Although bFGF is an important factor in the control of vascular growth, the mechanisms of its release from endothelial cells are still not well understood. We have shown before that shear stress induces bFGF release and that the integrin alpha(v)beta3 plays an important role in this process 1. Here, we investigated whether proteases could be involved in shear stress induced alpha(v)beta3 stimulation and which signaling cascade was activated by alpha(v)beta3. Porcine aortic endothelial cells (PAEC, 1st or second passage) were subjected to shear stress (16dyn/cm²) in a cone and plate apparatus. Compared to resting cells, shear stress induced a significant increase of bFGF release (84 ±9 vs 482 ±66 pg/mL; n=9). This increase went along with an enhanced proteolytic activity (3fold, n=6) in the supernatant of the cells. This proteolytic activity was due to an elastase as assessed by the substrate MeOSuc-Ala-Ala-Pro-Val-pNA. Inhibition of this proteolytic activity by aprotinin prevented the shear induced increase of bFGF release by 32 ±12% (n=9). Likewise, treatment with exogenous elastase (0.1- 2U/mL) resulted in an up to threefold increase of bFGF (n=9). The bFGF release induced by exogenous elastase was dependent on integrin alpha(v)beta3 since the a medium dose of Abxicimab (0,5 μg/mL) significantly reduced it by 32 ±12% (n=7). Immunohistochemistry using specific bFGF antibodies revealed a translocation of (peri-)nuclear distributed bFGF towards the cellular membrane after stimulation of PAEC with elastase or shear stress. In contrast, no translocation was observed when cells in suspension were treated with elastase. The bFGF translocation coincided with translocation of HSP27 to the cell membrane. Moreover, western blots demonstrated that elastase treatment resulted in HSP27 phosphorylation (n=4, each). This phosphorylation was due to an activation of p38 MAP kinase as assessed by the inhibitory effects (by 67%) of SB202190 (1 μM). Phosphorylated HSP27 and bFGF could be co-precipitated, indicating a close physical interaction between these two proteins (n=3). We conclude that shear stress treatment activates an elastase, which in turn initiates integrin alpha(v)beta3 dependent signaling cascades stimulating the release of bFGF. We further propose that this new model could help to understand the translation of mechanical stress into biological growth signals in the vascular wall.