Correlation between nucleocytoplasmic transport and caspase-3-dependent dismantling of nuclear pores during apoptosis.
During apoptosis (also called programmed cell death), the chromatin condenses and the DNA is cleaved into oligonucleosomal fragments. Caspases are believed to play a major role in nuclear apoptosis. However, the relation between dismantling of nuclear pores, disruption of the nucleocytoplasmic barrier, and nuclear entry of caspases is unclear. We have analyzed nuclear import of the green fluorescent protein fused to a nuclear localization signal (GFP-NLS) in tissue culture cells undergoing apoptosis. Decreased nuclear accumulation of GFP-NLS could be detected at the onset of nuclear apoptosis manifested as dramatic condensation and redistribution of chromatin toward the nuclear periphery. At this step, dismantling of nuclear pores was already evident as indicated by proteolysis of the nuclear pore membrane protein POM121. Thus, disruption of nuclear compartmentalization correlated with early signs of nuclear pore damage. Both these events clearly preceded massive DNA fragmentation, detected by TUNEL assay. Furthermore, we show that in apoptotic cells, POM121 is specifically cleaved at aspartate-531 in its large C-terminal portion by a caspase-3-dependent mechanism. Cleavage of the C-terminal portion of POM121, which is adjoining the nuclear pore complex, is likely to disrupt interactions with other nuclear pore proteins affecting the stability of the pore complex. A temporal correlation of apoptotic events supports a model where caspase-dependent disassembly of nuclear pores and disruption of the nucleocytoplasmic barrier paves the way for nuclear entry of caspases and subsequent activation of CAD-mediated DNA fragmentation.
Kihlmark
Madeleine
M
Section for Natural Sciences, Södertörns Högskola (University College), 141 89 Huddinge, Sweden.
Rustum
Cecilia
C
Eriksson
Charlotta
C
Beckman
Marie
M
Iverfeldt
Kerstin
K
Hallberg
Einar
E
D021581:Active Transport, Cell Nucleus / Q000502:physiology*; D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D001224:Aspartic Acid / Q000378:metabolism; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism*; D002460:Cell Line; D003593:Cytoplasm / Q000201:enzymology*; D053938:DNA Fragmentation / Q000502:physiology; D049452:Green Fluorescent Proteins; D006367:HeLa Cells; D006801:Humans; D008164:Luminescent Proteins; D008565:Membrane Proteins / Q000378:metabolism; D019913:Nuclear Localization Signals / Q000378:metabolism; D022022:Nuclear Pore / Q000201:enzymology*; D009687:Nuclear Proteins / Q000378:metabolism; D017434:Protein Structure, Tertiary / Q000502:physiology; D051381:Rats
D008164:Luminescent Proteins; D008565:Membrane Proteins; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins; C082264:Pom121 protein, rat; D049452:Green Fluorescent Proteins; D001224:Aspartic Acid; C505407:CASP3 protein, human; C505410:Casp3 protein, rat; D053148:Caspase 3; D020169:Caspases