Modulation of cell growth and transformation by doxycycline-regulated FGF-2 expression in NIH-3T3 cells.

The single-copy fibroblast growth factor 2 (FGF-2) gene encodes four coexpressed isoforms of different molecular masses. The 18-kDa FGF-2 is primarily localized in the cytoplasm, whereas the higher molecular mass isoforms (HMW FGF-2) localize to the nucleus and nucleolus. The overexpression of either 18-kDa FGF-2 or HMW FGF-2 promotes cell transformation in a dose-dependent manner. In NIH 3T3 cells, the selective overexpression of HMW FGF-2 but not of 18-kDa FGF-2 confers upon the cells the unique phenotype of growth in low serum-containing medium. Thus, the distinct intracellular localization and the level of expression of FGF-2 are pivotal requirements for the differential effects of FGF-2 isoforms on the cellular phenotype. On this basis, we established a doxycycline-regulatable FGF-2 expression system that permitted us to regulate the expression of each isoform in a time- and dose-dependent manner. We analyzed the growth properties of cells in the presence and absence of doxycycline in both normal and low serum-containing medium and in soft agar. The doxycycline-activated expression of 18-kDa FGF-2 did not allow growth in low serum medium. The growth of cells expressing HMW FGF-2 was increased by doxycycline under all three conditions, and a relationship between the level of HMW FGF-2 expression and cell growth was observed for all three conditions. This doxycycline-regulatable FGF-2 expression system provides a mechanism to analyze changes in FGF-2 targeted pathways and genes and to characterize pathways specifically activated by either the 18-kDa FGF-2 or the HMW FGF-2 isoforms.     

Differential intranuclear localization of fibroblast growth factor-2 isoforms and specific interaction with the survival of motoneuron protein

Fibroblast growth factor 2 (FGF-2) is an important modulator of cell growth and differentiation and a neurotrophic factor. FGF-2 occurs in isoforms, at a low molecular weight of 18,000 and at least two high molecular weight forms (21,000 and 23,000), representing alternative translation products from a single mRNA. In addition to its role as an extracellular ligand, FGF-2 localizes to the nuclei of cells. Here we show differential localization of the 18- and 23-kDa isoforms in the nuclei of rat Schwann cells. Whereas the 18-kDa isoform was found in the nucleoli, nucleoplasm, and Cajal bodies, the 23-kDa isoform localized in a punctuate pattern and associates with mitotic chromosomes suggesting different functional roles of the isoforms. Moreover, we show here that the 23-kDa FGF-2 isoform co-immunoprecipitates specifically with the survival of motor neuron protein (SMN). SMN is an assembly and recycling factor of the splicing machinery and locates to the cytoplasm, the nucleoplasm, and nuclear gems, where it co-localizes with 23-kDa FGF-2. Patients with spinal muscular atrophy suffer from fatal degeneration of motoneurons because of mutations and deletions of the gene for the SMN protein.     

A New 34-Kilodalton Isoform of Human Fibroblast Growth Factor 2 Is Cap Dependently Synthesized by Using a Non-AUG Start Codon and Behaves as a Survival Factor

Four isoforms of human fibroblast growth factor 2 (FGF-2) result from alternative initiations of translation at three CUG start codons and one AUG start codon. Here we characterize a new 34-kDa FGF-2 isoform whose expression is initiated at a fifth initiation codon. This 34-kDa FGF-2 was identified in HeLa cells by using an N-terminal directed antibody. Its initiation codon was identified by site-directed mutagenesis as being a CUG codon located at 86 nucleotides (nt) from the FGF-2 mRNA 5′ end. Both in vitro translation and COS-7 cell transfection using bicistronic RNAs demonstrated that the 34-kDa FGF-2 was exclusively expressed in a cap-dependent manner. This contrasted with the expression of the other FGF-2 isoforms of 18, 22, 22.5, and 24 kDa, which is controlled by an internal ribosome entry site (IRES). Strikingly, expression of the other FGF-2 isoforms became partly cap dependent in vitro in the presence of the 5,823-nt-long 3′ untranslated region of FGF-2 mRNA. Thus, the FGF-2 mRNA can be translated both by cap-dependent and IRES-driven mechanisms, the balance between these two mechanisms modulating the ratio of the different FGF-2 isoforms. The function of the new FGF-2 was also investigated. We found that the 34-kDa FGF-2, in contrast to the other isoforms, permitted NIH 3T3 cell survival in low-serum conditions. A new arginine-rich nuclear localization sequence (NLS) in the N-terminal region of the 34-kDa FGF-2 was characterized and found to be similar to the NLS of human immunodeficiency virus type 1 Rev protein. These data suggest that the function of the 34-kDa FGF-2 is mediated by nuclear targets.     

Fibroblast growth factor-2

Fibroblast growth factor-2 (FGF-2) is a heparin-binding growth factor which occurs in several isoforms resulting from alternative initiations of translation: an 18 kD cytoplasmic isoform and four larger molecular weight nuclear isoforms (22, 22.5, 24 and 34 kD). FGF-2 has pleiotropic roles in many cell types and tissues; it is a motogenic, angiogenic and survival factor which is involved in cell migration, cell differentiation and in a variety of developmental processes. Although devoid of signal peptide, it could be secreted. It acts mainly through a paracrine/autocrine mechanism involving high affinity transmembrane receptors and heparan sulfate proteoglycan low affinity receptors, but also through still unknown intracrine process(es) on intracellular targets. FGF-2 has many biological functions which are probably isoform-specific. Nevertheless, FGF-2 is not essential for embryonic development as knock-out mice for the growth factor are viable and fertile although they exhibit abnormalities in neuronal differentiation. Use of FGF-2 as therapeutic agent for the treatment of ischemic cardiovascular disease is promising and clinical trials are in progress.     

Nuclear fibroblast growth factor-2 interacts specifically with splicing factor SF3a66

Fibroblast growth factor 2 (FGF-2) has a dual role as a classical extracellular signaling protein and as an intracellular factor. Isoforms of FGF-2, resulting from alternatively used start codons on one mRNA species, locate differentially to nuclear compartments. In this study we aimed to analyze functions of intracellular FGF-2 by identification of interacting proteins. We identified the 66-kDa subunit of splicing factor 3a (SF3a66) as a binding partner in a yeast two-hybrid screen and confirmed this interaction by pull-down assays. The splicing factor interacted with the 18-kDa (FGF-2(18)) and with the 23-kDa (FGF-2(23)) isoforms, indicating an interaction with a domain common to both isoforms. Moreover, FGF-2 interacted with the C-terminus of SF3a66, a sequence that has not previously been assigned a functional role. In a functional neurite outgrowth assay, SF3a66 enhanced neurite lengths similar to FGF-2(18). We have previously identified the spliceosomal assembly factor survival of motoneuron (SMN) protein as a protein interacting specifically with the FGF-2(23) isoform [Claus et al., J. Biol. Chem. 278 (2003), 479-485]. The identification of two FGF-2 interacting proteins from the same biochemical pathway suggests a novel intranuclear role of FGF-2.     

Hepatocyte growth factor/scatter factor stimulates migration of muscle precursors in developing mouse tongue

Hepatocyte growth factor (HGF) stimulates the migration of myogenic cells during the development of skeletal muscles. The inactivation of HGF genes or that of its receptor, c-met, in mice causes hypoplasia of skeletal muscle organs, such as the tongue. Basic fibroblast growth factor (FGF-2) also induces migration of skeletal myoblasts. A comparison of the functions of HGF and FGF-2 in myogenesis revealed the crucial effect of HGF in the development of skeletal muscles. Unlike FGF-2, HGF induced migration of myoblasts from the developing mouse tongue. The differences between the activities of HGF and FGF-2 were determined by comparing their effects on the expression of matrix metalloproteinase-9 (MMP-9) in myoblasts, C2C12 cells, cultured in collagen-coated dishes. The results showed that HGF, but not FGF-2, stimulated MMP-9 expression, and that the stimulation was mediated through the activation of phosphoinositide 3-kinase (PI3K) which was not associated with FGF-2 signal transduction. Nevertheless, both growth factors exerted almost the same effect on the reduction of myogenin expression in, and on the proliferation of, C2C12 cells, suggesting that HGF, rather than FGF-2, plays a crucial role in the generation of skeletal muscles, including the tongue. Moreover, the specific role of HGF through the PI3K signal pathway is the induction of MMP-9 expression in, and the migration of, myoblasts.     

FGF-18, a Novel Member of the Fibroblast Growth Factor Family, Stimulates Hepatic and Intestinal Proliferation

The fibroblast growth factors (FGFs) play key roles in controlling tissue growth, morphogenesis, and repair in animals. We have cloned a novel member of the FGF family, designated FGF-18, that is expressed primarily in the lungs and kidneys and at lower levels in the heart, testes, spleen, skeletal muscle, and brain. Sequence comparison indicates that FGF-18 is highly conserved between humans and mice and is most homologous to FGF-8 among the FGF family members. FGF-18 has a typical signal sequence and was glycosylated and secreted when it was transfected into 293-EBNA cells. Recombinant murine FGF-18 protein (rMuFGF-18) stimulated proliferation in the fibroblast cell line NIH 3T3 in vitro in a heparan sulfate-dependent manner. To examine its biological activity in vivo, rMuFGF-18 was injected into normal mice and ectopically overexpressed in transgenic mice by using a liver-specific promoter. Injection of rMuFGF-18 induced proliferation in a wide variety of tissues, including tissues of both epithelial and mesenchymal origin. The two tissues which appeared to be the primary targets of FGF-18 were the liver and small intestine, both of which exhibited histologic evidence of proliferation and showed significant gains in organ weight following 7 (sometimes 3) days of FGF-18 treatment. Transgenic mice that overexpressed FGF-18 in the liver also exhibited an increase in liver weight and hepatocellular proliferation. These results suggest that FGF-18 is a pleiotropic growth factor that stimulates proliferation in a number of tissues, most notably the liver and small intestine.     

Testes‐specific transgene expression in insulin‐like growth factor‐I transgenic mice

Insulin‐like growth factor‐I (IGF‐I) is a low molecular weight peptide that mediates the cell proliferating actions of growth hormone. Evidence exists indicating that IGF‐I is produced by various cell types and this growth factor has been implicated in a variety of reproductive processes. To investigate the effect of IGF‐I over‐expression on reproductive systems, we generated three independent lines of transgenic mice harbouring a human IGF‐I cDNA (hIGF‐I) under the control of a Cytomegalovirus immediate early (CMV) promoter. The CMV promoter was used in an attempt to direct expression of IGF‐I into a variety of tissues both reproductive and non‐reproductive. Yet expression of the foreign hIGF‐I gene, determined by Northern blot, was found to occur only in the testicular tissues of the male mice, apparently due to methylation of the transgene in all the tissues tested except the testes, which demonstrate transgene hypomethylation. Evaluation of the transgene expression during testicular development revealed that expression begins between 10 and 15 days of development, coinciding with the appearance of the zygotene and pachytene primary spermatocytes during early spermatogenesis, therefore indicating germ line expression of the transgene. Extensive study of the CMV‐hIGF‐I transgenic lines of mice has revealed that the effects of the transgene expression do not extend beyond the testicular tissues. No significant differences (P > 0.05) in the IGF‐I serum levels, growth rates, or testicular histology have been observed between transgenic and non‐transgenic male siblings. The ability of transgenic males to produce offspring also appears unaffected. Evaluation of the IGF binding protein (IGFBP) levels in the testicular tissues of CMV‐hIGF‐I transgenic mice by Western ligand blot revealed an increase in the concentration of testicular proteins with molecular weights corresponding to IGFBP‐2 and IGFBP‐3. These results suggest that the testicular over‐expression of IGF‐I induces increased IGFBP localization in this tissue. Inhibition of IGF activity by the IGFBPs would explain the lack of a dramatic physiological effect in the CMV‐hIGF‐I transgenic mice, despite the presence of elevated testicular IGF‐I. The observation that testis specific IGF‐I overexpression induces localization of IGFBPs in this tissue confirms the existence of a well regulated testicular IGF system and supports the convention that this growth factor plays an important role in testicular function. Mol. Reprod. Dev. 54:32–42, 1999. © 1999 Wiley‐Liss, Inc.     

Effect of overexpressing fibroblast growth factor 2 protein isoforms in osteoblastic ROS 17/2.8 cells

Fibroblast growth factor-2 (FGF-2) is made by osteoblasts and modulates their function. There are high molecular weight (HMW) protein isoforms of FGF-2 that have nuclear localization sequences and a low molecular weight (LMW) 18 kDa FGF-2 protein that is exported from cells. Since FGF-2 is a trophic factor and potent mitogen for osteoblasts, the goal of this study was to utilize targeted overexpression of FGF-2 as a novel means of assessing different FGF-2 isoforms on osteoblastic cell viability and proliferation. Either LMW or HMW human Fgf2 cDNAs were cloned downstream of 3.6 kb alpha1(I)-collagen 5' regulatory elements (Col 3.6). A set of expression vectors, called Col3.6-Fgf2 isoforms-IRES-GFPsaph, capable of concurrently overexpressing either LMW or HMW FGF-2 isoforms concomitant with GFPsaph from a single bicistronic mRNA were built. Viable cell number in ROS 17/2.8 cells stably transfected with Vector (Col3.6-IRES-GFPsaph) versus each of the Col3.6-Fgf2-IRES-GFPsaph constructs were compared. In the presence of 1 or 10% serum, DNA synthesis was increased in cells expressing any isoform of FGF-2 compared with vector. However, cells transfected with HMW isoform had augmented DNA synthesis in 1 or 10% serum compared with cells expressing either ALL or LMW FGF-2 isoforms. A neutralizing FGF-2 antibody significantly reduced the mitogenic response in cells harboring ALL or the LMW FGF-2 isoforms but did not block the mitogenic effect of cells harboring the HMW isoforms. In summary, overexpression of any isoform of FGF-2 protein increased viable cell number and OB proliferation in the presence of low or high concentrations of serum. However, the HMW/nuclear isoforms preferentially mediate augmented OB proliferation. We conclude that differential expression of FGF-2 proteins isoforms is important in modulating OB function.     

The endogenous fibroblast growth factor-2 antisense gene product regulates pituitary cell growth and hormone production

Basic fibroblast growth factor (bFGF; FGF-2) is one of 19 related members of a growth factor family with mitogenic and hormone-regulatory functions. In Xenopus laevis oocytes, a 1.5-kb FGF-2 antisense (GFG) RNA complementary to the third exon and 3'-untranslated region (UTR) of FGF-2 mRNA has been implicated in FGF-2 mRNA editing and stability. The human homolog has been cloned, and we localized this gene by yeast artificial chromosome (YAC), somatic cell, and radiation hybrid panels to the same chromosomal site as FGF-2 (chromosome 4, JO4513 adjacent to D4S430), confirming this as a human endogenous antisense gene. The full-length GFG antisense RNA encodes a 35-kDa protein, which is highly homologous with the MutT family of antimutator nucleosidetriphosphatases (NTPases). We show that human pituitary tumors express FGF-2 and its endogenous antisense partner GFG. While normal pituitary expresses GFG but not FGF-2, pituitary adenomas express FGF-2 and have reduced levels of GFG; aggressive and recurrent adenomas expressed more FGF than GFG mRNA. To examine the effects of this antisense gene in the pituitary, we transfected the pituitary-derived GH4 mammosomatotroph cell line with constructs encoding the full-length human GFG cDNA. Transiently and stably transfected cells expressed the 35-kDa GFG protein that was localized to the cytoplasm. These cells exhibited enhanced PRL expression as documented by transiently transfected PRL-luciferase reporter assay and by endogenous PRL protein. GFG expression in these cells did not alter endogenous FGF-2 expression but increased the proportion of the higher molecular mass 22-kDa form of GH. Moreover, GFG expression inhibited cell proliferation as shown by [(3)H]thymidine incorporation, proliferating cell nuclear antigen (PCNA) nuclear staining, and cell cycle analysis. We conclude that the GFG-encoded protein has divergent hormone-regulatory and antiproliferative actions in the pituitary that are independent of FGF-2 expression. GFG represents a novel mechanism involved in restraining pituitary tumor cell growth while promoting hormonal activity.     

Nuclear activities of basic fibroblast growth factor: potentiation of low-serum growth mediated by natural or chimeric nuclear localization signals

Human basic fibroblast growth factor (FGF-2) occurs in four isoforms: a low molecular weight (LMW FGF-2, 18 kDa) and three high molecular weight (HMW FGF-2, 22, 22.5, and 24 kDa) forms. LMW FGF-2 is primarily cytoplasmic and functions in an autocrine manner, whereas HMW FGF-2s are nuclear and exert activities through an intracrine, perhaps nuclear, pathway. Selective overexpression of HMW FGF-2 forms in fibroblasts promotes growth in low serum, whereas overexpression of LMW FGF-2 does not. The HMW FGF-2 forms have two functional domains: an amino-terminal extension and a common 18-kDa amino acid sequence. To investigate the role of these regions in the intracrine signaling of HMW FGF-2, we produced stable transfectants of NIH 3T3 fibroblasts overexpressing either individual HMW FGF-2 forms or artificially nuclear-targeted LMW FGF-2. All of these forms of FGF-2 localize to the nucleus/nucleolus and induce growth in low serum. The nuclear forms of FGF-2 trigger a mitogenic stimulus under serum starvation conditions and do not specifically protect the cells from apoptosis. These data indicate the existence of a specific role for nuclear FGF-2 and suggest that LMW FGF-2 represents the biological messenger in both the autocrine/paracrine and intracrine FGF-2 pathways.     

Nuclear accumulation of fibroblast growth factor receptors is regulated by multiple signals in adrenal medullary cells.

In an effort to determine the localization of fibroblast growth factor (FGF) receptors (FGFR) that could mediate the intracellular action of FGF-2, we discovered the presence of high-affinity. FGF-2 binding sites in the nuclei of bovine adrenal medullary cells (BAMC). Western blot analysis demonstrated the presence of 103-, 118-, and 145-kDa forms of FGFR1 in nuclei isolated from BAMC. 125I-FGF-2 cross-linking to nuclear extracts followed by FGFR1 immunoprecipitation showed that FGFR1 can account for the nuclear FGF-2 binding sites. Nuclear FGFR1 has kinase activity and undergoes autophosphorylation. Immunocytochemistry with the use of confocal and electron microscopes demonstrated the presence of FGFR1 within the nuclear interior. Nuclear subfractionation followed by Western blot or immunoelectron microscopic analysis showed that the nuclear FGFR1 is contained in the nuclear matrix and the nucleoplasm. Agents that induce translocation of endogenous FGF-2 to the nucleus (forskolin, carbachol, or angiotensin II) increased the intranuclear accumulation of FGFR1. This accumulation was accompanied by an overall increase in FGF-2-inducible tyrosine kinase activity. Our findings suggest a novel mode for growth factor action whereby growth factor receptors translocate to the nucleus in parallel with their ligand and act as direct mediators of nuclear responses to cell stimulation.     

Overexpression of high molecular weight FGF-2 forms inhibits glioma growth by acting on cell-cycle progression and protein translation

In order to clarify the role of HMW FGF-2 in glioma development and angiogenesis, we over-expressed different human FGF-2 isoforms in C6 rat glioma cell line using a tetracycline-regulated expression system. Phenotypic modifications were analyzed in vitro and compared to untransfected cells or to cells over-expressing 18 kDa FGF-2 or all FGF-2 isoforms. In particular, we demonstrate that HMW FGF-2 has unique features in inhibiting glioma cell proliferation. HMW FGF-2 expressing cells showed a cell-cycle arrest at the G2M, demonstrating a role of HMW FGF-2 in controlling the entry in mitosis. Moreover, hydroxyurea was ineffective in blocking cells at the G1S boundary when HMW FGF-2 was expressed. We also show that the HMW FGF-2 isoforms inhibit 4E-BP1 phosphorylation at critical sites restoring the translation inhibitory activity of 4E-BP1. In vivo, inhibition of tumor growth was observed when cells expressed HMW FGF-2. This indicates that HMW FGF-2 inhibits tumor growth in glioma cells by acting on cell-cycle progression and protein translation.     

Vitamin D induced up-regulation of keratinocyte growth factor (FGF-7/KGF) in MCF-7 human breast cancer cells

Keratinocyte growth factor (FGF-7/KGF) is a secreted member of the fibroblast growth factor family, which functions primarily as an important paracrine mediator of cell growth and differentiation. Inhibitory pathways of vitamin D may also involve participation of some growth factors. To determine whether vitamin D may play a role in the expression of FGF-7, we investigated FGF-7 expression in human breast cancer cells treated with 1,25-dihydroxyvitamin D3, which inhibited the growth of the cells. By means of cDNA microarray, RT-PCR, and Western blot analysis, we have shown an increase in expression of FGF-7 on both mRNA and protein levels after vitamin D exposure. This is the first demonstration of vitamin D regulation of FGF-7 expression and its possible involvement in mediating growth and differentiation by vitamin D.     

心脏特异表达人源FAM55A转基因小鼠的建立

目的建立心脏特异表达的人源FAM55A转基因小鼠,为研究该基因在心肌病发病中的作用提供模型。方法 Western blot检测FAM55A在野生型小鼠与cTnTR141W转基因小鼠心脏组织中的表达变化及其在野生小鼠的组织表达谱。克隆人源FAM55A基因入α-MHC启动子下游构建a-MHC-FAM55A表达载体,显微注射法建立FAM55A转基因小鼠。PCR鉴定转基因首建鼠的基因型。Western blot鉴定人源FAM55A在转基因小鼠心脏中的表达,超声检测转基因小鼠心脏的几何构型和功能。HE染色检测转基因小鼠心脏的病理改变。结果 FAM55A在野生型小鼠心脏中有少量表达,在扩张型心肌病小鼠的心脏中表达增加。建立了1个心脏组织特异表达人源FAM55A转基因小鼠品系。与野生型小鼠相比,FAM55A转基因小鼠的心脏收缩期和舒张期左室前壁从1月龄到5月龄持续增厚,3月龄转基因小鼠心脏射血分数和短轴缩短率稍有增强,1月龄和5月龄转基因小鼠心脏功能则与同龄野生型小鼠相比无变化。组织学检测显示,转基因小鼠心脏左室心肌细胞不均匀肥大,但不发生紊乱。结论 FAM55A在扩张型心肌病小鼠的心脏中表达上调,建立了心脏特异表达的人源FAM55A转基因小鼠,为进一步和心肌病小鼠模型杂交,研究该基因在心肌病发病中的作用提供了工具。     

Faster nerve regeneration after sciatic nerve injury in mice over-expressing basic fibroblast growth factor

Basic fibroblast growth factor (FGF-2) is expressed in the peripheral nervous system and is up-regulated after nerve lesion. It has been demonstrated that administration of FGF-2 protects neurons from injury-induced cell death and promotes axonal regrowth. Using transgenic mice over-expressing FGF-2 (TgFGF-2), we addressed the importance of endogenously generated FGF-2 on sensory neuron loss and sciatic nerve regeneration. After sciatic nerve transection, wild-type and transgenic mice showed the same degree of cell death in L5 spinal ganglia. Also, the number of chromatolytic, eccentric, and pyknotic sensory neurons was not changed under elevated levels of FGF-2. Morphometric evaluation of intact nerves from TgFGF-2 mice revealed no difference in number and size of myelinated fibers compared to wild-type mice. One week after crush injury, the number of regenerated axons was doubled and the myelin thickness was significantly smaller in transgenic mice. After 2 and 4 weeks, morphometric analysis and functional tests revealed no differences in recovery of sensory and motor nerve fibers. To study the role of FGF-2 over-expression on Schwann cell proliferation during the early regeneration process, we used BrdU-labeling to mark dividing cells. In transgenic mice, the number of proliferating cells was significantly increased distal to the crush site compared to wild-types. We propose that endogenously synthesized FGF-2 influences early peripheral nerve regeneration by regulating Schwann cell proliferation, axonal regrowth, and remyelination.     

Cellular localization of fibroblast growth factor 2 (FGF-2) in benign prostatic hyperplasia

Fibroblast growth factor 2 (FGF-2, basic fibroblast growth factor) has been reported to be elevated in tissues from benign prostatic hyperplasia (BPH), the most frequent neoplastic disease in aging men. This suggests that FGF-2 may play a significant role in the development of BPH. In this study the cellular distribution pattern of FGF-2 in tissues from BPH has been investigated by immunohistochemical and molecular biological methods. Radioimmunoassay revealed high concentrations of FGF-2, ranging between 450 and 950 ng per g tissue. Immunoblots confirmed the presence of a 18 kDa FGF-2 in tissue extracts. By immunohistochemistry done with a polyclonal antibody to recombinant FGF-2 on paraffin sections, FGF-2 was localized in fibroblasts, endothelial cells and smooth muscle cells of tissue samples of BPH. Nuclei of these cells were labelled distinctly. Moreover the cytoplasm of smooth muscle cells was labelled moderately. No immunostaining was seen in prostatic epithelium. Non-radioactive in situ hybridization with digoxygenin-labelled oligonucleotides revealed the presence of mRNA for FGF-2 in smooth muscle cells of the prostatic stroma. These results provide evidence that FGF-2 may be produced locally in the human prostate as a stroma-specific mitogen and may play a causal role in the development of BPH.