Caspase-mediated cleavage of the chromosome-binding domain of lamina-associated polypeptide 2 alpha

Lamina-associated polypeptide 2 alpha (LAP2 alpha) is a nonmembrane-bound i soform of the LAP2 family involved in nuclear structure organization. Using various cell systems, including Jurkat, HL-60, and HeLa cells, and differe nt death-inducing agents, such as anti-Fas antibody, topoisomerase inhibito rs, and staurosporine, we found that LAP2 alpha was cleaved during apoptosi s as rapidly as lamin B in a caspase-dependent manner yielding stable N- an d C-terminal fragments of approximately 50 and 28 kDa, respectively. Based on fragment size and localization of immunoreactive epitopes, four potentia l cleavage sites were mapped between amino acids 403-485, These sites were located within a domain that has previously been described to be essential and sufficient for association of LAP2 alpha with chromosomes, suggesting t hat LAP2 alpha cleavage impairs its chromatin-binding properties. Immunoflu orescence microscopy demonstrated that, unlike full length protein, apoptot ic fragments did not colocalize with condensed chromatin, but remained in t he nuclear compartment as long as a single nucleus was visible. Subfraction ation analyses:showed that the N-terminal LAP2 alpha fragment was extracted from intranuclear structures in detergent/salt buffers, whereas the C-term inal fragment remained associated with a residual framework devoid of chrom atin, Our data suggest that early cleavage of LAP2 alpha is important for c hromatin reorganization during apoptosis.