A heparin-binding growth factor secreted by macrophage-like cells that is related to EGF

Lysophosphatidylcholine enhances cytokine-induced interferon gamma expression in human T lymphocytes

Accumulation of substantial numbers of activated T lymphocytes, as well as monocyte/macrophages, in focal areas of arterial intima appears to be a hallmark of atherogenesis. Our previous report demonstrated that lysophosphatidylcholine (lyso-PC), a polar phospholipid component that is increased in atherogenic lipoproteins and atherosclerotic lesions, can upregulate the expression of heparin-binding epidermal growth factor-like growth factor and the interleukin (IL)-2 receptor in cultured human peripheral T lymphocytes. In this study, we show that lyso-PC can also enhance interferon gamma (IFN-gamma) secretion and gene expression in human T lymphocytes. Lyso-PC-induced upregulation of IFN-gamma depended on the presence of IL-2, IL-12, or phytohemagglutinin in culture media and was similarly observed in both CD4+ and CD8+ subsets. Actinomycin D chase by Northern blotting showed that lyso-PC significantly prolonged IFN-gamma mRNA half-lives in human T cells. Transient transfection of IFN-gamma promoter-reporter gene construct in the human T-cell line Jurkat cells demonstrated that lyso-PC stimulated the transcription of IFN-gamma promoter-driven luciferase gene. Analyses of serial deletion mutations of IFN-gamma promoter revealed that the lyso-PC-responsive element is located between base pairs - 102 and -78 of the transcription initiation site of the IFN-gamma gene. Enhanced expression of IFN-gamma in T lymphocytes by lyso-PC may play a crucial role in atherogenesis.

Toxin binding site of the diphtheria toxin receptor: loss and gain of diphtheria toxin binding of monkey and mouse heparin-binding, epidermal growth factor-like growth factor precursors by reciprocal site-directed mutagenesis

The transmembrane precursor of the monkey (Mk) heparin-binding, epidermal growth factor-like growth factor (proHB-EGF) functions as a diphtheria toxin (DT) receptor, whereas the mouse (Ms) precursor does not. Previously, using chimeric Ms/Mk precursors, we have shown that DT resistance of cells bearing Ms proHB-EGF may be accounted for by several amino acid substitutions between residues 122 and 148 within the EGF-like domain and that Glu-141 is an important amino acid residue for DT binding. In this study, reciprocal site-directed mutagenesis was performed on the major non-conserved residues in the region of 122-148, alone or in combination, between Mk and Ms precursors to identify more precisely which amino acid residues are important for DT binding. Two approaches were used. The first, more traditional approach was to destroy DT sensitivity and binding of Mk proHB-EGF by substitution(s) with the corresponding Ms residue(s). From the single mutations, the greatest loss of DT sensitivity was observed with Mk/Glu-141His (approximately 4000-fold) and the next greatest with Mk/Ile-133Lys (approximately fourfold). The double mutations Mk/Leu-127Phe/Glu-141His, Mk/Ile-133Lys/Glu-141His and Mk/His-135Leu/Glu-141His resulted in complete toxin resistance (> 100000-fold). The second approach, both novel and complementary, was to gain DT binding and sensitivity of Ms proHB-EGF by substitution(s) with the corresponding Mk residue(s). Surprisingly, the single mutation Ms/His-141Glu resulted in the gain of moderate DT sensitivity (> 260-fold). The double mutation Ms/Lys-133Ile/His-141Glu and the triple mutation Ms/Lys-133Ile/Leu-135His/His-141Glu resulted in a progressive gain in toxin sensitivity (> 4700-fold and >16000-fold respectively) and affinity. This triple mutant cell line is essentially as sensitive (IC50 = 3.1 ng ml(-1)) as the highly toxin-sensitive monkey Vero cell line (IC50 = 4 ng ml(-1)), indicating that these three Mk residues enable the Ms proHB-EGF to act as a fully functional DT receptor. Taken together, these results indicate that Glu-141 plays the most critical role in DT binding and sensitivity and that two additional amino acid residues, Ile-133 and His-135, also play significant roles.

Opposing actions of the EGF family and opioids: heparin binding-epidermal growth factor (HB-EGF) protects mouse cerebellar neuroblasts against the antiproliferative effect of morphine

Endogenous opioids and opiate drugs of abuse inhibit the proliferation of cerebellar external granular layer (EGL) neuroblasts by mechanisms that are incompletely understood. Opioids do not act alone, rather multiple extracellular factors regulate granule cell neurogenesis and these undoubtedly act in concert with opioids to shape developmental outcome. We examined whether, heparin binding-epidermal growth factor-like growth factor (HB-EGF), a recently described member of the epidermal growth factor (EGF) family, might compete with an inhibitory opioid signal. The results confirmed our ongoing studies that morphine inhibited neuroblast proliferation, while HB-EGF enhanced cell replication. HB-EGF not only counteracted the antiproliferative morphine signal, but invariably enhanced DNA synthesis irrespective of morphine treatment. Our findings suggest that regional and temporal differences in the availability of endogenous HB-EGF may serve to limit the response of EGL neuroblasts to opioids, and HB-EGF may be neuroprotective in opiate drug abuse. If similar responses occur in vivo, then the EGF family and the opioid system may represent distinct and contrasting components of an extracellular signaling system serving to coordinate EGL neurogenesis.

Macrophage and microglia-like cells in the avian inner ear

Recent studies suggest that macrophages may influence early stages of the process of hair cell regeneration in lateral line neuromasts; numbers of macrophages were observed to increase prior to increases in hair cell progenitor proliferation, and macrophages have the potential to secrete mitogenic growth factors. We examined whether increases in the number of leukocytes present in the in vivo avian inner ear precede the proliferation of hair cell precursors following aminoglycoside insult. Bromodeoxyuridine (BrdU) immunohistochemistry was used to identify proliferating cells in chicken auditory and vestibular sensory receptor epithelia. LT40, an antibody to the avian homologue of common leukocyte antigen CD45, was used to label leukocytes within the receptor epithelia. Macrophages and, surprisingly, microglia-like cells are present in normal auditory and vestibular sensory epithelia. After hair cell loss caused by treatment with aminoglycosides, numbers of macrophage and microglia-like cells increase in the sensory epithelium. The increase in macrophage and microglia-like cell numbers precedes a significant increase in sensory epithelial cell proliferation. The results suggest that macrophage and microglia-like cells may play a role in releasing early signals for cell cycle progression in damaged inner ear sensory epithelium.

Complexity of EGF receptor signalling revealed in Drosophila

The multiple roles of the Drosophila epidermal growth factor receptor (EGFR) require that its activation is regulated precisely. Recent work has highlighted two important control mechanisms: the existence of multiple ligands with distinct properties and the interaction between EGFR pathway and other signalling pathways. The integration of signalling pathways into networks is beginning to be understood.

Cell surface ectodomain cleavage of human amphiregulin precursor is sensitive to a metalloprotease inhibitor. Release of a predominant N-glycosylated 43-kDa soluble form

Biosynthesis and processing of amphiregulin (AR) have been investigated in human colorectal (HCA-7, Caco-2) and mammary (MCF-7) cancer cell lines, as well as in Madin-Darby canine kidney cells stably expressing various human AR precursor (pro-AR) forms. Both cells expressing endogenous and transfected AR produce multiple cellular and soluble forms of AR with an N-glycosylated 50-kDa pro-AR form being predominant. Our results demonstrate that sequential proteolytic cleavage within the ectodomain of the 50-kDa pro-AR form leads to release of a predominant N-glycosylated 43-kDa soluble AR, as well as the appearance of other cellular and soluble AR forms. Cell surface biotinylation studies using a C-terminal epitope-tagged pro-AR indicate that all cell surface forms are membrane-anchored and support that AR is released by ectodomain cleavage of pro-AR at the plasma membrane. We also show that pro-AR ectodomain cleavage is a regulated process, which can be stimulated by phorbol 12-myristate 13-acetate and inhibited by the metalloprotease inhibitor, batimastat. In addition, we provide evidence that high molecular mass AR forms may retain the full-length N-terminal pro-region, which may influence the biological activities of these forms.

Heparin-binding EGF-like growth factor is cytoprotective for intestinal epithelial cells exposed to hypoxia

BACKGROUND

During recovery from intestinal ischemic injury, there is rapid growth of intestinal epithelia with regeneration of damaged villi. This study examines the effects of heparin-binding EGF-like growth factor (HB-EGF) on the recovery of intestinal epithelial cells exposed to hypoxia.

METHODS

The cytoprotective effects of HB-EGF were analyzed by placing IEC-18 cells in an anaerobic chamber with various timed HB-EGF treatments (prehypoxia, posthypoxia, pre- and posthypoxia, and no treatment). After 10 hours of hypoxia, lactate dehydrogenase (LDH) release, actin-filament (structural) integrity, adenosine triphosphate (ATP) levels, and posthypoxia proliferative activity were evaluated.

RESULTS

LDH analysis showed that HB-EGF exerted a cytoprotective effect during hypoxia. Pretreated cells had a significantly lower death rate during recovery (7.48%) compared with cells with no HB-EGF treatment (22.19%, P < .009). Confocal microscopic structural analysis of posthypoxia cells showed that F-actin structure was maintained in treated cells, whereas nontreated cells showed increased structural deterioration. ATP levels were significantly higher in the HB-EGF-treated cells compared with nontreated cells at 48 hours (P < .05). Finally, HB-EGF-treated cells had a significantly improved proliferative ability compared with nontreated cells during recovery from hypoxia (P < .05).

CONCLUSIONS

HB-EGF is a mitogenic growth factor for intestinal epithelial cells. Moreover, HB-EGF appears to protect intestinal epithelial cells from hypoxia, in part via maintenance of cytoskeletal structure and ATP stores. Finally, HB-EGF-treated cells also appear to have better proliferative abilities during recovery from hypoxia.

TGF alpha is dispensable for skin tumorigenesis in Tg.AC mice

Alterations in growth factor signaling pathways frequently accompany the development and maintenance of epithelial neoplasia. Transforming growth factor alpha (TGF alpha) and its epidermal growth factor receptor have been thought to play an especially important role in epithelial neoplasia. In this study, mice were derived genetically deficient (null) in functional TGF alpha expression and carrying the Tg.AC/v-Ha-ras transgene. The goals were to determine if (a) papillomagenesis was dependent on TGF alpha and (b) progression to malignancy was dependent on TGF alpha expression. Groups of male and female mice heterozygous or homozygous for the TGF alpha null allele and hemizygous for the Tg.AC transgene were treated twice weekly for 10 or 15 wk with doses of 12-O-tetradecanoylphorbol-13-acetate (TPA) known to produce papillomas in Tg.AC mice. Papillomas were readily induced in both male and female TGF alpha null mice. Malignant progression of papillomas was observed in all TGF alpha null treatment groups. Additionally, we examined the response of TGF alpha null mice to full thickness dorsal wounds, a stimulus known to promote papillomagenesis in Tg.AC mice. As in the TPA study, papillomas were induced in both male and female TGF alpha null mice. These studies indicate that TGF alpha is not required for the induction and maintenance of papillomas nor is it essential for the malignant conversion of papillomas in Tg.AC mice.

Neuronal and glial expression of heparin-binding EGF-like growth factor in central nervous system of prenatal and early-postnatal rat

We investigated heparin-binding epidermal growth factor-like growth factor (HB-EGF) gene and protein expression in the central nervous system of prenatal and early postnatal rats. Assay by northern blot analysis showed that the HB-EGF mRNA was markedly expressed in the brain. In situ hybridization and immunohistochemical techniques showed that concordant expression of HB-EGF mRNA and protein was widely observed in the neurons and interfascicular oligodendrocytes, especially in the cerebellum, the hippocampus, the cerebral cortex, the subventricular area, and the brain stem nuclei. The intense expression of the HB-EGF mRNA was related anatomically and temporally to the proliferating neuroblasts in the external granular layer of the cerebellum and the subventricular layer of the cerebrum. These findings suggest that HB-EGF acts as a mitogen for the neuroblasts. Moreover, HB-EGF expression was observed in the post-mitogenic cells, such as in the cells of the molecular layer, the white matter, the IGL, or the Purkinje cells of the cerebellum. Since EGF receptors are abundantly expressed in the post-mitogenic period, the HB-EGF mRNA expression observed in the post-mitogenic period in our study suggests that HB-EGF also has a non-mitogenic function. These results suggest that HB-EGF significantly contributes to the development of the brain.

ErbB2 expression increases the spectrum and potency of ligand-mediated signal transduction through ErbB4

Interleukin 3-dependent murine 32D cells do not detectably express members of the ErbB receptor family and do not proliferate in response to known ligands for these receptors. 32D transfectants were generated expressing human ErbB4 alone (32D.E4) or with ErbB2 (32D.E2/E4). Epidermal growth factor (EGF), neuregulin 1-beta (NRG1-beta), betacellulin (BTC), transforming growth factor-alpha (TGF-alpha), heparin binding-EGF (HB-EGF), and amphiregulin were analyzed for their ability to mediate mitogenesis in these transfectants. 32D.E4 responded mitogenically to NRG1-beta and BTC. Surprisingly, EGF also induced significant DNA synthesis and TGF-alpha was negligibly mitogenic on 32D.E4 cells, whereas HB-EGF and amphiregulin were inactive. Although coexpression of ErbB2 with ErbB4 in 32D.E2/E4 cells did not significantly alter DNA synthesis in response to NRG1-beta or BTC, it greatly enhanced mitogenesis elicited by EGF and TGF-alpha and unmasked the ability of HB-EGF to induce proliferation. EGF-related ligands that exhibited potent mitogenic activity on 32D.E2/E4 cells at low concentrations induced adherence, morphological alterations, and up-regulation of the Mac-1 integrin and FcgammaRII/III at higher concentrations. While 125I-EGF could be specifically crosslinked to both 32D.E4 and 32D.E2/E4 cells, its crosslinking capacity was greatly enhanced in the cotransfected cells. The ability of the various ligands to mediate proliferation and/or adhesion in the two transfectants correlated with their capacity to induce substrate tyrosine phosphorylation and to initiate and sustain activation of mitogen-activated protein kinase. We conclude that the ability of ErbB4 to mediate signal transduction through EGF-like ligands is broader than previously assumed and can be profoundly altered by the concomitant expression of ErbB2.

Plasma heparin-binding EGF-like growth factor levels in patients after partial hepatectomy as determined with an enzyme-linked immunosorbent assay

We recently showed that heparin-binding EGF-like growth factor (HB-EGF) has hepatotrophic effects. In this study, we developed an ELISA system with high specificity and sensitivity for human plasma HB-EGF. In 14 patients who underwent partial hepatectomy, plasma HB-EGF levels were measured serially after surgery. In patients who underwent gross hepatectomy (lobectomy and segmentectomy), plasma HB-EGF levels increased, reaching maximal levels approximately 5 to 7 days after surgery. In patients who underwent minor hepatectomy (subsegmentectomy), plasma HB-EGF levels did not increase. Maximal plasma HB-EGF levels were significantly higher in patients who had a percent increased volume of the remaining liver (%ILV) above 20% than those who had a %ILV below 20% (32.4 +/- 19.6 pg/ml vs 7.4 +/- 2.7, P < 0.05). The plasma HB-EGF values did not correlate with WBC counts, C-reactive protein, or alanine aminotransferase. Plasma HB-EGF may be a marker for liver regeneration after hepatectomy in humans.

Variation in the proregion structure of heparin-binding EGF-like growth factor precursors

In a previous study, we have isolated and characterized cDNA encoding a novel 'short form' of heparin-binding EGF-like growth factor (SF HB-EGF) (Loukianov et al., 1997). In the present work, we have found that cDNA for SF HB-EGF and for full-length HB-EGF are each represented by two variants, which we refer to as L and P forms. The L form is the previously known form of HB-EGF cDNA and encodes a leucine in position 33. The P form described in this report, encodes a proline in codon 33. The L33P substitution is predicted to cause a significant alteration in the proregion structure of SF HB-EGF and HB-EGF.

Extracellular calcium influx stimulates metalloproteinase cleavage and secretion of heparin-binding EGF-like growth factor independently of protein kinase C

The phorbol ester, tetradecanoyl-phorbol 13-acetate (TPA), stimulates rapid proteolytic processing of the transmembrane, pro- form of heparin-binding epidermal growth factor-like growth factor (HB-EGF) at cell surfaces, suggesting the involvement of protein kinase C (PKC) isoforms in the HB-EGF secretion mechanism. To test this possibility, we expressed a chimeric protein, consisting of proHB-EGF fused to placental alkaline phosphatase (AP) near the amino terminus of processed HB-EGF, in NbMC-2 prostate epithelial cells. The proHB-EGF-AP chimera localized to plasma membranes and functioned as a diphtheria toxin receptor. Secreted HB-EGF-AP bound to heparin and exhibited potent growth factor activity. The presence of the AP moiety allowed highly quantitative measurements of cleavage-secretion responses of proHB-EGF to extracellular stimuli. As expected, rapid secretion of HB-EGF-AP was induced in a time- and dose-dependent manner by TPA. However, this was also observed with the Ca2+ ionophore, ionomycin, suggesting the involvement of extracellular Ca2+ ions in the secretion mechanism. Ionomycin-induced secretion was inhibited by extracellular calcium chelation but not by the PKC inhibitors, GF109203X, staurosporine, or chelerythrine. The TPA-mediated secretion effect was inhibited by staurosporine, GF109203X, and by pretreatment with TPA, but not by calcium chelation. A small secretion response was induced by thapsigargin, which releases Ca2+ from intracellular stores, but this was completely eliminated by extracellular calcium chelation. Ionomycin- and TPA-induced HB-EGF-AP secretion was not dependent on the presence of the proHB-EGF cytoplasmic domain and was specifically inhibited by the metalloproteinase inhibitors 1,10-phenanthroline and tissue inhibitor of metalloproteinase-1 (TIMP-1). These data demonstrate that extracellular Ca2+ influx activates a membrane-associated metalloproteinase to process proHB-EGF by a pathway that does not require PKC.

Heparin-binding epidermal growth factor-like growth factor in experimental models of membranous and minimal change nephropathy

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is a recently described member of the epidermal growth factor (EGF) family. It binds to heparan sulfate proteoglycans via a cationic domain and is a potent mitogen for epithelial cells, fibroblasts and vascular smooth muscle cells. In the present study we have attempted to identify changes in quantity and distribution of HB-EGF in two models of acute glomerular epithelial cell injury, using Western blotting, immunohistochemistry and in situ hybridization. Prior to disease induction, Western blots showed some expression of HB-EGF protein within glomeruli. Within the first three days in the acute puromycin aminonucleoside (PAN) and passive Heymann nephritis (PHN) models, immunohistochemistry and in situ hybridization demonstrated an up-regulation of HB-EGF mRNA and protein in glomerular epithelial cells (GEC). In both cases, increased protein and mRNA was found prior to the onset of proteinuria and continued until day 21 post-induction, the last time point studied. Early in the course of the models, HB-EGF was localized to the cytoplasm of glomerular epithelial cells. At day 21, however, HB-EGF protein was distributed in a nodular pattern within GEC and along the glomerular basement membrane (GBM) in both models, suggesting that the secreted form might bind to the membrane. The increase in HB-EGF protein within glomeruli was confirmed by Western blots of glomerular membrane protein which, however, demonstrated a single 29 kDa species, consistent with the transmembrane form. These data are not consistent with binding of the secreted form of HB-EGF to the GBM. The transmembrane form of HB-EGF is able to signal in a juxtracrine fashion, so increased expression of HB-EGF mRNA and protein by GEC might contribute to the genesis of proteinuria through the initiation of abortive GEC mitogenesis.

Helicobacter pylori upregulates expression of epidermal growth factor-related peptides, but inhibits their proliferative effect in MKN 28 gastric mucosal cells

Acute exposure to Helicobacter pylori causes cell damage and impairs the processes of cell migration and proliferation in cultured gastric mucosal cells in vitro. EGF-related growth factors play a major role in protecting gastric mucosa against injury, and are involved in the process of gastric mucosal healing. We therefore studied the acute effect of H. pylori on expression of EGF-related growth factors and the proliferative response to these factors in gastric mucosal cells (MKN 28) derived from gastric adenocarcinoma. Exposure of MKN 28 cells to H. pylori suspensions or broth culture filtrates upregulated mRNA expression of amphiregulin (AR) and heparin-binding EGF-like growth factor (HB-EGF), but not TGFalpha. This effect was specifically related to H. pylori since it was not observed with E. coli, and was independent of VacA, CagA, PicA, PicB, or ammonia. Moreover, H. pylori broth culture filtrates stimulated extracellular release of AR and HB-EGF protein by MKN 28 cells. AR and HB-EGF dose-dependently and significantly stimulated proliferation of MKN 28 cells in the absence of H. pylori filtrate, but had no effect in the presence of H. pylori broth culture filtrates. Inhibition of AR- or HB-EGF- induced stimulation of cell growth was not mediated by downregulation of the EGF receptor since EGF receptor protein levels, EGF binding affinity, number of specific binding sites for EGF, or HB-EGF- or AR-dependent tyrosine phosphorylation of the EGF receptor were not significantly altered by incubation with H. pylori broth culture filtrates. Increased expression of AR and HB-EGF were mediated by an H. pylori factor > 12 kD in size, whereas antiproliferative effects were mediated by both VacA and a factor < 12 kD in size. We conclude that H. pylori increases mucosal generation of EGF-related peptides, but in this acute experimental model, this event is not able to counteract the inhibitory effect of H. pylori on cell growth. The inhibitory effect of H. pylori on the reparative events mediated by EGF-related growth factors might play a role in the pathogenesis of H. pylori-induced gastroduodenal injury.

Intercellular communication between vascular smooth muscle and endothelial cells mediated by heparin-binding epidermal growth factor-like growth factor and vascular endothelial growth factor

Heparin-binding epidermal growth factor-like growth factor (HB-EGF), a potent mitogen and migration factor for vascular smooth muscle cells (SMC), promoted neovascularization in vivo in the rabbit cornea. MRI demonstrated quantitatively the angiogenic effect of HB-EGF when introduced subcutaneously into nude mice. HB-EGF is not directly mitogenic to endothelial cells but it induced the migration of bovine endothelial cells and release of endothelial cell mitogenic activity from bovine vascular SMC. This mitogenic activity was specifically blocked by neutralizing anti-vascular endothelial growth factor (VEGF) antibodies. In contrast, EGF or transforming growth factor-alpha (TGF-alpha) had almost no effect on release of endothelial mitogenicity from SMC. In addition, RT-PCR analysis demonstrated that VEGF165 mRNA levels were increased in vascular SMC 4-10-fold by 0.35-2 nM of HB-EGF, respectively. Our data suggest that HB-EGF, as a mediator of intercellular communication, may play a new important role in supporting wound healing, tumor progression and atherosclerosis by stimulating angiogenesis.

Growth factors and the kidney in diabetes mellitus

Nephromegaly and mesangial matrix expansion observed in the diabetic kidney are all clues of a role of growth factors in the pathogenesis of these lesions. A growing body of evidence shows that changes in (1) insulin-like growth factor I regulation, and (2) the transforming growth factor beta loop exist in the kidney in the diabetic hypertrophic kidney and in diabetic glomerulosclerosis. However, other growth factors may be involved in some diabetic renal changes. The abnormalities in growth factor content and regulation, the role of growth factors in the diabetic kidney, and the effect of hyperglycemia and advanced glycosylation end products on growth factors in the kidney are reviewed.

Heparin-binding EGF-like growth factor in the human prostate: synthesis predominantly by interstitial and vascular smooth muscle cells and action as a carcinoma cell mitogen

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is an activating ligand for the EGF receptor (HER1/ErbB1) and the high-affinity receptor for diphtheria toxin (DT) in its transmembrane form (proHB-EGF). HB-EGF was immunolocalized within human benign and malignant prostatic tissues, using monospecific antibodies directed against the mature protein and against the cytoplasmic domain of proHB-EGF. Prostate carcinoma cells, normal glandular epithelial cells, undifferentiated fibroblasts, and inflammatory cells were not decorated by the anti-HB-EGF antibodies; however, interstitial and vascular smooth muscle cells were highly reactive, indicating that the smooth muscle compartments are the major sites of synthesis and localization of HB-EGF within the prostate. In marked contrast to prostatic epithelium, proHB-EGF was immunolocalized to seminal vesicle epithelium, indicating differential regulation of HB-EGF synthesis within various epithelia of the reproductive tract. HB-EGF was not overexpressed in this series of cancer tissues, in comparison to the benign tissues. In experiments with LNCaP human prostate carcinoma cells, HB-EGF was similar in potency to epidermal growth factor (EGF) in stimulating cell growth. Exogenous HB-EGF and EGF each activated HER1 and HER3 receptor tyrosine kinases and induced tyrosine phosphorylation of cellular proteins to a similar extent. LNCaP cells expressed detectable but low levels of HB-EGF mRNA; however, proHB-EGF was detected at the cell surface indirectly by demonstration of specific sensitivity to DT. HB-EGF is the first HER1 ligand to be identified predominantly as a smooth muscle cell product in the human prostate. Further, the observation that HB-EGF is similar to EGF in mitogenic potency for human prostate carcinoma cells suggests that it may be one of the hypothesized stromal mediators of prostate cancer growth.

Vascular endothelial growth factor induces heparin-binding epidermal growth factor-like growth factor in vascular endothelial cells

Although several cytokines and growth factors have been shown to regulate vascular endothelial growth factor (VEGF) production, little is known about how VEGF may regulate growth factors that have known mitogenic and chemotactic actions on mesenchymal cells (which are involved in the maturation of the angiogenic process). We investigated the effect of VEGF on heparin-binding epidermal growth factor-like growth factor (HB-EGF) expression in human umbilical vein endothelial cells. HB-EGF mRNA was induced by 8-fold after 2 h of VEGF stimulation, and it returned to base line within 6 h. VEGF did not alter the half-life of HB-EGF mRNA (55 min). Nuclear run-on experiments showed a 4.9-fold increase in HB-EGF gene transcription within 2 h of VEGF stimulation, and Western analysis demonstrated an associated increase in cellular HB-EGF protein. We found that platelet-derived growth factor-BB (PDGF-BB) mRNA was also induced 3-fold after 5 h of VEGF stimulation, whereas neither endothelin 1 nor transforming growth factor-beta1 was regulated by VEGF. Finally, conditioned medium from VEGF-stimulated endothelial cells produced an increase in DNA synthesis in vascular smooth muscle cells, and this effect was blocked by a neutralizing antibody to PDGF. The induction of HB-EGF and PDGF-BB expression in endothelial cells may represent the mechanism by which VEGF recruits mesenchymal cells to form the medial and adventitial layers of arterioles and venules during the course of angiogenesis.

Expression of heparin-binding epidermal growth factor-like growth factor in rat brain

According to a recent report, messenger RNA coding for a member of the epidermal growth factor (EGF) family, heparin-binding EGF-like growth factor (HB-EGF), is expressed in the central nervous system (CNS). To obtain information about the role of HB-EGF in the brain, we carried out Northern analysis, in situ hybridization, and immunohistochemical studies evaluating the distribution and amounts of the growth factor using cDNA HB-EGF probes and an antibody raised against synthetic HB-EGF propeptide. Northern analysis revealed transcripts for HB-EGF in all regions of normal rat brain. Immunohistochemically, HB-EGF was demonstrated extensively in neurons at levels varying according to location. HB-EGF mRNA also was detected in neurons, suggesting that the growth factor is produced in these cells. HB-EGF mRNA and immunoreactivity were also demonstrated in interfascicular oligodendrocytes. These findings suggest that HB-EGF is a physiologic ligand for brain EGF receptors, and is likely to be important in neural function.

Cytotoxic effects of basic FGF and heparin binding EGF conjugated with cytotoxin saporin on vascular cell cultures

Vascular smooth muscle cell (SMC) proliferation is an integral component of intimal lesion formation. In this study we compared the mitogenic effects of basic fibroblast growth factor (bFGF) and heparin binding epidermal growth factor (HBEGF) and the cytotoxic effects of bFGF and HBEGF conjugated with plant cytotoxin saporin (SAP) on vascular cell cultures. Human vascular SMCs and endothelial cells were cultured and FGF receptor-1 (FGFR-1) and EGF receptor (EGFR) expression were detected by immunohistochemical staining. Cells were grown in 24-well plates. Variable amounts of testing drugs (bFGF, HBEGF, SAP, bFGF-SAP, or HBEGF-SAP) were added to quadruplicate wells after 24 h. Cells without drugs were used as control. The total number of cells was counted at 72 h using a hemocytometer. The cultured human vascular SMCs and endothelial cells expressed both FGFR-1 and EGFR with predominant perinuclear localization. bFGF and HBEGF demonstrated equally potent mitogenic effects on SMC proliferation. SAP alone showed a limited cytotoxic effect on both SMCs and endothelial cells. bFGF had a more potent effect on endothelial cell proliferation than HBEGF. bFGF-SAP was equally cytotoxic for both SMCs and endothelial cells, while HBEGF-SAP had a more selectively cytotoxic effect on SMCs than on endothelial cells. These data suggest that the mitogenic effects of bFGF and HBEGF and the cytotoxic effects of bFGF-SAP and HBEGF-SAP may both be mediated by their corresponding growth factor receptors. Because of its selective cytotoxic effect on SMCs, HBEGF-SAP may become a more attractive agent for controlling intimal lesion formation.

Different growth properties in response to epidermal growth factor and interleukin-6 of primary keratinocytes derived from normal and psoriatic lesional skin

Epidermal growth factor (EGF) family members and its receptor (EGFR) are thought to have an important role in the proliferation of epidermal keratinocytes. In this report, we investigated the EGF/EGFR system in primary keratinocytes derived from normal and psoriatic lesional skin. EGF elicited the growth of both normal human keratinocytes (NHKs) and psoriatic lesional keratinocytes (PLKs). Interleukin-6 (IL-6) potentiated the EGF-dependent growth of NHKs, but has no observable effect on PLKs, while IL-6 itself showed no growth-stimulating activities in both cell types. Immunodetection and in situ hybridization analyses revealed that IL-6 induces EGFR expression in NHKs in a time- and dose-dependent manner. This EGFR expression decreased reversibly to an undetectable level when IL-6-treated NHKs were re-cultured in IL-6-free conditions. On the other hand, PLKs expressed high levels of EGFR even when unstimulated and the expression level was not affected by IL-6 stimulation. These results suggest that the EGF/EGFR system is involved in the growth of NHKs and PLKs and that IL-6 potentiates NHK growth partly through the induction of EGFR. The different EGFR regulatory system may contribute to the pathogenesis of psoriasis.

Purification and characterization of a recombinant human cripto-1 protein

Cripto-1 (CR-1) is a novel protein that contains a modified EGF-like motif and that does not directly bind to any of the known erb B type-1 receptor tyrosine kinase receptors. To more clearly define the biological effects of CR-1 and to more adequately compare the structure-function relationships of CR-1 with other members of the EGF family of growth factors, we have expressed a modified, full-length recombinant human CR-1 protein (rhCR-1) in E. coli and have devised a procedure for the solubilization, refolding and purification of a biologically active form of this protein. We have generated the mature form of hCR-1 from computer assisted predictions of potential signal peptide cleavage sites. Expression of the modified rhCR-1 protein in E. coli was limited to the inclusion bodies. The rhCR-1 protein was found to be expressed at high levels in bacterial cells when fused to a histidine-tag sequence. Refolding of rhCR-1 was found to be difficult because of the large number of cysteine residues in the protein which results in protein aggregation. By chemically modifying the cysteine residues in the rhCR-1 protein with 3-trimethylammoniopropyl methanethiosulfonate, additional positive charges have been introduced into the protein by this disulfiding reagent. This modification facilitates solubilization of the protein when rhCR-1 is denatured. The solubilized, denatured protein was then purified by CM cation exchange and C4 reverse phase HPLC chromatography and refolded in a redox buffer. The refolded, modified rhCR-1 protein was found to be biologically active by its ability to inhibit beta-casein expression, to stimulate the tyrosine phosphorylation of Shc and the activation of MAPK and by its capacity to facilitate branching growth of mouse mammary epithelial cells in type I collagen gels.

Specificity within the EGF family/ErbB receptor family signaling network

Recent years have witnessed tremendous growth in the epidermal growth factor (EGF) family of peptide growth factors and the ErbB family of tyrosine kinases, the receptors for these factors. Accompanying this growth has been an increased appreciation for the roles these molecules play in tumorigenesis and in regulating cell proliferation and differentiation during development. Consequently, a significant question has been how diverse biological responses are specified by these hormones and receptors. Here we discuss several characteristics of hormone-receptor interactions and receptor coupling that contribute to specificity: 1) a single EGF family hormone can bind multiple receptors; 2) a single ErbB family receptor can bind multiple hormones; 3) there are three distinct functional groups of EGF family hormones; 4) EGF family hormones can activate receptors in trans, and this heterodimerization diversifies biological responses; 5) ErbB3 requires a receptor partner for signaling; and 6) ErbB family receptors differentially couple to signaling pathways and biological responses.

Changes in macrophage colony-stimulating factor concentration in serum and follicular fluid in in-vitro fertilization and embryo transfer cycles

OBJECTIVE

To evaluate the changes of macrophage colony-stimulating factor concentration in serum and compare macrophage colony-stimulating factor concentration in follicular fluid (FF) through IVF-ET cycles.

DESIGN

Sera and the matched FFs were collected serially through the IVF-ET cycles and analyzed retrospectively with respect to macrophage colony-stimulating factor concentration.

SETTING

Department of Obstetrics and Gynecology of Kumamoto University Hospital.

PATIENT(S)

Ninety-four women underwent 129 cycles of ovulation induction by using GnRH agonist (GnRHa)-hMG-hCG for IVF-ET program.

INTERVENTION(S)

Serum and FF macrophage colony-stimulating factor concentrations were measured by ELISA.

MAIN OUTCOME MEASURE(S)

Concentrations of macrophage colony-stimulating factor in serum and FF.

RESULT(S)

Serum macrophage colony-stimulating factor concentration was gradually increased throughout ovarian stimulation, and reached a peak from the day of oocyte retrieval to 2 days after oocyte retrieval, whereas no significant change in macrophage colony-stimulating factor was observed in cases of poor ovarian response to hMG. The macrophage colony-stimulating factor concentration in follicles was significantly higher than that in sera on the day of oocyte retrieval, and the concentrations in follicles from which oocyte could be retrieved were significantly higher than those from which oocyte could not be retrieved.

CONCLUSION(S)

These results suggest that gonadotropins lead to an increase in ovarian macrophage colony-stimulating factor production, and that this macrophage colony-stimulating factor production in response to hMG administration is lost in poor ovarian responders. Thus, macrophage colony-stimulating factor may play an important role in the process of follicular maturation and ovulation as an intraovarian regulator.

Role of membrane-anchored heparin-binding epidermal growth factor-like growth factor and CD9 on macrophages

Heparin-binding epidermal-growth-factor-like growth factor (HB-EGF) is a potent mitogen for smooth-muscle cells (SMCs) belonging to the EGF family. We have previously determined that HB-EGF is expressed in macrophages and SMCs of human atherosclerotic lesions and that its membrane-anchored precursor, proHB-EGF, also has a juxtacrine mitogenic activity which is markedly enhanced by CD9, a surface marker of lymphohaemopoietic cells. Therefore, when both proHB-EGF and CD9 are expressed on macrophages, they may strongly promote the development of atherosclerosis. In the present study we have investigated the changes in proHB-EGF and CD9 in THP-1 cells during differentiation into macrophages and by the addition of oxidized low-density lipoproteins (OxLDL) and assessed juxtacrine growth activity of THP-1 macrophages for human aortic SMCs. HB-EGF and CD9 at both the mRNA and the protein level were up-regulated after differentiation into macrophages, and further expression of HB-EGF was induced by the addition of OxLDL or lysophosphatidylcholine. Juxtacrine induction by formalin-fixed growth was suppressed to control levels by an inhibitor of HB-EGF and was partially decreased by anti-CD9 antibodies. These results suggest that co-expression of proHB-EGF and CD9 on macrophages plays an important role in the development of atherosclerosis by a juxtacrine mechanism.

Matrix metalloproteinase-3 releases active heparin-binding EGF-like growth factor by cleavage at a specific juxtamembrane site

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is synthesized as a membrane-anchored precursor that is cleaved to release the soluble mature growth factor. The two forms are active as juxtacrine and paracrine/autocrine growth factors, respectively. The enzymes that process the HB-EGF transmembrane form are unknown. Accordingly, an in vitro assay was established using a fusion protein in which alkaline phosphatase (AP) replaced the transmembrane and cytoplasmic domains of HB-EGF (HB-EGF JM-AP). The fusion protein was anchored to agarose beads coated with anti-AP antibodies. Several matrix metalloproteinases (MMPs) were tested for the ability to release soluble HB-EGF in the in vitro system. MMP-3 released soluble 12-kDa immunoreactive and mitogenic HB-EGF within 30 min. On the other hand neither MMP-2 nor MMP-9 had any cleavage activities. A non-cleavable mutant was prepared by replacing the juxtamembrane (JM) region of HB-EGF with the JM region of CD4. The mutant HB-EGF, which in its full-length form was as active a juxtacrine growth factor as was the wild type HB-EGF in vivo, was not cleaved by MMP-3 in the in vitro assay. The C-terminal portion of the cleaved HB-EGF JM-AP that remained attached to the anti-AP beads was N-terminally sequenced and the MMP-3 cleavage site was determined to be Glu151-Asn152, a site within the JM domain. MMP-3 treatment also released soluble HB-EGF in vivo from MC2 cells expressing transmembrane HB-EGF precursor, at a level of about 2-fold above control. It was concluded that MMP-3 cleaves HB-EGF at a specific site in the JM domain and that this enzyme might regulate the conversion of HB-EGF from being a juxtacrine to a paracrine/autocrine growth factor.

Role of heparin-binding EGF-related peptides in proliferation and apoptosis of activated ras-stimulated intestinal epithelial cells

The ras mutation is a common and critical step in carcinogenesis. Autocrine growth factors are also known to play an important role in cancer cell growth and transformation. However, the contribution of autocrine growth factors in regulation of proliferation and apoptosis of activated ras-stimulated intestinal epithelium is not fully understood. Therefore, we constructed activated ras-transfected intestinal epithelial cell clones (IEC-ras) to examine the role of epidermal growth factor (EGF)-related peptides in the behavior of IEC-ras. Overexpression of EGF family growth factors (transforming growth factor alpha, heparin-binding EGF-like growth factor, amphiregulin and betacellulin) and stronger phosphorylation of the EGF receptor was observed in IEC-ras compared with control cells. IEC-ras proliferated more rapidly than control cells, and a specific EGF receptor kinase inhibitor, AG 1478, abolished the increased proliferation of IEC-ras. Heparitinase and chlorate also prevented increased proliferation of IEC-ras. Additionally, IEC-ras expressed more bcl-2 and was more resistant to apoptosis induction by UV radiation and mitomycin C. AG 1478 suppressed bcl-2 expression and inhibited resistance to apoptosis of IEC-ras. Heparitinase and chlorate had effects similar to those of AG 1478. Our data indicate that heparin-binding EGF family growth factors play an important role in both increased proliferation and resistance to apoptosis of ras-stimulated intestinal epithelial cells.

Heparin-binding EGF-like growth factor

HB-EGF is a heparin-binding member of the EGF family that was initially identified in the conditioned medium of human macrophages. Soluble mature HB-EGF is proteolytically processed from a larger membrane-anchored precursor and is a potent mitogen and chemotactic factor for fibroblasts, smooth muscle cells but not endothelial cells. HB-EGF activates two EGF receptor subtypes, HER1 and HER4 and binds to cell surface HSPG. The transmembrane form of HB-EGF is a juxtacrine growth and adhesion factor and is uniquely the receptor for diphtheria toxin. HB-EGF gene expression is highly regulated, for example by cytokines, growth factors, and transcription factors such as MyoD. HB-EGF has been implicated as a participant in a variety of normal physiological processes such as blastocyst implantation and wound healing, and in pathological processes such as tumor growth, SMC hyperplasia and atherosclerosis.

Expression of heparin-binding epidermal growth factor-like growth factor during pancreas development. A potential role of PDX-1 in transcriptional activation

The development of the pancreas appears to be regulated by various growth factors. We report here the expression of heparin-binding epidermal growth factor (EGF)-like growth factor (HB-EGF) in the developing pancreas. Immunostaining of fetal and neonatal rat pancreata, in which endocrine cells are visible as cell clusters often associated with primitive ducts or ductular cells, revealed that most of the cluster-forming cells and primitive ducts or ductular cells express HB-EGF protein. In contrast, the exocrine pancreas lacked HB-EGF expression. Based on findings that the expression pattern was similar to that of the homeodomain-containing transcription factor PDX-1 (IDX-1/STF-1/IPF1) and that the regulatory region of the HB-EGF gene contained sequences similar to the PDX-1-binding A element, we examined whether PDX-1 could be a potential activator of HB-EGF gene expression. The results of reporter gene analyses suggested that the HB-EGF gene promoter is PDX-1-responsive and that the activity of the promoter in pancreatic beta cell-derived betaTC1 cells depends on the PDX-1 binding site-like sequences. Gel-mobility shift analyses using an anti-PDX-1 antibody indicated that PDX-1 is a specific and dominant binding factor for an A element-like sequence in the HB-EGF gene. These observations suggest the possible involvement of HB-EGF in pancreas development. While PDX-1 is essential for pancreas development, HB-EGF may function as a mediator of PDX-1 and thus be involved in the development of the endocrine pancreas.

Enhancement of artificial juxtacrine stimulation of insulin by co-immobilization with adhesion factors

Insulin was co-immobilized with a cell adhesion factor--fibronectin or polyallylamine--on a surface-hydrolyzed poly(methyl methacrylate) film. Chinese hamster ovary cells overexpressing human insulin receptors were cultured on the film in the absence of serum or soluble proteins. While insulin immobilization did not affect cell adhesion, insulin immobilized on fibronectin-immobilized film reduced the adhesion. Addition of the tetrapeptide Arg-Gly-Asp-Ser (RGDS) inhibited cell adhesion onto fibronectin-immobilized films while cell adhesion onto polyallylamine-immobilized films was not inhibited by RGDS. Small amounts of immobilized insulin (1 to 10% of the amount of free insulin required to achieve cell growth acceleration) were sufficient to stimulate cell proliferation. The maximal mitogenic effect of immobilized insulin was greater than that of free insulin. In addition, co-immobilization with the adhesion factor remarkably enhanced the mitogenic effect. The phosphorylation of the receptor with free insulin attained the maximum degree very rapidly but ceased quickly. On the other hand, the receptor phosphorylation with immobilized insulin was accompanied by a longer induction period and lasted a longer period of time than that with free insulin. Insulin co-immobilization on fibronectin or polyallylamineimmobilized films reduced the induction period by enhancement of cell adhesion. The early and long-lasting receptor activation might have been caused by the greater mitogenic effect of co-immobilized biosignaling polypeptides.

Structure-function analysis of the diphtheria toxin receptor toxin binding site by site-directed mutagenesis

Diphtheria toxin (DT) binds to the epidermal growth factor (EGF)-like domain of human membrane-anchored heparin-binding EGF-like growth factor (proHB-EGF), the human DT receptor (DTR). DT does not bind to mouse proHB-EGF because of amino acid substitutions within the EGF-like domain. We made 10 independent mutants, replacing a single amino acid within the EGF-like domain of human DTR/proHB-EGF with the corresponding amino acid residue in mouse proHB-EGF. The mutant proteins were transiently expressed in mouse L cells either expressing or not expressing DRAP27/CD9, and DT binding was measured. DT binding activity of GST fusion proteins containing the mutated EGF-like domain was also determined by a cell-free binding assay. The largest effect was seen with E141H, and second largest effects were seen with F115Y and L127F in all of the assay systems. We conclude that Phe115, Leu127, and Glu141 are critical amino acid residues for DT binding. A computer model of the tertiary structure of the EGF-like domain of human DTR/proHB-EGF was made. The model predicts that three amino acid residues critical for DT binding activity, Phe115, Leu127, and Glu141, are all located on the same face of the EGF-like domain, suggesting that this face of DTR/proHB-EGF interacts with the receptor-binding domain of DT.

A novel juxtamembrane domain isoform of HER4/ErbB4. Isoform-specific tissue distribution and differential processing in response to phorbol ester

Human epidermal growth factor receptor 4 (HER4) is a member of the epidermal growth factor (EGF) receptor subfamily of receptor tyrosine kinases that is activated by neuregulins (NRG), betacellulin (BTC), and heparin-binding EGF-like growth factor. Sequencing of full-length human HER4 cDNAs revealed the existence of two HER4 isoforms that differed by insertion of either 23 or 13 alternative amino acids in the extracellular juxtamembrane (JM) region. The 23-amino acid form (HER4 JM-a) and the 13-amino acid form (HER4 JM-b) were expressed in a tissue-specific manner, as demonstrated by reverse transcriptase-polymerase chain reaction analysis of mouse and human tissues. Both isoforms were expressed in neural tissues such as cerebellum, whereas kidney expressed HER4 JM-a only and heart HER4 JM-b only. In situ hybridization using specific oligonucleotides demonstrated transcription of both JM-a and JM-b isoforms in the mouse cerebellum. Tyrosine phosphorylation analysis indicated that both receptor isoforms were activated to the same extent by NRG-beta1 and BTC, and to a lesser extent by NRG-alpha1 and heparin-binding EGF-like growth factor. A functional difference was found, however, in response to phorbol ester treatment. Stimulation of cells with phorbol ester resulted in a loss of 125I-NRG-beta1 binding and in a reduction of total cell-associated HER4 protein in HER4 JM-a transfectants but not in HER4 JM-b transfectants. It was concluded that novel alternatively spliced isoforms of HER4 exist, that they are distributed differentially in vivo in mouse and human tissues, that they are both activated by HER4 ligands, and that they may represent cleavable and noncleavable forms of HER4.

Expression of betacellulin and epiregulin genes in the mouse uterus temporally by the blastocyst solely at the site of its apposition is coincident with the "window" of implantation

In the mouse, the process of implantation is initiated by the attachment reaction between the blastocyst trophectoderm and uterine luminal epithelium that occurs at 2200-2300 h on day 4 (day 1 = vaginal plug) of pregnancy. Several members of the EGF family are considered important in embryo-uterine interactions during implantation. This investigation demonstrates that the expression of two additions to the family, betacellulin and epiregulin, are exquisitely restricted to the mouse uterine luminal epithelium and underlying stroma adjacent to the implanting blastocyst. These genes are not expressed during progesterone-maintained delayed implantation, but are rapidly switched on in the uterus surrounding the implanting blastocyst following termination of the delay by estrogen. These results provide evidence that expression of betacellulin and epiregulin in the uterus requires the presence of an active blastocyst and suggest an involvement of these growth factors in the process of implantation.

Gastric hyperplasia and increased proliferative responses of lymphocytes in mice lacking the COOH-terminal ankyrin domain of NF-kappaB2

The nfkb2 gene encodes the p100 precursor which produces the p52 protein after proteolytic cleavage of its COOH-terminal domain. Although the p52 product can act as an alternative subunit of NF-kappaB, the p100 precursor is believed to function as an inhibitor of Rel/NF-kappaB activity by cytoplasmic retention of Rel/NF-kappaB complexes, like other members of the IkappaB family. However, the physiological relevance of the p100 precursor as an IkappaB molecule has not been understood. To assess the role of the precursor in vivo, we generated, by gene targeting, mice lacking p100 but still containing a functional p52 protein. Mice with a homozygous deletion of the COOH-terminal ankyrin repeats of NF-kappaB2 (p100(-/-)) had marked gastric hyperplasia, resulting in early postnatal death. p100(-/-) animals also presented histopathological alterations of hematopoietic tissues, enlarged lymph nodes, increased lymphocyte proliferation in response to several stimuli, and enhanced cytokine production in activated T cells. Dramatic induction of nuclear kappaB-binding activity composed of p52-containing complexes was found in all tissues examined and also in stimulated lymphocytes. Thus, the p100 precursor is essential for the proper regulation of p52-containing Rel/NF-kappaB complexes in various cell types and its absence cannot be efficiently compensated for by other IkappaB proteins.

High concentration of glucose increases mitogenic responsiveness to heparin-binding epidermal growth factor-like growth factor in rat vascular smooth muscle cells

The effect of a high extracellular glucose concentration on the mitogenic response of rat vascular smooth muscle cells (SMCs) to heparin-binding epidermal growth factor-like growth factor (HB-EGF) was investigated. The mitogenic effect of HB-EGF was significantly greater in SMCs cultured in high glucose (25 mmol/L) than in cells cultured in low glucose (5.5 mmol/L) or at high osmolarity (5.5 mmol/L glucose plus 19.5 mmol/L mannitol). The mitogenic effect of epidermal growth factor (EGF), which shares the EGF receptor with HB-EGF, was not affected by glucose concentration. The mitogenic effect of HB-EGF was greater when incubated with heparan sulfate (HS) isolated from SMCs cultured in high glucose than with HS from cells cultured in low glucose. HS synthesized by cells in high glucose was of smaller molecular size and less sulfated than HS synthesized by cells in low glucose. The abundance of mRNA encoding HS-N-deacetylase/N-sulfotransferase (HS-NdAc/NST), a regulatory enzyme in the biosynthesis of HS, was decreased by high glucose in a protein kinase C-independent manner. These observations suggest that the enhanced mitogenic response to HB-EGF in SMCs cultured in high glucose may be attributable to changes in cell-associated HS. Downregulation of HS-NdAc/NST gene expression by high glucose may be related to the altered HS biosynthesis.

Immunohistochemical localization of heparin-binding epidermal growth factor-like growth factor in normal skin and skin cancers

Heparin-binding epidermal growth factor (EGF)-like growth factor is a 22-kDa glycoprotein that was originally identified as a secreted product of cultured human macrophages. Although the growth factor mRNA has been identified in various cells and tissues, the tissue distribution of the protein itself has rarely been demonstrated. In this study, the EGF-like growth factor was detected immunohistochemically in a variety of human skin samples by indirect immunofluorescence using a polyclonal rabbit antiserum raised against residues 26-41 of mature heparin-binding EGF. The keratinocytes of a variety of epithelium-derived structures demonstrated reproducible, specific staining for the EGF. In normal tissues, this staining was prominent in the basal cells of the epidermis and in the epithelial cells lining epidermal appendages such as hair follicles, sebaceous sweat glands and eccrine sweat glands. In addition, specific staining was detected in skin cancers derived from the basal epithelial cell layer, including basal and squamous cell carcinomas of the skin, with no staining detected in melanoma specimens. Immunoreactive heparin-binding EGF was characteristically associated with the surface of cells. With minor exceptions, the immunoreactive sites are identical to the known EGF receptor distribution in the skin, and suggest that keratinocyte-derived heparin-binding EGF may act in concert with other EGF family members in processes such as skin morphogenesis and wound repair, as well as in the development of skin cancers.

The effect of cilostazol, a cyclic nucleotide phosphodiesterase III inhibitor, on heparin-binding EGF-like growth factor expression in macrophages and vascular smooth muscle cells

Heparin-binding EGF-like growth factor (HB-EGF) is a mitogen for smooth muscle cells (SMC) and is detected in SMC and macrophages in atherosclerotic plaques, suggesting that HB-EGF may be associated with the pathogenesis of atherosclerosis. The present study indicates that cilostazol, a phosphodiesterase III inhibitor, suppresses the expression of HB-EGF in rat aortic SMC and in U-937 cells, a macrophage-like cell line, stimulated by lipopolysaccharide. Further, cilostazol diminished the induction of HB-EGF mRNA by methylglyoxsal, which is a reactive dicarbonyl metabolite produced as the result of a glycation reaction and which might be associated with macroangiopathy caused by hyperglycemia. Cilostazol suppressed the production of HB-EGF protein in the conditioned medium of SMC. These data suggest that cilostazol might act by suppressing the progression of atherogenesis by means of suppressing the expression of HB-EGF in SMC and macrophages.

Epidermal growth factor and betacellulin mediate signal transduction through co-expressed ErbB2 and ErbB3 receptors

Interleukin-3 (IL-3)-dependent murine 32D cells do not detectably express epidermal growth factor receptors (EGFRs) and do not proliferate in response to EGF, heregulin (HRG) or other known EGF-like ligands. Here, we report that EGF specifically binds to and can be crosslinked to 32D transfectants co-expressing ErbB2 and ErbB3 (32D.E2/E3), but not to transfectants expressing either ErbB2 or ErbB3 individually. [125I]EGF-crosslinked species detected in 32D. E2/E3 cells were displaced by HRG and betacellulin (BTC) but not by other EGF-like ligands that were analyzed. EGF, BTC and HRG also induced receptor tyrosine phosphorylation, activation of downstream signaling molecules and proliferation of 32D.E2/E3 cells. 32D transfectants were also generated which expressed an ErbB3-EGFR chimera alone (32D.E3-E1) or in combination with ErbB2 (32D. E2/E3-E1). While HRG stimulation of 32D.E3-E1 cells resulted in DNA synthesis and receptor phosphorylation, EGF and BTC were inactive. However, EGF and BTC were as effective as HRG in mediating signaling when ErbB2 was co-expressed with the chimera in the 32D.E2/E3-E1 transfectant. These results provide evidence that ErbB2/ErbB3 binding sites for EGF and BTC are formed by a previously undescribed mechanism that requires co-expression of two distinct receptors. Additional data utilizing MDA MB134 human breast carcinoma cells, which naturally express ErbB2 and ErbB3 in the absence of EGFRs, supported the results obtained employing 32D cells and suggest that EGF and BTC may contribute to the progression of carcinomas that co-express ErbB2 and ErbB3.

Neuregulin-3 (NRG3): a novel neural tissue-enriched protein that binds and activates ErbB4

We describe the identification of Neuregulin-3 (NRG3), a novel protein that is structurally related to the neuregulins (NRG1). The NRG1/neuregulins are a diverse family of proteins that arise by alternative splicing from a single gene. These proteins play an important role in controlling the growth and differentiation of glial, epithelial, and muscle cells. The biological effects of NRG1 are mediated by receptor tyrosine kinases ErbB2, ErbB3, and ErbB4. However, genetic studies have suggested that the activity of ErbB4 may also be regulated in the central nervous system by a ligand distinct from NRG1. NRG3 is predicted to contain an extracellular domain with an epidermal growth factor (EGF) motif, a transmembrane domain, and a large cytoplasmic domain. We show that the EGF-like domain of NRG3 binds to the extracellular domain of ErbB4 in vitro. Moreover, NRG3 binds to ErbB4 expressed on cells and stimulates tyrosine phosphorylation of this receptor. The expression of NRG3 is highly restricted to the developing and adult nervous system. These data suggest that NRG3 is a novel, neural-enriched ligand for ErbB4.

Enhanced production of an EGF-like growth factor by parenchymal macrophages following bleomycin-induced pulmonary injury

The secretion of molecular species related to epidermal growth factor (EGF) by pulmonary alveolar and parenchymal macrophages was investigated in an experimental model of pulmonary fibrosis in mice. Macrophages were isolated from cells obtained by bronchoalveolar lavage or by enzymatic disaggregation of lung tissue at intervals following induction of pulmonary injury by intratracheal injection of bleomycin. Production of EGF receptor-binding activity by these cells and concentrations of this activity in bronchoalveolar lavage fluid were measured using a radioreceptor assay. Following short-term culture under serum-free conditions, there was significantly increased production of EGF receptor-binding activity by parenchymal macrophages, which was demonstrable at 1 and 2 weeks after administration of bleomycin to susceptible C57BL/6 mice. The activity exhibited affinity for heparin and was completely blocked by an antibody to EGF. There was no such increase in production of receptor-binding activity by alveolar macrophages or in the concentration of activity in lavage fluids. Nor was there any significant increase in production of EGF receptor-binding activity by parenchymal macrophages from bleomycin-resistant BALB/c mice. These results imply that selective activation of interstitial macrophages to secrete an EGF-like growth factor may contribute to the development of pulmonary fibrosis.

Specific inhibition of hair follicle formation by epidermal growth factor in an organ culture of developing mouse skin

Embryonic mouse skin undergoes a drastic morphological change from 13 to 16 gestational days, i.e., formation of rudiments of hair follicles and stratification and cornification of interfollicular epidermis. To investigate underlying molecular mechanisms of the morphogenesis, we established an organ culture system that allows skin tissues isolated from 12.5- or 13.5-days postcoitus embryos to develop in a manner that is histologically and temporally similar to the process in vivo. Expression of differentiation markers of epidermal keratinocytes including cholesterol sulfotransferase and cytokeratin K1 was induced in culture, as it occurs also in vivo. The morphogenic process was observed by time-lapse videomicrography. In this culture system, epidermal growth factor (EGF) and transforming growth factor alpha specifically and completely inhibited the hair follicle formation with marginal effects on interfollicular epidermis. The inhibitory action by EGF was reversible and stage specific, i.e., at an early stage of the development of hair rudiments. Among known ligands to the EGF receptor, Schwannoma-derived growth factor and heparin-binding EGF were expressed in in vivo epidermis during the period of the initial formation of hair follicles. EGF receptor is expressed in epidermis throughout the developing period examined. Using an adenovirus vector, we demonstrated that the lacZ gene was transduced into the epidermal and dermal cell layers without appreciable toxicity. These results indicate that the present culture system provides a unique opportunity to investigate molecular mechanisms of skin morphogenesis including the role of EGF signaling under defined experimental conditions.

Hypertonic induction of the cell adhesion molecule beta 1-integrin in MDCK cells

Cells of many organisms adapt to osmotic stress by accumulating compatible organic osmolytes. In Madin-Darby canine kidney (MDCK) cells, a renal epithelial cell line widely used as a culture model for the study of osmotic regulation in mammals, extracellular hypertonicity induces genes responsible for the accumulation of organic osmolytes. We have recently cloned from these cells a partial cDNA corresponding to a member of the transmembrane 4 superfamily (tetraspan) family, CD9 antigen, and demonstrated its induction by hypertonicity [D. Sheikh-Hamad, J. D. Ferraris, J. Dragolovich, H. G. Preuss, M. B. Burg, and A. García-Pérez. Am. J. Physiol. 270 (Cell Physiol. 39): C253-C258, 1996]. An association between CD9 and potential regulatory proteins, such as the heparin-binding epidermal growth factor-like protein and the cell adhesion molecule beta 1-integrin, has been reported. Here, using beta 1-integrin-specific monoclonal antibodies and an antisense oligonucleotide probe, we demonstrate expression and hypertonic induction of beta 1-integrin in MDCK cells. Induction of the mRNA and protein occurs in 2 h and is maximal at 6 h, consistent with a regulatory role in the adaptation to osmotic stress. In addition, we show that accumulation of organic osmolytes markedly attenuates the hypertonic induction of the mRNA, a feature shared with genes involved in hyperosmotic stress response. Finally, we demonstrate that CD9 and beta 1-integrin are expressed in association at the cell membrane. Our findings suggest the existence of a cluster of integral membrane proteins that includes but may not be limited to CD9 and the adhesion molecule beta 1-integrin, which may play a role in the adaptation of kidney cells to osmotic stress, possibly at the regulatory level.

Quantitative determination of the epidermal growth factor receptor in cervical cancer and normal cervical epithelium by 2-color flow cytometry: evidence for down-regulation in cervical cancer

Expression of epidermal growth factor receptor (EGFR) was quantified by 2-color flow cytometry in cervical cancer (n = 73) and normal cervical epithelium (n = 11). EGFR was determined using a murine monoclonal EGFR antibody, and number of bound antibodies was quantified adding calibration beads with defined antigenic binding sites. Tumor cells were identified by simultaneous DNA staining. Epithelium of normal cervical tissue was detected by labeling for cytokeratin. Results were compared with EGFR quantification by autoradiography on cryostat sections using a radioligand binding assay. A high degree of correlation was found between the 2 methods. In cervical carcinomas 14,600 binding sites/cell (median; range, 160-283,000 binding sites/cell) were detected, considerably less compared with normal cervical squamous epithelium, which was 30,700 binding sites/cell (median; range, 19,900-44,000 binding sites/cell). This finding clearly contrasts with other reports of enhanced EGFR expression in cervical cancer. The discrepancy may be explained by contamination of tissue homogenates used for radioligand or enzyme immunosorbent assays by non-epithelial tissue elements with low or absent EGFR expression. Interference with quantitative EGFR determination in epithelial cells may result in false low estimates of EGFR expression predominantly in normal cervical tissue. This should be avoided by identifying tumor and normal epithelial cells prior to analysis. In our study, 63% of cervical cancers expressed low levels of EGFR compared with normal cervical epithelium, and only 10% showed overexpression. There is evidence that cervical carcinomas overexpressing EGFR represent a small, but biologically distinct group of cervical cancers exhibiting enhanced aggressiveness associated with poor survival of the patients.

Distribution of mRNA for human epiregulin, a differentially expressed member of the epidermal growth factor family

We have recently identified epiregulin as a new growth regulator and a member of the epidermal growth factor (EGF) family. Epiregulin has certain characteristics that are different from those of the classical members of the EGF family, EGF and transforming growth factor alpha, including mitogenic responses on several normal cells and binding to EGF receptors on epidermoid carcinoma A431 cells. In the present study we cloned and identified the expression of human epiregulin transcript. The human epiregulin gene encoded a 163-residue putative transmembrane precursor containing an EGF-like domain in the internal segment, and the structural organization was similar to that of other members of the EGF family that bind to EGF receptors. Northern blot analysis showed the expression of human epiregulin to be mainly on peripheral blood macrophages and the placenta in normal tissues, and was highest on epithelial tumour cell lines in various types of tumour cell lines. The expression profile was quite different from that of other members of the EGF family in normal and tumour cells. Recombinant expression in mammalian cells also showed that human epiregulin was secreted as a soluble form of approx. 5 kDa that is biologically active on the basis of the stimulation of DNA synthesis. Our findings suggest that epiregulin is involved in certain physiological processes such as maintenance or development of normal cell growth, and the progression of carcinomas.

Expression of mRNA for a short form of heparin-binding EGF-like growth factor

In this paper we report the cloning and characterization of cDNA encoding a novel, short form of heparin-binding EGF-like growth factor (SF HB-EGF), and show expression of specific mRNA in various tissues and cell types. Our data suggest that SF HB-EGF mRNA is a product of alternative splicing. Like normal HB-EGF, SF HB-EGF contains the signal peptide, the propeptide, the heparin-binding domain and the first two conservative disulfide loops of the EGF unit. Instead of the third disulfide loop, the spacer, the transmembrane and the cytoplasmic domains, SF HB-EGF has a nine amino acid tail.

mRNA expression of ligands of the epidermal-growth-factor-receptor in the uterus

Six different ligands of the epidermal-growth-factor receptor (EGFR) have been identified in the past. In some cervical squamous-cell carcinomas, an increased amount of proteins binding to the EGFR has been reported. In order to identify the mRNA of EGFR ligands (EGFRL), which might be overexpressed in cervical and endometrial cancers, we performed semi-quantitative reverse-transcription/polymerase chain reactions (RT-PCR) for all 6 EGFRL in RNA extracts of normal and malignant tissue samples of the human uterus. PCR products from RNA extracts of 83 patients were quantitated relative to the housekeeping gene and internal standard pyruvate dehydrogenase by analyzing the PCR kinetics of product synthesis. In extracts of normal cervix, the level of mRNA expression of the EGFRL was significantly higher than in endometrium. No significant difference was detected between normal cervix and cervical carcinomas. However, both in cervical and in endometrial cancers, mRNA expression was non-parametrically distributed and in some cervical cancers overexpression of transforming growth factor alpha (TGF-alpha), amphiregulin or EGF was observed. In endometrial cancers, mRNA levels of all EGFRL were higher than in normal endometrium. This increase was significant (p < 0.005) for TGF-alpha and amphiregulin. Thus, TGF-alpha mRNA is overexpressed in approximately 10% of cervical cancers and in the majority of endometrial cancers. Since TGF-alpha anti-sense therapy might represent a future strategy in such cancers, we also determined the absolute level of TGF-alpha mRNA expression by quantitative PCR using a cloned standard.

TGF-alpha, EGF, and their cognate EGF receptor are co-expressed with desmin during embryonic, fetal, and neonatal myogenesis in mouse tongue development

The developing mouse tongue provides a model for discrete patterns of morphogenesis during short periods of embryonic development. Occipital somite-derived myogenic cells interact with cranial neural crest-derived ecto-mesenchymal cells to form the musculature of the tongue. The biochemical signals that control close range autocrine and/or paracrine signaling processes required to establish the fast-twitch complex tongue musculature are not known. The present study was designed to test the hypothesis that desmin, epidermal growth factor (EGF), and transforming growth factor-alpha (TGF alpha) and their cognate receptor, epidermal growth factor receptor (EGFr), are co-expressed during tongue myogenesis and define specific developmental stages of tongue muscle cell differentiation. To test this hypothesis, we performed studies to analyze the timing, position, and concentration of desmin, TGF alpha, EGF, and EGFr from embryonic day 9 (E9) through birth in Swiss Webster mouse tongue development. Desmin, TGF alpha, EGF, and EGFr co-localized to cells of myogenic lineage in the four occipital somites and subsequently in myoblasts and myotubes from E9 through E17. By newborn stage, desmin is localized to discrete regions in myofibers corresponding to Z-line delimiting sarcomeres, and A-band within sarcomeres; immunostaining for desmin, TGF alpha, and EGF persisted in differentiated myotubes and striated skeletal muscle. Desmin increased from 0.01% at E11 to 0.51% of the total protein by E17 and at birth. Concomitantly, the patterns and increases in TGF alpha, EGF, and EGFr showed significant increases during the same developmental period. The temporal and positional co-localization of TGF alpha, EGF, and EGFr support the hypothesis that autocrine and paracrine regulation of desmin by actions of growth factor ligand and receptor defines critical stages of tongue myogenesis.

Interleukin-2 modulates the responsiveness to angiotensin II in cultured vascular smooth muscle cells

Preincubation with interleukin-2 (IL-2), a T cell-derived cytokine, enhanced the increase in intracellular Ca2+ ([Ca2+]i) induced by angiotensin II (AII) in vascular smooth muscle cells (VSMC). IL-2 itself did not affect the basal [Ca2+]i level or the maximal response of [Ca2+]i increase induced by AII. Furthermore, IL-2-induced enhancement was not observed in the absence of extracellular Ca2+, suggesting that IL-2 enhances Ca2+ influx induced by AII. IL-2 also enhanced the stimulation of DNA synthesis induced by AII, although IL-2 alone did not stimulate DNA synthesis. Genistein, an inhibitor of protein tyrosine kinases, significantly inhibited IL-2-induced enhancement of both Ca2+ influx and DNA synthesis induced by AII. A neutralizing antibody against heparin-binding epidermal growth factor-like growth factor (HB-EGF) partially inhibited IL-2-induced enhancement of DNA synthesis induced by AII. These findings suggest that autocrine HB-EGF is partially involved in the mechanism of IL-2-induced enhancement of DNA synthesis. On the other hand IL-2 stimulated both glycosaminoglycan (GAG) and prostacyclin syntheses and enhanced the stimulation of both GAG and prostacyclin syntheses induced by AII. Therefore, IL-2 may play important roles in the pathogenesis of atherosclerosis and vascular disease by modulating the responsiveness to AII in VSMC.