Mechanisms of fibroblast growth factor 2 intracellular processing: a kinetic analysis of the role of heparan sulfate proteoglycans.
The interaction of fibroblast growth factor 2 (FGF-2) with heparan sulfate proteoglycans (HSPG) has been demonstrated to enhance receptor binding and alter the intracellular distribution of internalized FGF-2. In the present study, the intracellular fate of FGF-2 was analyzed in vascular smooth muscle cells (VSMC) under native and HSPG-deficient conditions. HSPG-deficient cells were generated by treatment with sodium chlorate. Cells were incubated with FGF-2 at 37 degrees C for prolonged periods (0-48 h) to allow for FGF-2 uptake and processing. Processing of FGF-2 occurred in stages. Initially a family of low molecular weight (LMW) fragments (4-10 kDa) were detected that accumulated to much higher ( approximately 10-fold) levels in native compared to heparan sulfate-deficient cells. Pulse-chase experiments revealed that the half-life of these LMW intermediates was significantly greater in native ( approximately 18 h) compared to HSPG-deficient cells ( approximately 4 h). Rate constants for FGF-2 processing were derived by modeling the uptake and processing of FGF-2 as a set of first-order differential equations. The kinetic analysis indicated that the greatest differences between native and HSPG-deficient VSMC was in the formation of LMW and further suggested that these FGF-2 products appear to represent a stable subpool of internal FGF-2 that is favored in cells that contain HSPG. Thus, HSPG might function as a cellular switch between immediate and prolonged signal activation by heparin-binding growth factors such as FGF-2. In the absence of HSPG, FGF-2 can interact with and activate its receptor, yet in the presence of HSPG, FGF-2 might be able to mediate prolonged or unique biological responses through intracellular processes.
Sperinde
G V
GV
Departments of Biochemistry and Ophthalmology, Boston University School of Medicine, Boston, MA 02118, USA.
Nugent
M A
MA
D000818:Animals; D002478:Cells, Cultured; D003593:Cytoplasm / Q000378:metabolism; D004705:Endocytosis; D016222:Fibroblast Growth Factor 2 / Q000378:metabolism*; D006168:Guinea Pigs; D019812:Heparan Sulfate Proteoglycans / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D006801:Humans; D007424:Intracellular Fluid / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D008970:Molecular Weight; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism; D010446:Peptide Fragments / Q000378:metabolism; D011499:Protein Processing, Post-Translational / Q000235:genetics; D013997:Time Factors
D019812:Heparan Sulfate Proteoglycans; D010446:Peptide Fragments; D016222:Fibroblast Growth Factor 2