Effects of Mutations of a Phosphorylation Site in an Exposed Loop in Acidic Fibroblast Growth Factor*
- From the Department of Biochemistry at The Institute for Cancer Research, The Norwegian Radium Hospital, Montebello, 0310 Oslo, Norway
Abstract
Acidic fibroblast growth factor (aFGF) contains a phosphorylation site recognized by protein kinase C. A non-mitogenic mutant growth factor is devoid of this phosphorylation site. We have changed amino acids in and close to the phosphorylation site and studied the consequences of this for binding of the growth factor to high affinity receptors as well as to heparin. We have also studied the ability of the mutants to stimulate DNA synthesis and cell proliferation as well as phosphorylation of mitogen-activated protein kinase and the ability of the growth factor mutants to be transported to the nucleus. The results indicate that while the mutations strongly affect the ability of the growth factor to bind to heparin, they do not affect much the binding to the specific FGF receptors, activation of mitogen-activated protein kinase or transport of the growth factor to the nucleus. The mutations affect to various extents the ability of the growth factor to stimulate DNA synthesis and to induce cell multiplication. We find that phosphorylation of aFGF is not required for mitogenic activity. The data suggest that altered interaction of the growth factor with a cellular component different from the receptor, possibly a component in the nucleus, is the reason for the different mitogenicity of the different growth factor mutants.
Footnotes
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↵* This work was supported by The Norwegian Cancer Society, Novo Nordisk Foundation, The Norwegian Research Council for Science and Humanities, Blix Legat, Rachel and Otto Kr. Bruun’s Legat, and by The Jahre Foundation.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵‡ Fellow of The Norwegian Cancer Society.
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↵2 O. Klingenberg, A. Wi IJ dłocha, and S. Olsnes, our unpublished data.
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↵3 O. Klingenberg, A. Wi IJ dłocha, A. Rapak, D. Khnykin, L. Citores, and S. Olsnes, submitted for publication.
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↵4 O. Klingenberg, A. Wi IJ dłocha, and S. Olsnes, submitted for publication.
- Abbreviations:
- aFGF
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acidic fibroblast growth factor
- bFGF
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basic fibroblast growth factor
- FGFR
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fibroblast growth factor receptor
- MAP kinase
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mitogen-activated protein kinase
- PKC
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protein kinase C
- MBP
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maltose-binding protein
- FIBP
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aFGF intracellular binding protein
- PAGE
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polyacrylamide gel electrophoresis
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- Received December 10, 1998.
- Revision received March 23, 1999.
- The American Society for Biochemistry and Molecular Biology, Inc.
