STUDIES OF THE LAMIN PROTEINASE REVEAL MULTIPLE PARALLEL BIOCHEMICAL PATHWAYS DURING APOPTOTIC EXECUTION

Although specific proteinases play a critical role in the active phase of apoptosis, their substrates are largely unknown. We previously ide ntified poly(ADP-ribose) polymerase (PARE) as an apoptosis-associated substrate for proteinase(s) related to interleukin 1 beta-converting e nzyme (ICE). Now we have used a cell-free system to characterize prote inase(s) that cleave the nuclear lamins during apoptosis. Lamin. cleav age during apoptosis requires the action of a second ICE-like enzyme, which exhibits kinetics of cleavage and a profile of sensitivity to sp ecific inhibitors that is distinct from the PARP proteinase. Thus, mul tiple ICE-like enzymes are required for apoptotic events in these cell -free extracts. Inhibition of the lamin proteinase with tosyllysine '' chloromethyl ketone'' blocks nuclear apoptosis prior to the packaging of condensed chromatin into apoptotic bodies. Under these conditions, the nuclear DNA is fully cleaved to a nucleosomal ladder. Our studies reveal that the lamin proteinase and the fragmentation nuclease functi on in independent parallel pathways during the final stages of apoptot ic execution, Neither pathway alone is sufficient for completion of nu clear apoptosis. Instead, the various activities cooperate to drive th e disassembly of the nucleus.