The structure and function of the int-2 oncogene

Roles of Fibroblast Growth Factors and Their Therapeutic Potential in Treatment of Ischemic Stroke

Stroke is the leading cause of death worldwide, and its treatment remains a challenge. Complex pathological processes are involved in stroke, which causes a reduction in the supply of oxygen and energy to the brain that triggers subsequent cascade events, such as oxidative stress, inflammatory responses and apoptosis, resulting in brain injury. Stroke is a devastating disease for which there are few treatments, but physical rehabilitation can help improve stroke recovery. Although there are very few treatments for stroke patients, the discovery of fibroblast growth factors (FGFs) in mammals has led to the finding that FGFs can effectively treat stroke in animal models. As presented in this review, FGFs play essential roles by functioning as homeostatic factors and controlling cells and hormones involved in metabolism. They could be used as effective therapeutic agents for stroke. In this review, we will discuss the pharmacological actions of FGFs on multiple targets, including their ability to directly promote neuron survival, enhance angiogenesis, protect against blood-brain barrier (BBB) disruption, and regulate microglial modulation, in the treatment of ischemic stroke and their theoretical mechanisms and actions, as well as the therapeutic potential and limitations of FGFs for the clinical treatment of stroke.

Cyclin D1, EMS1 and 11q13 amplification in breast cancer

Chromosome locus 11q13 is frequently amplified in a number of human cancers including carcinoma of the breast where up to 15% carry this chromosomal abnormality. Originally 11q13 amplification was thought to involve a single amplicon spanning many megabases, but more recent data have identified four core regions within 11q13 that can be amplified independently or together in different combinations. Although the region harbors several genes with known or suspected oncogenic potential, the complex structure of the amplicons and the fact that 11q13 is gene-rich have made definitive identification of specific genes that contribute to the genesis and progression of breast cancer a difficult and continuing process. To date CCND1, encoding the cell cycle regulatory gene cyclin D1, and EMS1, encoding the filamentous actin binding protein and c-Src substrate cortactin, are the favored candidates responsible for the emergence of two of the four amplification cores.

Regulation of FGF-3 gene expression in tumorigenic and non-tumorigenic clones of a human colon carcinoma cell line

The FGF-3 gene is constitutively expressed in tumorigenic clones from the SW613-S human colon carcinoma cell line but is silent in non-tumorigenic clones. We have investigated the transcriptional mechanisms responsible for this differential expression. Mapping of DNase I-hypersensitive sites throughout the FGF-3 gene and the region extending 15 kilobases upstream disclosed differences in the patterns obtained between tumorigenic and non-tumorigenic cells. Transient expression assays carried out with a reporter gene driven by FGF-3 promoter fragments of various lengths (0.143 to 11 kilobases) did not reproduce the differential regulation of the resident gene between the two cell types. The same constructs did exhibit a differential activity in stable transfectants, suggesting the involvement of a chromatin-based mechanism in this regulation. Under these conditions, even the 143-base pair minimal promoter fragment was able to drive the differential expression of the reporter gene. During the course of these analyses, several transcriptional modulatory elements (mainly activators) were identified in the FGF-3 upstream region and were found to colocalize with DNase I-hypersensitive sites. Moreover, a putative new promoter was discovered 6 kilobases upstream of FGF-3. Altogether, these data provide a basis for the elucidation of the complex regulation of the human FGF-3 gene.

Sequence analysis of the transcription control region upstream of the human FGF-3 gene

With the purpose of studying the transcriptional regulation of the human FGF-3 gene, we have cloned and determined the nucleotide sequence of the 11-kbp region flanking its 5' end. Analysis of the sequence disclosed the presence of multiple repetitive elements. Remarkably, all of them were found to have inserted in the same orientation as the FGF-3 gene, suggesting that the whole upstream region could play a role in the control of its transcription. Unique regions within the sequence were scanned for the presence of transcriptional regulatory elements. A potential "Initiator" sequence preceded by several motifs homologous to binding sites for transcription factors pinpointed a putative promoter, 6 kbp upstream of the ATG codon for the FGF-3 protein. A 250-nt sequence stretch surrounding the "Initiator" was found to display punctate homology with the first (P1) of the three promoters (P1, P2 and P3) of the mouse Fgf-3/int-2 gene, specifically in the region of the transcriptional start sites. These data should be useful in studying the mechanisms of regulation of the FGF-3 transcription unit.

Retinoic acid-regulated expression of fibroblast growth factor 3 requires the interaction between a novel transcription factor and GATA-4

fgf-3 shows a complex spatial-temporal pattern of transcription during mouse development, and the gene product appears to be an important intercellular signaling molecule. Here we show that the major enhancer, which is obligatory for transcription, is composed of three elements with different properties. Both functional analyses in undifferentiated and differentiated F9 cells and characterization of DNA-protein complexes in vitro have identified the sequence motifs GTGACT(C), ATTGT, and GATA as the key transcription factor binding sites. The GTGACT(C) motif, while not essential, is required for full enhancer activity. However, binding at ATTGT is crucial for transcriptional activity and is required for cooperative binding at the proximal GATA site. The GATA binding site mediates the retinoic acid/dibutyryl cyclic AMP stimulation of transcription and correlates with the binding of Gata-4 which is induced by retinoic acid in differentiating F9 cells. The ATTGT and GATA motifs are inactive when placed separately on a minimal thymidine kinase (TK) promoter, but together they act as a strong retinoic acid-regulated enhancer. In undifferentiated F9 cells, gata-4 expression stimulates the fgf-3 promoter, whereas in differentiated F9 cells already expressing gata-4, no further increase in promoter activity was observed.

Fibroblast growth factor 3, a protein with dual subcellular localization, is targeted to the nucleus and nucleolus by the concerted action of two nuclear localization signals and a nucleolar retention signal

The major isoform of fibroblast growth factor 3 (FGF3) is initiated from a CUG codon, and the resultant product is distributed to the nucleus/nucleolus and secretory pathway. This dual subcellular localization is achieved in part by the competing effects of two classical intracellular targeting signals located near the amino terminus. At the extreme amino terminus is a short stretch of 29 amino acids before a signal peptide necessary for translocation into the endoplasmic reticulum, which is next to an adjacent bipartite nuclear localization signal. The carboxyl-terminal region of FGF3 is also implicated in nuclear/nucleolar localization. We describe here the characterization of carboxyl-terminal signals by showing they are capable of directing a heterologous protein, beta-galactosidase, to the nucleus. Furthermore, appending both the amino- and carboxyl-terminal domains onto beta-galactosidase, reproduces the dual subcellular localization properties of FGF3. Nuclear uptake of FGF3 appears to be signal-mediated since it binds to karyopherin alpha, the nuclear localization signal binding subunit of a heterodimeric receptor of the nuclear import machinery. The import of FGF3 into the nucleus is energy-dependent, and the inhibition of this process has demonstrated the importance of the nucleolar retention signal in nucleoplasmic and nucleolar accumulation.

Murine FGF-12 and FGF-13: expression in embryonic nervous system, connective tissue and heart

The molecular cloning of cDNAs encoding murine fibroblast growth factor-13 (FGF-13/FHF-2) and three isoforms of murine FGF-12 (FHF-1) is described. Like their highly conserved human counterparts, murine FGF-12 and FGF-13 are part of a distinct subfamily of FGF-like proteins characterized by a greater degree of amino acid sequence cross-homology and by conserved N-terminal domains which do not include secretion signal sequences. In addition to their expression in several adult tissues, both of these FGF genes are prominently and regionally expressed in midgestation mouse embryos, as revealed by in situ hybridization. Fgf12 and fgf13. RNAs were detected in developing central nervous system in cells outside the proliferating ependymal layer, and fgf13 RNA was also found throughout the peripheral nervous system. Fgf12 is expressed in developing soft connective tissue of the limb skeleton and in presumptive connective tissue linking vertebrae and ribs. Both FGF genes are also expressed in the myocardium of the heart, with fgf12 RNA found only in the atrial chamber and fgf13 RNA detected in both atrium and ventricle. On the basis of their novel structure and patterns of expression, FGF-12 and FGF-13 are anticipated to perform embryonic functions distinct from other known FGF molecules.

The zebrafish Fgf-3 gene: cDNA sequence, transcript structure and genomic organization

We report the isolation and characterization of genomic and cDNA clones encoding zebrafish fibroblast growth factor 3 (FGF3). An initial cDNA clone was generated by PCR amplification using degenerate oligo primers corresponding to a conserved region of protein found in the mouse and human homologues. Screening a cDNA library made from 30-33-h-old zebrafish embryos with this PCR product led to the isolation of two cDNA clones. Sequence analysis of the longest cDNA insert (1810 bp) revealed a 256-amino-acid (aa) orf. The central region, composed of approx. 155 aa, shares 78% identity with the analogous region of Xenopus laevis FGF3 and 72% identity with the product of the more distantly related human gene. However, the N-and C-terminal domains of zebrafish FGF3 are very different from those of other known homologues. The cDNA was used as a probe on genomic DNA to create a physical map of the locus and to isolate a genomic clone encompassing the entire coding region and 5' sequences. DNA sequencing and RNase protection analyses indicate that zebrafish Fgf-3 (ZFgf-3) is structurally analogous to the mouse gene and regulated through two different promoters. The transcription start point of the proximal promoter aligns to that of mouse promoter P3 and lies within a conserved region of sequence.

Receptor binding and mitogenic properties of mouse fibroblast growth factor 3. Modulation of response by heparin

fgf3 has been implicated in the embryonic and fetal development of the mouse and as an oncogene in murine breast cancer. We describe a procedure to purify the product of the mouse fgf3 gene and show it to be a potent mitogen for some epithelial cell lines. Using a receptor binding competition assay, Fgf3 was shown to bind with high affinity to the IIIb isoforms of Fgf receptor (FgfR) 1 and FgfR2 (ID50 = approximately 0.8 nM) and with a lower affinity to the IIIc variant of FgfR2 (ID50 = approximately 9 nM). No competition for the binding of 125I-Fgf1 was observed for FgfR1 (IIIc), FgfR3 (IIIb and IIIc), or FgfR4. Mitogenicity assays using BaF3 cells containing individual Fgf receptors showed a pattern of response in agreement with the receptor binding results. A comparison of two mammary epithelial cell lines showed a marked difference of potency and dependence upon heparin in their response to mouse Fgf3, suggesting a complex interaction between the ligand and its low and high affinity receptors.

Nucleolar association of fibroblast growth factor 3 via specific sequence motifs has inhibitory effects on cell growth

The dual subcellular fate of fibroblast growth factor 3 (FGF3) is determined by the competing effects of amino-terminal signals for nuclear localization and secretion (P. Kiefer, P. Acland, D. Pappin, G. Peters, and C. Dickson, EMBO J. 13:4126-4136, 1994). Mutation analysis has implicated additional basic domains in the carboxy-terminal region of the protein as necessary for nuclear uptake and the association of FGF3 with the nucleoli. Immunogold electron microscopy shows that FGF3 is predominantly within the dense fibrillar component of the nucleolus. A form of FGF3 that localizes exclusively in the nucleus and nucleolus was generated by removing signals for secretion, and expression of this nonsecreted FGF3 in a mammary epithelial cell line resulted in slowly growing colonies of enlarged cells. Thus, nuclear import and nucleolar association of FGF3 are determined by the concerted interaction of several distinct motifs, and the exclusive production of the nuclear isoform can inhibit DNA synthesis and cell proliferation.

Fibroblast growth factor (FGF) 3 from Xenopus laevis (XFGF3) binds with high affinity to FGF receptor 2

We demonstrate that purified fibroblast growth factor (FGF) 3 from Xenopus laevis (XFGF3) activates the mitogen-activated protein kinase pathway and induces DNA synthesis in quiescent cells. To characterize the high affinity cell surface receptors that mediate these responses, the ligand binding domains of different FGF receptors (FGFR) were expressed on COS-1 cells, and their affinity for XFGF3 was determined. Unlabeled XFGF3 efficiently competed with 125I-FGF1 for binding to the IIIb and IIIc isoforms of FGFR2, giving 50% displacement (ID50) at 0.3-0.8 nM. Higher XFGF3 concentrations were needed to displace 125I-FGF1 from FGFR3 and FGFR1 (ID50 approximately 4 and 21 nM, respectively), indicating that XFGF3 has a lower affinity for these receptors. No association of XFGF3 with FGFR4 was found using this assay. FGFR2 isoforms isolated from both mouse and Xenopus showed similar high affinity binding of XFGF3 as determined by direct binding assays (Kd values in the range of 0.2-0.6 nM). These results indicate that the binding specificity of XFGF3 is different from that of other FGFs, and identifies FGFR2 as its high affinity receptor.

Identification of positive and negative regulatory elements involved in the retinoic acid/cAMP induction of Fgf-3 transcription in F9 cells

The proto-oncogene Fgf-3 has been implicated as an important signalling molecule in vertebrate development. In the mouse, it is expressed for a limited time at a multitude of sites from embryonic day 7 to birth. Transcription of Fgf-3 initiates at three promoter regions resulting in the generation of various mRNAs which nevertheless all encode the same protein products. A 1.7kb DNA fragment which encompasses these regions was joined to the CAT reporter gene and shown to function as a promoter in embryonal carcinoma cells. In stable transfectants the promoter retains its retinoic acid inducibility, initiating transcription at the same cap-sites as the endogenous gene. In differentiated F9 cells, transient transfection of progressive and targeted deletion mutants of the promoter region has revealed at least two positive and three negative regulatory elements. With one exception, loss of these elements was shown to dramatically affect promoter activity in stable transfectants of F9 cells. However the promoter remained inducible by retinoic acid to differing degrees, apart from deletions encompassing PS-4A which essentially abolished promoter activity in both undifferentiated and differentiated cells. The sequences of these potential regulatory regions were further defined using DNase-I footprinting, revealing some similarities to consensus binding sites for known transcription factors.

Retention of fibroblast growth factor 3 in the Golgi complex may regulate its export from cells

The fibroblast growth factors (FGFs) fall into two distinct groups with respect to their mode of release from cells. Whereas FGF1 and FGF2 lack conventional signal peptides, the remaining members have typical features of secreted proteins. However, the behavior of mouse FGF3 is anomalous, since, despite entering the secretory pathway and undergoing primary glycosylation, its release from transfected COS-1 cells is very inefficient compared with that of FGF4 and FGF5. To investigate the unusual properties of FGF3, we analyzed the processing, secretion, and intracellular localization of a series of site-directed mutants as well as chimeras produced by fusing parts of FGF3, FGF4, and FGF5. Wild-type FGF3 was shown to accumulate in an immature form in the Golgi complex, from where it is slowly released into the extracellular matrix. Removing or relocating the Asn-linked glycosylation site further impaired its release, and exchanging the signal peptide or carboxy terminus had little effect. In contrast, a chimeric protein with an amino terminus from FGF5 was efficiently secreted and biologically active in cell transformation assays. The data suggest that a structural feature of FGF3 involving the amino-terminal region and glycosylation site has a significant bearing on its passage through the Golgi complex and may regulate the secretion of the ligand.

Retention of fibroblast growth factor 3 in the Golgi complex may regulate its export from cells

The fibroblast growth factors (FGFs) fall into two distinct groups with respect to their mode of release from cells. Whereas FGF1 and FGF2 lack conventional signal peptides, the remaining members have typical features of secreted proteins. However, the behavior of mouse FGF3 is anomalous, since, despite entering the secretory pathway and undergoing primary glycosylation, its release from transfected COS-1 cells is very inefficient compared with that of FGF4 and FGF5. To investigate the unusual properties of FGF3, we analyzed the processing, secretion, and intracellular localization of a series of site-directed mutants as well as chimeras produced by fusing parts of FGF3, FGF4, and FGF5. Wild-type FGF3 was shown to accumulate in an immature form in the Golgi complex, from where it is slowly released into the extracellular matrix. Removing or relocating the Asn-linked glycosylation site further impaired its release, and exchanging the signal peptide or carboxy terminus had little effect. In contrast, a chimeric protein with an amino terminus from FGF5 was efficiently secreted and biologically active in cell transformation assays. The data suggest that a structural feature of FGF3 involving the amino-terminal region and glycosylation site has a significant bearing on its passage through the Golgi complex and may regulate the secretion of the ligand.

Consistent chromosomal anomalies in keratinocyte cell lines derived from untreated malignant lesions of the oral cavity

Cytogenetic analysis has been carried out on 8 early passage cell lines derived from 8 untreated human oral squamous cell carcinomas. Clonal aberrations were detected in the karyotypes of each cell line. A high frequency of breakpoints were noted on chromosomes 1, 7, 8, 9, 11, and X. An isochromosome 8 was present in 6 out of 8 cell lines; isochromosome 9 (3 cell lines) and isochromosome 11 (1 cell line) were also found. In 4 out of 8 cell lines X chromosome harboured breakpoints, a novel finding in oral squamous cell carcinomas. Breakpoints were common on chromosome 1, with 1p12-p13 most frequently involved. Tandem duplication of 11q13-q23, which contains a number of growth regulatory genes, was also noted in 2 cases. We correlate the sites of proto-oncogenes and other growth control genes with chromosomal breakpoints and suggest that several of these may play a role in the pathogenesis of oral cancer.

Coamplification of the hst and bcl-1 oncogenes in advanced squamous cell carcinomas of the head and neck

Squamous cell carcinomas of the head and neck from 40 untreated patients were analysed for rearranged or amplified proto-oncogenes by Southern blot hybridisation. The bcl-1 and the hst genes were coamplified 8-32-fold in 5 patients (12.5%). Only males with stage III and IV disease showed coamplification of these oncogenes. Northern blot analysis of the positive samples did not show expression of bcl-1 or hst genes. In contrast, a third oncogene located on chromosome 11 (Ha-ras-1) was not amplified in these tumours. Disease development was observed in all cases over a minimum period of 3 years. Survival of the patients with coamplification of hst/bcl-1 seemed to be shorter than of those with stage III and IV disease without amplification. This difference was not significant probably due to the small number of investigated patients.

Angiogenesis and angiogenesis inhibitors in paediatric diseases

Angiogenesis, the generation of new capillaries from existing blood vessels, is rarely observed in the healthy organism, but can present during various paediatric diseases. In this review, we describe recent progress in the understanding of pathological angiogenesis and approaches for an improved therapy of angiogenic childhood diseases.

The Int-2/Fgf-3 oncogene product is secreted and associates with extracellular matrix: implications for cell transformation

NIH3T3 cells transformed by mouse Int-2/Fgf-3 cDNA express a series of Int-2-related products representing discrete stages of processing and glycosylation. We confirm that in at least two highly transformed clonal lines, Int-2 products acquire further modifications and are efficiently secreted into the culture medium. Secreted proteins become associated with the cell surface and extracellular matrix and can be displaced by addition of soluble glycosaminoglycans, specifically heparin, heparan sulfate, and dermatan sulfate. Increasing concentrations of heparin not only compete for Int-2 binding in a dose-dependent manner but also inhibit the growth of these cells and revert the transformed phenotype. These findings reaffirm the notion that extracellular or surface-bound Int-2 protein is instrumental in the morphological transformation of these cells.

The Int-2/Fgf-3 oncogene product is secreted and associates with extracellular matrix: implications for cell transformation

NIH3T3 cells transformed by mouse Int-2/Fgf-3 cDNA express a series of Int-2-related products representing discrete stages of processing and glycosylation. We confirm that in at least two highly transformed clonal lines, Int-2 products acquire further modifications and are efficiently secreted into the culture medium. Secreted proteins become associated with the cell surface and extracellular matrix and can be displaced by addition of soluble glycosaminoglycans, specifically heparin, heparan sulfate, and dermatan sulfate. Increasing concentrations of heparin not only compete for Int-2 binding in a dose-dependent manner but also inhibit the growth of these cells and revert the transformed phenotype. These findings reaffirm the notion that extracellular or surface-bound Int-2 protein is instrumental in the morphological transformation of these cells.

Growth factors and cancer

Signaling pathways that mediate the normal functions of growth factors are commonly subverted in cancer. Oncogenes identified by a variety of approaches have been shown to function at critical steps in mitogenic signaling. Progression through the cell cycle requires the coordinated actions of members of two complementary classes of growth factors, and oncogenes appear to replace the actions of one set of these growth factors. Growth factors can also influence normal cell differentiation, and constitutive activation of growth-promoting pathways in cancer cells can modulate the cell phenotype as well. Paracrine actions of growth factors and cytokines may also influence the stepwise series of genetic events that lead to malignancy. New approaches for cancer therapy are being developed that intervene at various steps in growth factor signaling pathways.

Cell transformation by kFGF requires secretion but not glycosylation

The Kfgf gene, which encodes a member of the fibroblast growth factor family, was originally discovered by assaying human tumor DNA for dominantly transforming oncogenes. The 22-kD kFGF product contains a single site for asparagine-linked glycosylation and an amino-terminal signal peptide for vectorial synthesis into the endoplasmic reticulum and eventual secretion. To determine whether these features are necessary for transformation, we have constructed mutants of kFGF that are impaired for glycosylation or secretion. All mutants retained the ability to induce DNA synthesis when added to quiescent cells, and the absence of glycosylation had no appreciable effect on the transformation efficiency on NIH3T3 cells. In contrast, mutants of kFGF that remain in the cytoplasm or are retained in the secretory pathway, through addition of a KDEL motif, score negative in standard transformation assays. Since transformation by either the glycosylated or unglycosylated form of kFGF can be reversed by addition of suramin, the data imply that secretion of kFGF, or surface localization of the ligand/receptor complex, is a prerequisite for transformation.

Growth factors in development, transformation, and tumorigenesis

Mammalian tissue development and regeneration take place within a milieu of regulatory growth factors. These affect many parameters of cell development, such that survival, proliferation, differentiation, and certain aspects of cell behavior are all influenced by a balance between stimulatory and inhibitory signals. The precise effect of any given factor is determined by the responding cell type, the concentration of factor, and the presence of other stimuli, such that some growth factors may fulfill a variety of functions under different circumstances. Classically, growth factor stimuli are transmitted into the cell via activation of specific, transmembrane receptors that modify key regulatory proteins in the cytoplasm. These in turn affect the decisions controlling proliferation and differentiation, including changes in gene expression and reactivity to other factors. There are indications that some factors may function both extra- and intracellularly and that this characteristic is correlated with potential oncogenicity. The relatively low transforming ability of extracellular factors alone is probably attributable to the limitations imposed by down-regulation of their cell surface receptors. Aberrant production of secreted growth factors can, however, play decisive roles in tumorigenesis by increasing the proliferation rate and degree of cellular autonomy and extending the area available for tumor expansion.

Gene amplification on chromosome band 11q13 and oestrogen receptor status in breast cancer

We have analysed DNA from 183 primary breast cancers for amplification or rearrangement of a number of cellular proto-oncogenes, focusing primarily on a cluster of markers on the long arm of chromosome 11. Two of these oncogenes, INT2 and HST1, both of which encode members of the fibroblast growth factor family, are implicated in the generation of virally induced mammary tumours in mice. Here we confirm earlier reports that the q13 region of chromosome 11, in which these genes are tandemly linked, is modestly amplified in approximately 15% of primary human breast cancers. This amplification is confined, with one exception, to cases in which the oestrogen receptor (ER) levels are in excess of 20 fmol/mg protein (P = 0.001). However, DNA amplification does not usually result in detectable expression of either the INT2 or HST1 gene. The data imply that some other gene in the vicinity must contribute to the development of a subset of ER-positive tumours and that assessing the amplification of this region of DNA may be of value in defining a separate category of ER-positive tumour.

Angiogenic growth factors

Angiogenesis, the formation of new blood vessels, plays a central role in a variety of physiological and pathological processes such as embryonic development, wound healing and tumor growth. It is a complex, multi-step process that involves the migration and proliferation of capillary endothelial cells. Several factors that stimulate the proliferation of endothelial cells in vitro have been shown to induce angiogenesis in vivo. Among these angiogenic growth factors are wide-spectrum multifunctional mitogens (e.g. the fibroblast growth factors) and the recently identified factors with distinct specificity for vascular endothelial cells (e.g. the platelet-derived endothelial cell growth factor). Another group of factors apparently induce angiogenesis indirectly (e.g. transforming growth factor-beta) by stimulating target cells to release angiogenic factors or by other mechanisms. The differential expression, release and activation of these factors might regulate angiogenesis under various physiological and pathological conditions.