Fibroblast growth factors (FGFs) are important angiogenic growth factors. While basic FGF (FGF2) is well established as a potent inducer of angiogenesis much less is known about other FGFs possibly expressed by EC. We investigated the expression of all known FGFs, their main tyrosine kinase receptors and antagonists by RT-PCR analysis in human umbilical vascular endothelial cells (HUVECs) to obtain a complete expression profile of this important growth factor system in model endothelial cells (EC). In addition to FGFR1IIIc, which is considered as the major FGF receptor in EC, HUVECs express similar levels of FGFR3IIIc, detectable amounts of FGFR2IIIc and a new FGF receptor without an intracellular kinase domain (FGFR5). HUVECs express several secreted FGFs, including FGF5, 7, 8, 16 and 18 and two members of the fibroblast growth factor homologous factors (FHFs), not yet reported to be expressed in EC. The expression panel was compared with that obtained from human vascular smooth muscle cells (VSMCs) and human aortic tissue. Human umbilical artery smooth muscle cells (HUASMCs) and HUVECs express the identical FGF receptor and ligand panel implicating that both cell types act, according the FGF signals more as an entity than as individual cell types. Expression of Fgf1, 2, 7, 16 and 18 and the antagonists Sprouty 2,3 and 4 was demonstrated for all analysed cDNAs. The IIIc isoforms of FGFR1 and 2 and the novel FGFR5 were expressed in the aorta, but expression of the FGF receptor 3 was not detected in cDNAs derived from aortic tissue. In the VSMC of rat aortic tissue and in HUASM cultured cells we could demonstrate FGF18 immunoreactivity in the nucleus of the cells. The expression of several secreted FGFs by EC may focus the view more on their paracrine effects on neighbouring cells during tissue regeneration or tumor formation.

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The major isoform of fibroblast growth factor 3 (FGF3) is initiated from a CUG codon, and the resultant product is distributed to the nucleus/nucleolus and secretory pathway. This dual subcellular localization is achieved in part by the competing effects of two classical intracellular targeting signals located near the amino terminus. At the extreme amino terminus is a short stretch of 29 amino acids before a signal peptide necessary for translocation into the endoplasmic reticulum, which is next to an adjacent bipartite nuclear localization signal. The carboxyl-terminal region of FGF3 is also implicated in nuclear/nucleolar localization. We describe here the characterization of carboxyl-terminal signals by showing they are capable of directing a heterologous protein, ␤-galactosidase, to the nucleus. Furthermore, appending both the amino-and carboxyl-terminal domains onto ␤-galactosidase, reproduces the dual subcellular localization properties of FGF3. Nuclear uptake of FGF3 appears to be signal-mediated since it binds to karyopherin ␣, the nuclear localization signal binding subunit of a heterodimeric receptor of the nuclear import machinery. The import of FGF3 into the nucleus is energydependent, and the inhibition of this process has demonstrated the importance of the nucleolar retention signal in nucleoplasmic and nucleolar accumulation. Fibroblast growth factors (FGFs)1 are structurally related proteins encoded by at least 10 distinct genes in mammals (Refs. 1 and 2; reviewed in Refs. 3 and 4). Members of the FGF family demonstrate a variety of properties, depending on cell type and context, such as induction of proliferation, differentiation, stimulation of motility, and enhanced survival (reviewed in Refs. 3 and 4). FGFs induce cell to cell signaling by interacting with high affinity cell surface receptor, although there is also a requirement for ligand presentation by a glucosaminoglycan-containing low affinity receptor (reviewed in Ref. 5). Four receptor genes have been identified that encode high affinity FGF binding receptors, but the number of receptor species is extended by alternative splicing, which changes the ligand binding specificity of some receptors (reviewed in Refs. 6 and 7). Binding of FGF to its receptors initiates signal transduction, ultimately leading to a change in gene expression and cell function. However, there is evidence that FGF1, FGF2, and FGF3 can directly translocate to the nucleus, thereby providing the potential for an alternative intracrine signaling pathway (8 -16).FGF3 (int2) was first identified as a proto-oncogene in virally induced mouse mammary tumors (reviewed in Refs. 17 and 18). Its role in tumorigenesis was strengthened by transgenic mouse studies, which showed that inappropriate ectopic expression in the mammary gland resulted in a partial recapitulation of the disease (19 -21). In situ hybridization revealed that normal expression of FGF3 is primarily restricted to prenatal mouse development, where RNA was found at a variety of sites at specific times (22, 23)...

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