The mitogenic activity of fibroblast growth factor-1 correlates with its internalization and limited proteolytic processing

Abstract

The fibroblast growth factor-1 (FGF-1) mitogenic signal transduction pathway is not well characterized, and evidence indicates that FGF-1 binding to and activation of cell-surface receptors is not solely sufficient for a full mitogenic response. Although initiation of the phosphorylation signaling cascades are likely important in FGF-1-induced mitogenic signaling, there appear to be additional signaling requirements. In this study, we demonstrate that FGF-1 internalization and subsequent processing correlates with the mitogenic potential of the growth factor on NIH 3T3 cells. Using site-directed mutants of FGF-1 and inhibitors of the endocytic and degradative pathways, we provide evidence for growth factor internalization and exposure to an acidic environment as necessary components of FGF-1-induced mitogenesis. In addition, a protease-sensitive event(s) appears critical for a complete mitogenic response to FGF-1, whereas, this protease sensitivity was not detected under the same conditions for serum-stimulated mitogenesis. Therefore, proteolytic modification of internalized FGF-1 may result in the activation of additional, intracellular signaling events.

Thromboxane A 2 Receptor Agonists Antagonize the Proangiogenic Effects of Fibroblast Growth Factor-2

“…23,24 Sustained internalization of FGF-2/FGFR1 complexes has been shown to be crucial for the mitogenic and chemotactic effects of FGF-2. 43 Little is known about the mechanism(s) that regulate FGF-2/FGFR1 complex internalization, although it is thought to be phosphorylation dependent 44 and mediated through caveolae. 45 Whereas such a significant role for ␣ v ␤ 3 in FGFR1 internalization was unexpected, it is a logical regulatory step, because ␣ v ␤ 3 also localizes to caveolae.…”

Highly Stable Mutants of Human Fibroblast Growth Factor-1 Exhibit Prolonged Biological Action

“…This is in agreement with the data presented by Wesche et al,74 who demonstrated that the molecule of FGF-1 rigidified with three engineered disulfide bonds was translocated into the cell as effectively as the wild-type. On the other hand, our study is contrary to the observations made by Grieb & Burgess,71 who suggested that protease-sensitive event(s) can be critical for full mitogenic response. Here, we show that mutants of increased stability and slower intracellular degradation not only maintained normal mitogenic activity in the presence of heparin, but also showed an enhanced one in the absence of this stabilizing polysaccharide.…”

“…[65][66][67][68][69][70][71][72] Our data show that upon internalization two of our most stable mutants were not degraded, in sharp contrast to the wild-type behavior ( Figure 8). Therefore, the improved mitogenic activity can result from the resistance to proteolysis both outside and inside the cell.…”

Fibroblast growth factor 2 endocytosis in endothelial cells proceed via syndecan-4-dependent activation of Rac1 and a Cdc42-dependent macropinocytic pathway

“…Such proteoglycan-dependent uptake has been localized to uncoated pits, in keeping with our finding of non-clathrin-dependent uptake, and proceed at a relatively slow pace, once again consistent with the kinetics of syndecan-4 internalization observed in this study (Gleizes et al, 1995). The functional significance of syndecan-4-dependent FGF2 internalization has not been established but previous studies have suggested that FGF1 uptake is required for its full mitogenic effect (Grieb and Burgess, 2000).…”