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First published online July 2, 2007
doi: 10.1242/10.1242/jcs.011080

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Unconventional secretion: an extracellular trap for export of fibroblast growth factor 2

Heidelberg University Biochemistry Center (BZH), Im Neuenheimer Feld 328, 69120 Heidelberg, Germany

e-mail: walter.nickel{at}bzh.uni-heidelberg.de

Accepted 23 May 2007

Several secretory proteins are released from cells by mechanisms that are distinct from the classical endoplasmic reticulum (ER)/Golgi-mediated secretory pathway. Recent studies unexpectedly revealed that the interaction between one such protein, fibroblast growth factor 2 (FGF-2), and cell surface heparan sulfate proteoglycans (HSPGs) is essential for secretion. FGF-2 mutants that cannot bind to heparan sulfates are not secreted, and cells that do not express functional HSPGs cannot secrete wild-type FGF-2. FGF-2 appears to be secreted by direct translocation across the plasma membrane in an ATP- and membrane-potential-independent manner. I propose that its translocation across the membrane is a diffusion-controlled process in which cell surface HSPGs function as an extracellular molecular trap that drives directional transport of FGF-2.

Key words: Fibroblast growth factor 2, Membrane translocation, Unconventional protein secretion, Nonclassical export