QUANTITATIVE EXPORT OF FGF-2 OCCURS THROUGH AN ALTERNATIVE, ENERGY-DEPENDENT, NON-ER GOLGI PATHWAY/

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.