Involvement of TLCK-sensitive serine protease in colchicine-induced cell death of sympathetic neurons in culture

Superior cervical ganglion (SCG) cells from neonatal rats underwent apoptosis upon treatment with colchicine, a microtubule-disrupting agent. Western blotting and activity measurements showed that caspase-3 was indeed activated, but its peptide inhibitor (Ac-DEVD-CHO) neither suppressed nuclear fragmentation nor rescued the neurons from cell death. z-VAD-fmk, the general inhibitor of caspases, prevented nuclear fragmentation and delayed the cell death. Moreover, N-alpha -tosyl-L-lysine chloromethyl ketone (TLCK), but not N-alpha -tosyl-Lphenylalanine chloromethyl ketone (TPCK), prevented nuclear fragmentation and provided neuronal protection as well. The combination of both z-VAD-fmk and TLCK provided a long-term neuronal protection (>4 days), whereas neither one alone could do so, suggesting that there are both caspase-dependent and -independent pathways. TLCK-sensitive serine protease is also likely to act upstream of caspase-3 in a caspase-dependent pathway. Electron microscopic observations demonstrated that z-VAD-fmk suppressed nuclear fragmentation and improved mitochondrial swelling, but failed to prevent vesicular formation, which resulted in a slowly-occurring necrosis. More importantly, TLCK effectively blocked this abundant vesicular formation along with suppressing chromatin condensation. Thus, the combination of both conferred a nearly normal morphology, which is consistent with the results of cell survival experiments. These findings clearly indicate that TLCK-sensitive serine protease plays multiple roles in caspase-dependent and -independent pathways of colchicine-induced cell death, and suggest a novel mechanism underlying a necrotic pathway involving ER swelling and vesicular formation. J. Neurosci. Res. 66:601-611, 2001. (C) 2001 Wiley-Liss, Inc.