Expression, processing, and properties of int-2

Functional evolutionary history of the mouse Fgf gene family

Fibroblast Growth Factors (FGFs) are polypeptides with diverse activities in development and physiology. The mammalian Fgf family can be divided into the intracellular Fgf11/12/13/14 subfamily (iFGFs), the hormone-like Fgf15/21/23 subfamily (hFGFs), and the canonical Fgf subfamilies, including Fgf1/2/5, Fgf3/4/6, Fgf7/10/22, Fgf8/17/18, and Fgf9/16/20. However, all Fgfs are evolutionarily related. We propose that an Fgf13-like gene is the ancestor of the iFgf subfamily and the most likely evolutionary ancestor of the entire Fgf family. Potential ancestors of the canonical and hFgf subfamilies, Fgf4-, Fgf5-, Fgf8-, Fgf9-, Fgf10-, and Fgf15-like, appear to have derived from an Fgf13-like ancestral gene. Canonical FGFs function in a paracrine manner, while hFGFs function in an endocrine manner. We conclude that the ancestral Fgfs for these subfamilies acquired this functional diversity before the evolution of vertebrates. During the evolution of early vertebrates, the Fgf subfamilies further expanded to contain three or four members in each subfamily.

The Fgf families in humans, mice, and zebrafish: their evolutional processes and roles in development, metabolism, and disease

Fibroblast growth factors (Fgfs) were originally isolated as growth factors for fibroblasts. However, Fgfs are now recognized as polypeptide growth factors of ca. 150-250 amino acid residues with diverse biological activities and expression profiles. The Fgf signaling system has been identified in multicelluar but not in unicellular organisms. In contrast to the only two Fgf genes and one Fgf receptor (Fgfr) gene in Caenorhabditis elegans, both the human and mouse Fgf and Fgfr gene families comprise twenty-two and four members, respectively. Their evolutional processes indicate that the Fgf and Fgfr gene families greatly co-expanded during the evolution of early vertebrates. The expansion of the Fgf and Fgfr gene families has enabled this signaling system to acquire diversity of function and a nearly ubiquitous involvement in many developmental and physiological processes. The zebrafish fgf gene family comprises twenty-seven members with several paralogs generated by an additional genome duplication. The mouse and zebrafish are useful models for studying gene functions. Fgf knockout mice have been generated. Several Fgf knockout mice die in the embryonic or early postnatal stages, indicating crucial roles for these genes in various developmental processes. However, other Fgf knockout mice survive with subtle phenotypic alterations. Their functions might be redundant. Studies using zebrafish embryos with mutated or knockdown fgfs also indicate that fgfs play crucial roles in development in that species. Although most Fgfs act in development in a paracrine and/or autocrine manner, some have potential roles in metabolism in an endocrine manner. In humans, Fgf signaling disorders result in hereditary diseases and cancers.

Characterization of the baculovirus Bombyx mori nucleopolyhedrovirus gene homologous to the mammalian FGF gene family

We characterized a gene of the baculovirus Bombyx mori nucleopolyhedrovirus (BmNPV) homologous to the mammalian fibroblast growth factor (FGF) family. We termed it vfgf, and examined its transcription and the properties of the gene product (vFGF). RT-PCR analysis showed that vfgf is one of the baculovirus early genes, although there are no consensus sequences of the baculovirus early gene promoters. 5'-RACE analysis revealed that its transcription started at 10 nucleotides upstream of the translation start codon. vFGF has a hydrophobic amino terminus (approximately 16 amino acids), which is a typical signal sequence. As expected, vFGF was efficiently secreted from BmNPV-infected BmN cells. Because possible glycosylation sites are found at positions 44 (Asn) and 171 (Asn), we examined whether BmNPV vFGF is glycosylated or not. Cleavage of recombinant vFGF with PNGase F revealed that BmNPV vFGF was glycosylated. We also found that secretion of vFGF is completely blocked by the treatment of Tunicamycin, which blocks N-linked glycosylation. This is the first report to characterize a virus-encoded FGF.

Identification of a novel fibroblast growth factor, FGF-22, preferentially expressed in the inner root sheath of the hair follicle

We isolated cDNA encoding a novel fibroblast growth factor (FGF-22) (170 amino acids) from human placenta. Of the FGF family members, FGF-22, which appears to be a secreted protein, is most similar to FGF-10 and FGF-7 (approximately 46% and approximately 40% amino acid identities, respectively). The human FGF-22 gene was localized on chromosome 19p13.3. We also isolated mouse cDNA encoding FGF-22 (162 amino acids) from the skin. Mouse FGF-22 shows high homology (87% amino acid identity) to human FGF-22. Mouse FGF-22 mRNA was found to be preferentially expressed in the skin among the mouse adult tissues examined by Northern blotting analysis. By in situ hybridization, FGF-22 mRNA in the skin was found to be preferentially expressed in the inner root sheath of the hair follicle. Therefore, FGF-22 is expected to be a unique FGF that plays a role in hair development.

Identification of a novel fibroblast growth factor, FGF-23, preferentially expressed in the ventrolateral thalamic nucleus of the brain

We isolated mouse cDNA encoding a novel FGF (251 amino acids). As this is the 23rd documented FGF, we termed it FGF-23. FGF-23 has a hydrophobic amino terminus ( approximately 24 amino acids), which is a typical signal sequence. As expected, recombinant mouse FGF-23 was efficiently secreted by High Five insect cell-infected recombinant baculovirus containing the cDNA, indicating that FGF-23 is a secreted protein. We also isolated human cDNA encoding FGF-23 (251 amino acids), which is highly identical ( approximately 72% amino acid identity) to mouse FGF-23. Of human FGF family members, FGF-23 is most similar to FGF-21 and FGF-19 ( approximately 24% and approximately 22% amino acid identities, respectively). Human FGF-23 gene was localized on the chromosome 12p13 and found to be tandem linked (within 5.5 kb) to human FGF-6 gene. The expression of FGF-23 mRNA in mouse adult tissues was examined by real-time quantitative polymerase chain reaction. FGF-23 mRNA was mainly expressed in the brain and thymus at low levels. The localization of FGF-23 mRNA in the brain was examined by in situ hybridization. FGF-23 mRNA in the brain was found to be preferentially expressed in the ventrolateral thalamic nucleus. Therefore, FGF-23 is expected a unique FGF that plays roles in the function of the ventrolateral thalamic nucleus.

FGF-20, a novel neurotrophic factor, preferentially expressed in the substantia nigra pars compacta of rat brain

We have isolated cDNA encoding a novel FGF (212 amino acids) from rat brain. Because this is the 20th documented member of the FGF family, we tentatively term it FGF-20. Among FGF family members, FGF-20 is most similar to FGF-9 and FGF-16 (70 and 62% amino acid identity, respectively). Human FGF-20 gene was found in the human genomic sequence mapped to the 8p21.3-p22 region. Human FGF-20 is highly identical to rat FGF-20 (95% amino acid identity). FGF-20 mRNA was preferentially expressed in rat brain among the adult major tissues examined. The localization of FGF-20 mRNA in rat brain was also examined by in situ hybridization. FGF-20 mRNA was preferentially expressed in the substantia nigra pars compacta. To examine the biological activity of FGF-20, recombinant rat FGF-20 was produced by insect cells infected with recombinant baculovirus containing rat FGF-20 cDNA. Recombinant rat FGF-20 enhanced the survival of midbrain dopaminergic neurons. The present results indicate that FGF-20 is a novel neurotrophic factor preferentially expressed in the substantia nigra pars compacta of rat brain.

Identification of a novel FGF, FGF-21, preferentially expressed in the liver

We isolated cDNA encoding a novel FGF (210 amino acids) from mouse embryos. As this is the 21st documented FGF, we tentatively term it FGF-21. FGF-21 has a hydrophobic amino terminus ( approximately 30 amino acids), which is a typical signal sequence, and appears to be a secreted protein. The expression of FGF-21 mRNA in mouse adult tissues was examined by Northern blotting analysis. FGF-21 mRNA was most abundantly expressed in the liver, and also expressed in the thymus at lower levels. We also isolated human cDNA encoding FGF-21 (209 amino acids). Human FGF-21 is highly identical ( approximately 75% amino acid identity) to mouse FGF-21. Among human FGF family members, FGF-21 is most similar ( approximately 35% amino acid identity) to FGF-19.

Structure and expression of the mRNA encoding a novel fibroblast growth factor, FGF-18

We isolated the cDNA encoding a novel member (207 amino acids) of the fibroblast growth factor (FGF) family from rat embryos. Because this protein is the 18th documented member of the FGF family, we tentatively termed it FGF-18. We have also determined mouse and human FGF-18 with high amino acid identity (99.5 and 99.0%) to rat FGF-18, respectively. Among FGF family members, FGF-18 is most similar (52.7% amino acid identity) to FGF-8 and FGF-17. FGF-18 has a typical signal sequence at its amino terminus. Recombinant rat FGF-18, which was efficiently secreted by High Five insect cells infected with recombinant baculovirus containing the cDNA, induced neurite outgrowth in PC12 cells. The expression of FGF-18 mRNA was examined in adult rat tissues and embryos by Northern blotting analysis and in situ hybridization. FGF-18 mRNA of approximately 2. 7 kilobases was preferentially detected in the lung among adult rat tissues examined. In rat embryos, FGF-18 mRNA was detected in several discrete regions at embryonic days 14.5 and 19.5 but not at E10.5. The temporal and spatial patterns of FGF-18 mRNA expression in embryos are quite different from those of FGF-8 and FGF-17 mRNAs reported. The present results indicate that FGF-18 is a unique secreted signaling molecule in the adult lung and developing tissues.

Characterization of recombinant human fibroblast growth factor (FGF)-10 reveals functional similarities with keratinocyte growth factor (FGF-7)

A newly identified member of the fibroblast growth factor (FGF) family, designated FGF-10, is expressed during development and preferentially in adult lung. The predicted FGF-10 protein is most related to keratinocyte growth factor (KGF, or FGF-7). The latter is unique among FGFs in that it binds and signals only through the FGF receptor (FGFR2b) isoform KGF receptor (KGFR) expressed specifically by epithelial cells. In order to examine the biological and biochemical properties of human FGF-10, we isolated the cDNA and expressed its encoded protein in bacteria. The recombinant protein (rFGF-10) was a potent mitogen for Balb/MK mouse epidermal keratinocytes with activity detectable at 0.1 nM and maximal at around 5 nM. Within this concentration range, FGF-10 did not stimulate DNA synthesis in NIH/3T3 mouse fibroblasts. rFGF-10 bound the KGFR with high affinity comparable to that of KGF, and did not bind detectably to either the FGFR1c (Flg) or FGFR2c (Bek) receptor isoforms. The mitogenic activity of FGF-10 could be distinguished from that of KGF by its different sensitivity to heparin and lack of neutralization by a KGF monoclonal antibody. These results indicate that FGF-10 and KGF have similar receptor binding properties and target cell specificities, but are differentially regulated by components of the extracellular matrix.

Structure and expression of a novel fibroblast growth factor, FGF-17, preferentially expressed in the embryonic brain

We isolated the cDNA encoding a novel member (216 amino acids) of the fibroblast growth factor (FGF) family from rat embryos. As this protein is the 17th documented member of the FGF family, we tentatively termed it FGF-17. We have also determined the structures of mouse and human FGF-17 with high amino acid identity (100 and 98.6%) to rat FGF-17, respectively. Among FGF family members, FGF-17 is most similar (53.7% amino acid identity) to FGF-8. FGF-17 has a typical signal sequence at its amino terminus. As expected, recombinant rat FGF-17 was efficiently secreted by High Five insect cells infected with recombinant baculovirus containing the cDNA indicating that FGF-17 is a secreted protein. FGF-17 mRNA of approximately 2.1 kb was detected in rat embryos at E14.5, but not at E10.5 and E19.5 by Northern analysis. The mRNA was found to be preferentially expressed in the neuroepithelia of the isthmus and septum of the rat embryonic brain at E14.5 by in situ hybridization. The present results indicate that FGF-17 might be a novel secreted signaling molecule in the induction and patterning of the embryonic brain.

Structure and expression of a novel member, FGF-16, on the fibroblast growth factor family

We have isolated cDNA encoding a novel member (207 amino acids) of the FGF family from the rat heart by homology-based polymerase chain reaction. As this protein is the 16th documented member of the FGF family, we tentatively term it FGF-16. Among FGF family members, FGF-16 is most similar (73% amino acid identity) to FGF-9. We have also determined the structure of human FGF-16 with high amino acid sequence identity (98.6%) to rat FGF-16. Although the predicted FGF-16 amino acid sequence lacks a typical signal sequence, recombinant rat FGF-16 was efficiently secreted by Sf9 insect cells infected with recombinant baculovirus containing the cDNA. FGF-16 mRNA was predominantly expressed in the rat heart among the adult major tissues examined. The expression profile of FGF-16 mRNA was quite different from those of other members of the FGF family. In rat embryos, FGF-16 mRNA was predominantly expressed in the brown adipose tissue. However, the expression decreased greatly after birth. These results indicate that FGF-16 in embryos might play a role in development of the brown adipose tissue.

Identification of a MMTV insertion mutation within the coding region of the Fgf-3 protooncogene

The Fgf-3 protooncogene (previously called int-2) is a target of proviral insertion mutations in mammary tumors induced by the mouse mammary tumor virus (MMTV). These insertion mutations result in the transcriptional activation of Fgf-3, which is not normally expressed in the adult mammary gland. Previous mapping studies of numerous Fgf-3 insertion mutations have failed to reveal any provirus integrations within the gene coding region. This finding is consistent with the hypothesis that oncogenesis occurs in this system as a consequence of up-regulation of Fgf-3 transcription, rather than from alterations of the gene product. During an analysis of a new cohort of tumors from the WXG-2 mouse strain, a breast tumor was identified which had a MMTV provirus integrated 24 bp upstream of the Fgf-3 stop codon. This insertion mutation generated a fusion transcript which was readily detectable in tumor RNA by RT-PCR. The predicted protein product of this fusion transcript is missing 8 aa of native sequence and contains an additional 8 aa of cryptic MMTV-encoded sequence. These data document the first exception to the generalization that the Fgf-3 coding region is not disrupted by MMTV insertion mutation.

Structure and expression of human fibroblast growth factor-10

We isolated the cDNA encoding a novel member of the human fibroblast growth factor (FGF) family from the lung. The cDNA encodes a protein of 208 amino acids with high sequence homology (95.6%) to rat FGF-10, indicating that the protein is human FGF-10. Human FGF-10 as well as rat FGF-10 has a hydrophobic amino terminus ( approximately 40 amino acids), which may serve as a signal sequence. The apparent evolutionary relationships of human FGFs indicate that FGF-10 is closest to FGF-7. Chromosomal localization of the human FGF-10 gene was examined by in situ hybridization. The gene was found to map to the 5p12-p13 region. Human FGF-10 (amino acids 40 to 208 with a methionine residue at the amino terminus) was produced in Escherichia coli and purified from the cell lysate. Recombinant human FGF-10 (approximately 19 kDa) showed mitogenic activity for fetal rat keratinizing epidermal cells, but essentially no activity for NIH/3T3 cells, fibroblasts. The specificity of mitogenic activity of FGF-10 is similar to that of FGF-7 but distinct from that of bFGF. In structure and biological activity, FGF-10 is similar to FGF-7.

Transient expression of FGF-5 mRNA in the rat cerebellar cortex during post-natal development

Previously, we showed that fibroblast growth factor (FGF) receptor-4 mRNA was transiently expressed in proliferative granule cells of the external granule layer of the rat cerebellar cortex during early post-natal development (A. Miyake et al., Mol. Brain Res., 31 (1995) 95-100). In this study, we examined the expression of FGF-5 mRNA in the rat brain during post-natal development by in situ hybridization. FGF-5 mRNA was transiently expressed in granule cells of the internal granule layer of the cerebellar cortex during early post-natal development. The temporal sequence of FGF-5 mRNA expression was similar to that of FGFR-4 mRNA expression. As the proliferation of granule cells in the external granule layer and their migration through the molecular layer into the internal granule layer actively occur during these periods, the present findings suggest that FGF-5 as well as FGFR-4 might play important roles in the proliferation and/or migration of granule cells during the post-natal development of the cerebellar cortex.

Spatially restricted expression of fibroblast growth factor-10 mRNA in the rat brain

Fibroblast growth factor (FGF)-10 is a novel member of the FGF family. Although FGF-10 mRNA was preferentially expressed in the lung, the mRNA was also expressed, although at low levels, in the brain. We examined the localization of FGF-10 mRNA along with FGF-7 mRNA in the rat brain by in situ hybridization. FGF-10 mRNA showed spatially restricted expression in some regions of the brain, including the hippocampus, thalamus, midbrain and brainstem, although FGF-7 mRNA was not expressed in any of the brain regions examined. FGF-10 mRNA was strongly expressed in several restricted nuclei, especially in motor nuclei, including the oculomotor nucleus, dorsal motor nucleus of vagus, motor trigeminal nucleus, facial nucleus and hypoglossal nucleus. This localization pattern was distinct from those of aFGF, bFGF FGF-5 and FGF-9 mRNAs reported previously. The cellular localization of FGF-10 mRNA showed that the mRNA in the brain was preferentially expressed in neurons but not in glial cells. The present findings indicate that FGF-10, an additional member of the FGF family expressed in the brain, has a distinct role in the brain.

Structure and expression of the rat mRNA encoding a novel member of the fibroblast growth factor family

We isolated the cDNA encoding a novel member of the fibroblast growth factor (FGF) family from rat embryos by homology-based polymerase chain reaction. The FGF-related cDNA encodes a protein of 215 amino acids (approximately 24 kDa), which has a conserved approximately 120-amino acid core with approximately 30-60% amino acid sequence identity with the FGF family. This protein with a hydrophobic amino terminus appears to be a secreted protein. The cDNA was translated in a coupled in vitro transcription-translation system. The molecular mass of the translation product was observed to be approximately 26 kDa. The expression of the FGF-related mRNA in the rat embryo and adult tissues was determined by Northern analysis and in situ hybridization. The mRNA was expressed in several discrete regions of the embryo. In adult tissues, the mRNA was preferentially expressed in the lung. The expression profile of the FGF-related mRNA was different from those of other FGF family mRNAs. As this protein is the 10th documented protein related to FGFs, we tentatively term this protein FGF-10.

The rat FGF-5 mRNA variant generated by alternative splicing encodes a novel truncated form of FGF-5

We isolated rat FGF-5 cDNA and its variant from the embryo. The FGF-5 cDNA encodes a protein of 266 amino acid residues. The variant cDNA encodes a protein of 121 amino acid residues, the N-terminal 117-amino acid sequence of which is identical to that of FGF-5. Thus the variant cDNA encodes a novel truncated form of FGF-5. The rat FGF-5 gene consists of three exons (exons 1-3). The variant cDNA lacks the nucleotide sequence of exon 2, indicating that the variant mRNA is generated by alternative splicing. The variant mRNA as well as the FGF-5 mRNA was detected in the embryo and adult brain. This is the first description of the mRNA for a truncated form of FGF within the FGF family.

Rat fibroblast growth factor receptor-4 mRNA in the brain is preferentially expressed in cholinergic neurons in the medial habenular nucleus

We examined the cellular localization of fibroblast growth factor receptor (FGFR)-4 mRNA preferentially expressed in the medial habenular nucleus by in situ hybridization. FGFR-4 mRNA was expressed in the ventral part of the medial habenular nucleus. FGFR-4 mRNA was colocalized with choline acetyltransferase mRNA to a high degree (more than 90%), indicating that FGFR-4 mRNA-expressed cells are cholinergic neurons. The present finding indicates that FGFR-4 in the brain has a function specific to cholinergic neurons in the ventral part of the medial habenular nucleus.

Fibroblast growth factor 3 is tumorigenic for mouse mammary cells orthotopically implanted in nude mice

Fibroblast growth factor-3 (Fgf-3) is involved in mouse mammary tumorigenesis since the Fgf-3 gene is a main target for mouse mammary tumor virus (MMTV) insertional activation. Its action has been correlated with the appearance of pregnancy-dependent tumors. We describe here the effects on normal mouse mammary EF43 cells of the short Fgf-3 protein form which enters the secretory pathway. The genes, Fgf-3 AUG or Fgf-4 for comparison, were introduced in the mammary cells by means of retroviral vectors. Fgf-3 expression did not modify EF43 cell morphology, had no effect on growth in soft agar nor on the inhibitory action exerted on cell growth by TGF-beta 1; however, it allowed the cells to grow under low serum conditions in the absence of insulin and EGF. The Fgf-3-expressing cells were not tumorigenic in nude mice when injected s.c., but tumors developed when the cells were implanted in the mammary gland. The tumors appeared after some latency; they had a slow growth phase followed by a phase of increased growth rate. An identical tumoral growth pattern was observed in ovariectomized nude mice. These results show that the secreted Fgf-3 form can initiate tumorigenesis and that the induced tumors are hormone-independent. The mammary-gland environment, however, is required for the EF43 cells to grow and differentiate. During that process, which resembles natural cell growth during mammary-gland development at pregnancy, the cells could pass through a stage which is specifically sensitive to Fgf-3.

Transient expression of FGF receptor-4 mRNA in the rat cerebellum during postnatal development

The fibroblast growth factor (FGF) receptor-4 mRNA in the adult rat brain is expressed preferentially in the medial habenular nucleus. In this paper, we examined the expression of FGFR-4 mRNA in the brain during postnatal development. Interestingly, in addition to the persistent expression of FGFR-4 mRNA in the medial habenular nucleus, FGFR-4 mRNA was transiently expressed in the proliferative zone of the external granule layer of the developing cerebellum. The localization and transient expression of FGFR-4 mRNA in the developing cerebellum suggest that FGFR-4 mRNA was expressed by proliferative granule cells. The present findings indicate that FGFR-4 in the brain has an important role in the postnatal development of the cerebellar cortex.

Localization of fibroblast growth factor-9 mRNA in the rat brain

We examined the localization of fibroblast growth factor-9 (FGF-9) mRNA in the rat brain by in situ hybridization. FGF-9 mRNA was moderately or weakly expressed in widespread regions including the olfactory bulb, caudate putamen, cerebral cortex, hippocampus, thalamus, hypothalamus, midbrain, brainstem and cerebellum. However, FGF-9 mRNA was also strongly expressed in several specific nuclei including the red nucleus and oculomotor nucleus in the midbrain, the vestibular nucleus and facial nucleus in the brainstem and the medial cerebellar nucleus, interposed cerebellar nucleus and lateral cerebellar nucleus in the cerebellum. The cellular localization of FGF-9 mRNA indicated that the mRNA in the rat brain was expressed preferentially in neurons, although FGF-9 was originally isolated from human glioma cells. The localization profile of FGF-9 mRNA is different from those of aFGF, bFGF and FGF-5 mRNAs reported previously. The present findings indicate that FGF-9 has a unique role in the brain.

Differential expression patterns of mRNAs for members of the fibroblast growth factor receptor family, FGFR-1-FGFR-4, in rat brain

We have examined the region-specific expression of mRNAs for four members of rat FGF receptor family, FGFR-1, FGFR-2 FGFR-3, and FGFR-4, in rat brain by in situ hybridization. The FGFR-1, FGFR-2, and FGFR-3 mRNAs were expressed widely but differentially in the brain. However, the FGFR-4 mRNA was not expressed in the brain. The FGFR-1 mRNA was strongly expressed in several regions including the hippocampus, cerebellum, and pedunculopotine tegmental nucleus. The FGFR-2 mRNA expression was high in the choroid plexus, and moderate in the fiber-rich regions (the corpus callosum, external capsule, and internal capsule) and the olfactory bulb. The FGFR-3 mRNA was expressed diffusely in the brain. We have also examined the cellular localization of these mRNAs in the brain. Although the FGFR-1 mRNA was expressed preferentially in neurons, the FGFR-2 and FGFR-3 mRNAs were expressed preferentially in glial cells. The present findings that the FGFR-1, FGFR-2, and FGFR-3 mRNAs were expressed widely but with region- and cell-specificity in the brain indicate that these receptors have different roles in the brain.

Rat FGF receptor-4 mRNA in the brain is expressed preferentially in the medial habenular nucleus

The fibroblast growth factor (FGF) receptor family consists of four members, FGFR-1, FGFR-2, FGFR-3 and FGFR-4, that are closely related receptor tyrosine kinases. We examined the expression of rat FGFR-4 mRNA in the brain by in situ hybridization and compared it with that of the mRNAs for other FGF receptors. In contrast with FGFR-1, FGFR-2 and FGFR-3 mRNAs which are expressed widely in the brain, the FGFR-4 mRNA in the brain is expressed preferentially in the medial habenular nucleus neurons. The present finding indicates that FGFR-4 has a function specific to the medial habenular nucleus.

Immunolocalization of basic fibroblast growth factor to the microvasculature of human brain tumors

BACKGROUND

Microvascular proliferation, a prominent feature of tumors of the central nervous system, is a prime target for anti-cancer therapy.

METHODS

Because basic fibroblast growth factor (bFGF) plays a key role in the regulation of angiogenesis, surgical specimens from 52 human brain tumors were examined by immunocytochemical studies with a murine monoclonal antibody to bFGF. Sections from these tumors also were incubated with Ki-67 monoclonal antibody to measure the growth fraction.

RESULTS

Immunostaining for bFGF was observed in 45 of 52 (87%) neoplasms, reacting with 97% of the malignant brain tumors and 67% of benign tumors (P < 0.01). The nonreactive tumors were a medulloblastoma and 7 of 21 (33%) benign, noninvasive, slow-growing neoplasms (1 acoustic schwannoma, 3 meningiomas, 2 pituitary adenomas, and 1 cholesteatoma). The indices of proliferation (Ki-67 labeling) were lower for the 21 benign tumors (1.2 +/- 1.1%) than the 31 malignant tumors (10.3 +/- 10.5%; P < 0.001). The bFGF was immunolocalized in the tumor cell nuclei in 23 of 52 tumors (44%) and in the cytoplasm of 8 of 52 (15%) tumors. Immunostaining to bFGF was prominent in the microvascular endothelial compartment in 84% of the malignant tumors and only 52% of benign tumors (P < 0.01). Immunostaining was not present after preabsorption of the antibody with pure human recombinant bFGF.

CONCLUSIONS

The presence of bFGF predominantly within the tumor microvasculature indicates a cellular depot for this potent growth factor that mediates angiogenesis and tumorigenesis. These data support a role for bFGF in the transition from the benign to the malignant phenotype.