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

Toxicokinetic study of recombinant human heparin-binding epidermal growth factor-like growth factor (rhHB-EGF) in female Sprague Dawley rats

PURPOSE

To determine the toxicity and pharmacokinetics of recombinant heparin-binding epidermal growth factor-like growth factor in female Sprague Dawley rats following intra-bladder and intravenous administration.

MATERIALS AND METHODS

rhHB-EGF was administered once daily for 6 or 27 days at doses of 3, 10, or 30 microg/kg. 125I-rhHB-EGF was administered on day 7 or 28 for pharmacokinetic analysis. Toxicity was assessed by general appearance and behavior, gross necropsy, blood chemistry and microscopic evaluation.

RESULTS

Plasma AUCss of [125I] rhHB-EGF equivalents following IB administration for 7 days were 4.28+/-2.29, 7.75+/-2.70, and 7.11+/-1.42 ng ml(-1) h(-1) at doses of 3, 10, and 30 microg/kg, respectively. Following IV administration, the AUCss on day 7 increased from 27.0+/-2.66 to 124+/-5.09 and 385.11+/-7.57 ng ml(-1) h(-1) with increasing the dose from 3 to 10 and 30 microg/kg. Similar AUCss data was obtained after 28 day administration. No toxicity was evident upon gross examination. Histologic examination revealed subacute inflammation and lymphocytic infiltration of the urinary bladder in animals from all groups dosed by the IB route.

CONCLUSIONS

Plasma and bladder concentrations of recombinant human [125I] rhHB-EGF equivalents were significantly lower following the IB route than following IV administration. Histologic tissue examination indicated no toxicity attributable to rhHB-EGF.

Amino-terminal deletion of heparin-binding epidermal growth factor-like growth factor4-127 stimulates cell proliferation but lacks insulin-like activity

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) Northern analysis demonstrated a novel 0.8-kb liver-specific HB-EGF transcript in addition to the endogenous 2.5-kb HB-EGF full-length transcript present in kidney, lung and liver tissues. Reverse transcriptase-polymerase chain reaction screening of liver RNA suggests that the 0.8-kb HB-EGF transcript lacks at least a portion of the amino-terminal EGF-like domain. In light of these data, we have constructed a human HB-EGF cDNA (HB-EGF(DeltaN)) which lacks 373 bp, encoding the majority of the extracellular EGF-like domain, while maintaining the ectodomain 'shedding' site, transmembrane and cytoplasmic domains.

OBJECTIVE

The goal of this study is to characterize the ability of HB-EGF(DeltaN) to (i) stimulate cell proliferation and (ii) determine whether down-regulation of insulin-like growth factor-binding protein (IGFBP)-3 and -4 mRNA is regulated by soluble, mature HB-EGF or HB-EGF C.

MATERIALS AND METHODS

HB-EGF(DeltaN) encodes nucleotides +1-10 of exon 1 linked to nucleotides 383-627 of the carboxy-terminal portion of exon 3 through exon 5.

RESULTS

Expression of HB-EGF(DeltaN) in mouse fibroblasts (MLC) resulted in 6.5- and 8-kDa HB-EGF immunoreactive proteins, stimulated tyrosine phosphorylation of p42 kDa and cell proliferation in MLC, but lacked the ability to bind EGF receptors. Finally, HB-EGF(DeltaN) failed to down-regulate IGFBP-3 and -4 mRNA when expressed in normal rat kidney cells.

CONCLUSIONS

These findings demonstrate that amino-terminally truncated, membrane-bound form of HB-EGF stimulates cell proliferation but lacks insulin-like signalling, suggesting that insulin-like signalling is mediated by soluble, mature HB-EGF binding to EGF receptors.

Betacellulin-delta4, a novel differentiation factor for pancreatic beta-cells, ameliorates glucose intolerance in streptozotocin-treated rats

We previously described a novel alternatively spliced mRNA transcript of the betacellulin (BTC) gene. This splice isoform, termed BTC-delta4, lacks the C-loop of the epidermal growth factor motif and the transmembrane domain as a result of exon 4 'skipping'. In this study, we expressed BTC-delta4 recombinantly to explore its biological function. When BTC-delta4 was expressed in COS-7 cells, it was secreted largely into the culture medium, in contrast to BTC. Unlike BTC, highly purified recombinant BTC-delta4 produced in Escherichia coli failed to bind or induce tyrosine phosphorylation of either ErbB1 or ErbB4, nor did it antagonize the binding of BTC to these receptors. Consistent with this, BTC-delta4 failed to stimulate DNA synthesis in Balb/c 3T3 and INS-1 cells. However, BTC-delta4 induced differentiation of pancreatic beta-cells; BTC-delta4 converted AR42J cells to insulin-producing cells. When recombinant BTC-delta4 was administered to streptozotocin-treated neonatal rats, it reduced the plasma glucose concentration and improved glucose tolerance. Importantly, BTC-delta4 significantly increased the insulin content, the beta-cell mass, and the numbers of islet-like cell clusters and PDX-1-positive ductal cells. Thus, BTC-delta4 is a secreted protein that stimulates differentiation of beta-cells in vitro and in vivo in an apparent ErbB1- and ErbB4-independent manner. The mechanism by which BTC-delta4 exerts this action on beta-cells remains to be defined but presumably involves an, as yet, unidentified unique receptor.

Comparative analysis of spore coat formation, structure, and function in Dictyostelium

Dictyostelium produces spores at the end of its developmental cycle to propagate the lineage. The spore coat is an essential feature of spore biology contributing a semipermeable chemical and physical barrier to protect the enclosed amoeba. The coat is assembled from secreted proteins and a polysaccharide, and from cellulose produced at the cell surface. They are organized into a polarized molecular sandwich with proteins forming layers surrounding the microfibrillar cellulose core. Genetic and biochemical studies are beginning to provide insight into how the deliveries of protein and cellulose to the cell surface are coordinated and how cysteine-rich domains of the proteins interact to form the layers. A multidomain inner layer protein, SP85/PsB, seems to have a central role in regulating coat assembly and contributing to a core structural module that bridges proteins to cellulose. Coat formation and structure have many parallels in walls from plant, algal, yeast, protist, and animal cells.

Identification of an alternatively spliced mRNA transcript of human betacellulin lacking the C-loop of the EGF motif and the transmembrane domain

This paper describes the cloning and characterization of a novel cDNA encoding a short form of betacellulin (BTC-beta), and reports the expression of this mRNA in a variety of human tissues and cell types. BTC-beta is likely the result of alternative splicing. This splicing event leads to the generation of an mRNA encoding an unusual BTC precursor in which the C-loop of the EGF domain and the transmembrane domain are deleted while the remainder of the mature molecule is fused in-frame to the C-terminal cytoplasmic tail.

Granulocyte-Macrophage Colony-Stimulating Factor Induces Expression of Heparin-Binding Epidermal Growth Factor–Like Growth Factor/Diphtheria Toxin Receptor and Sensitivity to Diphtheria Toxin in Human Neutrophils

Heparin-binding epidermal growth factor–like growth factor (HB-EGF) is a widely expressed EGF superfamily member that induces mitogenic and/or chemotactic activities toward different cell types through binding to EGF receptors 1 or 4. Membrane-bound HB-EGF exerts growth activity and adhesion capabilities and possesses the unique property of being the receptor for diphtheria toxin (DT). Using molecular and functional techniques, we show that human polymorphonuclear granulocytes (PMN), which did not express HB-EGF in resting conditions, expressed it at mRNA and protein level, following incubation with granulocyte-macrophage colony-stimulating factor (GM-CSF). Other classic agonists for PMN (including lipopolysaccharide, phagocytable particles, tumor necrosis factor-, or G-CSF) failed to induce HB-EGF. The effects of GM-CSF on HB-EGF mRNA levels were concentration-dependent, reached a plateau after 1 to 2 hours of stimulation, and did not require protein synthesis. After GM-CSF treatment, membrane-bound HB-EGF was detected by flow cytometry. At the same time, PMN acquired sensitivity to the apoptosis-promoting effect of DT, which, moreover, specifically suppressed the GM-CSF–induced priming of formyl-methionyl-leucyl-phenylalanine–stimulated superoxide anion release. Finally, soluble HB-EGF was detected in the PMN culture medium by a specific enzyme-linked immunosorbent assay. Thus, we provide evidence that HB-EGF is specifically inducible by GM-CSF in PMN and represents a novel peptide to be included in the repertoire of PMN-derived cytokines.

Granulocyte-Macrophage Colony-Stimulating Factor Induces Expression of Heparin-Binding Epidermal Growth Factor–Like Growth Factor/Diphtheria Toxin Receptor and Sensitivity to Diphtheria Toxin in Human Neutrophils

Heparin-binding epidermal growth factor–like growth factor (HB-EGF) is a widely expressed EGF superfamily member that induces mitogenic and/or chemotactic activities toward different cell types through binding to EGF receptors 1 or 4. Membrane-bound HB-EGF exerts growth activity and adhesion capabilities and possesses the unique property of being the receptor for diphtheria toxin (DT). Using molecular and functional techniques, we show that human polymorphonuclear granulocytes (PMN), which did not express HB-EGF in resting conditions, expressed it at mRNA and protein level, following incubation with granulocyte-macrophage colony-stimulating factor (GM-CSF). Other classic agonists for PMN (including lipopolysaccharide, phagocytable particles, tumor necrosis factor-, or G-CSF) failed to induce HB-EGF. The effects of GM-CSF on HB-EGF mRNA levels were concentration-dependent, reached a plateau after 1 to 2 hours of stimulation, and did not require protein synthesis. After GM-CSF treatment, membrane-bound HB-EGF was detected by flow cytometry. At the same time, PMN acquired sensitivity to the apoptosis-promoting effect of DT, which, moreover, specifically suppressed the GM-CSF–induced priming of formyl-methionyl-leucyl-phenylalanine–stimulated superoxide anion release. Finally, soluble HB-EGF was detected in the PMN culture medium by a specific enzyme-linked immunosorbent assay. Thus, we provide evidence that HB-EGF is specifically inducible by GM-CSF in PMN and represents a novel peptide to be included in the repertoire of PMN-derived cytokines.

Heparin-Binding Epidermal Growth Factor–Like Growth Factor/Diphtheria Toxin Receptor Expression by Acute Myeloid Leukemia Cells

Heparin-binding epidermal growth factor–like growth factor (HB-EGF) is an EGF family member expressed by numerous cell types that binds to EGF receptor 1 (HER-1) or 4 (HER-4) inducing mitogenic and/or chemotactic activities. Membrane-bound HB-EGF retains growth activity and adhesion capabilities and the unique property of being the receptor for diphtheria toxin (DT). The interest in studying HB-EGF in acute leukemia stems from these mitogenic, chemotactic, and receptor functions. We analyzed the expression of HB-EGF in L428, Raji, Jurkat, Karpas 299, L540, 2C8, HL-60, U937, THP-1, ML-3, and K562 cell lines and in primary blasts from 12 acute myeloid leukemia (AML) cases, by reverse-transcriptase polymerase chain reaction (RT-PCR) and Northern blot and by the evaluation of sensitivity to DT. The release of functional HB-EGF was assessed by evaluation of its proliferative effects on the HB-EGF–sensitive Balb/c 3T3 cell line. HB-EGF was expressed by all myeloid and T, but not B (L428, Raji), lymphoid cell lines tested, as well as by the majority (8 of 12) of ex vivo AML blasts. Cell lines (except for the K562 cell line) and AML blasts expressing HB-EGF mRNA underwent apoptotic death following exposure to DT, thus demonstrating the presence of the HB-EGF molecule on their membrane. Leukemic cells also released a fully functional HB-EGF molecule that was mitogenic for the Balb/c 3T3 cell line. Factors relevant to the biology of leukemic growth, such as tumor necrosis factor- (TNF-), 1,25-(OH)2D3, and especially all-trans retinoic acid (ATRA), upregulated HB-EGF mRNA in HL-60 or ML-3 cells. Granulocyte-macrophage colony-stimulating factor (GM-CSF) induced HB-EGF mRNA and acquisition of sensitivity to DT in one previously HB-EGF–negative leukemia case. Moreover, the U937 and Karpas 299 cell lines expressed HER-4 mRNA. This work shows that HB-EGF is a growth factor produced by primary leukemic cells and regulated by ATRA, 1,25-(OH)2D3, and GM-CSF.

Heparin-Binding Epidermal Growth Factor–Like Growth Factor/Diphtheria Toxin Receptor Expression by Acute Myeloid Leukemia Cells

Heparin-binding epidermal growth factor–like growth factor (HB-EGF) is an EGF family member expressed by numerous cell types that binds to EGF receptor 1 (HER-1) or 4 (HER-4) inducing mitogenic and/or chemotactic activities. Membrane-bound HB-EGF retains growth activity and adhesion capabilities and the unique property of being the receptor for diphtheria toxin (DT). The interest in studying HB-EGF in acute leukemia stems from these mitogenic, chemotactic, and receptor functions. We analyzed the expression of HB-EGF in L428, Raji, Jurkat, Karpas 299, L540, 2C8, HL-60, U937, THP-1, ML-3, and K562 cell lines and in primary blasts from 12 acute myeloid leukemia (AML) cases, by reverse-transcriptase polymerase chain reaction (RT-PCR) and Northern blot and by the evaluation of sensitivity to DT. The release of functional HB-EGF was assessed by evaluation of its proliferative effects on the HB-EGF–sensitive Balb/c 3T3 cell line. HB-EGF was expressed by all myeloid and T, but not B (L428, Raji), lymphoid cell lines tested, as well as by the majority (8 of 12) of ex vivo AML blasts. Cell lines (except for the K562 cell line) and AML blasts expressing HB-EGF mRNA underwent apoptotic death following exposure to DT, thus demonstrating the presence of the HB-EGF molecule on their membrane. Leukemic cells also released a fully functional HB-EGF molecule that was mitogenic for the Balb/c 3T3 cell line. Factors relevant to the biology of leukemic growth, such as tumor necrosis factor- (TNF-), 1,25-(OH)2D3, and especially all-trans retinoic acid (ATRA), upregulated HB-EGF mRNA in HL-60 or ML-3 cells. Granulocyte-macrophage colony-stimulating factor (GM-CSF) induced HB-EGF mRNA and acquisition of sensitivity to DT in one previously HB-EGF–negative leukemia case. Moreover, the U937 and Karpas 299 cell lines expressed HER-4 mRNA. This work shows that HB-EGF is a growth factor produced by primary leukemic cells and regulated by ATRA, 1,25-(OH)2D3, and GM-CSF.

Retinoid regulation of heparin-binding EGF-like growth factor gene expression in human keratinocytes and skin

Retinoic acid (RA) has profound effects on epidermal homeostasis; however, the molecular mechanisms by which retinoids regulate keratinocyte cell proliferation and differentiation are not well understood. Here we report that mRNA expression of heparin-binding EGF-like growth factor (HB-EGF), a member of the EGF family of growth factors, is induced by RA in human keratinocytes and skin, and is overexpressed in the context of epidermal hyperplasia in vivo. Treatment of normal adult human keratinocytes with micromolar concentrations of RA significantly induced the expression of HB-EGF. The response was efficiently blocked by specific inhibitors of ErbB tyrosine kinase activity, MAP kinase kinase (MEK), or p38 stress-activated protein kinase. RA also enhanced the induction of HB-EGF mRNA in human skin organ culture, an ex vivo model system displaying many similarities to wound healing in vivo. HB-EGF transcripts were markedly increased in human skin by topical treatment with RA under conditions known to provoke epidermal hyperplasia. HB-EGF transcripts were also markedly overexpressed in the hyperplastic epidermis of psoriatic lesions, relative to normal skin. These results support the hypothesis that the effects of RA on epidermal hyperplasia are mediated at least in part by HB-EGF, and suggest that signal transduction mechanisms other than or in addition to nuclear RA receptors contribute to this effect.

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.