Heparin-dependent fibroblast growth factor activities: effects of defined heparin oligosaccharides

Heparin and related molecules have been identified as important participants in fibroblast growth factor (FGF) signaling although the mechanisms of action remain unclear. We have used heparin oligosaccharides to examine steps in the signaling process which could be affected by the polysaccharide. Immobilized FGF-1 and FGF-2 bound all sizes of oligosaccharides tested, ranging from tetrasaccharide to decasaccharide, at physiological salt concentration. Each group of oligosaccharide was eluted from the FGF affinity columns in several peaks, and larger oligosaccharides showed higher apparent affinity for the immobilized growth factors compared to the shorter ones. Heparin hexasaccharides were the smallest fragments providing complete protection of FGF-1 and FGF-2 against trypsin digestion. Tetrasaccharides, however, were able to provide partial protection. The requirement of heparin for ligand-receptor interaction was evaluated in receptor binding assays using Sf9 insect cells engineered to overexpress different recombinant FGF receptor (FGFR) species including FGFR1 beta, FGFR1 alpha or FGFR4 at the cell surface. In these assays hexasaccharides were the smallest fragments capable of stimulating FGF-receptor interaction. Over the range of concentrations examined, neither hexasaccharides nor octasaccharides were able to stimulate receptor binding to the level attained by intact heparin. In fact, these oligosaccharides interfered with the ability of intact heparin in promoting FGF-receptor binding. The presence of both stimulatory and inhibitory activities in hexasaccharide and octasaccharide populations could be attributed to structural heterogeneity within the oligosaccharide preparations. However, similar observations were obtained with "highly-sulfated" structurally homogeneous preparations of hexasaccharide and octasaccharide, although these molecules generally had greater stimulatory and less inhibitory activity than their structurally heterogeneous counterparts. Hexasaccharides were found to be the smallest fragments able to potentiate the FGF-1-induced 3T3 cell proliferation while their effect on FGF-2 signaling was less clear. These observations suggest that heparin can modulate FGF-signaling at several stages with different end results.

Growth and differentiation of periodontal ligament-derived cells in serum-free defined culture

We have developed a serum-free medium for the growth and differentiation of periodontal ligament-derived cells (PLC). In addition, the expression of both fibroblast growth factor (FGF) and FGF receptor (FGFR) in the PLC was investigated by immunohistochemical examination, heparin affinity chromatography (HAC), and reverse transcription-polymerase chain reaction (RT-PCR) analysis. Optimal growth of the cells was achieved in Iscove's modified Dulbecco's medium supplemented with insulin, transferrin, 2-mercaptoethanol, 2-ethanolamine, sodium selenite, and oleic acid in type-I collagen-coated dishes. Both FGF-1 and FGF-2 stimulated cell growth and inhibited differentiation as measured by inhibition of alkaline phosphatase activity of the cells. An immunohistochemical analysis of FGF-1 and FGF-2 revealed that immunoreactive FGF-1 and FGF-2 were detected predominantly in the cytoplasm of growing cells. In addition, perinuclear FGF-1 staining and nuclear FGF-2 staining were observed in the same growing cells. In contrast, a faint diffuse staining of FGF-1 and FGF-2 was detected in cytoplasm of the confluent differentiated cells. The 2.15 M NaCl eluate from HAC of the cell extracts exhibited growth-promoting activities for the PLC, and it also stimulated the growth of human umbilical vein-derived endothelial cells and inhibited binding of [125I]-FGF to its receptors, indicating the cells produced FGFs or FGF-like growth factors. RT-PCR analysis revealed that the cells expressed FGFR-1 mRNA but not mRNAs for FGFR-2, FGFR-3 and FGFR-4 mRNA. These results suggest that the FGF-FGFR-1 system plays an important role in the growth and differentiation of periodontal ligament-derived cells.

Immunohistochemical localization of fibroblast growth factor-1 (FGF-1), FGF-2 and fibroblast growth factor receptor-1 (FGFR-1) in pleomorphic adenoma of the salivary glands

Fibroblast growth factor-1 (FGF-1) and FGF-2 are heparin-binding polypeptides that are potent mitogens for neoplastic cells. In this study, fibroblast growth factor-1 (FGF-1), FGF-2, and fibroblast growth factor receptor-1 (FGFR-1) were immunohistochemically analyzed in 10 patients with pleomorphic adenoma of the salivary gland by using specific monoclonal antibodies. The tumor tissues were histopathologically classified as: tubular, solid, myxoid or chondroid. Both FGF-1 and FGF-2 were immunohistochemically identified in the tumor cells of all histological types. In addition, immunoreactive FGF-2 was also found in the basement membrane of tubular type tumor cells. Conversely, FGFR-1-positive tumor cells were essentially confined to the tubular and solid areas of tumors. Tumor cells in the myxoid and chondroid areas were FGFR-1 immunonegative. These results suggest that the co-expression of FGF and its receptor appears to be related to the proliferative activity of tumor cells in the tubular and solid areas, whereas loss of FGF receptor expression may be associated with the differentiation of tumor cells into myxoid and chondroid tissue types.

Serological evaluation of soluble CD44 in renal cancer

In this study, we examined the feasibility of using elevated serum CD44 concentration as an indicator in renal cancer. We performed enzyme-linked immunosorbent assays using 63 sera obtained from 47 patients with renal cancer and 16 healthy controls and evaluated the clinico-pathological parameters. The concentration of soluble CD44 standard (sCD44std), indicating the concentration of all circulating CD44 isoforms, was significantly higher in renal cancer patients than in normal individuals (745+/-170 ng/ml vs. 563+/-159 ng/ml, P=0.001). The concentration of soluble CD44 splice isoforms sharing exon v6 (sCD44v6) was also higher in the same patients (287+/-121 vs. 220+/-59, P=0.056). However, there were no correlations between the concentrations of sCD44std or sCD44v6 and clinico-pathological parameters such as grade, stage, histological type, tumor size and growth type. The ratio of sCD44std/sCD44v6 was higher in the rapid growth-type cancers than in the slow growth-type cancers (3.95+/-2.12 vs. 2.63+/-0.82, P = 0.014). These findings suggested that the serum concentration of unknown soluble CD44 isoforms not sharing exon v6, which are present in sCD44std, increases in patients with rapid growth-type cancers. These findings indicated that sCD44std and sCD44v6 are not useful indicators of tumor burden and metastasis in patients with renal cancer, but that an unknown sCD44 isoform(s) plays a role in the biological behavior of the rapid growth-type cancers.

Induction of FGF-7 after kidney damage: a possible paracrine mechanism for tubule repair

A member of the fibroblast growth factor (FGF) family, keratinocyte growth factor (FGF-7 has unique specificity for epithelial cells. We investigated the role of FGF-7 in repair of proximal tubular damage caused by S-(1,1,2,2-tetrafluoroethyl)-L-cysteine (TFEC). In situ hybridization localized FGF-7 to interstitial cells in the medulla and outer stripe of the outer medulla. Interstitial FGF-7 expression increased throughout the kidney 1 day after TFEC treatment. FGFR2 IIIb mRNA was high in the papilla and medulla and also increased after TFEC administration. By in situ hybridization, FGFR2 IIIb was localized to the tubular epithelium, particularly in collecting ducts. Proliferation of collecting duct epithelial cells increased in adult kidney after damage to the proximal tubule. FGFR2 IIIb, but not FGF-7, mRNA was also expressed by rat proximal tubule epithelial (RPTE) cells in vitro, and FGF-7 increased DNA synthesis in RPTE. Thus FGFR2 IIIb and FGF-7 expression is segregated between epithelial and interstitial cells forming a paracrine growth factor loop. These results raise the possibility that a novel paracrine growth loop is activated by chemical damage and regulates epithelial cell growth during tubular repair.

Molecular modeling and deletion mutagenesis implicate the nuclear translocation sequence in structural integrity of fibroblast growth factor-1

The sequence NYKKPKL in the NH2 terminus of fibroblast growth factor (FGF)-1 has been proposed to affect the long term activities of FGF-1 through its function as a nuclear translocation signal or its role in stabilization of the structure required to sustain binding and activation of the transmembrane receptor kinase. A dynamic molecular model of FGF-1 docked into a duplex of the FGF receptor ectodomain and a hexadecameric heparin chain suggests that the NYKKPKL sequence does not directly interact with heparin or the receptor, but rather the lysine-leucine residues within the sequence indirectly stabilize a major receptor-binding domain. Concurrent with a marked increase in dependence on exogenous heparin for optimal activity, sequential deletion of residues in the NYKKPKL sequence in FGF-1 resulted in a progressive loss of thermal stability, resistance to protease, mitogenic activity, and affinity for the transmembrane receptor. The largest change resulted from deletion of the entire sequence through the lysine-leucine residues. In the presence of sufficiently high concentrations of heparin, the deletion mutants exhibited mitogenic activity equal to wild-type FGF-1. The results confirm that a primary role of the NYKKPKL sequence domain is to maintain the structural integrity of FGF-1 required for optimal binding to and activation of the heparan sulfate-transmembrane receptor complex.

Divalent cations and heparin/heparan sulfate cooperate to control assembly and activity of the fibroblast growth factor receptor complex

Polypeptides of the fibroblast growth factor (FGF) family are ubiquitous bioregulators within tissues whose activity is controlled by heparan sulfates within the pericellular matrix. FGF and the ectodomain of their transmembrane tyrosine kinase receptors (FGFR) exhibit heparin-binding domains that when juxtaposed in a FGF middle dotFGFR complex can accommodate a single, potentially bivalent, decameric polysaccharide chain in a ternary complex. Here we show that the interaction of heparin with FGF ligands is not affected by divalent cations. In contrast, the high affinity interaction (apparent Kd = 10 nM) of heparin with FGFR requires Ca2+ or Mg2+ at physiological concentrations. Divalent cations maintain FGFR in a heparan sulfate-dependent state in respect to FGF binding and an FGF- and heparan sulfate-dependent state in respect to autophosphorylation. A model is proposed where divalent cations and heparan sulfate cooperate to maintain FGFR in a conformation that restricts trans-phosphorylation between intracellular kinase domains. The restriction is overcome by FGF or constitutively as a common consequence of diverse mutations in FGFR associated with skeletal and craniofacial abnormalities.

Reconstitution of a pentameric complex of dimeric transforming growth factor beta ligand and a type I, II, III receptor in baculoviral-infected insect cells

Two transmembrane serine-threonine kinases (type I and II receptors), a membrane-anchored proteoglycan (type III), and a homodimeric ligand participate in the transforming growth factor beta type one (TGF beta 1) signal transduction complex. The expression of recombinant receptors in insect cells co-infected with up to three recombinant baculoviruses was employed to study interactions among the ectodomains of the three types of receptors and the TGF beta 1 ligand in absence of uncontrollable extrinsic factors in mammalian cells. Multi-subunit complexes were assembled in intact cells and purified on glutathione-conjugated beads for analysis by tagging one of the subunits with glutathione S-transferase (GST). Intrinsic ligand-independent interactions were observed among receptor subunits as follows: type III-III, type I-I, type III-I, and type II-I. The homeotypic complex of type II-II receptors and the heterotypic type III-II interaction was ligand dependent. The type I, but not the type III, subunit displaced about 50% of the type II component in either ligand-dependent homomeric type II-type II complexes or heteromeric type III-type II complexes to form type II-I or type III-II-I oligomers, respectively. The type II subunit displaced type I subunits in oligomers of the type I subunit. Specificity of type I receptors may result from differential affinity for the type II receptor rather than specificity for ligand. A monomeric subunit of the TGF beta 1 ligand bound concurrently to type III and type II or type III and type I receptors, but failed to concurrently bind to the type II and type I subunits. The binding of TGF beta 1 to the type I kinase subunit appears to require an intact disulfide-linked ligand dimer in the absence of a type III subunit. The combined results suggest a pentameric TGF beta signal transduction complex in which one unit each of the type III, type II, and type I components is assembled around the two subunits of the dimeric TGF beta ligand. An immobilized GST-tagged subunit of the receptor complex was utilized to assemble multi-subunit complexes in vitro and to study the phosphorylation events among subunits in the absence of extrinsic cell-derived kinases. The results revealed that (a) a low level of ligand-independent autophosphorylation occurs in the type I kinase; (b) a high level of autophosphorylation occurs in the type II kinase; (c) both the type III and type I subunits are trans-phosphorylated by the type II subunit; and (d) the presence of both type I and II kinases complexed with the type III subunit and dimeric TGF beta 1 ligand in a pentameric complex causes maximum phosphorylation of all three receptor subunits.

Androgen-dependent expression of fibroblast growth factor-1 in submaxillary gland of mouse

We have purified a 16,000 dalton protein that stimulates growth of human umbilical cord vein-derived endothelial cells (HUV-EC) from mouse submaxillary glands by using heparin-Sepharose affinity and C4 reverse phase chromatography. The purified molecule was identified as an FGF-1 on the basis of its biological activities, its affinity for heparin and its N-terminal amino-acid sequence. The concentrations of FGF-1 in the submaxillary gland of male or testosterone-treated female mice were about 12 times those of untreated females or castrated males. The 2.3 and 4.1 kb FGF-1 mRNAs were expressed in the glands of male mice older than 4 weeks but not in the glands of female mice. These results suggest that FGF-1 may have important functions for growth, differentiation and development of mouse submaxillary glands, and it may act as an endocrine hormone.

Immunohistochemical study of overexpression of fibroblast growth factor-1 (FGF-1), FGF-2, and FGF receptor-1 in human malignant salivary gland tumours

Fibroblast growth factor-1 (FGF-1) and FGF-2 are broad spectrum mitogens. The expression of FGF-1, FGF-2, and their receptor, FGF receptor-1 (FGFR-1), was examined in malignant salivary gland tumours and normal salivary glands, using immunohistochemical methods. In seven cases of adenoid cystic carcinoma (ACC), both duct-like cells and modified myoepithelial cells were apparently immunopositive for FGF-1, FGF-2, and FGFR-1. In five cases of mucoepidermoid carcinoma (MC), all three types of tumour cells including epidermoid cells, and intermediate cells expressed immunoreactive FGF-1, FGF-2, and FGFR-1. In these malignant salivary gland tumours, increased expression of FGFR-1 correlated with the intensity of both FGF-1 and FGF-2 immunoreactivity. In contrast to malignant salivary gland tumours, eight cases of normal salivary gland showed negative immunostaining for FGF-1, FGF-2, and FGFR-1 while four cases were weakly immunoreactive for FGF and its receptor. These results demonstrate that malignant salivary gland tumours overexpress FGF-1, FGF-2, and FGFR-1 compared with normal salivary glands and suggest that these growth factors may play an important role in facilitating neoplastic progression in human salivary glands.

Expression of fibroblast growth factor-1 (FGF-1), FGF-2 and FGF receptor-1 in a human salivary-gland adenocarcinoma cell line: evidence of growth

Fibroblast growth factor-1 (FGF-1) and FGF-2 are heparin-binding polype ptides which express potent mitogenic properties in neoplastic cells. In the present study, we have examined the contribution of endogenous FGF-1 and FGF-2 to the autocrine growth of HSY human salivary-gland adenocarcinoma cells in vitro. Using specific monoclonal antibodies against FGF-1 and FGF-2, immunohistochemical analysis of HSY cells revealed strong expression of both FGF-1 and FGF-2 in the cytoplasm and nucleus. Consistent with these data, 2 molecular mass species of FGF-1 (16 and 18 kDa) and 3 FGF-2 (18, 24 and 27 kDa) were identified in HSY cells by Western-blot analysis. Scatchard analysis of FGF binding sites on HSY cells indicated the presence of 23,000 [125I]FGF-1 binding sites/cells with a dissociation constant (KD) of 178 pM and 13,000 [125I]FGF-2 binding sites/cell with a KD of 102 pM. In addition, HSY cells were shown to express the mRNA for FGF receptor-1 (FGFR-1) by reverse transcription-polymerase chain reaction (RT-PCR), confirming the existence of high-affinity FGF binding sites. The influence of endogenous FGF-1 and FGF-2 on HSY cell growth was evaluated by suppressing the expression and activity of FGF by using anti-sense oligonucleotides and neutralizing antibodies. The addition of 50 micron FGF-1-specific anti-sense oligonucleotides to HSY cells resulted in a 61% inhibition of cell growth, while 50 microM FGF-2-specific anti-sense oligonucleotides resulted in a 76% inhibition. These effects were dose-dependent and specific, since sense oligonucleotides were ineffective in inhibiting HSY cell growth at the same concentration. Furthermore, HSY cell growth was suppressed in the presence of anti-FGF-1 or anti-FGF-2 neutralizing antibody, resulting in a 58% inhibition at 8 micromilligrams/ml. Our observations suggest that FGF-1 and FGF-2 may act as autocrine regulators by interacting with FGF receptors on HSY cells.

Nuclear localization of a complex of fibroblast growth factor(FGF)-1 and an NH2-terminal fragment of FGF receptor isoforms R4 and R1alpha in human liver cells

FGF ligands and FGF receptor 1 (FGFR1) appear associated with the nucleus in addition to their extracellular and transmembrane locations. After receptor-dependent internalization in liver cells, radiolabeled 16-kDa FGF-1 appears in a 40-kDa covalent complex with a cellular protein. In this report, we show that in a human hepatoma cell line, HepG2, which expresses both FGFR4 and FGFR1, the 40-kDa complex cross-reacts with antibodies against the ectodomain of both types of receptors. In addition to antibody against FGF-1, a polyclonal antiserum against the three immunoglobulin (Ig)-like loop ectodomain of FGFR4 and a monoclonal antibody to a 19-residue sequence in the NH2-terminus of the NH2-terminal Ig Loop I of the three loop splice variant of FGFR1 (FGFR1alpha) reacts with the complex. A monoclonal antibody against an epitope in FGFR1 downstream of the inter-loop I/II sequence which reacts with intact FGFR1 failed to cross-react with the 40-kDa complex. Cell fractionations and indirect immunofluorescent localization revealed that the 40-kDa complex associates with the particulate fraction of cells, particularly the nucleus and associated cytoskeletal elements. We propose that the NH2-terminal Ig-loop of the three loop isoforms of FGFR, which are generally associated inversely with cell growth, may play a role at or in the nucleus in addition to modification of affinity of the FGFR ectodomain for heparan sulfate and FGF ligand.

Expression of CD44 splice variants in bladder cancer

BACKGROUND

Recently, it was noted that CD44 participates in a wide variety of cell-cell or cell-matrix interactions including tumor metastasis and the altered expression of CD44 splice variants is helpful in the diagnosis of colon and breast cancer. The purpose of the study was to investigate altered expression of CD44 in bladder cancer.

METHODS

Thirty-three surgical specimens of 22 patients and seven bladder cancer cell-lines were analyzed by various methods including RT-PCR-Southern blotting. Northern blotting, and flow-cytometric analysis.

RESULTS

In RT-PCR analysis, the hematopoietic variant and numerous additional variants were detected in all cell-lines and almost all surgical specimens. In three out of seven cell-lines of bladder cancer (42.9%), especially numerous larger bands (ladder pattern) were detected using RT-PCR. These three cell-lines expressed a smaller quantity of CD44 mRNAs and CD44 molecules than the other four cell-lines. In eighteen out of 22 (81.8%) bladder cancer specimens, we detected larger variants that exceed 1500 base pairs, compared with the detection in four out of eleven (36.4%) visually normal mucosa specimens (P < 0.05). However, there was no correlation between the expression of the larger variants and clinicopathological features.

CONCLUSION

The quantitative and qualitative change of CD44 variants were demonstrated in bladder cancer.

High-level expression of the CD44 variant sharing exon v10 in renal cancer

To examine whether renal cell carcinoma displays altered CD44 expression we performed reverse transcription-polymerase chain reaction (RT-PCR) analysis of CD44 in 38 specimens from renal cancer, normal kidney and metastases of 19 patients and 6 renal cancer cell lines. To detect the CD44 variants, we utilized the RT-PCR Southern blot method. One out of 19 (5.3%) renal cancer specimens expressed a larger molecular weight band than 1 kb by RT-PCR analysis, in contrast to previous findings in colon and breast cancer. The band patterns in RT-PCR were different in 14/17 (82.4%) cases between normal kidney and tumors, and a band of about 700 bp was especially marked in 12/17 (70.6%) tumor specimens and 4/6 (66.7%) cell lines. By cloning and sequencing of the 700 bp band, we found that this variant is identical to the CD44 variant sharing only exon v10. Examination by Northern blot analysis has revealed that all tumors express a higher level of CD44 mRNA than paired normal kidneys. These findings suggested that the CD44 variants sharing exon v10 play some role in renal cancer.

Frequency of mutations of insulin receptor gene in Japanese patients with NIDDM

To examine the prevalence of abnormalities in the insulin receptor structure gene in Japanese with non-insulin-dependent diabetes mellitus (NIDDM), a population of 51 patients with NIDDM was screened for mutations in this gene. Patient genomic DNAs of both alleles corresponding to 22 exons of the gene were amplified by polymerase chain reaction (PCR). The PCR products on pUC19 were sequenced. Three patients with heterozygous missense mutation Thr831-->Ala831 in exon 13 and one patient with heterozygous missense mutation Tyr1334-->Cys1334 in exon 22 of the beta-subunits were identified. Linkage analysis of one of the families plus statistical studies showed that the mutation Thr831-->Ala831 is possibly responsible for the onset of NIDDM. In COS cells transiently expressing both mutant receptor cDNAs and a cDNA of a M(r) 85,000 regulatory subunit of phosphatidylinositol 3-kinase (PI 3-kinase), the mutation Tyr1334-->Cys1334 impaired binding of the receptor with the M(r) 85,000 subunit of PI 3-kinase, but linkage analysis of the family showed that the mutation did not cosegregate with NIDDM in the pedigree. Therefore, one missense mutation (Thr831-->Ala831) in the insulin receptor, as found in three patients, is possibly involved in the etiology of a subset of the 51 NIDDM patients.

[Expression of CD44 variant form in human renal cell carcinoma]

To examine whether renal cell carcinoma display altered CD44 expression we performed reverse transcriptase-polymerase chain reaction (RT-PCR) analysis of CD44 in the tissues resected from 19 patients with renal cell carcinoma and 6 renal cancer cell lines. To detect the CD44 variants, we utilized the RT-PCR Southern blot method reported by Matsumura et al. In 12 of 17 (70.6%) cases, about a 700 base pairs band was emphasized in cancerous tissues compared with normal kidney. Moreover, we found that this isoform is the CD44 variant sharing only exon v10. Examination by Northern blot analysis has revealed that all tumors express a higher level of CD44 variants sharing exon v10. Our findings suggest that this variant form plays some roles in renal cell carcinoma.

Alternately spliced NH2-terminal immunoglobulin-like Loop I in the ectodomain of the fibroblast growth factor (FGF) receptor 1 lowers affinity for both heparin and FGF-1

Alternate splicing of a single exon encoding an NH2-terminal immunoglobulin (Ig) disulfide loop in the ectodomain of the fibroblast growth factor receptor (FGFR) types 1 and 2 results in alpha and beta isoforms that exhibit 3- and 2-Ig loops, respectively. Previously we demonstrated that alternately spliced Loop I has no independent ligand binding activity but is sufficiently interactive with the ligand- and heparin-binding site formed by Loops II and III to lower affinity for the same fibroblast growth factor (FGF) ligand. Here we show that a lower affinity of FGFR1 alpha for heparin parallels the lower affinity for FGF-1. A mutant of FGFR1 alpha in which the sequence between Loops I and II was deleted exhibits high affinity for both FGF-1 and heparin and other properties of the FGFR1 beta isoform, which include resistance to degradation by trypsin and display of specific antibody epitopes. This suggests that the interloop sequence facilitates the interaction of Loop I with Loops II and III. Lack of expression of both exons coding for Loop I and the sequence between Loops I and II in the FGFR2 gene characterizes rat prostate tumor cells, which exhibit a loss of the low affinity class of FGF receptors. Although the exon coding for the sequence between Loops I and II is alternately spliced in the FGFR2 beta isoform, coordinate expression with the exon coding for Loop I results in the functional differences between the FGFR alpha and FGFR beta variants.

Ligand-specific structural domains in the fibroblast growth factor receptor

Two tandem immunoglobulin-like disulfide loops (Loops II and III) linked by a short connecting sequence in the ectodomain of the fibroblast growth factor receptor kinase compose the binding sites for glycosaminoglycan and fibroblast growth factor (FGF) ligands. Alternate splicing of exons IIIb and IIIc coding for the COOH-terminal half of Loop III confers high affinity for FGF-7 or FGF-2, respectively, on the fibroblast growth factor receptor ectodomain without effect on the binding of FGF-1. Here we show that a 139-amino acid fragment composed of Loop II, the inter-Loop II/III sequence, and a short segment of the NH2 terminus of Loop III is sufficient and near the minimal requirement for binding of FGF-1, FGF-2, and FGF-7. Extension of the fragment by five additional highly conserved residues (SD(P/A)QP) within a distinct constitutive structural domain (fl1) in Loop III restricts the binding of FGF-7 without effect on FGF-1 and FGF-2. Since the presence of exon IIIc in the full-length ectodomain does not change this ligand binding profile, we suggest that alternately spliced exon IIIc plays no active role in binding of the three ligands. In contrast, exon IIIb actively abrogates the restriction on the binding of FGF-7 and concurrently lowers the affinity for FGF-2.

Variation in equation coefficients in the gravimetric method to determine brain water content

The gravimetric method to determine the tissue water content is widely used for studying brain edema because the tissue water content can be calculated from only the density of the wet tissue using a gradient column. This method has been used in only a few studies of cerebellar water content. We estimated the water content of the cerebellar cortex by the gravimetric method and compared the results with those measured by the conventional drying-weighing method, and found a significant difference. We therefore propose modified coefficients for the equation for the water content of the cerebellar cortex as follows: % tissue water content = 456.13(1/wet tissue density) - 356.13 This equation and the drying-weighing method were used to investigate normal and edematous cerebellar cortices after compression with an epidural balloon. The modified equation provided results consistent with the drying-weighing method. Differences in the total experimental system including the breed and pre-experimental condition of the cats may be factors in variations in measured values. We recommend that investigators establish equation coefficients valid for individual experimental systems.

The role of insulin in activation of two enhancers in the mouse GLUT1 gene

We identified two enhancer elements of the mouse GLUT1 gene responsive to serum, growth factor, and oncogenes; the first enhancer element (enhancer-1) is located 2.7 kilobases upstream of the cap site of the gene, and the second one (enhancer-2) is located in the second intron of the gene (Murakami, T., Nishiyama, T., Shirotani, T., Shinohara, Y., Kan, M., Ishii, K., Kanai, F., Nakazuru, S., and Ebina, Y. (1992) J. Biol. Chem. 267, 9300-9306). In the present work, we describe the role of insulin in activation of these two enhancers. NIH/3T3 HIR3.5 cells, which express a large number of insulin receptors, were stably transformed by hybrid genes containing the enhancer(s) and promoter of GLUT1 gene and the coding region of chloramphenicol acetyltransferase (CAT) gene as a reporter gene. In stable transformants of the reporter gene without the enhancers, the CAT mRNA was not induced by insulin; however, in clones containing the reporter gene with enhancer-1, the CAT mRNA was induced by insulin at 30 min and reached a maximum at 1 h. In clones transfected by the reporter gene with enhancer-2, the CAT mRNA was induced at 1 h and reached a maximum at 3 h. To determine the early response element to insulin in enhancer-1, transformants of hybrid reporter genes containing truncated or mutated enhancer-1 were examined. The homologous sequence with the serum response element in enhancer-1 is essential for an early response to insulin.

Inositolhexakisphosphate (InsP6): an antagonist of fibroblast growth factor receptor binding and activity

Fibroblast growth factors (FGF), which have been implicated in tumor cell growth and angiogenesis, have biological activities that appear to be mediated by both heparinlike extracellular matrix sites and transmembrane tyrosine kinase receptor sites. In the present study, we demonstrated that inositolhexakisphosphate (InsP6) inhibits basic FGF (bFGF) binding to heparin. Our spectrofluorometric analyses demonstrated that InsP6 not only bound to bFGF, presumably within the bFGF heparin-binding domain, but also protected bFGF from degradation by trypsin. Also, InsP6 inhibited the cellular binding of bFGF and other fibroblast growth factor family members such as acidic FGF (aFGF) and K-FGF in a saturable and dose-dependent manner. Furthermore, concentrations as low as 100 microM InsP6 inhibited bFGF-induced DNA synthesis in AKR-2B fibroblasts, as well as the growth of bFGF- and K-FGF-transfected NIH/3T3 cells. Together, these results indicate that InsP6 may serve as a useful antagonist of FGF activity.