Excision of DNA loop domains as a common step in caspase-dependent and -independent types of neuronal cell death

Treatment of rat cerebellar granule neurons with the phosphatase inhibitor, okadaic acid (OKA) or the excitatory neurotransmitter, L-glutamate, result ed in progressive cell death associated with apoptotic-like changes in nucl ear morphology. The OKA-induced neurotoxicity was accompanied by the activa tion of caspase-3 (ICE-related cysteine protease) and the development of an oligonucleosomal DNA ladder, whereas neither activation of caspase-1, -2, -3, -5, or -9, nor internucleosomal DNA fragmentation accompanied L-glutama te-induced neurotoxicity. At the same time, both OKA and L-glutamate induce d a similar pattern of nuclear DNA disintegration into high molecular weigh t (HMW)-DNA fragments of about 50-100 kb, which are widely believed to orig inate from the excision of DNA loop domains. Z-DEVD-fmk, a specific caspase -3 inhibitor, as well as a general caspase inhibitor, z-VAD-fmk, inhibited both the internucleosomal- and HMW-DNA fragmentation in OKA-treated neurons . However neither z-DEVD-fmk nor z-VAD-fmk had any obvious inhibitory effec t on the formation of HMW-DNA fragments induced by L-glutamate. The results indicate that the formation of the HMW-DNA fragments in cerebellar granule neurons accompanies both caspase-dependent and -independent types of cell death, indicative of multiple mechanisms in the regulation of excision of D NA loop domains during neuronal cell death. (C) 2000 Elsevier Science B.V. All rights reserved.