Possible involvement of a novel protease in neurite outgrowth of PC12 cells

A tripeptide aldehyde protease inhibitor (Ac-Leu-Leu-Nle-al, ALLNal), among many other protease inhibitors, initiates neurite outgrowth in PC12h cells. The neuritogenesis induced by this inhibitor is different in some aspects from that induced by NGF; one or two long neurites are initiated from the cell body and differentiation is transient. The results provide evidence that the protease inhibitor and nerve growth factor elicit neurite initiation by different mechanisms and suggest the existence of a novel protease which modulates neurite initiation in PC12 cells. To identify the target protease, Leu-Leu-Leu-al was immobilized and used as a ligand for affinity chromatography of the protease. A protein with an apparent molecular weight of 33 kDa was isolated specifically from the cytoplasmic fraction of PC12 cells using the affinity column. The same protein was identified in the brains of 1-day postnatal rats, but the amount was much less in the brains of adult rats. Thus, we suggest that the 33-kDa protein regulates neurite initiation in nervous systems, possibly as a protease which degrades membrane proteins or the cytoskeletal framework.