Addition of protease inhibitors to culture medium of neuroblastoma cells induces both neurite outgrowth and phosphorylation of microtubule-associated protein MAP-1B.

The addition of two synthetic peptides with antiprotease activity to the culture medium of mouse neuroblastoma cells results in the promotion of neurite outgrowth. One of these peptides has a sequence corresponding to the reactive center of protease nexin-1 and inhibits both trypsin and thrombin. Its effect on neuroblastoma cells is similar to that found on serum withdrawal from the culture medium, giving rise to cells with one or two long neurites, and is reversed upon the addition of thrombin to the culture medium. The sequence of the other peptide is present in one of the precursor proteins of the main component of the amyloid plaques of Alzheimer's disease patients' brains, and corresponds to protease nexin-2. It can inhibit trypsin but fails to inhibit thrombin at low doses. Its effect on neuroblastoma cells is slightly different from that observed after serum deprivation, as a significant proportion of stellate cells, with short and branched neurites, is observed. An increase in the phosphorylation of microtubule-associated protein MAP-1B, which accompanies neurite outgrowth induced by serum deprivation, is also observed upon addition of the two antiprotease synthetic peptides, although the nexin-2 (amyloid) peptide induces a less marked increase in phosphorylated MAP-1B than does the nexin-1 peptide. These results may be correlated with the different antiprotease activities of both synthetic peptides, thus suggesting a role for a balance between trypsin-like and thrombin-like proteases and their inhibitors in eliciting neurite outgrowth under normal and pathological conditions.