Structural analysis of the gene for human acidic fibroblast growth factor

Cloning of an intracellular protein that binds selectively to mitogenic acidic fibroblast growth factor

In addition to its extracellular action, there is evidence that acidic fibroblast growth factor (aFGF) acts inside cells. To identify intracellular proteins interacting with aFGF, we screened a HeLa cell library in the yeast two-hybrid system using pLex-aFGF as a bait. A clone binding to aFGF, but not to the non-mitogenic mutant aFGF-K132E, was isolated and characterized. The insert contained an open reading frame corresponding to a novel protein of 42 kDa. The protein, termed aFGF intracellular binding protein (FIBP), is mainly hydrophilic and does not contain an N-terminal signal sequence. In vitro-translated FIBP bound specifically to a fusion protein of maltose-binding protein and aFGF. FIBP became post-translationally associated with microsomes added to the cell-free protein synthesizing system, and the membrane-associated protein bound aFGF with high efficiency. Immunoblots and fluorescence microscopy demonstrated that the protein is present in nuclei and, to a lesser extent, associated with mitochondria and other cytoplasmic membranes. The possibility is discussed that FIBP may be involved in the mitogenic action of aFGF.

S100A13 is involved in the regulation of fibroblast growth factor-1 and p40 synaptotagmin-1 release in vitro

We have previously characterized the release of the signal peptide sequence-less fibroblast growth factor (FGF) prototype, FGF-1, in vitro as a stress-induced pathway in which FGF-1 is released as a latent homodimer with the p40 extravesicular domain of p65 synaptotagmin (Syn)-1. To determine the biologic relevance of the FGF-1 release pathway in vivo, we sought to resolve and characterize from ovine brain a purified fraction that contained both FGF-1 and p40 Syn-1 and report that the brain-derived FGF-1:p40 Syn-1 aggregate is associated with the calcium-binding protein, S100A13. Since S100A13 binds the anti-inflammatory compound amlexanox and FGF-1 is involved in inflammation, we examined the effects of amlexanox on the release of FGF-1 and p40 Syn-1 in response to stress in vitro. We report that while amlexanox was able to repress the heat shock-induced release of FGF-1 and p40 Syn-1 in a concentration-dependent manner, it had no effect on the constitutive release of p40 Syn-1 from p40 Syn-1 NIH 3T3 cell transfectants. These data suggest the following: (i) FGF-1 is associated with Syn-1 and S100A13 in vivo; (ii) S100A13 may be involved in the regulation of FGF-1 and p40 Syn-1 release in response to temperature stress in vitro; and (iii) the FGF-1 release pathway may be accessible to pharmacologic regulation.

Fibroblast growth factor (FGF) homologous factors: new members of the FGF family implicated in nervous system development

Four new members of the fibroblast growth factor (FGF) family, referred to as fibroblast growth factor homologous factors (FHFs), have been identified by a combination of random cDNA sequencing, data base searches, and degenerate PCR. Pairwise comparisons between the four FHFs show between 58% and 71% amino acid sequence identity, but each FHF shows less than 30% identity when compared with other FGFs. Like FGF-1 (acidic FGF) and FGF-2 (basic FGF), the FHFs lack a classical signal sequence and contain clusters of basic residues that can act as nuclear localization signals. In transiently transfected 293 cells FHF-1 accumulates in the nucleus and is not secreted. Each FHF is expressed in the developing and adult nervous systems, suggesting a role for this branch of the FGF family in nervous system development and function.

The role of angiogenesis in the tumor growth of Syrian hamster pancreatic cancer cell line HPD-NR

BACKGROUND/AIMS

New therapeutic approach is required for pancreatic cancer, one of the most intractable malignancies. The role of angiogenesis in the tumor growth of a Syrian hamster pancreatic cancer cell line HPD-NR, which closely resembles its human counterpart, was investigated.

METHODS

Angiogenic activity was measured as stimulation of growth of human umbilical vein endothelial cells (HUVEC), and angiogenic factors produced by HPD-NR cells were identified by reverse-transcription polymerase chain reaction and Northern blot analysis. Then in vitro and in vivo antitumor effects of a potent angiogenesis inhibitor, O-(chloroacetylcarbamoyl)fumagillol (AGM-1470), were examined.

RESULTS

The conditioned medium of HPD-NR cells stimulated the growth of HUVEC, and four hamster angiogenic factors were detected with an overexpression of transforming growth factor alpha and vascular endothelial growth factor messenger RNAs. AGM-1470 specifically inhibited the growth of HUVEC and that of HPD-NR tumors in vivo with decreased vascularity of the tumors but not the growth of HPD-NR cells in vitro.

CONCLUSIONS

The results suggest that angiogenesis plays an important role in tumor growth of HPD-NR cells and can be a new target of medical therapy for pancreatic cancer.

Expression of fibroblast growth factors and their receptors in acquired immunodeficiency syndrome-associated Kaposi sarcoma tissue and derived cells

BACKGROUND

Fibroblast growth factors (FGF), such as basic FGF, have been implicated in the development of Kaposi sarcoma (KS) in vitro. The expression of several genes of the FGF family and their receptors in KS tumor lesions and KS-derived cells were evaluated.

METHODS

Cultures of KS-derived cells were established. The expression of FGF family members and their receptors in these cells and in fresh biopsies from KS tumors was evaluated by reverse transcription polymerase chain reaction (RTPCR). The RTPCR products were confirmed by nucleotide sequencing.

RESULTS

The expression of basic FGF and FGF receptor-1 (flg) was detected in all the samples tested. Acidic FGF (aFGF) and FGF-5 were detected in two of six and four of six KS tumor specimens, respectively, whereas both of these growth factors were expressed in all of the cell cultures, including six KS-derived cell cultures and human endothelial cells and smooth muscle cells. FGF-6 was expressed in two of six KS tumor specimens, but was not expressed in any of the cultured KS cells. Like flg, bek was expressed in all tissue samples and KS-derived cell cultures except in one KS specimen obtained from the patient's tongue showing expression of a high level of FGF-6.

CONCLUSIONS

These results suggest that the expression of FGF in KS tumors with the coexpression of FGF receptors may provide a basis for autocrine and paracrine mechanisms contributing to the development of KS.

Emergence of the keratinocyte growth factor multigene family during the great ape radiation

The structural gene for human keratinocyte growth factor (KGF), a member of the fibroblast growth factor family, consists of three coding exons and two introns typical of other fibroblast growth factor loci. A portion of the KGF gene, located on chromosome 15, is amplified to approximately 16 copies in the human genome, and these highly related copies (which consist of exon 2, exon 3, the intron between them, and a 3' noncoding segment of the KGF transcript) are dispersed to multiple human chromosomes. The KGF-like sequences are transcriptionally active, differentially regulated in various tissues, and composed of three distinct classes of coding sequences that are 5% divergent from each other and from the authentic KGF sequence. Multiple copies of KGF-like genes were also discovered in the genomic DNAs of chimpanzee and gorilla but were not found in lesser apes (gibbon), Old World monkeys (African green monkey and macaques), mice, or chickens. The pattern of evolutionary occurrence suggests that a primordial KGF gene was amplified and chromosomally dispersed subsequent to the divergence of orangutan from African apes but before the trichotomous divergence of human, chimpanzee, and gorilla 5-8 million years ago. The appearance of a transcriptionally active and chromosomally dispersed multigene KGF family may have implications in the evolution of the great apes and humans.

Subcellular localization of bFGF in human retinal pigment epithelium in vitro

Basic fibroblast growth factor is a polypeptide mitogen with potential biological roles in angiogenesis, differentiation, and the survival of neurons. To study the expression and subcellular distribution of basic fibroblast growth factor in human retinal pigment epithelium in vitro, affinity-purified antipeptide antibodies were generated against a 15 amino acid sequence in the amino-terminus of this growth factor. Analysis of the cross reactivity and specificity of the affinity-purified antibodies demonstrated no ability to recognize acidic fibroblast growth factor and the ability to label specifically the major known forms of basic fibroblast growth factor in whole-cell lysates of retinal pigment epithelium in vitro. Examination of paraformaldehyde- or glutaraldehyde-fixed pigment epithelium at the light and electron microscopic levels revealed prominent localization of basic fibroblast growth factor to the nucleus and nucleolus. In cells fixed with organic reagents, prominent cytoplasmic staining was noted in addition to the nuclear staining seen in aldehyde fixed cells. Investigation of subcellular fractions by Western blot analysis indicated cytosolic as well as nuclear localization of the basic fibroblast growth factor. These analyses, however, demonstrated that the higher molecular weight forms of basic fibroblast growth factor predominate in the nucleus.

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.

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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Molecular mechanisms of tubulointerstitial hypertrophy and hyperplasia

Adult kidneys, which are principally composed of tubulointerstitium, do not normally regenerate or expand their working pool of functional cells at a very high rate. Loss of kidney tissue, however, can lead to some compensatory renal enlargement. The catalytic forces initiating such exchanges have not been fully articulated by current experimental endeavors. Increasing evidence, nevertheless, does suggest that factors other than simple changes in renal hemodynamics may be involved in this process. Different cellular elements in the tubulointerstitial microenvironment probably modulate changes in tubular enlargement or size through a complex cytokine network. Autocrine and paracrine stimulation of enlargement by different local growth factors also seem to play a pivotal role. After binding to cellular receptors, these factors activate signal transduction pathways resulting in expression of immediate early genes, which by themselves can synchronize the expression of subsequent genes through the medium of transacting factors. The renal enlargement response can also be modified by endocrine hormones that can activate such genes directly and/or stimulate other adjunctive processes, like receptor expression for the regional binding of growth factors. Furthermore, renal enlargement is under negative feedback of inhibitory factors like TGF beta. It is possible, for example, that special genes exist which are only expressed to arrest enlargement. It has been further suggested that activation of the Na+/H+ antiporter is a common denominator in renal enlargement. Recent findings, however, indicate that the activation of this antiporter is not always necessary, and might rather be a parallel event rather than a key phenomena in tubular enlargement. G0/G1 transition of tubular cells seems to involve similar factors in tubular hypertrophy and hyperplasia. The factors which are responsible for the final determination of the enlargement pattern (hypertrophy vs. proliferation) are unknown. The separation between hypertrophy and hyperplasia, although suggested by striking differences in cellular regulation, may be somewhat artificial, since responses leading to tubular enlargement also exist in circumstances where hyperplasia and hypertrophy are combined events. Recently it has been proposed that growth factors stimulate gluconeogenesis in proximal tubular cells producing hyperplasia, whereas factors inhibiting gluconeogenesis might induce hypertrophy. Whether the common pathway message of this intriguing hypothesis is correct still requires further validation.(ABSTRACT TRUNCATED AT 400 WORDS)

The gene for human acidic fibroblast growth factor encodes two upstream exons alternatively spliced to the first coding exon

We have isolated two cDNA clones encoding human acidic fibroblast growth factor (aFGF) which represent the utilization of alternative upstream exons in aFGF mRNA. Isolation and sequence analysis of genomic clones spanning the first coding exon and each of the upstream sequences confirms that the divergent 5' sequences are separate exons, spliced alternatively to the first coding exon 34 nucleotides upstream of the initiator AUG codon. Restriction mapping of the genomic clones provides a minimum size estimate of 45 kilobase pairs for the aFGF locus.