Differential expression in Escherichia coli of the alpha and beta forms of heparin-binding acidic fibroblast growth factor-1: potential role of RNA secondary structure

Synthetic DNA fragments encoding the entire open-reading frame of human heparin-binding growth factor-1 (HBGF-1 beta) and its NH2-terminal truncated form (HBGF-1 alpha) were constructed. When both constructs were expressed in Escherichia coli under control of the trp-lac promoter, biologically active HBGF-1 alpha, but not HBGF-1 beta was produced in high yield. However, high level expression of HBGF-1 beta was obtained using the T7 polymerase expression vector. Computer analysis of HBGF-1 beta predicts the potential for the formation of exaggerated RNA secondary structure near the translation initiation codon and this could be implicated in contributing to the poor translation of HBGF-1 beta under the trp-lac promoter.

Serum, phorbol ester, and polypeptide mitogens increase class 1 and 2 heparin-binding (acidic and basic fibroblast) growth factor gene expression in human vascular smooth muscle cells

Vascular smooth muscle cell proliferation is regarded as a key early event in the pathogenesis of atherosclerosis. Heparin-binding growth factor (HBGF)-1 and HBGF-2, also referred to as acidic and basic fibroblast growth factor, are potent mitogens for human vascular smooth muscle cells. These cells coexpress HBGF-1 and HBGF-2 and thus represent a vessel wall source for both polypeptides. In this report, we demonstrate that HBGF-1 and HBGF-2 expression is increased when quiescent human smooth muscle cells are treated with fetal bovine serum. The kinetics of HBGF-1 and HBGF-2 mRNA accumulation following serum treatment are distinct. In addition, HBGF-1 transcripts remain elevated for a longer time period; this may reflect the different decay rates of the HBGF-1 and HBGF-2 mRNAs. Serum-inducible HBGF-1 and HBGF-2 mRNA expression does not occur when RNA synthesis is repressed by actinomycin D but can occur in the presence of cycloheximide, an inhibitor of protein synthesis. Immunoprecipitation experiments indicate that serum treatment also increases HBGF-1 and HBGF-2 production. Smooth muscle cells treated with phorbol 12-myristate 13-acetate or certain combinations of polypeptide growth factors also express increased levels of HBGF-1 and HBGF-2 transcripts. Potential sources for these growth factors in vivo include platelets, macrophages, and T lymphocytes; thus, smooth muscle cells located at sites of vascular injury or inflammation may express elevated levels of HBGF-1 and HBGF-2.

Amplification and sequencing of mRNA encoding acidic fibroblast growth factor (aFGF) from porcine heart

Progredient stenosis of coronary arteries can induce angiogenic processes, which are probably regulated by polypeptide growth factors like aFGF. Using applications of reverse transcription-polymerase chain reaction, we amplified and sequenced an mRNA encoding aFGF in the porcine myocardium. A DNA fragment of expected size encoding aFGF was amplified with human and bovine aFGF specific oligonucleotide primers in porcine heart. Identity of amplified PCR product to aFGF sequence was confirmed by internal reamplification, Southern hybridization and sequencing of asymmetrically amplified PCR products. The nucleotide sequence analysis of porcine aFGF revealed a homology of 94% to the human and 92% to the bovine cDNA sequences respectively. The amino acid sequence was homologous to the known sequences except for three alterations in the human and thirteen in the bovine aFGF sequences.

Human dermal fibroblasts express multiple bFGF and aFGF proteins

We investigated the regulation of expression of bFGF and aFGF in cultures of normal human dermal fibroblasts grown in a defined, serum-free medium which did not contain FGF. Under these conditions we detected three molecular weight forms of bFGF protein [18.0, 23.0, and 26.6 kiloDaltons (kD)] and three molecular weight forms of aFGF protein (18.4, 19.2, and 28.6 kD) in these cells using western blot analysis. The addition of fetal bovine serum (FBS) to these cultures caused an accumulation of all three molecular weight forms of bFGF protein with a more dramatic accumulation of the 23.0 and 26.6 kD forms. In contrast, the addition of FBS to the cultures had no effect on the level of aFGF proteins. Analysis of mRNA isolated from cells grown in serum-free medium revealed multiple species of both bFGF and aFGF RNA with molecular weights that correlated with our previous observations. The abundance of all bFGF mRNA species increased dramatically after serum treatment while the abundance of aFGF mRNA species increased only slightly. Our observations demonstrate that factor(s) present in FBS elevate the levels of bFGF mRNA and protein beyond the levels already present in the cultures growing in serum-free medium. Moreover, both bFGF and aFGF protein are present in these cells as multiple molecular weight species. Some of these forms are higher in apparent molecular weight than would be predicted from ATG-initiated primary translation products of these genes. We also show that the cells used for this study proliferate in response to bFGF and aFGF, thus, it is possible that the growth of these cells could be subject to autocrine/paracrine control in certain conditions.

Cytotoxic activity of chimeric proteins composed of acidic fibroblast growth factor and Pseudomonas exotoxin on a variety of cell types

Chimeric proteins composed of acidic fibroblast growth factor (acidic FGF) and several forms of Pseudomonas exotoxin (PE) that cannot bind to the PE receptor have been produced in Escherichia coli by expressing chimeric genes in which DNA encoding acidic FGF is fused to various mutant forms of PE. These acidic FGF-PE fusion proteins were found to be cytotoxic to a variety of tumor cell lines including hepatocellular (PLC/PRF/5 and HEPG2), prostatic (LNCaP), colon (HT29), and breast (MCF-7) carcinomas at concentrations of 1-70 ng/ml. The cytotoxic effects of acidic FGF-PE were FGF-receptor specific as demonstrated by competition with excess acidic FGF and by showing that acidic FGF-PE bound to the FGF receptor with the same affinity as acidic FGF. Furthermore, the cell-killing activity of acidic FGF-PE was toxin-mediated, as an acidic FGF-PE mutant, which does not possess ADP-ribosylation activity, failed to kill cells. These findings demonstrate that acidic FGF-PE is a potent cytotoxic molecule that can be targeted to FGF receptor-bearing cells. Because acidic FGF is a potent angiogenic molecule, cytotoxic acidic FGF-PE chimeras may have utility as anti-angiogenic agents. These molecules could be helpful in determining the functional role of FGF receptors in cellular processes.

Serum response heterogeneity among nonsmall cell lung cancer cell lines

This study examined the morphology, in vitro growth, and two genetic responses to serum stimulation in the nonsmall cell lung cancer (NSCLC) cell lines SK-Lu-1, SK-MES-1, A427, and A549. Morphologically, all four were NSCLC: SK-Lu-1 was undifferentiated, the remainder were adenocarcinoma variants. SK-Lu-1 and SK-MES-1 were slow growing with low-anchorage independent growth capacity; the A427 and A549 lines were fast growing with high-anchorage independent growth capacity. All of the lines expressed basic fibroblast growth factor (bFGF) as a dominant 7.1 kb transcript at amounts significantly lower than in control human lung fibroblasts. bFGF expression could be upregulated by serum exposure in several nontransformed human cell lines, but only the SK-Lu-1 NSCLC cells increased bFGF after serum exposure (482%) compared with a peak increase of 1222% in the fibroblast controls. All of the NSCLC cell lines increased c-fos in response to the same serum stimulations. These results show that growth-factor gene expression can be modulated in NSCLC, and that significant differences exist among NSCLC cell lines commonly used as laboratory correlates of human disease.

Cloning and sequence analysis of the human acidic fibroblast growth factor gene and its preservation in leukemia patients

Acidic fibroblast growth factor (aFGF), also known as heparin-binding growth factor 1, is a mitogen for a variety of mesoderm- and neuroectoderm-derived cells. Several different aFGF mRNA species resulting from alternative splicing have been reported. These results suggest that the gene structure and regulatory mechanism for gene expression of aFGF are complex. As a first step toward understanding aFGF gene structure, we have isolated nine overlapping genomic DNA clones spanning 54 kbp and determined the complete DNA sequences of all three coding exons. Comparison of the nucleotide sequences between the human and bovine DNA showed that the sequence similarity extended 2400 bp downstream from the coding region. Cloning of the aFGF gene allowed us to characterize this locus in acute nonlymphocytic leukemia (ANLL) patients. A fraction of ANLL patients (10-20%) have a deletion in the long arm of chromosome 5, whose distal breakpoint overlaps the aFGF locus. Therefore, a prospective cohort of eight ANLL patients was screened using three different repetitive sequence-free probes derived from the aFGF locus. Using beta-globin gene as a normalization probe for hybridizing band intensities, we conclude that there is no allelic loss or gross rearrangement within the 40 kbp stretch of the aFGF gene locus in ANLL patients with or without 5q- deletion. Consistent with this observation, the aFGF mRNA was not detected in the mononuclear cells derived from either an ANLL patient or a normal individual as judged by the reverse transcription and polymerase chain reaction. We also identified a DNA fragment, 10.7 kbp upstream from the first coding exon of human aFGF, whose sequence is conserved in both the primate and rodent genomes. Further characterization of this fragment is likely to provide insight into the significance of this high degree of conservation.

Prominent expression of acidic fibroblast growth factor in motor and sensory neurons

Several growth factors originally characterized and named for their action on a variety of cells have more recently been suggested to be importantly involved in the development and maintenance of the nervous system. Acidic fibroblast growth factor (aFGF) is a member of a family of seven structurally related polypeptide growth factors. The cells responsible for expression of aFGF in the nervous system of adult rats have been identified using an affinity-purified antibody to aFGF in immunohistochemical studies and synthetic oligonucleotide probes for in situ hybridization studies. High levels of aFGF expression were observed in motoneurons, primary sensory neurons, and retinal ganglion neurons. Glial cells did not express detectable amounts of aFGF. Confocal and electron microscopic analysis suggested that a large portion of aFGF immunoreactivity was associated with the cytoplasmic face of neuronal membranes, consistent with the hypothesis that aFGF is a sequestered growth factor.

Tissue- and development-specific expression of HBGF-1 mRNA

The gene for heparin-binding growth factor-1 (HBGF-1) encodes a 15.5-18 kDa polypeptide that affects the proliferation and differentiation of a broad range of mammalian cells and is widely distributed among normal adult tissues. In this study, we show that normal tissues of the adult rat express HBGF-1 transcripts in one of three patterns: a 4.4 kb mRNA was the predominant HBGF-1 transcript in brain, heart and lung; a 1.4 kb mRNA was the predominant transcript in the liver; approximately equal levels of the 1.4 and 4.4 kb mRNAs were found in the kidney. HBGF-1 expression was localized in two tissues: central nervous system expression of HBGF-1 was significantly higher in the brain stem compared to the cerebrum and cerebellum; renal expression of HBGF-1 was significantly higher in the medulla compared to the cortex. Analysis of the postnatal changes in HBGF-1 expression using the newborn rat kidney revealed that the level of HBGF-1 mRNA is low at birth and does not rise to adult levels until the seventh postnatal day. These findings demonstrate that HBGF-1 expression is specific for tissue type and stage of development.

A sequence tagged site (STS) detects EcoRI polymorphisms in the human acidic fibroblast growth factor gene

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Heparin-binding (fibroblast) growth factors are potential autocrine regulators of esophageal epithelial cell proliferation

A serum-free culture system supplemented with neural tissue extract for normal and tumor human esophagi was applied to the culture of mouse esophageal epithelium. Similar to mouse mesenchyme and skin epithelium, esophageal epithelial lines (MEE) emerged after serial culture. The cells had an apparent unlimited life span but retained morphology and other characteristics of normal epithelial cells. The cells formed a small cyst consisting of keratinized squamous epithelium in syngenic hosts. A screen for growth factors that stimulated growth of the nonmalignant MEE cells in the absence of neural extract revealed that epidermal growth factor (EGF) and heparin-binding (fibroblast) growth factors (HBGF) were most effective. An HBGF-like activity was apparent in extracts of rapidly proliferating but not quiescent MEE cells at low or confluent densities. A cloned cell line (MEE/C8) was selected from MEE cell cultures in the absence of neural extract. MEE/C8 cells proliferated independent of either EGF or HBGF at rates equal to MEE cells, cell extracts exhibited HBGF-like activity at all stages of proliferation, and the cells formed large invasive tumors in syngenic hosts. The HBGF-like activity present in extracts of tumorigenic MEE/C8 and proliferating nonmalignant MEE cells had properties similar to HBGF-1 (acidic fibroblast growth factor). These results constitute a cultured mouse esophageal epithelial cell model for study of conversion of immortalized premalignant cells to malignant cells, and suggest that conversion from a state of cell cycle-dependent autocrine expression of one or more members of the HBGF family to a state of constitutive expression correlates with and may contribute to malignancy.

Developmental changes of acidic fibroblast growth factor (aFGF) transcription and expression in mouse brain

In order to increase our knowledge of the in vivo role of acidic fibroblast growth factor (aFGF) in the central nervous system, we have examined aFGF levels during mouse brain development. Using a specific polyclonal antibody raised against aFGF, we measured levels of aFGF-immunoreactive material (IRMaFGF) in extract of total mouse brain taken at different days of development. We found that the level of measurable IRMaFGF remained low and without significant variation during fetal brain development (0.2 ng/mg of extracted proteins). During the first 11 days postnatal (P0 to P11), IRMaFGF increased from 0.5 to 1.5 ng/mg. Between P11 and P14 IRMaFGF levels went up more rapidly, reaching 5 ng/mg. From P30 to adulthood a constant value of 2.5 ng/mg was measured, aFGF content in the different brain extracts was further characterized by its affinity for heparin-Sepharose, its elution at 1 M NaCl from this column and its capacity to induce thymidine incorporation in quiescent fibroblasts. These results were confirmed at the mRNA level. Northern blot analyses of poly A+ mRNA from brains with a specific riboprobe for bovine aFGF, revealed a major 4.5-Kb transcript and a minor 2.7-Kb transcript detectable only in postnatal brains. A similar pattern to that observed for IRMaFGF was seen with these mRNA transcripts, indicating that these aFGFmRNA are translated in the mouse brain. Our results suggest that aFGF may act in the postnatal phases of brain maturation.

Differentiating and mature neurons express the acidic fibroblast growth factor gene during chick neural development

We have previously isolated and characterized acidic fibroblast growth factor (aFGF) from the embryonic chick brain. To analyze the expression of the gene encoding this growth factor a cDNA clone was isolated. The predicted amino acid sequence was found to be highly conserved (90%) between human and chick. Using single-stranded DNA probes, aFGF gene expression was detectable at day 3.5 in the embryonic chick brain. The mRNA level of the 1.7 kb transcript increased during embryonic development and reached the highest level in the adult brain. In situ hybridization results confirmed these developmental changes and revealed a localized expression in neurons. In the adult, Purkinje cells, deep cerebellar and brainstem neurons showed a high level of aFGF mRNA. In the embryonic brain, localized expression in neurons was detectable from day 6 onward. aFGF mRNA was also present in neurons of the peripheral nervous system. In dorsal root ganglia, aFGF was found to be expressed after embryonic day 6. Cells of blood vessels and the ependyma did not express detectable amounts of aFGF mRNA. These results suggest that aFGF may have a function as a differentiation or maintenance factor for postmitotic neurons or as a growth or differentiation factor for other cells in the nervous system mainly in later stages of development.

Secreted or nonsecreted forms of acidic fibroblast growth factor produced by transfected epithelial cells influence cell morphology, motility, and invasive potential

Addition of exogenous acidic fibroblast growth factor (aFGF) to NBT-II epithelial carcinoma cells results in fibroblastic transformation and cell motility. We have generated aFGF-producing NBT-II cells by transfection with recombinant expression vectors containing human aFGF cDNA, or the human aFGF cDNA coupled to a signal peptide (SP) sequence. The effects of the nonsecreted and the secreted 16-kDa growth factor on the morphology, motility, and cell invasive potential (gelatinase activity) were compared. aFGF coupled to a SP was actively secreted out of the producing cells. The secretion of aFGF was not necessary for induction of gelatinase activity, as this was observed in NBT-II cells producing aFGF with or without SP. Production of aFGF, whether secreted or not secreted, resulted in increased in vitro motility of most isolated clones; however, there was no correlation between aFGF level and motility rate. The data suggest that expression of aFGF in NBT-II cells induces metastatic potential through an autocrine or intracrine mechanism.

Conversion of cysteine to serine residues alters the activity, stability, and heparin dependence of acidic fibroblast growth factor

Acidic fibroblast growth factor (aFGF) is a broad spectrum mitogen that is stabilized by complexation with heparin and heparan proteoglycans. The monomeric human protein contains 3 reduced cysteine residues of unknown function, the first 2 of which are conserved among all seven known fibroblast growth factors. The influence of these free sulfhydryl groups on the level, stability, and heparin dependence of the mitogenic activity at physiological temperature and pH is characterized using a complete set of site-directed mutants in which either any 1, 2, or all 3 of the cysteine residues are converted to serines. Mutants of aFGF in which either any 2 or all 3 cysteine residues are substituted by serines are more active, have longer activity half-lives, and are less heparin dependent than wild-type aFGF. In contrast, wild-type aFGF and the three mutants that each retain 2 cysteine residues inactivate more rapidly in the absence of heparin by a nonproteolytic mechanism but are markedly stabilized by heparin. This cysteine-mediated destabilization of aFGF not only diminishes its activity in the absence of heparin in tissue culture but also could functionally restrict its activity in vivo to the vicinity of mast cell-derived heparins and heparan proteoglycans associated with cell surfaces and basement membranes.

Expression of acidic fibroblast growth factor mRNA in the developing and adult rat brain

We have localized acidic fibroblast growth factor (aFGF) mRNA in the developing and adult rat brain using in situ hybridization histochemistry. Prenatally, hybridization to aFGF mRNA was observed throughout the brain, with the strongest signal associated with cells of the developing cortical plate. Postnatally, labeling was localized to specific neuronal populations. In the hippocampus, labeling of the pyramidal cell layer and dentate granule cells was observed and became progressively more intense with maturation. Labeling was also observed in both the external and internal granule cell layers of the developing cerebellum. Pyramidal cells of the neocortex as well as neurons of the substantia nigra and locus ceruleus also express aFGF. This pattern persists into adulthood, although the intensity of the labeling is significantly reduced in the adult brain. These patterns of hybridization correlate with specific developmental events and suggest that aFGF plays a significant role in both central nervous system development and neuronal viability in the adult brain.

The mRNAs encoding acidic FGF, basic FGF and FGF receptor are coordinately downregulated during myogenic differentiation

Acidic and basic fibroblast growth factors (FGFs) are members of a family of proteins that exert pleiotropic effects in a range of cell types including skeletal myocytes. Previous studies demonstrate that exogenously supplied FGFs stimulate proliferation of myoblasts and inhibit their differentiation in culture, but little information is available concerning endogenous expression of FGFs by skeletal myocytes. In this study acidic and basic FGF mRNAs were found to be expressed in murine and rat skeletal muscle, and expression was demonstrated to vary with the tissue and species examined. Myogenic cell lines were then analyzed to determine if FGFs are expressed in myoblasts, and if so, whether expression is regulated during myogenic differentiation. Murine Sol 8 and rat L6 myoblasts were found to express acidic and basic FGF mRNAs, and the expression of both growth factors was downregulated at the transcriptional level during myogenic differentiation. A decrease in expression of the mouse homologue of the human FGF receptor paralleled the decrease in acidic and basic FGF mRNAs in Sol 8 cells, indicating that the decrease in FGF receptor abundance previously observed during myogenic differentiation is regulated at the mRNA level. The results of this study suggest that a coordinate decrease in endogenously produced acidic and basic FGFs and their cognate receptor may participate in the regulation of myogenic differentiation. Furthermore, the observation that expression of a myogenic determination gene, myogenin, increases as FGF transcripts decline, together with previous data demonstrating suppression of myogenin expression by FGF, suggest a mechanism whereby endogenously produced FGFs may exert their effect on differentiation.

Structure-function studies of heparin-binding (acidic fibroblast) growth factor-1 using site-directed mutagenesis

The heparin-binding or fibroblast growth factors (HBGFs) modulate cell growth and migration, angiogenesis, wound repair, neurite extension, and mesoderm induction. Relatively little is known regarding the precise mechanism of action of these growth factors or the structural basis for their action. A better understanding of the structural basis for the different activities of these proteins should lead to the development of agonists and antagonists of specific HBGF activities. In this report, we summarize evidence that indicates that the heparin-binding and mitogenic activities of HBGF-1 can be dissociated from the receptor-binding activities of the growth factor by site-directed mutagenesis of a single lysine residue. Thus, the mutant HBGF-1 has normal receptor-binding activity and is capable of stimulating tyrosine kinase activity and proto-oncogene expression but is not able to elicit a mitogenic response. A similar dissociation of early events such as proto-oncogene expression from the mitogenic response is observed when the human wild-tupe HBGF-1 is used in the absence of added heparin. These results indicate that intracellular sites of action by the growth factor may be required to complete the mitogenic response. Further evidence for this idea is provided by transfection experiments where NIH 3T3 cells are engineered to produce large quantities of wild-type or mutant HBGF-1. Production of wild-type induces a transformed phenotype, whereas over-production of the mutant does not. The majority of both forms of the protein is found in the nuclear fraction of the transfected cells. Additional site-directed mutagenesis of putative nuclear translocation sequences in the wild-type protein do not affect mitogenic activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Acidic fibroblast growth factor overexpression in corneal epithelial wound healing

aFGF expression was studied in normal and regenerating cornea of adult rats. aFGF mRNA and proteins were expressed mainly in corneal epithelium but not in stroma. After burning of the epithelium by iodine vapours, the intact epithelial cells migrated to cover the wounded area during the first 4 days and then divided to reconstitute a normal multilayered epithelium 6 days after injury. aFGF mRNA localized by in situ hybridization on regenerating epithelium showed a peak between 6 hr and 2 days after denudation, decreasing to basal levels 6 days later. This induction of aFGF mRNA preceded the increased amount of aFGF peptides, as assessed by indirect immunofluorescence staining. Thus aFGF overexpression is clearly correlated with active migration in epithelial wound healing.

Transformed phenotype conferred to NIH/3T3 cells by ectopic expression of heparin-binding growth factor 1/acidic fibroblast growth factor

Heparin-binding growth factor 1 (HBGF-1), also known as acidic fibroblast growth factor, is a potent mitogen and angiogenic factor found in tissues such as brain, kidney and heart. The genomic and cDNA sequences indicate that HBGF-1 does not have a typical signal peptide sequence. HBGF-1 was shown to be localized to the extracellular matrix of cardiac myocytes, but the mechanism of secretion is not presently known. We have cloned the HBGF-1 cDNA which allowed us to directly test the biological activity, mechanism of secretion and transforming potential of the recombinant protein. A previous report showed that the truncated HBGF-1 confers partial transformed phenotype to the recipient fibroblasts. However, expression of full-length HBGF-1 has not been reported. The HBGF-1 coding sequence was cloned into the retroviral expression vector, SVX, and transfected into NIH/3T3 cells. Transfectants expressing full-length HBGF-1 protein at high levels form foci and grow to a higher cell density than the parental NIH/3T3 cells. Western blotting analysis showed that the recombinant HBGF-1 is a unique band of approximately 20 kDa and can be detected in the cell homogenate but not in the conditioned medium. NIH/3T3 cells were conferred anchorage independence when HBGF-1 was provided exogenously. We showed the transformed cells are capable of growing on soft agar even in the absence of exogenously-provided HBGF-1. Transfected cells expressing HBGF-1 also induced tumor formation when injected into nude mice. Thus NIH/3T3 cells acquired a full spectrum of transformed phenotype when full length HBGF-1 was expressed at high levels.

High-level production of human acidic fibroblast growth factor in E. coli cells: inhibition of DNA synthesis in rat mammary fibroblasts at high concentrations of growth factor

Recombinant human acidic fibroblast growth factor has been produced in E. coli cells at a level of at least 50 mg/l culture. The recombinant and natural acidic fibroblast growth factors are almost identical to one another when tested on rat mammary fibroblasts for their ability to stimulate DNA synthesis, to bind to the high-affinity surface receptors of the cells and to inhibit DNA synthesis when present in the culture medium at high concentrations. The recombinant acidic fibroblast growth factor binds to two cell-surface polypeptides of molecular masses 160 kDa and 140 kDa, which are the same size as the receptors for basic fibroblast growth factor, and it binds preferentially to the smaller polypeptide.

Recovery of mitogenic activity of a growth factor mutant with a nuclear translocation sequence

Heparin-binding growth factor-1 (HBGF-1) is an angiogenic polypeptide mitogen for mesoderm- and neuroectoderm-derived cells in vitro and remains biologically active after truncation of the amino-terminal domain (HBGF-1 alpha) of the HBGF-1 beta precursor. Polymerase chain reaction mutagenesis and prokaryotic expression systems were used to prepare a mutant of HBGF-1 alpha lacking a putative nuclear translocation sequence (amino acid residues 21 to 27; HBGF-1U). Although HBGF-1U retains its ability to bind to heparin, HBGF-1U fails to induce DNA synthesis and cell proliferation at concentrations sufficient to induce intracellular receptor-mediated tyrosine phosphorylation and c-fos expression. Attachment of the nuclear translocation sequence from yeast histone 2B at the amino terminus of HBGF-1U yields a chimeric polypeptide (HBGF-1U2) with mitogenic activity in vitro and indicates that nuclear translocation is important for this biological response.

Expression and regulation of mRNA coding for acidic and basic fibroblast growth factor and transforming growth factor alpha in cells derived from human skin

We investigated the regulation of mRNAs coding for acidic fibroblast growth factor (aFGF), basic fibroblast growth factor (bFGF), and transforming growth factor-alpha (TGF alpha) in cultures of human neonatal foreskin fibroblasts, keratinocytes, and melanocytes. Each cell type was propagated in an optimized serum-free medium. In rapidly growing fibroblasts, the addition of fetal bovine serum caused a modest induction of aFGF message within 2 h in conjunction with a concomitant elevation of bFGF transcripts. In these same cells, TGF alpha mRNA could not be detected in any experimental condition. In contrast, keratinocytes rapidly growing in the presence of epidermal growth factor (EGF) contained transcripts for TGF alpha that increased substantially when these cells were treated with serum. This observation suggests that factors present in serum can elevate the levels of TGF alpha mRNA beyond the levels already present in keratinocyte cultures growing in the presence of EGF. These same keratinocyte cultures had low to undetectable levels of bFGF or aFGF message, and the levels of these mRNAs were not affected by serum treatment. Treatment of keratinocytes proliferating in the presence of EGF with TGF beta for 48 h caused expression of bFGF mRNA in four of six independent cell strains. TGF beta-enhanced expression of bFGF mRNA occurred as early as 12-24 h after TGF beta exposure. TGF beta did not enhance the expression of mRNA for aFGF or TGF alpha in keratinocytes. Melanocytes failed to express detectable levels of mRNA coding for any of these growth factors in the presence of absence of TGF beta or serum.(ABSTRACT TRUNCATED AT 250 WORDS)

Localization of acidic fibroblast growth factor (aFGF) mRNA in mouse and bovine retina by in situ hybridization

Acidic fibroblast growth factor (aFGF) mRNA has been detected in adult mouse or bovine retina by in situ hybridization with bovine aFGF cDNA clones. It is localized on ganglion cell layer, inner nuclear layer, photoreceptors and slightly on pigmented epithelium. This synthesis of aFGF in highly specialized retinal cell types is discussed in the framework on current views about the role of FGF in retinal cell biology.

Characterization of the hamster DDT-1 cell aFGF/HGBF-I gene and cDNA and its modulation by steroids

Syrian hamster DDT-1 cells are derived from smooth muscle of the ductus deferens. DDT-1 cell growth is increased by the addition of testosterone (T). Acidic fibroblast growth factor (aFGF) or basic fibroblast growth factor (bFGF) also known as heparin binding growth factor I and II (HBGF-I and HBGF-II) can replace T in the stimulation of growth in these cells. This phenomenon is correlated with testosterone's ability to elevate aFGF/HBGF-I mRNA. The increase steady-state levels of aFGF/HBGF-I mRNA were documented by northern blots and by in situ hybridization. Using a 520 bp human aFGF/HBGF-I cDNA probe, a genomic clone with a 38 kb DNA insert was isolated from a cosmid library. By restriction enzyme analysis and southern hybridization, it was determined that there are three coding exons. DNA sequence analysis showed all of the coding region and 3' noncoding sequences were on this clone. A 5' noncoding exon not in the 38 kb insert is indicated, based on the cDNA sequences and genomic sequences of aFGF/HBGF-I's from hamster DDT-1 cells and several other species. The cDNA for hamster aFGF/HBGF-I was isolated from a DDT-1 lambda gt11 library and sequenced. Comparison of the coding region of aFGF/HBGF-I from four species shows a greater than 90% conservation of amino acid sequence.

Disulfide bonds are neither required, present, nor compatible with full activity of human recombinant acidic fibroblast growth factor

Human acidic fibroblast growth factor (aFGF) is a potent broad-spectrum mitogen that contains three Cys residues within its monomeric structure. We have found that site-directed mutants in which any one of these Cys residues is converted to serine remain highly active, although variably dependent on heparin, so none of the three possible intramolecular disulfide bonds that can be formed are required for mitogenic activity. Furthermore, a dispensable disulfide bond that might stabilize the active conformation is not present since all three Cys residues are accessible to chemical modification in recombinant as well as brain-derived aFGFs. Finally, formation of a disulfide bond between the two Cys residues conserved among all seven known members of the FGF family results in a virtually inactive product that can subsequently be reactivated by reduction. Thus, despite the extracellular function of aFGF, its Cys residues do not form intramolecular disulfide bonds in the active conformation.