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21 (17): 4480-4490

Copyright © 2002 by the European Molecular Biology Organization.

Vesicle transmembrane potential is required for translocation to the cytosol of externally added FGF-1

Jedrzej Malecki, Antoni Wiedlocha, Jørgen Wesche, and Sjur Olsnes1

Institute for Cancer Research, The Norwegian Radium Hospital, 0310 Montebello, Oslo, Norway 1 Corresponding author e-mail: sjur.olsnes{at}labmed.uio.no

Abstract: Externally added fibroblast growth factor-1 (FGF-1) is capable of crossing cellular membranes to reach the cytosol and the nucleus in a number of cell types. We have monitored the translocation of the growth factor by two methods: phosphorylation of FGF-1, and prenylation of an FGF-1 mutant that contains a C-terminal prenylation signal. Inhibition of endosomal acidification by ammonium chloride or monensin did not block the translocation of FGF-1, whereas bafilomycin A1, a specific inhibitor of vacuolar proton pumps, blocked translocation completely. A combination of ionophores expected to dissipate the vesicular membrane potential (valinomycin plus monensin) also fully inhibited the translocation. The inhibition of translocation by bafilomycin A1 was overcome in the presence of monensin or nigericin, while ouabain blocked translocation under these conditions. The data indicate that translocation of FGF-1 to cytosol occurs from the lumen of intracellular vesicles possessing vacuolar proton pumps, and that a vesicular membrane potential is required. Apparently, activation of vesicular Na+/K+-ATPase by monensin or nigericin generates a membrane potential that can support translocation when the proton pump is blocked.

Key Words: Keywords: FGF-1/protein translocation/vesicular membrane potential

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Science Signaling. ISSN 1937-9145 (online), 1945-0877 (print). Pre-2008: Science's STKE. ISSN 1525-8882