Basic fibroblast growth factor: lysine 134 is essential for its neuroprotective activity.

Basic fibroblast growth factor (bFGF) is a heparin-binding growth factor known to cause cell proliferation, angiogenesis and neuroprotection. We have performed site-directed mutagenesis to identify the amino acids that are essential for heparin/growth factor interaction and for neuroprotection. Binding to heparin-acrylic beads was markedly reduced when lysine in position 134 of bFGF was replaced by alanine. Wildtype (wt)-bFGF was shown to protect rat primary cultures of embryonic hippocampal neurons against damage caused by staurosporine and to reduce the infarct size in mice after focal cerebral ischemia. These neuroprotective effects of wt-bFGF could not be shown for the mutant bFGF(K134A). Furthermore, phosphorylation of Akt and ERK1/2 was significantly reduced in cultured neurons treated with bFGF(K134A) indicating diminished intracellular signaling compared to neurons treated with wt-bFGF. In conclusion, lysine at position 134 of bFGF is essential for bFGF to bind heparin, then to interact with its receptor and, subsequently, to protect neurons against damage.