormal hepatocyte function are potentially curable through gene therapy. Retroviral vectors offer the potential for permanent correction of such conditions. These vectors generally require cell division to occur to allow provirus entry into the nucleus, initiated in many experimental protocols by partial hepatectomy. We have explored methods to improve the efficiency of retroviral gene transfer that avoid the need for liver damage.

METHODS

Triiodothyronine (T3) and keratinocyte growth factor (KGF) were used to induce hepatic proliferation in rats. The effects of intraportal and peripheral administration of a modified retrovirus that encoded the Lac Z gene during growth factor-induced liver hyperplasia were analyzed.

RESULTS

T3 initiated hepatocyte proliferation midzonally; after KGF, proliferation was more diffuse. Optimal concentrations of T3 and KGF acted synergistically to induce proliferation in 61% of hepatocytes in the intact liver. This enabled in vivo hepatocyte transduction, leading to gene expression by up to 7.3% of hepatocytes after intraportal retroviral vector administration and 7. 1% after peripheral venous administration.

CONCLUSIONS

T3 and KGF act synergistically to induce hepatocyte proliferation in undamaged liver. The liver can be simply transduced with integrating vectors via the peripheral venous system during a wave of growth factor-induced proliferation.