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Nuclear localization of endogenous basic fibroblast growth factor in cultured endothelial cells
P Dell'Era1, M Presta, G Ragnotti
1Department of Biomedical Sciences and Biotechnologies, School of Medicine, University of Brescia, Italy.
Insights
Endothelial cells contain basic fibroblast growth factor (bFGF) in both the cytoplasm and nucleus. This study shows endogenous bFGF is sorted to the nucleus of endothelial cells.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Basic fibroblast growth factor (bFGF) is a potent mitogen involved in various cellular processes.
- The intracellular localization and function of bFGF are not fully understood, particularly in endothelial cells.
Purpose of the Study:
- To investigate the presence and localization of bFGF within endothelial cells.
- To determine if endogenous bFGF is actively sorted to the nucleus.
Main Methods:
- Indirect immunofluorescence using anti-human placental bFGF antibodies.
- Heparin-Sepharose affinity chromatography for bFGF isolation.
- Quantitation of bFGF by biological and immunological assays.
- Immunoprecipitation of newly synthesized bFGF.
Main Results:
- bFGF-like reactivity was detected in the cytoplasm and nucleus of adult and fetal bovine aortic endothelial cells.
- Biologically active bFGF was isolated from GM 7372 cell nuclei.
- GM 7372 cells contain approximately 100,000 bFGF molecules per nucleus, constituting 25-30% of total cellular bFGF.
- Newly synthesized bFGF is localized to the nucleus, even in the presence of suramin, which blocks cell surface receptor binding.
Conclusions:
- Endogenous bFGF undergoes intracellular sorting to the nucleus of endothelial cells.
- Nuclear localization of bFGF suggests potential roles beyond extracellular signaling.
Abstract:
Indirect immunofluorescence using anti-human placental bFGF antibodies demonstrates the presence of bFGF-like reactivity in the cytoplasm and in the nucleus of adult bovine aortic endothelial cells and of normal and transformed fetal bovine aortic endothelial AG 7680 and GM 7372 cells. Biologically active immunoreactive Mr 18,000 bFGF can be isolated by heparin-Sepharose affinity chromatography from the extract of GM 7372 cell nuclei. Quantitation of bFGF content by biological and immunological methods indicates that 100,000 bFGF molecules per nucleus are present in GM 7372 cells, with nuclear bFGF corresponding to 25-30% of total cellular bFGF. Immunoprecipitation experiments demonstrate that the nuclear localization of newly synthesized bFGF occurs when GM 7372 cells are biosynthetically labeled both in the absence and in the presence of suramin, a molecule that inhibits the binding of bFGF to its plasma membrane receptor. Thus the data indicate that endogenous bFGF undergoes an intracellular sorting to the nucleus of the endothelial cell.
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