Rz. Florkiewicz et al., QUANTITATIVE EXPORT OF FGF-2 OCCURS THROUGH AN ALTERNATIVE, ENERGY-DEPENDENT, NON-ER GOLGI PATHWAY/, Journal of cellular physiology, 162(3), 1995, pp. 388-399
Although basic fibroblast growth factor (bFGF/FGF-2) is found outside
cells, it lacks a conventional signal peptide sequence; the mechanism
underlying its export from cells is therefore unknown. Using a transie
nt COS-l cell expression system, we have identified a novel membrane-a
ssociated transport pathway that mediates export of FGF-2. This export
pathway is specific for the 18-kD isoform of FGF-2, is resistant to t
he anti-Golgi effects of Brefeldin A, and is energy-dependent. In FGF-
2-transfected COS-1 cells, this ER/Colgi-independent pathway appears t
o be constitutively active and functions to quantitatively expert meta
bolically-labeled 18-kD FGF-2. Co-transfection and co-immunoprecipitat
ion experiments, using a vector encoding the cytoplasmic protein neomy
cin phosphotransferase, further demonstrated the selectivity of this e
xport pathway for FGF-2. When neomycin phosphotransferase was appended
to the COOH-terminus of 18-kD FGF-2, the chimera was exported. Howeve
r, the transmembrane anchor sequence of the integral membrane glycopro
tein (G protein) of vesicular stomatitis virus (VSV) blocked export. T
he chimeric protein localized to the plasma membrane with its FGF-2 do
main extracellular and remained cell-associated following alkaline car
bonate extraction. Taken together, the data suggest that FGF-2 is ''ex
ported'' from cells via a unique cellular pathway, which is clearly di
stinct from classical signal peptide-mediated secretion. This model sy
stem provides a basis for the development and testing of therapeutic a
gents which may block FGF-2 export. Such an intervention may be of con
siderable use for the treatment of angiogenesis-dependent diseases inv
olving FGF-2. (C) 1995 Wiley-Liss, Inc.