Thermal sensitivity of nuclear pore complexes as a potential early driver of heat-induced cell death

To examine cellular responses to mild hyperthermia at nominally sublethal temperatures (∼40-45 °C), where irreversible injury and cell death occur only after several minutes of exposure, and to identify a plausible early mechanism underlying heat-induced cell death.

Experimental observations were made in mammalian cells exposed to 40-45 °C for several minutes or briefly to 50 °C for 1-2 s. Nuclear-cytoplasmic compartmentalization, cell morphology, adhesion, proliferation, and apoptosis were assessed to characterize the sequence of cellular changes following thermal exposure.

Cells exposed to 40-45 °C for several minutes lost nuclear-cytoplasmic compartmentalization before overt morphological signs of cell death. Normally excluded cytoplasmic proteins entered the nucleus, whereas nuclear proteins redistributed into the cytoplasm. Brief heating to 50 °C for 1-2 s produced the same nuclear permeability phenotype in all exposed cells. Nuclear envelope leakage behaved as an all-or-nothing event: cells that retained nuclear compartmentalization survived and continued proliferating, whereas cells with leaky nuclei rapidly rounded up, lost adhesion, and detached within 1-2 h. Detached cells never re-adhered and consistently underwent apoptosis within 15-17 h, as detected by YO-PRO-1 staining.

These observations indicate that loss of nuclear compartmentalization is an early, irreversible event in heat-induced cell death. Because nuclear pore complex (NPC)-mediated selective macromolecular transport is indispensable for cell survival, irreversible NPC damage appears to severely limit cellular recovery. Irreversible impairment of NPC selectivity is therefore proposed as the most parsimonious explanation for observed heat-induced nuclear leakiness.