Five FGF receptors with distinct expression patterns

The prognostic significance of basic fibroblast growth factor in cutaneous malignant melanoma

Basic fibroblast growth factor (bFGF) is a growth factor and an angiogenesis factor which may play a role in the evolution of cutaneous malignant melanoma (CMM). In this study, we evaluated the distribution of bFGF in CMM using immunochemical methods and correlated the pattern of bFGF expression with the clinical course. Formalin-fixed, paraffin-embedded sections of 46 CMMs were immunostained with a high-affinity purified antibody raised against human bFGF. CMM were categorized into lesions that exhibited subsequent recurrence (local, regional and/or systemic) or recurrence-free lesions. The minimum follow-up time was 5 years. Expression of bFGF within the tumors and in peritumoral and intratumoral blood vessels was similar in the two groups. Comparable results were attained when 8 recurring vs 8 non-recurring CMM, selected from the above tumors, were matched for age, gender, anatomic site and tumor thickness. These results suggest that the biologic behavior of CMM may not be predicted by immunoreactivity to bFGF in CMM cells or in the local tumor vasculature.

Changes associated with tyrosine phosphorylation during short-term hypoxia in retinal microvascular endothelial cells in vitro

The occlusion of capillary vessels results in low oxygen tension in adjacent tissues which triggers a signaling cascade that culminates in neovascularization. Using bovine retinal capillary endothelial cells (BRCEC), we investigated the effects of short-term hypoxia on DNA synthesis, phosphotyrosine induction, changes in the expression of basic fibroblast growth factor receptor (bFGFR), protein kinase C (PKC alpha), heat shock protein 70 (HSP70), and SH2-containing protein (SHC). The effect of protein tyrosine kinase (PTK) and phosphatase inhibitors on hypoxia-induced phosphotyrosine was also studied. Capillary endothelial cells cultured in standard normoxic (pO2 = 20%) conditions were quiesced in low serum containing medium and then exposed to low oxygen tension or hypoxia (pO2 = 3%) in humidified, 5% CO2, 37 degrees C, tissue culture chambers, on a time-course of up to 24 h. DNA synthesis was potentiated by hypoxia in a time-dependent manner. This response positively correlated with the cumulative induction of phosphotyrosine and the downregulation of bFGFR (M(r) approximately 85 kDa). Protein tyrosine kinase inhibitors, herbimycin-A, and methyl 2,5-dihydroxycinnamate, unlike genistein, markedly blocked hypoxia-induced phosphotyrosine. Prolonged exposure of cells to phosphatase inhibitor, sodium orthovanadate, also blocked hypoxia-induced phosphotyrosine. The expression of HSP70, PKC alpha, and SHC were not markedly altered by hypoxia. Taken together, these data suggest that short-term hypoxia activates endothelial cell proliferation in part via tyrosine phosphorylation of cellular proteins and changes in the expression of the FGF receptor. Thus, endothelial cell mitogenesis and neovascularization associated with low oxygen tension may be controlled by abrogating signaling pathways mediated by protein tyrosine kinase and phosphatases.

Alternative splicing in fibroblast growth factor receptor 2 is associated with induced epithelial-mesenchymal transition in rat bladder carcinoma cells

We described previously that acidic fibroblast growth factor (aFGF), but not basic fibroblast growth factor (bFGF), can induce the rat carcinoma cell line NBT-II to undergo a rapid and reversible transition from epithelial to mesenchymal phenotype (EMT). We now find that NBT-II EMT is stimulated by keratinocyte growth factor (KGF) in cells grown at low density. Accordingly, a high-affinity receptor showing 98% homology to mouse FGF receptor 2b/KGF receptor was cloned and sequenced from NBT-II cells. Northern analysis indicated that mRNA for FGF receptor 2b/KGF receptor was drastically down-regulated within 1 wk in aFGF-induced mesenchymal NBT-II cells. This decrease coincided with an up-regulation of FGF receptor 2c/Bek, a KGF-insensitive, alternatively spliced form of FGF receptor 2b/KGF receptor. Functional studies confirmed that KGF could not maintain EMT induction on mesenchymal NBT-II cells. FGF receptor 1 and FGF receptor 2c/Bek could also support EMT induction when transfected into NBT-II cells in response to aFGF or bFGF. Such transfected cells could bind bFGF as well as aFGF. Therefore, EMT can be induced through different FGF receptors, but EMT may also regulate FGF receptor expression itself.